## Latest Accepted Articles

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To address the issues of high alkalinity of red mud, complex chemical composition and low resource utilization rate, mine filling materials with red mud in collaboration with fly ash and other multi-solid wastes were prepared, the development law of red mud composites ratio on the compressive strength of backfill was compared. The hydration mechanism of cemented paste backfill was revealed by means of X-ray diffractometer, scanning electron microscope. Through eluviation test and toxic leaching test, the solid alkali mechanism, leaching behavior and toxic ion solidification mechanism of backfill were explored. The results show that the mass ratio of red mud composite material is red mud∶fly ash∶cement=3∶7∶0.4, the compressive strengths of the filling body are 0.76, 1.35 and 1.87 MPa for 3, 7 and 28 d, respectively, and the material cost is 78.08 yuan/t, which satisfy the requirements of mine filling and mining. Under the synergistic interlocking effect of red mud-fly ash-cement, the filling body produces hydration products which are mainly C-S-H gel, ettringite and gmelinite, and the smaller the mass ratio of red mud: fly ash, the larger the specific surface area of fly ash, the denser the structure of the filling body, and the better the alkali fixation effect. The ettringite and C-S-H gels make the toxic ion leaching concentration of red mud composites meet the requirements of Class I solid waste in GB 8978-1996 “Integrated wastewater discharge standard” through physical sequestration and chemical combination.
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With the development and efficient utilization of nuclear energy in China, uranium has become one of the common pollutants in surface water, groundwater and soil. The removal of U(VI) from uranium-containing wastewater has become an urgent environmental problem to be solved. Hydroxyapatite modified bentonite composite hydroxyapatite modified bentonite (HAP/BTN) was successfully prepared by a simple one-step hydrothermal method using bentonite, disodium hydrogen phosphate and calcium nitrate as raw materials. The adsorption performance of HAP/BTN on uranium in wastewater was investigated. The effects of pH, rotation speed, temperature, dosage and time on the adsorption performance were discussed by orthogonal test. The results showed that under the conditions of pH=6.0, rotation speed=100 r·min−1, room temperature (298.15 K), HAP/BTN dosage of 1 g·L−1 and t=30 min, the removal rate of 10 mg·L−1 uranium-containing wastewater could reach 98%, and the maximum adsorption capacity was 186.45 mg·g−1. The adsorption process was more in line with the Langmuir model and pseudo-second-order kinetics. Thermodynamic parameters show that the adsorption of uranium on HAP/BTN was a spontaneous endothermic process, combined with XPS and XRD results, confirmed that the adsorption of uranium by HAP/BTN was mainly attributed to complexation reaction, chemical adsorption, electrostatic and ion exchange.
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To explore the shear performance of glass fiber reinforced polymer (GFRP) bars in concrete after fire and high temperature, nine temperature conditions of 100°C, 150°C, 200°C, 300°C, 350°C, 400°C, 500°C, 650°C and 800°C were selected to treat the GFRP bars placed in concrete, and the horizontal shear tests were carried out on the obtained bar specimens. The method of predicting the horizontal shear strength of GFRP bars in concrete after exposure to high temperature was discussed using the results of this study and some existing tests. Test and analytical results show that within 300°C there is a hysteresis phenomenon in the surface temperature of GFRP bars in concrete. Their high temperature deterioration is significantly lower than that of the bare bars, as well as the shear strength degradation is also relatively slow. As the temperature exceeds 300°C and the concrete surface cracks continue to develop, the deterioration of embedded GFRP bars caused by high temperature gradually enlarges, meanwhile, the shear strength decreases sharply, which shows a similar degradation pattern to that of bare bars. At high temperature of 300°C which is close to the thermal decomposition temperature of resins, the shear strength retention rate of GFRP bars decreases linearly from 76.4% to 46.5% with the constant temperature time increasing from 1h to 3h. Based on the hyperbolic tangent function model, a prediction model for the horizontal shear strength of GFRP bars in concrete after high temperature was established and model’s predictions were in good agreement with test values. Finally, considering a shear strength retention factor of 0.7, the predictions of fire resistance time of GFRP bars with different cover thickness were proposed, which can provide some references for engineering application.
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The evaluation of residual stress after winding and curing process is the basement for the optimization design of winding process scheme and the achievement of pre-service stressing design. In this paper, three kinds of winding tension strategies, e.g. constant tension (40N), loose inside and tight outside tension (20N-40N-60N), and tight inside and loose outside tension (60N-40N-20N), were used to prepare the composite winding cylinders on the steel mould and PA6 mould by the dry winding process, respectively. The internal residual stresses were analyzed by measuring the released strain and spring-in angle during cutting process. With the aid of element birth and death technique, numerical model of the layer-by-layer winding process were created and the distributions of residual stress during winding were calculated. Subsquently, the curing process was simulated based on the constitutive model of CHILE (Tg). The after-curing residual stress and after-cutting spring-in deformation were predicted. It is shown that both the curing stress and the winding tension stress contribute to the total residual stresses. However, due to the further releasing of winding residual tension during the curing process, the total residual stresses are lower than the sum of the winding residual stresses and curing residual stresses. The impact of the winding tension strategies on total residual stresses is not affected by curing operation. The contribution of winding tension to the total residual stress is affected by the mould material used. The larger thermal deformation of the mould, the weaker the influence of winding tension strategy. For the situations with same mould, the winding cylinder with loose inside and tight outside (20N-40N-60N) tension strategy shows the smallest after-cutting spring-in angle and the one with tight inside and loose outside (60N-40N-20N) tension strategy shows the largest after-cutting spring-in angle. For the cases with same tension strategy, the winding cylinders made on PA6 mould give much larger after-cutting spring-in angle than that made on steel mould.
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The desalination evaporator based on the solar interface water evaporation technology can realize the desalination and purification of seawater, but the evaporation rate of the evaporator is low at present. In this work, the composite aerogel of polyvinyl alcohol and sodium alginate was prepared by directional freezing. At the same time, carbon nanotube materials were used as light absorbing materials. The effects of the composition, proportion and content of light absorbing materials of the composite aerogel on the evaporation performance of evaporator water were explored. The research found that the composite aerogel evaporator has a light absorption rate of up to 97% and excellent seawater desalination performance. The water evaporation rate under a sun light can reach 2.7 kg·m−2·h−1. In the long-term alternating process of light and darkness, the salt crystals accumulated on the surface of the evaporator will automatically melt and disappear, playing a self-cleaning effect, and can achieve long-term sustainable evaporation. It has broad application prospects in the field of seawater desalination.
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Composite materials have been widely used in architecture, medicine, aerospace and other fields because of their excellent properties, however, the damage monitoring of composite materials has always been one of the difficult problems concerned by experts and scholars at home and abroad. In this paper, shape memory alloy (SMA) was embedded in the composite, and the strain transfer effect of the interface layer was considered. Using the resistance sensing characteristics of SMA, a plastic damage monitoring model of SMA composite based on strain transfer was established, which realizes the real-time monitoring of plastic damage strain of composite materials. Based on the monitoring model, the effects of different material parameters on the average strain transfer rate between SMA and composite were discussed, and the damage monitoring behaviors of SMA under different initial states and temperature conditions were discussed. The results show that decreasing the thickness of the interface layer, increasing the shear modulus of the interface layer and increasing the embedded length of SMA all increase the average strain transfer rate of the interface. The change of SMA resistance and the plastic damage strain of the composite are piecewise linear. This study can provide a theoretical basis for further optimization design and application of SMA composite damage monitoring.
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Antimicrobials are indispensable drugs to inhibit bacterial infection. The overuse of conventional antibacterial (antibiotics) leads to the gradual enhancement of antimicrobial resistance of bacteria, which poses a serious threat to human health. As a new type of nano antibacterial material, carbon dots have the advantages of high anti antibacterial ability, wide range of raw materials, low cytotoxicity and good biocompatibility. Novel nano composite materials constructed by combining carbon dots with traditional antibacterial agents show great application prospects in the antibacterial field. This paper reviews the research progress on antibacterial mechanisms and applications of carbon dots and their composites. Firstly, the main factors affecting on the antibacterial performance of carbon dots are systematically analyzed by summarizing their antibacterial mechanisms. Secondly, the new nano composite materials combining carbon dots with traditional antibacterial agents and their applications in the antibacterial field are introduced. Finally, problems in the antibacterial application research of carbon dots and their composites are summarized and prospects are put forward, so as to provide reference experience for the design and synthesis of carbon dot composites with efficient and long-time antibacterial properties.
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To clarity the preparation of anti-overburden/de-icing coating and improve its properties on composite materials, the anti-overburden/de-icing mechanisms were systematically introduced in this article, including the structure, properties and influencing factors of superhydrophobic, super lubricating and composite coating finishing process. From the technical characteristics of textile composite coating finishing, the latest research anti-icing/de-icing functional finishing of textile composites was summarized. Finally, considering the weak weather resistance, poor shape plasticity and hard disassemble of present materials, the views that couple the advantages of different coating finishing technology to develop flexible type, composite synergy proof anti-overburden/de-icing functional textile materials were put forward. The review article may promote the development and research of cover/deicing function textile composite materials.
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The ASTM 3059—18 standard incorporated high temperature residual mechanical properties into the flame retardant index of resin matrix composites, which broke through the traditional chemical flame retardant concept of composites, and marked that the concept of structural flame-retardant has been valued by the designer.In this study, the self-made polysiloxane modified epoxy resin (EP-Si) was blended with phenolic resin (PF), supplemented with inorganic powder and glass fiber reinforcement. the effects of polysiloxane modified epoxy resin and inorganic powder on the high temperature residual strength of glass fiber/phenolic composites were studied by means of mechanical properties, thermogravimetric analysis(TGA), cone calorimeter(CCT) and scanning electron microscope(SEM). The experimental results show that when the amount of EP-Si is 40wt%, the flexural strength and high temperature residual flexural strength of the composite is 384.4 MPa and 53.3 MPa, respectively, which is 78.7% and 85.1% higher than PF composite. With appropriate proportion of inorganic powder, the maximum residual flexural strength can reach 85.1 MPa, which is 195.5% higher than PF composite. After heat-treated, PF composite containing silicon expands along thickness, while PF composite shrinks along thickness. The pyrolysis residual rate of the PF composite containing silicon is higher and oxidative degradation of the surface layer is faster. but the content of CO generated in the inner layer is lower than that of PF composite. The inorganic pyrolysis product of resin matrix containing silicon protects inner layer resin and fibers. The distribution of the in-situ pyrolysis inorganic product is more uniform, the good compatibility with inorganic powder and possible co-sintering effect further isolates the oxygen intrusion, improves structural integrity and high temperature residual strength.
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Copper nanowires not only have excellent electrical conductivity comparable to silver, but also have good light transmittance and flexural resistance due to the size effect at the nanoscale. In addition, it is far cheaper than gold and silver, hence it is an ideal electrode material for preparing flexible electronic devices. The synthesis methods of copper nanowires were systematically reviewed, such as template method, vapor deposition method, electrospinning technology, and chemical liquid phase method. Purification technologies based on water-hydrophobic organic solvent system and acid treatment for copper nanowires were introduced. Various cladding materials with core-shell structure and corresponding cladding technologies used to improve the oxidation resistance and stability of copper nanowires were listed, including inert metals, carbon-based materials, and organic polymer materials. The application status of flexible electronic devices integrating high-quality copper nanowires (or their composites) with flexible substrates (paper-based, polyurethane, and polyethylene terephthalate, etc.) in the fields of flexible transparent electrodes, energy storage/conversion, and flexible sensors were concluded. Finally, the challenges faced in practical application were prospected.
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The research on the generated cutting heat and cooling strategies plays a crucial role in the optimization of process parameters and the control of hole’s surface quality in drilling of Fiber Reinforced Composite (FRC). In this paper, the review and prospect on the drilling heat during drilling FRC is systematically analyzed and summarized from three aspects: the theoretical research of drilling heat, research on the influence of drilling heat on machining quality, influencing factors and control strategies of drilling heat during drilling. Firstly, the theoretical research of drilling heat formation mechanism, heat conduction and heat damage prediction, and numerical simulation of cutting heat in FRC drilling process were summarized. Then, the main measurement methods of FRC drilling heat and the effect of cutting heat on the quality of hole machining were introduced. Meanwhile, the influencing factors of cutting heat and its auxiliary processing methods to control FRC drilling heat were discussed. Finally, the current existing problems and key points on the next study of FRC drilling heat were summarized.
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In order to compensate for the defects of the traditional Cu2S counter electrode in the liquid polysulfide electrolyte, it shows higher electrocatalytic activity against the electrode. In this paper, carbon nanofibra-supported bimetallic sulfide NiS2-FeS2 (NiS2-FeS2/CNFs) counterelectrode has been successfully prepared by electrospinning technology and a simple one-step hydrothermal method, which shows excellent electrochemical performance when applied to quantum dot sensitized solar cells (QDSSCs). At the same time, NiS2-FeS2 composites with different concentrations show great differences under scanning electron microscopy (SEM), and the preparation of paired electrodes loaded with carbon nanofibers also has a great impact on the battery performance. Therefore, this paper focuses on exploring the effect of NiS2-FeS2/CNFs counter electrode with different concentrations prepared by hydrothermal method on the photoelectric performance of QDSSCs assembled by the counter electrode, so as to obtain the best counter electrode concentration. The experimental results show that when the NiS2-FeS2/CNFs concentration ratio is 0.8, the maximum photoelectric conversion efficiency (PCE) of the battery is 8.05%.
