2021 Vol. 38, No. 11
2021, 38(11): 3799-3807.
doi: 10.13801/j.cnki.fhclxb.20210104.002
Abstract:
Thetraditional neutral ink is mostly made of acrylic resin as thickener, and does not have the ability to conduct electricity. Therefore, this study explored the mixing of carboxymethyl cellulose (CMC) and multi-wall carbon nanotubes (MWCNT) to make the prepared ink conductive after writing. CMC-MWCNT conductive ink was prepared by ultrasonic and written on paper with a neutral pen. The stability, rheological property, writing property, corrosion resistance, electrical conductivity, and folding stability of the prepared conductive ink were analyzed, and compared with Chenguang neutral ink (CG) on the market. When the amount of CMC is 0.3wt% and 0.6wt% respectively, the Zeta potential, yield stress and yield viscosity of conductive ink are all low, ink leakage occurred during writing. And the line resistance of writing is small, but the resistance increases a lot after 100 times of folding, increasing by 32.3% and 17.9%, respectively. When CMC is added at 0.9wt%, 1.2wt% and 1.5wt%, respectively, the absolute value of Zeta potential of conductive ink is greater than 30 mV, and the system is in a stable state. The yield stress and viscosity increased