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The ongoing surge in demand for energy and the increasing environmental crisis makes the high-performance energy storage device become a research hotspot in recent years. Based on the power and energy density, energy storage devices can be divided into electrochemical capacitors, secondary batteries, and fuel cells, etc. Electrode material play an important role in the preparation of energy storage with green environment protection and high performance. Nanocellulose has great application potential and development prospect in the preparation and performance improvement of energy storage materials due to their natural abundance, environmental sustainability, high specific surface area, excellent mechanical properties and biocompatibility. In this paper, the classification, preparation, modification of nanocellulose and nanocellulose composites were summarized, the application and research progress of the mixing of nanocellulose with electroactive substances and the preparation of hydrogel, aerogel, paper/film composites based on nanocellulose and as carbon precursors in electrode materials were mainly introduced.
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Compared with metal, ceramic or other structural materials, continuous fiber-reinforced polymer composites can offer significant advantage for their excellent design tailorability, mechanical properties, fracture toughness, good resistance to corrosion and fatigue, and are widely used in aerospace, transportation, energy, machinery and other fields. The organic combination of continuous fiber-reinforced polymer composites and additive manufacturing technology has the potential to promote new revolution for weight saving and structure-function integrated manufacturing of high-end equipment. This paper reviewed the recent research progress of extrusion and impregnation methods, printing temperature, auxiliary process, printing speed, printing spacing and geometric construction methods in additive manufacturing of continuous fiber composites. The influence of various process parameters on properties of the formed parts was emphatically discussed. Finally, the present challenges and future development directions have been prospected for reference.
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With the rapid development of flexible pressure sensors in the fields of health detection, electronic skin and wearable electronic devices, the research on fabrication of high-performance flexible piezoresistive sensors has become prevalent. The performance of flexible pressure sensors can be optimized by nanomaterials because of their surface and interface effects, small size effects and macroscopic quantum tunneling effects. Nanomaterials based pressure sensor has the advantages of small size, wide detection range and high sensitivity. In this paper, the latest research progress of nanomaterials in flexible pressure sensors in recent years is reviewed.
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Coral sand is widely used as a preferred building material for emergency projects of reef islands in the South China Sea. The mechanical properties of coral mortar are normally low due to the loose porosity, low particle strength and easy breakage of coral sand, making it hard to meet the requirements of practical projects. It is well recognized that graphene oxide (GO) can effectively improve the mechanical properties of coral mortar, but limited studies focus on the dynamic mechanical properties of GO-modified coral mortar under impact loads. In this study, a series of impact compression tests and microscopic tests were conducted on GO-modified coral mortar to investigate effects of GO content and strain rate on its dynamic mechanical properties and microscopic behaviors, respectively. Experimental results demonstrate that stress-strain curves of coral mortar could be approximately divided into four stages, and the development patterns of the curves were combinedly influenced by GO content and strain rate. The dynamic compressive strength of GO-modified coral mortar firstly increases and then decreases with increasing GO content, with a maximum value at 0.03wt% of GO content. Also, the dynamic strengthening factor (DIF) and toughness index of GO-modified coral mortar show obvious strain-rate effects. Microstructural observations imply that the addition of GO could drive hydration products to fill the cracks or large pores inside coral mortar, leading to improvements in its structural integrity and impact resistance performance.
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For the corrosion and wear failure of materials used in the marine environment, the (CrFeNiAl)100-xMox high-entropy alloy coatings were prepared on 304 stainless steel (304ss) by laser cladding. The phase composition, microstructure, hardness, wear resistance and corrosion resistance of the coatings were analyzed. The results show that the coatings are composed of BCC+B2 phases. With the increase of Mo, the content of B2 phase gradually increases, and nano scale B2 phase precipitates in the dendrite. The hardness of the coating increases with the increase of Mo content, the highest hardness reaches 636.6 HV0.2, and the wear resistance increases gradually. The corrosion current density firstly decreases and then increases with the increase of Mo, indicating that the corrosion resistance of the coating firstly increases and then decreases in 3.5 wt% NaCl solution. The results of immersion corrosion show that the coatings are selectively dissolved in the interdendritic region. The corrosion current density and passivation current density of (CrFeNiAl)92Mo8 coating are lower than 304 ss, and the corrosion resistance is the best with good wear resistance. Adding appropriate Mo element can improve the wear resistance and corrosion resistance of (CrFeNiAl)100-xMox coatings.
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To solve the problem of poor bonding effect of polyurethane (PU)/metal at room temperature when Chemlok218 was used as adhesive, a highly active PU modifier was used to modify phenolic resin (PF) in Chemlok218 to form a PF@NCO transition layer between Chemlok218 coating and PU. FTIR and TG analysis showed that the NCO group in PU modifier reacted with the hydroxyl group of PF to form carbamate group, and the surface energy of PF@NCO could be improved. The compatibility with PU had increased. When the mass ratio of Chemlok218 to PU modifier is 80∶20, the peel strength of PF@NCO-20 reaches 23.4 kN·m−1, which is 58.1% higher than that of pure Chemlok218, and the whole PU/metal bonding sample had no bonding weaknesses and defects. The purpose of this paper is to provide a reference for solving the problem of bonding strength of PU/metal at room temperature.
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To study the change law of bubble defects before and after the sintering of yttria-stabilized tetragonal zirconia (Y-TZP) ceramics and the influence of bubble defects on fracture toughness of materials, the flaws of 3Y-TZP ceramic before and after sintering were observed by X-ray microscope, and the variation law of defects was obtained. Then, testing the bending strength of 3Y-TZP, 4Y-TZP, and 5Y-TZP ceramic with different yttrium oxide content under the condition of natural defects or artificially introduced volume defects, and calculating the Weibull modulus and fracture toughness. The failure modes of each group were observed under SEM. The results show that sintering can repair the bubble defects of zirconia ceramics, and the repair rate is about 74.12%. When the diameter is less than 10 μm, the repair rate is up to 97.22%. When the diameter is more than 40 μm, the repair rate is only 20%. The diameter of more than 80% of bubble defects after sintering shall not exceed 20 μm. The bending strength of zirconia ceramics decreases with the increase of yttrium oxide content. The introduction of volume defects significantly reduce the bending strength of zirconia ceramics, of which 4Y-TZP ceramic has the best stability, and the strength decreased by only 8.64%. 5Y-TZP ceramic is the most sensitive to defects, and the strength decreased by 22.58%. The fracture toughness decreases with the increase of yttrium oxide content. The depth (a) and half-width (c) of the introduced volume defect will affect the fracture toughness of zirconia ceramics. The fracture toughness increases first and then decreases with the increase of a/c, reaching a peak value when a/c≈1.5.
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The discrete mechanical properties of SiC/SiC composites originate from their structural units and microstructural features. In this paper, for the unidirectional fiber bundle SiC/SiC composites with the simplest structure, the strength distribution pattern was analyzed by the two-parameter Weibull distribution and the median estimated distribution, and the discrete nature was revealed based on the deep learning of the microstructure of each group element (matrix, interface phase, and fiber) of the composites. The results show that the tensile strengths of the unidirectional fiber bundle SiC/SiC prepared in the small and medium test furnaces are located at (331.02 MPa, 407.82 MPa) and (161.09 MPa, 540.95 MPa), respectively; the former Weibull modulus (20.59) is 75.7% higher than the latter (5.01), indicating an increase in the dispersion of the medium test. The results of deep learning of fracture morphology show that matrix cracking, interface deflection and fiber fracture pullout are the main failure mechanisms, and due to the distribution of matrix crack spacing at (83.2 μm, 107.8 μm), the calculation by the micromechanical equation indicates that matrix nonuniformity is the main reason affecting the reliability of the composites.
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Photocatalytic reduction technology of CO2 can not only achieve energy saving and emission reduction, but also alleviate energy shortage, which is in line with today's concept of green and sustainable development. By employing electrospun TiO2 nanofibers as substrate, bismuth- rich Bi4O5Br2/TiO2 composite fibers were prepared combining with in-situ hydrothermal reduction method. The composition, morphology and photoelectric properties were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), high resolution transmission electronmicroscopy (HRTEM), X-ray photoelectric spectroscopy (XPS), ultraviolet-visible absorption spectrum (UV-vis) and carbon adsorption. The results show that the band gap of Bi4O5Br2/TiO2 composite fibers becomes width, there is obvious absorption in the visible light band, and the reduction ability of photogenerated electrons is enhanced. Bi4O5Br2/TiO2 composite fibers can reduce CO2 to CH4 and CO, while the enrichment of the metal Bi can not only improve the adsorption capacity of the catalyst for acidic CO2 molecules and enhance the conversion efficiency, but also change the photocatalytic reaction path and generate alcohol products such as CH3OH. The CH4, CO and CH3OH yields of the optimized photocatalyst Bi@Bi4O5Br2/TiO2 composite fibers were 3.87, 1.06 and 0.32 μmol·h−1·g−1, respectively, after simulated sunlight irradiation 3 h. This work paves new opportunities for exploring high-efficiency CO2 photoreduction catalysts.
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A flexible strain sensor is a device that converts changes in external stress into electrical signals. It overcomes the shortcomings of traditional rigid sensors such as high hardness and poor human adaptability. As a wearable device, it has great development prospects in the field of human motion monitoring. However, in harsh conditions or extreme environments, there are still risks such as signal output distortion and easy corrosion. The superhydrophobic flexible strain sensor combines the water repellency, surface self-cleaning, anti-corrosion and anti-fouling of the superhydrophobic coating with the high ductility and high sensitivity of the flexible strain sensor, which enhances the performance of the sensor and broadens the applications in human motion monitoring. This paper reviews the basic performance parameters of superhydrophobic flexible strain sensors, the commonly used construction materials and construction methods as well as their functions and applications in human motion monitoring, and provides perspectives on this field.
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To solve the problems such as poor compatibility with the cementitious matrix and high cost of current bacterial carriers, a type of self-healing concrete by immobilizing non-axenic bacteria into recycled aggregate (RA) with enhancement was proposed. The reasonable enhancement time of RA and its effect on the compressive strength of concrete were first investigated. Then, the crack-healing capacity and the crack-filling precipitations of concrete immobilizing non-axenic bacteria were studied. The test results show that the reasonable enhancement time of the RA using biodeposition of non-axenic bacteria is 7 days. The water absorption and crushing index of recycled coarse aggregate (RCA) decrease by 27% and 20%, respectively. The compressive strength of concrete prepared with the enhanced RCA increases by 12.9%. After 28 days of healing, the average values of healed crack widths and completely healed percentages of cracks of the concrete specimens by immobilizing non-axenic bacteria into RA with enhancement are up to 0.28 mm and 60%. The maximum width value of healed cracks reaches 1.26 mm. The water permeability coefficients of the concrete specimens can decrease by up to 99.7% compared to that without crack-healing. The crack-filling precipitations of self-healing concrete by immobilizing non-axenic bacteria exhibit regular cubic shapes. The crystals of these precipitations are calcite.
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Low velocity impact on the structural free edge would threaten the safety of laminated composite structures. In this paper, experimental and numerical investigations were conducted to study the edge-on impact behaviors of T700/YPH307 composite laminates. Visual inspection, ultrasonic C-scanning, electron microscopy and X-ray computed tomography (CT) technique were performed to detect the post-impact damage status of composite laminates subjected to edge-on impact, which could further reveal 3D spatial distribution of internal damage. Based on the Mohr’s theory of fracture plane, a continuum damage mechanics model, considering fracture plane angle within anisotropic materials, was established. And with combination of cohesive zone model, the initiation, propagation and interaction of complicated edge-on impact damage modes, i.e. intra-laminar fiber and matrix failure and inter-laminar delamination, could be characterized in detail. There is a good agreement between numerical and experimental results. It is suggested that failure mechanisms induced by edge-on impact mainly include two distinct characteristics, namely the generation of localized debris wedge beneath the impactor corresponding to peak value of impact force, and the bending fracture of outer plies due to the wedge effect at the stage of stable fluctuations in impact force. Furthermore, it is found that the internal damage would be more serious with the impact energy increasing, while stacking sequence has a relatively small influence on the edge-on impact responses and damage morphology.
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With the increasing development of industrial production, the demand for gas sensors is growing. Given that triethylamine is easily harmful to the human body, it is important to develop a gas sensor that can effectively detect triethylamine. Considering the shortcomings of common gas sensors with high working temperature and high energy consumption, a gas sensing material that can quickly detect triethylamine at room temperature was proposed in this paper. Through the combination of electrospinning, heat treatment and in-situ chemical oxidation polymerization, the inorganic-organic composite, WO3@ Polyaniline (PANI) nanofibers, was successfully synthesized with controllable component content. Scanning electron microscopy, X-ray diffraction, energy dispersive X-ray spectrometer and Fourier transform infrared spectroscopy were used to characterize the morphology, element content and functional groups of the as-prepared samples. The composite demonstrates fibrous morphology with PANI uniformly distributed on the surface of WO3 nanofibers, forming WO3@PANI core-shell structure. The WO3@PANI composite nanofibers show good sensing performance to triethylamine at room temperature. In addition, excellent sensing properties are also achieved, such as excellent triethylamine selectivity, stable response under high humidity condition, wide concentration detection range (50–5000 μg/g triethylamine) and good response-recovery characteristics. Compared with sensing performance of pristine PANI and WO3 nanofibers, the enhanced sensing response of WO3@PANI composite nanofibers is mainly attributed to the p-n heterojunction formed between WO3 and PANI.
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In order to enhance the seismic capacity of concrete flexural members, a graded reinforcement scheme with the glass fiber reinforced plastic (GFRP) bars and the steel bars was developed to make a graded distribution of bearing capacity that matches the external force distribution, and then multiple-plastic regions were formed. Five concrete flexural members with different graded reinforcement parameters were designed, and the comparison parameters included the height of the grades, the type of bars, the reinforcement ratios and the construction methods. Through the pushover experiment, the formation and mechanical effects of multi-plastic regions were studied, and the formation mechanism of multi-plastic regions was analyzed in details. The results show that the reasonable graded reinforcement scheme can form multi-plastic regions in the concrete flexural member. The number and development degree of plastic regions significantly affect the seismic behaviours of members. The formation condition of the multi-plastic regions is that the external moment is between the sectional yield moment and ultimate moment in several grades. The development level of each plastic region can be effectively controlled by adjusting the length and reinforcement of the grades, and the failure position and failure mode of the member can be designed. A great increment provided by GFRP bars with line elasticity properties on the bending bearing capacity after yielding is a key factor for the formation and regulation of multi-plastic regions.
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In order to solve the problem that graphene (G) is uniformly dispersed in cement slurry and its dosage is too high when it is functionalized into cement-based materials, a graphene (G-SD) with both high conductivity and water solubility was selected as a conductive filler. The effect of sodium lignosulfonate (MN) on the dispersion ability of G-SD in saturated calcium hydroxide solution (CH) used for simulated cement pore solution in the presence of polycarboxylate superplasticizer(PCE)and the effects of G-SD on the resistivity , electrothermal properties , snow melting and deciding , and thermoelectric properties of cement paste were investigated. The absorbance test shows that when the mass ratio of MN to G-SD is 3∶1, the dispersion of G-SD reaches the best. The electrical performance test shows that percolation threshold of graphene cement-based materials is 0.4wt%. What's more, good electrothermal performance are shown under the threshold, the temperature of cement paste specimen can be increased by 320 ℃ for 20 min with 30 V voltage, and 4 cm thick ice layer can be basically melted within 25 min, so it possesses good potential for deicing and snow-melting. The thermoelectric properties shows that Seebeck coefficient of cement paste specimen is 154.4μV/K when the content of G-SD is 0.1wt% by the cement mass. The above studies show that G-SD can endow cement-based materials with excellent electrical, thermal and thermoelectric functional properties at very low dosage.
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To explore the shear performance and the corresponding mechanisms of Carbon Fiber Reinforced Polymer (CFRP) strengthened Reinforced Concrete (RC) shear walls, a three-dimensional numerical model based on the Hashin damage criteria that captures the CFRP-concrete interface debonding behaviors was developed. Using the proposed model, the influences of shear span ratio, CFRP ratio and wrapping method on the shear capacities of the CFRP-strengthened RC shear wall were investigated. It is found that: (1) the external CFRP strips effectively mitigate the development of the shear primary cracks; (2) the increasing shear span ratio reduces significantly the shear contribution provided by CFRP strips on the CFRP-strengthened RC shear walls; (3) the shear contribution of CFRP is not linearly dependent on the number of CFRP layers. From qualitative to quantification analysis, the influence coefficient of shear span ratio and CFRP layer was introduced based on the numerical calculations. Furthermore, writing in the form of the American Code (ACI 440.2R-17), a calculation formula characterizing the shear contribution of CFRP was established. By comparing with the experimental data, it is noticed that the proposed formula gives more accurate descriptions on the influence of shear span ratio, CFRP ratio and wrapping method on the shear contribution of CFRP. The average absolute error between the prediction results and the experimental results is 8.0%, thus, verifying the effectiveness of the proposed calculation method.
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Abstract: Oily sewage is ubiquitous in the petrochemical industry, machinery manufacturing and other fields. Direct discharge not only wastes water and oil resources, pollutes the ecological environment, but also affects the survival and health of human beings and other organisms. The traditional oil-water separation method has strong limitations, such as poor economy and low separation efficiency. Based on 316 stainless mesh, a superhydrophilic/underwater oleophobic membrane that is resistant to long-term water immersion and oil pollution was developed. The water-based acrylic acid resin and water-based epoxy topcoat resin were selected as the binder, and the substrate was pretreated with phytic acid. The superhydrophilic/underwater oleophobic membrane coated with water-based coating was prepared using a one-step spraying method. It is found that the separation efficiency of wastewater with different oils can reach more than 98%, the water flux can reach more than 14000 L/(m2·h·bar), and the intrusion pressure of oil is 4.65 kPa. After 50 cycles of separating wastewater with N-hexane, the separation efficiency of the membrane can still reach more than 98%. After 180 days of water immersion, the membrane still maintains superhydrophilicity with a water flux of more than 6500 L/(m2·h·bar). After adding a small amount of surfactant of sodium dodecyl sulfate, the water flux of the membrane decreases by less than 50% after 50 pollution and cleaning cycles. This study provides technical references for the development and preparation of superhydrophilic separation membranes in the field of refined oily wastewater treatment.
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This study aims to explore the crushing deformation characteristics and underlying energy dissipating mechanisms of carbon-fibre-reinforced plastic (CFRP)-aluminum-aluminum foam hybrid tubes under both axial (0°) and oblique (10°) loads. Quasi-static compressive tests for net CFRP tubes, net aluminum (Al) tubes, net aluminum foams (Af), Al-Af hybrid tubes and CFRP-Al-Af hybrid tubes were performed first; the energy absorptions of the Al-Af hybrid columns are always higher than that of the sum net parts under loading angles of 0° and 10°; the energy absorption of the CF-Al-Af hybrid columns reduces under a 0° loading angle while improves remarkably under a 10° loading angle compared with the sum of net parts. Next, numerical models for these hybrid tubes and the corresponding net parts were developed in LS-DYNA, and numerical results indicate that the energy absorption improvement of Al tubes promotes the load-carrying enhancement of Al-Af and CF-Al-Af hybrid tubes, because the Al tubes in hybrid happen more stable symmetric deformation compared with the “symmetric-diamond” hybrid deformation of the net Al tubes; whereas the energy absorption reductions of external CF tubes primarily decrease energy absorption of CF-Al-Af hybrid tubes, because the CFRP tubes in the hybrid occur axial splitting failure due to compressions of inner Al tubes. Finally, the analytical models on mean crushing forces for CF-Al-Af hybrid columns and corresponding net components under axial load were developed, and the results indicate that the developed analytical models can better predict the mean crushing forces of both hybrid columns and net parts.
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To reduce the porosity of 3D printing continuous fiber reinforced polymer (CFRP) composites and improve the degree of resin impregnation on fibers, it is of great necessity to conduct research on the preparation and 3D printing performance of melt-impregnated continuous fiber prepreg filaments, as well as develop integrated fiber prepreg equipment. With glass fiber (GF) and carbon fiber (CF) as reinforcement, and polycarbonate (PC) as matrix, this study aims to develop a melt-impregnated prepreg wire preparation process and study the influence of the impregnation process on prepreg wire properties. Besides, using prepreg yarn as the raw material, this study is aimed at studying the effect of 3D printing forming process parameters on the fiber content, porosity and mechanical properties as well. The results indicated that when the tensile strength of continuous glass fiber reinforced polycarbonate (CGF/PC) prepreg filament was 627.8 MPa, the printing temperature was 260°C, the layering thickness was 0.10 mm, the scan spacing was 1.0 mm, the fiber content of continuous carbon fiber reinforced polycarbonate (CCF/PC) composite was 28.66vol%, the tensile strength and modulus were respectively 644.8 MPa and 85.6 GPa, and the optimized porosity was 3.87%. When the printing temperature was 280°C, the layering thickness was 0.14 mm, and the scan spacing was 1.2 mm, the fiber content of continuous glass fiber reinforced polycarbonate (CGF/PC) composite turned out to be 51.35vol%, the tensile strength and modulus were respectively 381.4 MPa and 23.6 GPa, and the optimized porosity was 4.41%.
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In this paper, oxidized hyaluronic acid (OHA) was synthesized by oxidizing hydroxyl groups on hyaluronic acid (HA) with sodium periodate. OHA/HPCS self-healing hydrogel was prepared by using OHA and hydroxypropyl chitosan (HPCS) as raw materials. The aldehyde group on OHA reacted with the amino group of HPCS to form dynamic imine bond through Schiff base reaction. In this paper, the microscopic morphology and properties of OHA/HPCS self-healing hydrogel was characterized by Fourier Transform infrared spectroscopy (FT-IR), UV-Vis spectrophotometer (UV-Vis), scanning electron microscopy (SEM), rheology and 1H NMR. OHA/HPCS hydrogels have a porous structure, and the results showed that the pore size ranged from 70 to 200 μm by changing the amount of OHA. With the increase of the dosage of OHA, the pores in the OHA/HPCS hydrogels increased, the pore size became smaller, the swelling ratio of OHA/HPCS became smaller, and the degradation rate became slower. OHA/HPCS hydrogel could self-heal within 4 h at room temperature without external stimulation. OHA/HPCS hydrogel can release anticancer drug of gemcitabine in sustained way, with a cumulative release percent of 70%-84% in 12 days. OHA/HPCS hydrogels have the properties of sustained release gemcitabine, indicating that OHA/HPCS hydrogels have potential application prospects in the field of drug release.
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To explore a kind of triaxial cross-linked hollow fiber membrane (HFM) with self-cleaning performance, polyacrylonitrile based HFM which was prepared by wet processing was chemically modified into amidoximated PAN hollow fiber membranes. Then the active groups were coordinated with metal ions (Fe3+) randomly to achieve metal coordinated amidoximation PAN hollow fiber membranes with triaxial cross-linked structure. Preparation process, structural composition, surface morphology, hydrophilic and hydrophobic properties, membrane flux and retention, self-cleaning performance of the hollow fiber membranes were studied. Results show that the amidoximation rate of the membranes increases with the rise of time, temperature and hydroxylamine hydrochloride concentration during the modification process, and the modification levels would affect the crystallinity of the hollow fiber membranes so as to enhance the adsorption of small molecules into the fiber material. Although the Fe ions on the membranes would impact their crystal structure, hydrophilic property and membrane flux, but the triaxial cross-linked structure would promote the retention performance for bovine serum albumin to 88%. Besides, Fenton catalytic system coupled by Fe(III) and H2O2 endows FePAN-HFM with antifouling and self-cleaning properties and the flux recovery rate reaches to 84.6% significantly.
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In recent years, flexible pressure sensors with three-dimensional mesh structure show high reversible compressibility and good sensitivity, and their complex network shape is also conducive to the construction of stable conductive network, which is widely used in human health monitoring, wearable devices, medical diagnosis and other fields. In this study, a carbonized wood sponge(CWS)/TPU composite pressure sensor with three-dimensional layered structure based on natural balsa wood was designed to construct a stable three-dimensional conductive network and optimize the sensing performance. The catalytic treatment, carbonization process, sensing performance and human applicability of the sensor were characterized. The results show that the carbon yield of the light wood-based CWS/TPU sensor by catalytic treatment and high temperature carbonization can reach 20.15%, the compressive strain can reach at 60%, and the maximum pressure sensing sensitivity (S) can reach 12.87 kPa−1 in the pressure range of 0-4 kPa. Moreover, the sensor still has good sensing stability and environmental stability even after 5000 compression/release cycles, showing good sensing performance. The sensor was successfully used to monitor hand movement, walking and pulse in real time, which shows the potential application value of the sensor in motion and health monitoring.
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In order to study the bonding performance of bamboo scrimber bar-bamboo biochar mortar interface, pull-out tests were carried out on 85 bamboo scrimber bar-bamboo biochar mortar specimens. The effects of surface modification methods of bamboo bar, equivalent diameter of bamboo bar, compressive strength of mortar and bond lengths on the bond properties were also taken into consideration. The different bonding failure modes of the pull-out specimens were observed. The bond-slip curve, bonding strength and slippage were obtained. The failure mechanism was analyzed. A bond-slip constitutive model of bamboo scrimber bar-bamboo biochar mortar interface was established, and the effective surface modification method of bamboo scrimber bar was obtained. The results of the study show that there are three failure modes of the specimens under different initial conditions, including mortar splitting failure, bamboo bar tensile failure and bamboo bar pulled-out failure, among which mortar splitting failure is the most common. The failure process can be divided into micro-slip stage, slip stage, descending stage and residual stage. The bonding strength of the mortar interface can be increased by 13-46 times by modifying the surface of the bamboo bar. The interfacial bonding performance decreases with the increase of bonding length and equivalent diameter, and the effect of mortar strength on bonding strength is not obvious. It is recommended to modify the bamboo scrimber bar through the two methods of sticking sand and coating epoxy mortar. On the basis of ensuring bonding performance, it can improve the peeling of water absorption and expansion of bamboo bands during the maintenance process and the problem of the structure failing in advance. According to the experimental bond-slip curve, the bond-slip constitutive model of bamboo scrimber bar-bamboo biochar mortar treated by sticking sand was proposed. The bond-slip constitutive model can accurately predict the bond behavior between bamboo scrimber bar and mortar. After verification, the model is also applicable to the bonding interface destruction in the test under the other modification of bamboo.
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Nano-silica (NS) modified asphalt is satisfactory in mechanical properties but is expensive. Fumed-silica (FS) is also a nanoscale material and the price is only 1/10 of NS. To evaluate the feasibility of FS replacing NS, using 3 wt% original silica (OS), fumed silica (FS), hydrophobic nano silica (MNS) as modifier, the rheological properties of corresponding modified asphalt were studied compared with matrix asphalt (Esso, ES) by the multi-stress creep recovery test (MSCR), linear amplitude scanning test (LAS) and bent beam rheological test (BBR). The results show that the optimal modifier FS has the best effect on the rutting resistance at high temperature and the fatigue resistance at intermediate temperature for asphalt, and the least negative effect on the low temperature performance. The mechanism for these results was explored by SEM, temperature scanning test (TeS), variable temperature infrared spectroscopy (VT-IR), TGA and DSC. The intrinsic primary aggregates of FS and unique ES-hydroclusters system played a key role in the performance of FS-asphalt composite. Therefore, fumed SiO2 is a cost-effective nano-scale material used to modify asphalt.
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3D printing technology provides multi-scale, multi-material and multi-dimensional manufacturing capability for microwave absorber, which is beneficial to take advantage of the combination of material loss and structural loss. In this work, a three-layer periodic crisscrossed structural microwave absorber was fabricated by using FeSiAl-MoS2-GN/PLA composite filaments, and the effects of the geometric parameters of the unit cell and the combination of materials of each layer on the absorption performance of the complex structural absorber were investigated. The effective absorption bandwidth (EAB, for RL≤−10 dB) of the absorber is 12.7 GHz when the graphene content of dielectric layer, absorption layer and matching layer is 0wt%, 5wt% and 4wt% in turn. At the same time, the EAB value are greater than 10 GHz when the incident angles of TE polarized wave and TM polarized wave are less than 40° and 70°, respectively. This study provides a theoretical and applied basis for the design and manufacture of wide-angle and broadband wave absorbers due to the experimental results are basically consistent with the simulation results.
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Biochar is a product of pyrolysis of biomass under anoxic conditions, but the common biochar has a small specific surface area, underdeveloped pore structure, few surface active groups and poor removal effect. In this paper, biochar was prepared from sorghum (GC) and grapefruit peel (YC) by surface treatment using four substances to obtain biochar, where the prepared sorghum/KOH (GC-KH) and grapefruit peel/KOH (YC-K) powders had obvious surface porosity, confirming the feasibility of the process. With a specific surface area of 2,096.05 m2/g and an average pore size of 4.12 nm, GC-KH is rich in oxygen-containing functional groups on its surface, providing a good structural space and active sites for adsorption. The effect of dosing volume, initial pH, contact time and initial concentration on phosphate adsorption was investigated in batch experiments to assess the ionic strength. The isotherm results show that the Langmuir model can describe the equilibrium data well, and the maximum adsorption capacity of GC-KH for phosphate at pH 7 is 74.73 mg/g, which has significant advantages such as rapid response and provides an innovative pathway for efficient removal of phosphate from wastewater.
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Transition metal-based electrocatalysts with abundant reserves and low cost have been widely studied as potential substitutes for efficient oxygen evolution reaction (OER) precious metal electrocatalysts, but there are still problems of poor activity and conductivity. Here, a Co-MOF (ZIF-67) as precursor was designed to prepare a nitrogen-doped carbon (NC) based CoWO4 (CoWO4/NC) catalyst was reported with abundant oxygen vacancy through pyrolysis after adoption Tungsten chloride (WCl6). The feeding ratio and calcination temperature of the catalyst were explored. OER performance in alkaline medium was tested. The test results showed that the catalyst prepared at a feeding ratio of 1∶1 and a calcination temperature of 550℃ exhibited a lower overpotential (346 mV, J=10 mA·cm−2), a lower Tafel slope (65 mV·dec−1) and a higher conductivity. The stability of the catalyst under alkaline conditions was tested by the timing potential method. The performance did not degrade significantly within 22 hours. This work provides a new idea for the research of transition metal-based catalyst and has certain guiding significance for the design of catalyst.
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Tetracycline hydrochloride (TC-HCl), which can be released into the aquatic environment through excreta, poses a potential threat to aquatic systems and human health due to its stable structure and difficult biodegradability. As one of the photocatalytic materials of great interest, BiOCl development applications are limited by the low solar light utilization and the hight rate of photogenerated electron-hole recombination. In this study, Fe-doped BiOCl porous microspheres self-assembled from two-dimensional nanosbeets were synthesized by a one-pot solvothermal method without the addition of surfactants, and the degradation properties for TC-HCl was investigated. The results showed that Fe doping narrowed the forbidden band width of BiOCl, thereby improving the light absorption intensity and broadening the photoresponse range to the visible region. Fe doping accelerates the separation of photogenerated carriers and improves the photocatalytic performance of BiOCl. The 0.15-Fe/BiOCl has the best removal effect on TC-HCl (30 mg/L), and the removal rate can reach 92% after dark adsorption and photocatalysis. Combined with the experimental results, the mechanism of photocatalytic degradation of TC-HCl by Fe-doped BiOCl under visible light was revealed in this study, and the reasons for the reduction of cycling activity were analyzed, which provided a promising method for the preparation of transition metal-doped BiOCl materials with high photocatalytic activity and feasible insights for improving the cycling activity of materials.
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The interfacial properties between polymer and fiber are particularly important for improving the mechanical properties of composites. In this paper, the surface of nano-SiO2 was modified by polyurethane (PU) capped by isocyanate (—NCO), and the surface of carbon fiber (CF) was modified by KH550. Bacause of the high reactivity of —NH2 and —NCO, the covalent bond was formed between CF and nano-SiO2 particles through PU molecular chain. The results show that the introduction of PU polar molecular chain improved the surface energy and wettability of CF. Compared with the CF directly grafted with nano particles by KH550(CF-KH550-SiO2), the surface energy of the CF with nano particles linked by PU(CF-KH550-PU-SiO2) molecules increased by 23.0%, and the grafting rate and dispersion uniformity of surface nano SiO2 particles also improved significantly. Compared with the untreaed CF/epoxy resin (EP) composites, the interfacial strength (IFSS) and the interlaminar shear strength (ILSS) of CF-KH550-PU-SiO2/EP composites increased by 72.9% and 47.9% respectively. Compared with the CF-KH550-SiO2/EP composites, the interfacial strength (IFSS) and the interlaminar shear strength (ILSS) of CF-KH550-PU-SiO2/EP composites increased by 17.3 % and 11.2% respectively.
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Functional emulsion is one of the hot topics because of their functional factors. Bio-macromolecules hyaluronic acid (HA), lysozyme (Lys) and trace metal element zinc can self-assemble to prepare Lys-Zn2+/HA colloidal particles by electrostatic interaction. The effects of different raw material concentration on the properties of colloidal particles were studied to obtain colloidal nanoparticles under optimal assembly conditions. The size and morphology of the colloidal particles were characterized by nanometer particle size analyzer and scanning electron microscope. The results show that the formed colloidal particles have a spherical structure with a particle size of about 300 nm. The colloidal particles have surface activity and can be reassembled at the oil (containing fat-soluble vitamin D3)-water interface to stabilize oil-in-water functional Pickering emulsions. The effects of pH and salt concentration on the properties and emulsifying properties of colloidal particles were investigated in detail. The sustained release properties of the emulsion to trace metals and vitamin D3 functional factors were studied with the optimum emulsion performance. The results show that the emulsion has a certain sustained-release performance for both water-soluble and fat-soluble functional factors and has potential applications in the fields of food, medicine and cosmetics.
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The development of renewable, low-cost and environmentally friendly electrode materials with fast ion/electron transfer rate and adjustable surface chemistry is an urgent need for the development of current energy storage devices. In recent years, biomass carbon materials have attracted much attention because of their low cost, renewable and good cycling performance, but their low specific capacitance and energy density affect their practical applications. Here, the biomass waste was transformed into carbon materials with good chemical properties, and the transition metal oxide Fe2O3 was composite by heteroatom-doped biomass carbon materials, taking advantage of the complementary strengths of Fe2O3 and nitrogen doped carbon was used to prepare Fe2O3/ nitrogen-doped biomass carbon (NBCs) composite materials by one-step carbonization, showing excellent electrochemical performance. The results show that the specific capacitance of Fe2O3/NBCs as the negative electrode material is 575 F·g−1 at a current density of 1 A·g−1. At the same time, Fe2O3/NBCs-700°C and NiCoFe-P were used as cathode and cathode materials respectively to assemble asymmetric supercapacitors, achieves an energy density of 33 W·h·kg−1 at a power density of 800 W·kg−1. The assembled asymmetric supercapacitors also exhibit excellent cycling stability, maintaining 82.35% capacitance after 3500 cycles. Therefore, Fe2O3/NBCs is a promising electrode material for supercapacitors as negative electrode materials.
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The organic piezoelectric sensor prepared by electrospinning is better flexibility, light weight and breathability than the traditional pressure sensor, which has attracted much attention in the field of wearable sensor research. In this paper, a method of preparing BiCl3/P(VDF-TrFE) composite film by electrospinning was proposed, and the flexible piezoelectric sensor was designed and prepared with the composite film as the functional layer. After a certain amount of BiCl3 was added, the scanning electron microscope analysis showed that the average diameter of the fiber increased from 619 nm to 1158 nm, and the surface became smoother. The X-ray diffraction pattern confirmed the stability of the composite film β phase content has been significantly improved. The piezoelectric response testing results show that the peak to peak Voc and Isc of P(VDF-TrFE) composite films with 2wt% BiCl3 are 16.8 V and 164 nA, Compared with pure P (VDF TrFE) piezoelectric film, it is obviously improved, 215% and 224% times. The pressure sensing testing results show that the piezoelectric film is good linear output characteristics under the pressure of 1.28 N. A flexible wearable force sensing keyboard was designed with this film, which can collect fingers pressing force and duration time. And it provides a reference solution on smart fabrics such as flexible keyboard applications.
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With the rapid development of aerospace, military, and electronic technologies, packaging methods and packaging materials have become important constraints for electronic devices to further achieve miniaturization, lightweight, and high performance. Phased array radar T/R module packaging materials have experienced from the first generation of Kovar alloy to the second generation of copper-tungsten alloy, and the emergence of the third generation of lightweight materials with aluminum as the matrix in recent years - silicon carbide particle reinforced aluminum matrix composite material and high silicon aluminum alloy, and the problems in the preparation and processing technology of the two have become an important bottleneck restricting the comprehensive promotion and application of the third generation of materials. In this paper, the preparation methods, machining properties, welding processes, and surface treatment of the new generation of packaging materials are reviewed, and the research technology status of the processing and application of the new generation of phased array radar T/R module packaging composites is introduced in detail, and its development trend prospects.
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With the continuous progress of science and technology, the rapid popularization of 5G technology and the rapid development of wearable devices, life is becoming more and more convenient. Meanwhile, electromagnetic interference poses a threat to the health of people and the operation of precision electronic devices. Nowadays, traditional electromagnetic interference shielding materials can no longer meet the daily needs of people's life, lightweight polymer-based electromagnetic interference shielding materials have attracted more and more attention. This study summarized the electromagnetic interference shielding mechanism, and the influence of polymer structures on electromagnetic interference shielding performance, reviewed the preparation methods, electromagnetic shielding properties, and related mechanisms of advanced carbon/polymer materials, metal/polymer materials, and novel Mxene/polymer materials, discussed their advantages and limitations, and prospected the key challenges, potential applications and development prospects of lightweight polymer-based electromagnetic shielding materials in the future.
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Highly efficient, stable cathode is crucial to lithium-oxygen battery. A high performance, integrated Au-N-CNT/SS cathode with interpermeable channels was constructed by chemical vapor deposition and photoreduction, in which the high catalytic Au nanoparticles were loaded on nitrogen doped carbon nanotubes with three-dimensional permeable of stainless steel mesh. The morphology and composition of the Au-N-CNT/SS were investigated by SEM, TEM, XPS, XRD and Raman spectrum. The problems of poor mechanical stability, carbonaceous cathode decomposition and serious side reactions were avoided by the suitable channel structure, high conductivity, superior mechanical properties, structural stability of Au-N-CNT/SS. Taking Au-N-CNT/SS as the integrated cathode for lithium-oxygen battery, the utilization of binder is avoided. The mechanical strength of the lithium-oxygen battery is enhanced, and the side reactions are effectively reduced, contributing to the enhanced electrochemical/chemical stability. The high conductivity, interpenetrated structure and sufficient pores provide a fast electron transport and mass transfer channel. The highly efficient Au nanoparticles are favorable to improving the oxygen reduction/oxygen evolution reaction kinetics on cathode, accelerating the generation and decomposition of discharge products. The rate performance (keeping the discharge voltage at 2.4 V with a high current density of 1.0 mA·cm−2), specific capacity (8.47 mA·h·cm−2) and cycle performance (160 cycles) of lithium-oxygen battery are greatly improved.
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Using the round pot granulation method, through the design and optimization of the microcapsule process and formulation parameters, microcapsules with clay solidifying agent, bentonite, MgO expansion agent and microcrystalline cellulose as the core material and ethyl cellulose (EC) as the core material were prepared. For the microcapsules of the wall material, the influence of the components of the microcapsule core material on the self-healing effect of the self-healing microcapsule/cementitious composite material was explored by orthogonal experiments, and the optimal composition of the microcapsule core material was determined: that is, the clay curing agent is 10wt% , MgO expansion agent is 35wt%, microcrystalline cellulose is 6wt%, and bentonite is 49wt%. The results show that the compressive strength of self-healing microcapsule/cementitious composite decreases with the increase of the content of microcapsules. When the content (mass to cement) of microcapsules is 3%, the compressive strength of self-healing microcapsule/cementitious composite is only dropped by 4% with a high strength recovery rate of 103.8%. The deformation behavior of self-healing microcapsule/cementitious composites during loading was traced and tested by the digital speckle correlation method (DSCM). From the stress-strain curve, strain field distribution, gray correlation coefficient eigenvalues (Stc) and strain eigenvalues (Sts), the self-healing mechanism of self-healing microcapsule/cementitious composite is based on the fact that when the microcapsules rupture, the cement-based homologous substances(AFt, Mg(OH)2) are generated to fill the cracks, limit the development of cracks, and achieve the purpose of repairing cracks.
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In order to prepare a new type of safe, stable and efficient nano silver composite antibacterial agent, silver nanoparticles/chitosan (AgNPs/CS) was biosynthesized by by one-step method using Chimonanthus praeco petal extract and chitosan as reducing agent and stabilizing agent, respectively. The optimal preparation procedure was determined by single factor experiment. The products were characterized by UV-vis absorption spectroscopy, transmission electron microscopy and X-ray diffraction, and their antibacterial activity, anti-drug resistance, stability as well as biological safety were comprehensively evaluated. The experimental results showed that the AgNPs/CS had the characteristic absorption peak of AgNPs at 451 nm, and the evenly dispersed AgNPs were spherical with average diameter of 12.83 nm, and the crystals had a face-centered cubic structure. The AgNPs/CS show antibacterial activity against aquatic pathogens both in vitro and in vivo, and had excellent anti-drug resistance, biosafety and stability. Therefore, AgNPs/CS is an ideal composite antibacterial agent, which has a prospective application in aquaculture field.
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In-situ TiB2/Al composite is a new type of aluminum matrix composite, which has the advantages of high specific strength and specific stiffness, good performances on wear resistance, electrical conductivity and thermal conductivity, a variety of matrix alloy candidates, low raw material cost, simple and diversified manufacturing and heat treatment processes. The existing research on the fatigue of in-situ TiB2/Al composites mainly focuses on the strengthening mechanism in micro-scale and the general understanding of its fatigue performance is not sufficient. It is also lack of fatigue test data of in-situ TiB2/Al composite for the engineering use. High cycle fatigue properties of the in-situ TiB2 particle reinforced 7050 aluminum alloy composite (in-situ TiB2/7050) were experimentally investigated with comparison to 7050-Al, the matrix alloy of the composite. The results reveal that the fatigue strength of the in-situ TiB2/7050 is apparently higher than that of 7050-Al. The fatigue limits of in-situ TiB2/7050 are improved by 24.59% and 13.56% for stress ratios 0.1 and 0.5 separately, resulting from the increase of fatigue resistance induced by the tiny TiB2 particles. The results at different stress concentration levels show that the notch sensitivity of in-situ TiB2/7050 is higher than that of 7050-Al, which may attribute to TiB2 particles impeding the plastic deformation of the aluminum alloy matrix in the composite. Despite the higher notch sensitivity, the fatigue resistance the notched composite is still higher than that of the 7050-Al. Therefore, in-situ TiB2/7050 is a promising material for lightweight structure application to replace traditional aluminum alloy in certain circumstances and achieve the joint improvement of static strength and fatigue performance.
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The purpose is to reveal the deterioration law of mechanical properties for elastomer composites at different service environments and promote their popularization and application in the field of solvent-free coatings. Ultra high molecular weight polyethylene/elastomer (UHMWPE/EL) composites were prepared. Application environments such as hydrothermal aging, low-temperature embrittlement and climate aging were simulated, and the evolution process and laws of various mechanical properties for elastomer and its composites at different environments were studied. The damage status of shape auto restore ability for composites at different deformations and temperatures was evaluated. Finally, the durability and environmental adaptability of composites were proved. The results show that after continuous exposure for 7 days or 81 hours at different application environments, the retention rates of mechanical properties for UHMWPE/EL composites are more than 90%, which meet the requirements of specifications. And the mechanical properties of composites decrease 15%−20% after being exposed to hygrothermal environment, cold environment and weathering environment for 30 days. The composites have obvious thermal stability and automatic shape recovery ability, and the recovery rates at different deformation modes of tension, bending and torsion are over 90%.
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In order to study the reinforcing mechanism of carbon nanotubes (CNTs) on the mechanical and thermal stability of nitrile rubber (NBR) O-ring, 1%CNT/NBR and 2%CNT/NBR composite O-ring were prepared by mechanical blending and hot pressing. The mechanical properties of CNT/NBR composite O-ring were tested on the basis of SEM, EDS and FT-IR. The results show that with the increase of CNT content, the elastic modulus and rigidity of CNT/NBR composite O-ring increase. The tensile strength of 1%CNT/NBR O-ring reaches 12.6 MPa due to the formation of C—O bond. The increase of CNT content in NBR matrix can improve the thermal stability of CNT/NBR composite O-ring, and the phase transition temperature of 2%CNT/NBR reaches 297℃. The excellent aging resistance of 1%CNT/NBR composites is attributed to the fact that CNT makes NBR matrix produce CN triple bond functional groups. High-performance CNT/NBR composite O-ring has certain application value in the field of aviation seals.
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Exploring electromagnetic wave (EMW) absorbing materials with excellent performance is the main method to solve electromagnetic pollution. However, it remains a challenge to meet the high performance and practical application requirements of materials simultaneously. Conductive carbon black (CCB)@nano ferroferric oxide (Fe3O4)/natural rubber (NR) absorbing films with excellent mechanical and EMW absorption properties were prepared by sol-gel method, plasticizing, blending and vulcanization, and the mechanical and EMW absorbing properties of the films were controlled by adjusting the addition amount of CCB@Fe3O4. The introduction of the CCB@Fe3O4 composites greatly ameliorates the interfacial loss and polarization loss of the films, in which the CCB can enhance the mechanical properties while improving the dielectric constant and conductivity of the materials. The film achieves the minimum reflection loss (RL) of -40.5 dB and maximum effective absorption bandwidth (EAB) of 2.4 GHz with the thickness of 5.0 mm when the CCB@Fe3O4 was added at 29wt%, and exhibited the optimal tensile strength, hardness and wear properties. The remarkable EMW absorbing properties of the material originate from impedance matching, strong EMW attenuation and high conduction loss caused by the synergistic effect of dielectric-magnetic loss. This work provides a new mentality for the structure design and practical application of natural rubber-based absorbing films.
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To improve the crashworthiness of C-channel carbon fiber reinforced polymer (CFRP) thin-walled structures, the energy absorption characteristics and failure behavior of the structures under axial crushing load were studied. Considering the delamination effect, the progressive damage model of C-channel CFRP thin-walled structure was established. The quadratic stress failure and the nonlinear damage evolution criterion based on the mixed-mode energy method were used to predict the initial interlaminar failure and damage evolution, respectively. For this structure, the hybrid-angle chamfer trigger and steeple trigger were proposed, and the effects of different trigger configurations on the crashworthiness index and failure mode of C-channel CFRP thin-walled structures were compared and analyzed. The results show that the initial peak load corresponding to the hybrid-angle chamfer trigger decreases with the increase of the hybrid angle; The initial peak load can be effectively reduced by reducing the contact area between the hybrid-angle chamfer trigger and the loading plate at the initial crushing stage; The hybrid-angle steeple trigger can improve the failure process and has a positive effect on improving the crashworthiness of the structure.
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Carbon fiber-epoxy resin composites have excellent properties such as high strength and high modulus, corrosion and fatigue resistances, and are widely used as structural materials in civil engineering. Nylon 6 has advantages of great fracture toughness, self-lubrication, friction and wear reduction, etc. Its incorporation as a filler in short-cut carbon fiber-epoxy composites is expected to significantly improve mechanical and frictional wear properties. In this paper, a high performance composite with excellent mechanical properties, high temperature resistance, low coefficient of friction and wear rate was prepared through using short-cut carbon fiber-epoxy resin composites modified with nylon 6 based on the resin selection method. The effect of the addition of nylon 6 on the thermal, mechanical and frictional wear properties of composite was investigated, and the mechanism of nylon 6 on its performance enhancement was revealed by combining microscopic morphology and structural analysis. It was found that the tensile fracture toughness of the modified composites increased by 199% with the addition of 7.5wt.% nylon 6, and the fracture damage mode changed from brittle fracture to ductile fracture, the tensile fracture morphology changed from “plain” to “gully” and the glass transition temperature increased by 15.2℃. The addition of 10wt.% nylon 6 significantly reduced the frictional coefficient (~80%), wear rate (~53%), scratch width (~22%) and line roughness (~15%) of the composites. The improvement mechanism can be attributed to the fact that nylon 6 assisted in the formation of a uniform and dense lubricant isolation film on the scratch surface, which changed the wear type of the composites from the severe fatigue wear to the slight adhesive wear or abrasive wear.
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By compounding rice straw with phenolic resin (PF) foam, to improve the shortcomings of PF foam itself, such as high brittleness and poor mechanical strength, and to investigate the effects of length (8 cm, 12 cm and 16 cm) and form (cross-cutting straw, slope-cutting straw and grinding straw fiber) of rice straw on the physical properties, mechanical and combustion properties of the composite material. The results show that the inner and outer surfaces of rice straw have an obvious mechanical engagement with PF foam; the bending strength, compressive strength and tensile strength perpendicular to the board surface of rice straw/PF foam composite are better than PF foam; the bending strength of 16 cm long slope-cutting rice straw/PF foam composite reaches 1.18 MPa, which is 195% higher than PF; The compressive stress at 10% strain and tensile strength perpendicular to the plate surface of 16 cm long grinding rice straw/PF foam composite were 251.30 kPa and 121.26 kPa, respectively, which were 112.1% and 20.7% higher than PF. The vertical combustion and limited oxygen index test (LOI) results showed that PF foam has better wrapping effect on straw, the thermal stability of the composite was almost the same as that of PF foam, with almost no change in oxygen index value. The flammability test results of both rice straw/PF foam composite and PF foam meet the requirements of B1 class building materials, which shows an excellent fire resistance. To sum up, 8 cm slope-cutting rice straw reinforced PF foam composite has an optimal integrated mechanical property.
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With the rapid development of highly-integrated and highly-powered 5G communication and wearable electronic devices, the electromagnetic interference and electromagnetic pollution problems caused by electromagnetic waves are becoming increasingly serious. It is urgent to develop lightweight, mechanically strong and environmentally friendly electromagnetic shielding composites. Herein, the lightweight and mechanically strong MXene/bacterial cellulose (BC) composite aerogels with directional porous structures are prepared via the liquid nitrogen directional freezing followed by freeze drying method using biomass BC as matrix and conductive Ti3C2Tx MXene as functional fillers. The effects of Ti3C2Tx MXene mass fraction on the microstructures, conductive and mechanical properties, as well as EMI shielding properties of the composite aerogels are investigated in detail. The results show that the composite aerogels with a Ti3C2Tx MXene mass fraction of 40wt% exhibit a low mass density of 18.3 mg/cm3, as well as the highest electrical conductivity and electromagnetic interference shielding effectiveness (EMI SE) of 459.3 S/cm and 72 dB (at a thickness of 4 mm) in X band with an absorption dominated EMI shielding mechanism. Owing to the abundant hydrogen bonding interactions, the composite aerogels exhibit a high compression strength of 38.3 kPa, which is 116.1% higher than that of pure BC aerogels.
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The research on improving the interlayer mechanical properties and heat resistance of epoxy resin matrix composites through toughening modification of epoxy resin matrix has important engineering application value. Modified resin (ES) was prepared by condensation reaction of hydroxyl terminated polydimethylsiloxane and epoxy resin, and glass fiber reinforced epoxy resin matrix composite (ES-GF) was prepared by vacuum introduction method. The interlaminar mechanical properties of the composite were measured by double cantilever beam and short beam shear tests. The thermal resistance of the composite was evaluated by thermogravimetry and dynamic mechanical thermal testing. The interlaminar mechanical properties and thermal resistance of the corresponding glass fiber reinforced unmodified epoxy matrix composites (EP-GF) were also tested for comparative analysis. In order to analyze the physical mechanism of strengthening the interlaminar mechanical properties and improving the heat resistance of the composite, the tensile strength, tensile modulus, flexural strength, flexural modulus, tensile elongation at break, pendulum impact strength and microstructure characteristics of the epoxy resin before and after modification were also measured and characterized. The experimental results show that, compared with EP-GF, the release rate of type I critical strain energy (fracture toughness) of ES-GF is increased by 98.1%, and the interlaminar shear strength is increased by 13.3%. The strengthening of interlaminar mechanical properties is attributed to the comprehensive effect of Si—O bond flexible chain segment, "ductile points" playing a "nail anchor" role and improvement of fiber/matrix wettability. The maximum thermal weight loss rate of ES decreased by 33.1%, and the final residue at 800 ℃ increased by 13.5 times. Before Tg, the storage modulus of ES GF is 1.3 GPa higher than that of EP GF, and after Tg, the storage modulus of ES GF is nearly 1.3 GPa higher than that of EP GF, and the glass transition temperature of siloxane modified epoxy resin is slightly increased.
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Due to the high strength and lightweight, epoxy-based composite have extremely application value in the fields of aerospace and automotive. However, the brittle nature of epoxy resin significantly hindering their application in actual engineering, it is a great challenge to improve the strength and toughness of epoxy-based composite. Herein, we develop an architecture epoxy-based composite lattice with strengthening zones and toughening zones, which are rationally assembled into a layered structure and fabricated by direct ink writing (DIW, a kind of 3D Printing). The physical and chemical properties of epoxy-based composite and filaments were characterized by rotational rheometer and optical microscope, and a universal testing machine were used to test the mechanical properties of epoxy-based composite lattice with different structure. It is indicating that the specific strength, toughness and fracture toughness of epoxy-based composite lattice were increased by 94.78%, 482% and 17.4% compared to solid composite, respectively. From the fracture surfaces and finite element analysis, it can be concluded that the strengthening zones ensure the structural strength, the toughening zones can effectively share the external deformation and prevent the crack propagation. The current research provides a new idea for the design of structural nanocomposites and a theoretical basis for the fabrication and engineering application of high strength and toughness epoxy-based composite.
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Molybdenum disulfide (MoS2) is easy to be oxidized when used at high temperature, which leads to significant deterioration of its tribological properties, showing a high friction coefficient. In order to improve the tribological properties of MoS2 lubricant under high temperature environment, core-shell MoS2@SiO2 Nanocomposites was formed by hydrothermal method and improved Stöber method. The morphology, size and composition of the nano materials were characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM) and X-ray diffraction (XRD). The micro results show that the core-shell structure composite was successfully prepared, with an average particle size of 250 nm. The high temperature friction test of prepared MoS2@SiO2 solid lubrication coating was carried out, and the MoS2 coating was used as a comparison. The morphology and structure of the coating were characterized by SEM and XRD, and the wear rate of the coating was characterized by a 3D profiler. The results show that the friction coefficient of the MoS2@SiO2 coating at 680℃ was 0.2 and relatively stable, while MoS2 coating rapidly failed. The MoS2@SiO2 coating had better wear resistance, with a wear rate 25.86% lower than that of MoS2 coating. After the friction tests, MoS2 still exists in the wear scar area of the MoS2@SiO2 coating, which was covered by the lubricating film; However, the substrate in the wear zone of MoS2 coating was completely exposed. The results show that the coating of SiO2 shell delayed the rapid oxidation of MoS2 at high temperature, and the synergistic lubricating extend the service life of the coating.
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Constructing thermal conductive pathways in polymer matrix with interconnected high conductive thermal fillers is an effective strategy to enhance the thermal conductivity of the composites. In this paper, eutectic Sn-Bi alloy (Sn57Bi43) nanoparticles are deposited on the surface of aluminum oxide (Al2O3) microspheres by coreduction method to prepare Al2O3-Sn57Bi43 hybrids as thermal conductive and electrical insulating fillers for epoxy resin. During the heat curing of epoxy resin, Sn57Bi43 nanoparticles on the Al2O3 surface melt and bridge the separate fillers together to form effective thermal conductive pathway, thus enhance the thermal conductivity of the composites. When filler volume fraction is 60%, the thermal conductivity of Al2O3-Sn57Bi43 /epoxy composites is 2.95 W·(m·K)−1, 62.1% higher than that of Al2O3/epoxy composites (1.82 W·(m·K)−1). The results of Fogyel and Agari simulation demonstrate that the deposition of Sn57Bi43 on Al2O3 surface reduce the thermal contact resistance between fillers and form thermally conductive networks more easily. The Al2O3-Sn57Bi43/epoxy composites exhibit higher dielectric loss, lower dielectric strength and volume resistivity than Al2O3/epoxy composites, still with electrical insulating properties. What is more, the tensile strength of the Al2O3-Sn57Bi43/epoxy composites is improved, because the improved interfacial properties of filler-matrix and the formed networks could transfer stress and prevent crack expansion.
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Water stimulus responsive materials can undergo reversible color or fluorescence emission change process under the external stimulus of water. Because of its low cost, non-toxic, compatibility with existing inkjet printing technology and other advantages, it is an ideal choice to achieve rewritable. Meanwhile, it shows great application potential in information storage, security and anti-counterfeiting. In this review, the research progress of water responsive compound material based on organic small molecules in the past five years is systematically reviewed. Inductive materials are classified from the viewpoints of water induced proton transfer, water induced configuration change, water induced proton transfer combined with configuration change sensing principle. The achievements and technologies in design principles, optical physical properties and information storage applications are summarized. It is hoped to provide ideas for further developing the application of water responsive composites in the field of green writing and anti-counterfeiting, promoting the development of related industries.
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In order to investigate the degradation law of bonding performance of CFRP-clay brick interface under sulfate soaking environment, the test was conducted by accelerated corrosion of CFRP-clay brick specimens with 10% mass fraction of sulfate solution, and the material properties were measured, and the change law of bearing capacity and bonding strength of CFRP-clay brick interface was analyzed by collecting the parameters of strain and bearing capacity. The study shows that sulfuric acid immersion has no significant effect on the mechanical properties of CFRP sheet and resin adhesive, but has a significant effect on the compressive strength of clay brick, which decreases by 34.50% after 180d sulfate immersion. For the ultimate bearing capacity and bond strength of CFRP-clay brick interface, it is found that the width of CFRP has an effect on both the bearing capacity and bond strength of the interface, increasing the width of the interface can increase the bearing capacity of the interface, but the bond strength of the interface will decrease as a result, and the larger the bond width is, the more significant the degradation of the bond performance of the interface under the effect of continuous sulfate immersion. Based on the test, the comprehensive influence coefficient of sulfate is introduced and calculated in two different ways to establish the CFRP-clay brick interfacial bearing capacity relationship model considering the influence of continuous sulfate soaking. The model can predict the degradation of the CFRP-clay brick interface by continuous sulfate soaking.
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Three-dimensional(3-D) braided glass fiber/epoxy resin composite thin-walled tubes with three braiding angles of 15°, 25°, and 35° were prepared by 3-D braiding molding technology and resin transfer molding process (RTM). The quasi-static compression performance test of 3-D braided composite thin-walled tubes was carried out at low temperature(−100℃, −50℃), normal temperature(20℃) and high temperature field (80°C, 110°C, 140°C and 170°C). The effects of temperature and braiding angle on compression properties and compression failure pattern of 3-D braided composite thin-walled tubes were studied based on X-ray micro-computer tomography (Micro-CT). The results show that the quasi-static compression behavior of 3-D braided composite thin-walled tubes has a significant temperature effect. As the temperature increases, the failure mode of the braided composite thin-walled tubes changes from local shear failure to large-area debonding of the fiber tows-matrix interface. The braiding angle has different effects on the compressive strength, compressive modulus and specific energy absorption of 3-D braided composite thin-walled tubes. The braided composite thin-walled tubes with small braiding angle have a higher orientation along the braided yarn direction which can withstand greater axial compounding, so the compression performance is better.
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Three-dimensional (3-D) electrode materials are ideal candidates for use in fabricating high-performance supercapacitors, owing to their unique network structure and excellent electrochemical properties. Although cellulose nanofibers (CNF) and multiwall carbon nanotubes (MWCNT) are widely used in the development and design of electrode materials, how to use their unique one-dimensional nanostructures and inherent physical properties to build high-performance 3-D electrode materials remains a huge challenge. Herein, an aerogel film produced by the freeze-drying self-aggregation of MWCNTs and CNFs was used as the “filling,” and an inter-connected 3-D network of nickel foam (NF) as the “framework,” for well-design and fabrication of an MWCNT/CNF-NF hybrid materials (named as MCN). Benefiting from the excellent conductivity and high specific surface area of the MCN, it is exceptionally suitable for use as the electroactive material platform in the fabrication of high-performance electrodes. Therefore, in this work, the high-performance PPy-MCN freestanding electrodes were successfully prepared by optimizing the time of the electroactive material polypyrrole. As expected, the electrode exhibits a high areal capacity of 2217.8 mF·cm−2 (=869.9 F·g−1) at a current density of 5 mA·cm−2, with good stability even after 3000 charge-discharge cycles.
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To study the effect of fiber reinforced plastic (FRP) grid-engineered cementitious composite (ECC) matrix strengthened method on the deflection of reinforced concrete (RC) beams, flexural performance test was carried out on 10 RC beams. Each test variable which does effect on the deflection of RC beams strengthened with FRP grid- ECC matrix composite was analyzed, and a model for calculating the deflection of reinforced beams was derived. The test results show that the FRP grid-ECC matrix strengthened method can significantly improve the ultimate bearing capacity and flexural stiffness of the test beams, in which the ultimate load carrying capacity of the reinforced beam increases from 27.9% to 67.4%, the mid-span deflection decreases from 30.7% to 43.7%, and the reinforced beams occur suitable reinforcement damage with obvious ductile characteristics. The FRP grid has a strong influence on flexural performance of reinforced beams, and its grid thickness is proportional to the strengthening effection. The thickness, matching ratio and interface treatment method of ECC reinforcement layer have little effect on the flexural performance of the reinforced beam, and the sanding treatment improves the interface bonding performance of the reinforcement layer better than other interface treatment methods. The deflection calculation model of reinforced beams is derived based on the specification, and its calculating values agree well with the testing values, so the model is a reference for the deflection calculation of RC beams strengthened with FRP grid-ECC matrix composite.
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In order to improve the mechanical properties and water resistance of magnesium oxychloride cement and solve the problem of resource disposal of abandoned crop highland barley straw, highland barley straw ash(HBSA) prepared by calcination and grinding under certain conditions was used to improve the mechanical properties and water resistance of magnesium oxychloride cement. First of all, the mechanical properties of magnesium oxychloride cement mortar (MOCM) with different HBSA mixing methods and amounts were tested, and the changing laws of the flexural strength, compressive strength, flexural compression ratio and softening coefficient of MOCM were tested respectively. Secondly, the pore structure and microstructure of MOCM were tested and analyzed to further explain the mechanism of the influence of HBSA on the mechanical properties of MOCM. The results show that MOCM can obtain higher mechanical properties and water resistance when HBSA was added with the external mixing method. When the content of HBSA is 5wt%, MOCM has the highest flexural strength and compressive strength; When the content of HBSA is 10wt%, the compressive strength loss of MOCM in saturated state is the smallest, and the water resistance is the best. When HBSA is added with the external mixing method and the content is 10wt%, the proportion of harmful pores and more harmful pores in the pore structure of MOCM is significantly reduced, and the proportion of harmless pores and less harmful pores is significantly increased. The hydration product Mg(OH)2 in MOCM can react with the active SiO2 in HBSA to generate a large number of M-S-H gel, which effectively fills the harmful pores in MOCM, hinders the transmission and erosion of water, and improves the water resistance of MOCM.
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The preparation of polymeric materials with good mechanical properties and efficient self-healing properties at room temperature has been a difficult challenge. Herein, a lignin-reinforced self-healing polyurea elastomer was prepared by a two-step process (polyurea reaction and schiff base reaction) using natural aromatic-based lignin as the reinforcing phase. The effects of lignin content on the thermal, UV-blocking and mechanical properties of T-L-PUA were investigated and the self-healing property and recyclability based on dynamic reversible imine bonding (C=N) of T-L-PUA were analyzed. The results show that the thermal stability of T-L-PUA is significantly enhanced with the increase of lignin ratio, where the maximum increase of residual carbon is 16.6% compared with the sample without lignin. The low transmittance of T-L-PUA in the UV region(280~400 nm)helps to realize the UV-blocking function. Compared with the average transmittance of T-PUA (41.6%), the average transmittance of all T-L-PUAs is around 0.2%. The best mechanical property appears at 20wt% of lignin addition, and the corresponding tensile strength of T-L-PUA is 12.44 MPa, which is 937% higher than that of pure polyurea elastomer. T-L-PUA exhibits good self-healing properties. When T-L-PUA is repaired at room temperature for 48h, the recovery efficiencies of tensile strength and elongation at break is above 91% and 94%, respectively. In addition, the T-L-PUA can also be recovered by the hot-pressing and solvent dissolution processes, and the mechanical properties remain largely unchanged after remolding.
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Carbon fiber reinforced poly aryl ether ketone (SCF35/PAEK) thermoplastic composites were prepared using two different melt viscosities of domestic high performance poly aryl ether ketone resins (PAEK-L and PAEK-H) and domestic T300 grade carbon fibers (SCF35), and the effects of resin matrix viscosity and impact energy and impact energy on the impact properties of the composites were investigated. In addition, the internal morphology of quasi-static indentation specimens was characterized by Micro-CT to study the impact damage mechanism of the composites. The results show that PAEK-L resin matrix composite with lower fluidity has higher impact resistance than PAEK-H resin matrix composite with higher fluidity. The impact energy loss of the SCF35/PAEK-L composite system is ~7% lower than that of the SCF35/PAEK-H composite system, its damage area is ~90% smaller, and its compression strength after impact reaches ~307 MPa at an impact energy of 6.67 J/mm, which is ~50% higher than that of SCF35/PAEK-H composite system(205 MPa). The depth of surface dent in SCF35/PAEK-L composites tends to increase with the increase of impact energy, and the compression strength after impact tends to decrease with the increase of impact energy, and the compression strength after impact is ~268 MPa when the depth of surface dent of the composites reaches about 1.0 mm, i.e., when the threshold value of barely visible impact damage (BVID) is reached. In addition, the results of quasi-static indentation tests show that the surface dent of SCF35/PAEK-L composite after impact is mainly caused by plastic deformation of the resin matrix and fiber flexure, the cracks around the surface dent are caused by compressive stress, the fiber on the back side of the specimen is fractured under the action of tensile stress during the impact process, the fiber on the bottom layer of the specimen sprouts interlayer cracks under the action of shear force, with the increase of flexural deformation of the specimen, the degree of fiber fracture increases and the interlayer cracks gradually expand.
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Carbon fiber reinforced polymer (CFRP) composites are widely used because of their excellent properties such as high specific strength and high specific modulus, but their mechanical properties along the thickness are poor due to the laminar structure characteristics and the intrinsic brittleness of epoxy resin, and they are prone to delamination under out-of-plane impact and in-plane compression loads, which in turn reduce the strength of the composites. Therefore it is especially important to improve the interlaminar fracture toughness of the composites. In this paper, we attempt to improve the interlaminar fracture toughness of the composite by introducing highly oriented carbon nanotube fiber veils in the interlaminar region. To ensure that the fiber veils are well infiltrated by the resin, they are first immersed in an epoxy resin solution diluted with acetone. After the acetone evaporated, it is inserted into the interlayer region of the homemade carbon fiber prepreg and subsequently cured by a hot pressing process. The Mode I and Mode II interlaminar fracture toughness of the toughened samples are evaluated via ASTM testing standards. Combined with the optical microscopic observation of the cross-section and scanning electron microscopy analysis of the fracture surface, the crack propagation paths are clearly shown and the interlaminar toughening mechanisms of CNT fiber veils are revealed. The results show that the Mode I and Mode II interlaminar fracture toughness of CNT veil toughened samples are improved by 37.4% and 41.8%, respectively. The toughening mechanisms mainly include matrix toughening, strengthening carbon fiber bridging and crack deflection.
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ZIF-7 crystals were in situ grown on graphene oxide (Go) by three synthetic routes, and the resulting graphene oxide/ZIF-7 composites (GZR-n) were characterized by PXRD, FT-IR, SEM, TEM, and N2 isothermal adsorption-desorption. The effects of the synthetic routes on the growth, crystallinity, microscopic morphology and pore size of ZIF-7 crystals on graphene oxide were investigated. ZIF-7 crystals were grown on the surface and sheet of graphene oxide by three synthetic routes. The crystallinity of ZIF-7 crystals on GZR-n was significantly enhanced and some were wrapped by graphene oxide. The shape and size of ZIF-7 crystals growing on GZR-n were modulated by the synthesis routes. In particular, the ZIF-7 crystals were spherical particle with a dimeter of 50 nm in GZR-II. For GZR-I and GZR-III, the ZIF-7 crystals were regular polyhedron with a size of 200 nm. Additional, their dispersion properties in solvents, adsorption properties and kinetic simulations for organic dyes were explored. GZR-n showed good dispersion in methanol and chloroform. Compared with ZIF-7 crystals, the adsorption capacities of GZR-I, GZR-II and GZR-III for methylene blue were increased by 226%, 302% and 278%, respectively. The kinetic simulations indicated that the adsorption of GZR-II and GZR-III for methylene blue was chemisorption and that of GZR-I was physical adsorption.
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To evaluate the mechanical properties of ceramic composites affected by coating defects, the SiC coated plain woven C/SiC composite by precursor impregnation and pyrolysis (PIP) process was taken in consideration. Firstly, the observation and statistical analysis of initial defects on SiC coating were performed, then a non-stress oxidation test at 900℃ was conducted, and the damage status of carbon fiber around coating defects was obtained. According to the actual characteristics of the oxidation test, a microscale model of SiC matrix and carbon fiber containing typical coating defects was established. Based on the evolution of oxidation interface under diffusion-controlled reaction mechanism, a simulation on the development of fiber overall damage was carried out and stiffness reduction was calculated. The results show that oxy-gases entered from coating defects diffuse through inner pores of composites and react with carbon fiber, causing tensile modulus reduction in consistency with weight loss, both of which are capable of evaluation on the oxidation extent of composites. The overall damage topography of carbon fiber is determined by the types of coating defects. Under the same distribution scale, damaged zone induced by cracking defects contains larger range of stress concentration compared with that induced by spalling defects. Judgement on the properties of thermal structure at high temperature is supported with the comparison of oxidation damage induced by different coating defects.
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For the repair structures of aircraft metal components with one-sided CFRP patches, the tensile tests on repair specimens with different repair processes (wet lay-up, prepreg and pre-curing methods) and CFRP patch parameters were carried out. The ultimate load, failure mode and interface of the specimens were observed. The three-dimensional (3D) finite element (FE) model has been established. Based on 3D Hashin failure criteria, the damage initiation and evolution in CFRP were simulated. The damages of the adhesive layer and delamination of CFRP were simulated with cohesive zone model. The FE model was validated by experimental and theoretical analysis. The results show that the three repair processes have different interface morphology and failure modes. The wet lay-up method has the best repair effect, 3.3 times of the pre-curing method and 1.3 times of the prepreg method. With the increase of patch thickness, the ultimate load first increases, then decreases, and finally tends to be stable. The failure mode gradually evolves from patch delamination, mixed failure of fiber breakage and adhesive layer damage to adhesive layer shear failure. The best patch thickness is 7 layers, about 1.05mm in thickness. With the increase of patch length, the ultimate load first increases and then decreases linearly. The damage of the adhesive layer starts from the center and both ends of the joint and evolves to the middle region. The best patch length is 80 mm. The results reported herein could provide useful guidance for the application of aviation maintenance engineering.
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Based on the static three-point bending and dynamic three-point bending experiments, the influence of the inclined angle of the conch shell element on the fracture behavior of the specimen under different strain rates was studied. Four groups of samples were prepared by 3D printing using two kinds of matrix materials, soft phase and hard phase. Based on quasi-static and dynamic three-point bending impact experiments, the load-displacement curves and initiation work of four groups of samples were obtained. The results show that the structure has different crack deflection paths under different strain rates. At lower strain rates, the 45 ° sample has higher strength, better energy absorption effect and better fracture toughness; At higher strain rate, the strength and toughness of 45° samples are better. Finally, through the drop weight experiment, the influence of different impact speeds on the failure of the mixed design structural plate was studied, and the critical failure speed and two failure modes were obtained. The drop weight experiment shows that when the impact velocity reaches 1.8 m/s, further increasing the impact velocity to 2.0 m/s has no obvious effect on the dynamic response of the structure. The proportion of the energy absorbed before the crack initiation and the energy absorbed after the crack initiation in the total energy absorption tends to be stable.
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In view of the poor durability of concrete in freezing-thawing environment and the cost problems caused by traditional improvement methods, municipal solid waste incineration tailing was used as lightweight aggregate to prepare specified density concrete which can improve the frost resistance and reduce the cost. Taking the light-weight concretes with water-binder ratio 0.3 and tailing lightweight aggregate content of 25wt%, 50wt% and 75wt% as the research objects, the freeze-thaw environment in severe cold regions was simulated. The freeze-thaw deterioration law of specified density concrete was explored by macro-indices such as spalling amount, mass loss, strength loss and dynamic elastic modulus loss, and the freeze-thaw degradation was revealed from the aspects of water absorption saturation, pore structure characteristics and bone-grain interface of specified density concrete. Finally, a damage degradation model for light concrete was developed using the damage mechanics theory. According to the findings, the durability damage of ordinary concrete caused by freeze-thaw cycle erosion is more serious than that of specified density concrete, and more mortar peeling occurs on the surface of ordinary concrete. The frost resistance of concrete can be considerably increased by the inclusion of tailing lightweight aggregate. Under the condition of freeze-thaw cyclic corrosion, the durabilities of the specified density concretes mixed with 25wt%, 50wt% and 75wt% tailing lightweight aggregate are improved by 15.2%, 30.3% and 33.3% higher than that of ordinary concrete, respectively. The porosity structure and interface characteristics of the specified density concrete are improved by strengthening the internal curing function, increasing the number of beneficial pores and increasing the strength of the bone-slurry interface, and the freeze-thaw erosion durability is improved. The freeze-thaw change rule and damage degree of specified density concrete may be studied more thoroughly thanks to the specified density concrete degradation model's fitting degree based on damage mechanics, which is above 0.97.
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Ti/Al laminated composite plates have the advantages of high strength and corrosion resistance of titanium alloy, light weight and low price of aluminum alloy, and have a wide range of potential applications in aerospace, automobile manufacturing, underwater equipment and other fields. In order to investigate the connection behavior of Ti/Al laminated composite members, vacuum electron beam welding (EBW) was used to weld Ti/Al laminated composite members, and the microstructure, interface behavior and mechanical properties of the welded joints were studied. The results showed that: Compared with single-side welding, the mechanical properties of welded Ti/Al laminated composite plates can be effectively improved by double-sided Al welding followed by Ti welding. There are no obvious defects at the interface of welded Ti/Al joints, and there are obvious intermetallic compounds (IMCs) layers at the interface of welded Ti/Al joints. The formation sequence of the compounds is TiAl3, TiAl and TiAl2. TiAl2 is the product of a series of reactions in which TiAl is used as an intermediate. Under the condition that the electron beam of Al layer remains unchanged at 43 mA, with the increase of the electron beam of Ti layer, the tensile strength and elongation of the welded joint both increase first and then decrease. The maximum tensile strength and elongation can reach 304.6 MPa and 10.4%, which is 57% of the strength of the base metal. The fracture mechanism of welded joint is mainly brittle fracture at IMCs position.
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In order to study the dynamic response of porous metal ceramic functionally graded rectangular plate under low velocity impact, a numerical analysis model based on Hertzian elastic theory and first-order shear deformation plate theory was presented, the analytical solution of response of porous cermet functionally graded rectangular plate under low velocity impact was obtained. According to Hamilton's principle, the equation of motion of functionally graded rectangular plate was derived, a spring-mass (S-M) model with two degrees of freedom was introduced to obtain the time-dependent contact forces during impact, using the Duhamel principle and Navier method to calculate the transverse displacement of porous functionally graded rectangular plate. The results obtained were compared with literature data to verify the validity. On this basis, the influence of related parameters on the impact resistance of functionally graded rectangular plate was compared and analyzed. The results show that with the decrease of porosity, functionally graded index and width to thickness ratio, the maximum transverse displacement of the functionally graded rectangular plate decreases, energy absorption and impact resistance are increased.
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In order to study the photo-Fenton properties of FeOCl combined with carbon materials, g-C3N4/FeOCl nanocomposites are prepared by a simple calcination method according to the different composite mass ratios of g-C3N4 and FeCl3·6H2O. Composition, structure, and optical properties of the composite samples tested by XRD, SEM, TEM, XPS, UV-vis, EIS, and Transient photocurrent testing. The results show that the g-C3N4/FeOCl composite has a layered nanorod stacking structure with the good light response and carrier separation capability. When the composite ratio of g-C3N4 to FeOCl is 1∶20, it exhibits excellent photo-Fenton performance, and the degradation rate of rhodamine B (RhB) reaches 92.4%. And after three cycles, the efficiency of the composite material in degrading RhB remained at 80.1% that showing good stability. Based on the experimental results, the Z-type heterojunction between g-C3N4 and FeOCl was proposed to improve the separation efficiency of photogenerated carriers, and the possible mechanism of photo Fenton degradation of RhB by Z-type heterojunction was discussed.
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In the synthesis of polymers and polymer composites, it is still a challenge to observe the real-time and dynamic evolution of material structure and provide implications for property prediction. As one of the methods to characterize the microscopic and submicroscopic structures of substances, Small Angle X-ray Scattering (SAXS) technology can reflect unique microscopic conformational information, and can systematically study the morphological characteristics and formation process of chain-like, network-like, and layered polymers. The analysis of the formation mechanism of the aggregated structure of molecular materials, and their macroscopic performance prediction are very important. In this paper, three common methods for SAXS applications in current polymer materials research were presented, i.e., the peak observation, the model fitting, and the annular integration. Based on the above three methods, this paper introduced the practical functions of SAXS in studying different polymer materials, such as dynamic observation of the microstructural evolution process, and obtaining large-scale and statistically significant microstructural parameters. After comparing and evaluating the application methods and influences of SAXS in different polymer materials, it was concluded that SAXS plays a comprehensive role that is difficult to replicate in the study of complex polymer materials. It was hoped that this paper could serve as a primer to attract researchers’ attention to understand SAXS technology, provide alternative research methods for the investigation of complex polymers, and expand the application of SAXS in wider fields to solve more problems.
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Ti3CNTx/TMAOH was prepared when tetramethylammonium hydroxide(TMAOH) was selected as the intercalating agent. Adsorption performance of Ti3CNTx/TMAOH on Sr2+ in simulated radioactive wastewater was evaluated. The synthesized Ti3CNTx/TMAOH was characterized by SEM-EDS, XRD, BET and FTIR. In the batch experiment, the effects of the dosage of adsorbent Ti3CNTx/TMAOH, time, pH and competitive ions on Sr2+ removal were investigated. The results show that the removal rate of Sr2+ is 99.28% when the dosage is 1.0 g·L−1, pH is 6, and the time is 10 min. The inhibition order of competitive ions is Ca2+\begin{document}$\text{ > > }$\end{document}Mg2+\begin{document}$\text{ > }$\end{document}K+\begin{document}$\text{ > }$\end{document}Na+\begin{document}$\text{ > }$\end{document}Cs+. After four adsorption-desorption cycles, the Sr2+ removal rate is 69.56%. The adsorption is consistent with the pseudo-second-order kinetic. The adsorption isotherm data conforms to the R-P model. 93.80% and 68.49% Sr2+ can be removed in tap water and lake water, respectively. Sr2+ is adsorbed by Ti3CNTx/TMAOH via ion exchange, surface chelation, electrostatic adsorption and interlayer interception.
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Abstract:
With the rapid development of China’s domestic space engineering, the harsher requirements are put forward for lightweight, dimensional stability, thermal protection efficiency and long service capability of the thermal protection system. Rigid nanoporous phenolic resin-based composites (RMI/PR) are prepared via a sol-gel polymerization and ambient-pressure gradient drying using rigid mullite ceramic tile as the reinforcement and hybrid phenolic resin as matrix. The effects of resin concentration on the microstructure, mechanical properties, thermal insulation properties and ablative properties of the composites are systematically studied. The results show that mullite ceramic tile has obvious transverse isotropy, and the room-temperature thermal conductivity in the Z direction is 0.036 W/(m∙K). With the increase of the resin concentration from 15wt.% to 45wt.%, the densityof RMI/PR increases from 0.52 g/cm3 to 0.85 g/cm3, and the most probable pore size of the resin matrix decreases sharply from 2081 nm to 32 nm. With the increase of resin concentration, the room-temperature thermal conductivity of RMI/PR increases slowly and all of them are less than 0.07 W/(m∙K), but its mechanical properties are significantly enhanced and the maximum compressive strength in the Z direction of composites is up to 20.8 MPa. After static heat insulation test at 1000oC for 300 s, the backside temperature of composites decreases from 277oC to 240oC. Under the oxy-acetylene ablation at 2000oC for 30 s, the linear ablation rate of the composites is reduced from 0.200 mm/s to 0.081 mm/s, indicating that the increase of resin concentration can significantly improve the high-temperature thermal insulation properties and ablation resistance of the composites.
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Abstract:
Quartz fiber (QF) reinforced poly (silica-containing arylacetylene) (PSA) composite is a new type of highly promising new wave-transparent materials with highly heat-resistance. However, the brittleness and low molecular polarity of PSA resins, combined with the smooth surface of quartz fibers, results in a weak interfacial adhesion, and low interlaminar shear strength (ILSS) of the composites. In this paper, silicon-containing arylacetylene resin was modified by copolymerizing with styrene (ST). As a consequence, the crosslinking density was decreased, the crosslinking network got homogenized, and the crack resistance of the resin against load was improved. Finally, the ILSS of Quartz fiber reinforced PSA composites was improved. The properties of the resin and composites were characterized with differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), dynamic mechanical analysis (DMA), mechanical property testing, dielectric property testing, rheological property testing. The results showed that the addition of ST didn’t affect the curing process of the resin. With the increase of ST content, the heat resistance of modified PSA resin decreased to some extent, but its Td5 was still close to 500℃, which was much higher than the expected application temperature of 350℃. The modified composite also maintained the good dielectric properties with dielectric constant of 3.09 and tan δ of 0.002. The results also showed that the addition of ST significantly improved ILSS. For instance, the ILSS of QF/PSA-15ST increased by 53.0% at room temperature and 98.3% at 350℃. Compared with that at room temperature, the retention rate of interlaminar shear strength at 350℃ was 78.3%, which was much higher than that before modification (60.4% ).
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Abstract:
High thermal performance thermoplastic, poly(ether ketone ketone) (PEKK), was used as the matrix for in-situ impregnation 3D printing with continuous carbon fiber (CCF) to prepare continuous carbon fiber/poly(ether ketone ketone) composites (CCF/PEKK). The effects of layer thickness, flow ratio, print temperature and build orientation in 3D printing process parameters on the internal structure, matrix crystallization, surface quality and mechanical properties of the composites were systematically investigated. The microstructure of 3D printed CCF/PEKK was observed by scanning electron microscopy, the crystallization properties of the matrix were analyzed by X-ray diffraction, the surface morphologies of 3D printed CCF/PEKK was observed and analyzed by ultra-deep field microscopy, and the flexural properties and interlaminar shear strength of CCF/PEKK were also tested. The results shows that with the layer thickness of 0.2 mm, the flow ratio of 85%, the printing temperature of 395°C, and the build orientation of flat, the performance of 3D printed CCF/PEKK is optimal, including the flexural strength of 302.0 MPa and the interlaminar shear strength of 24.1 MPa. The flexural strength of CCF/PEKK is improved by 194% compared with 3D printed pure PEKK, and the interlaminar shear strength is improved by 113% after process optimization. It indicates that 3D printed CCF/PEKK has the potential to manufacture complex structural engineering parts without using any additional optimization.
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Abstract:
The high value-added utilization of corn straw can not only reduce pollution and resource waste, but also has far-reaching significance for exploring the industrial utilization of corn straw and sustainable agricultural development. Using microcrystalline cellulose (CSMCC) prepared from corn straw as raw material, 1-butyl-3-methylimidazolium chloride ([Bmim]Cl) as solvent system, dandelion extract (DE) and tea polyphenol (TP) as antibacterial agents, antibacterial composite film was prepared by blending method. The morphology and structure of the composite film were characterized by Fourier Transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy and thermogravimetric analysis, and the mechanical, optical, barrier and antibacterial properties were tested and analyzed. The results show that DE and TP are well combined with cellulose base film. The composite antibacterial agent DE-TP antibacterial composite film has better tensile strength (52.60±6.33 MPa), oxygen barrier performance (oxygen transmission coefficient is (1.65±0.25)×10−11 cm3·cm/(cm2·s·Pa)) and better inhibition effect on Escherichia coli and Staphylococcus aureus than the DE and TP antibacterial composite films. At the same time, compared with the cellulose base film, elongation at break of DE-TP antibacterial composite film increased by 53.96%, and the light transmittance is (82.56±0.26)%, which has good mechanical and optical properties. It provides a new idea for the research and development of environment-friendly antibacterial composite film, which is important for controlling food spoilage and efficient utilization of biological resources.
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Abstract:
Plain-woven carbon fiber-reinforced plastic ( PW-CFRP ) shows high damage tolerance characteristics and is widely used in the aerospace field. However, PW-CFRP is a multi-scale composite material, and the traditional micro and macro scales cannot study its cutting mechanism well. Therefore, this paper uses mesoscopic cutting simulation methods to study its chip formation mechanism. In this paper, a mesoscopic three-dimensional orthogonal cutting simulation model was established according to the geometric structure characteristics of PW-CFRP, and the orthogonal cutting experiment was carried out to verify the simulation model. The material removal mechanism of PW-CFRP with different fiber braiding directions in cutting process was studied. The results show that the maximum relative error between the simulation and experimental results of cutting force and surface damage is less than 15 % under the same process parameters, and the reliability of the simulation model is verified. The maximum damage depth of fiber bundles in each fiber orientation is 0° < 45° < 90° < 135°. The plain-woven structure of warp and fill weaving has inhibitory effect on the machining damage. The support constraint between adjacent fiber bundles hinders the damage expansion, and its maximum processing damage depth will not exceed the maximum width of the fiber bundle section. The thickness of the matrix layer near the fiber is an important factor in the formation of processing damage. The resin-rich area has a good supporting effect on the fiber and can effectively suppress the damage. The resin-starved area has weak support for the fiber, and the damage is easy to expand here, making the surface damage of the material arc-shaped distribution.
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Abstract:
Fatigue delamination is one of the most severe damage mode for laminated composites. A new cohesive zone model was adopted in this article for modeling fatigue delamination propagation in laminated composites, in which the G-N curve and Paris’ law were linked. This model was developed based on a new interpretation of fatigue delamination propagation: fatigue delamination propagation is a result of multiple onsets. A new fatigue cohesive constitutive law was constructed for describing fatigue damage accumulation in the inter-laminar interface of composites. All the parameters used in the constitutive law are with clear physical meaning and can be calibrated from the experimental G-N curve. Compared to the existing models for fatigue delamination in composites, the constitutive law developed in this model works independently in each element, without algorithms for getting the global crack information or tracking crack tip position. Considering the different deformation fields around the crack tip under mode II loading conditions, a new fatigue damage accumulation law was developed for mode II FDP, and the predicted Paris’ law for mode II was compared well with the experimental results.
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In order to obtain nanomaterials with better dispersal, filling and barrier properties, which were used as fillers to enhance the protection of the epoxy coatings for cement mortar, the polydopamine (PDA), which was prepared by self-polymerization of dopamine hydrochloride (DA) and silane coupling agent (KH550), was utilized to modify nano hexagonal boron nitride (hBN) and nano silicon dioxide (SiO2), respectively, to obtain two nanomaterials PDABN and functionalised SiO2(fSiO2) by polymerization reactions. A new nanomaterial, polydopamine hexagonal boron nitride - functionalised silicon dioxide (PDABN-fSiO2), was synthesized, and it was mixed with epoxy to prepare a modified coating. The coating was covered on the surface of cement mortar to enhance its carbonation resistance. The microscopic characteristics of nano materials were observed by FT-IR, SEM-EDS and XPS. The modified effect of epoxy coating by nano PDABN-fSiO2 was analyzed by carbonation experiments and permeability tests. Results indicate that the prepared nano PDABN-fSiO2 has a layer-particle structure and better dispersion in coating, which can effectively slow down the penetration of CO2 in the coating. Compared with the blank coating, the carbonation depth of the cement mortar coated with nano PDABN-fSiO2/epoxy coating is decreased by 68.7%, 72.9% and 64.8% at 7, 14 and 28 days of carbonation, respectively, and the permeability of its coating is decreased by 34.7% at 48 hours. Thus, the epoxy coating with nano PDABN-fSiO2 can significantly improve the carbonation resistance of cement mortar and reduce its permeability.
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Abstract:
Graphene nanosheets (GNSs) reinforced aluminum-magnesium (Al-Mg) matrix composite foams (G-AMCFs) were successfully prepared by ball milling and powder metallurgy foaming. The effects of GNSs on pore morphology, microstructure and quasi-static compressive mechanical properties of Al-Mg foams were studied. The results show that the addition of GNSs can increase pore nucleation sites and cause the segregation of magnesium oxide (MgO) around the GNSs. With the increment of GNSs content, the pore size of G-AMCFs increases. The compressive mechanical properties of 0.25 wt% G-AMCFs are the best. Compared with Al-Mg foams, the energy absorption capacity, yield strength and plateau stress of 0.25 wt% G-AMCFs are increased by 43.6%, 42.9% and 28.1%, respectively. Meanwhile, 0.25 wt% G-AMCFs show good ductile deformation behavior. The cell structure with high content of G-AMCFs (0.75 wt%) deteriorates which leads to a decrease in mechanical properties, but the yield strength is still higher than that of Al-Mg foams. The enhancement mechanism of compo-site foams includes dispersion strengthening, load transfer and precipitation strengthening.
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Abstract:
N-C3N4/BiOClxI1-x S-type heterojunctions were prepared by a facile one-step hydrothermal method. The crystal form, morphology, structure, elemental composition, surface functional groups and optical properties of the samples were characterized by XRD, XPS, SEM, TEM, FTIR and UV-Vis. The photocatalytic activity of N-C3N4/BiOClxI1-x oxidation of organic pollutants and reduction of Cr(VI) was investigated. The results show that N-C3N4/BiOClxI1-x sample exhibited the effective enhancement in light absorption. The charge carriers were generated by the transfer of the photoinduced electron from N-C3N4 to BiOClxI1-x across the interface under irradiation, which inhibited the recombination of electron-hole pairs. Under visible light irradiation, 20%N-BiOCl0.5I0.5 exhibited high activity, the degradation rate of phenol reached 98.53% with 2.5 h of visible light irradiation. Meanwhile, the reduction rate of Cr(VI) of 20% N-BiOCl0.5I0.5 reached to 99.11% with 1 h of visible light irradiation. 20%N-BiOCl0.5I0.5 showed good stability after five cycles. The TOC removal rate of degradation phenol by 20%N-BiOCl0.5I0.5 within 3 hours was 80.21%. Combined with capture experiment, ESR and DFT calculation, the improvement activity of N-C3N4/BiOClxI1-x was attributed to the formation of S-type heterojunction, the internal electric field based on different Fermi levels between N-C3N4 and BiOClxI1-x, as well as band bending and Coulomb force, which together accelerated spatial separation of photogenerated carriers and orderly electron flow.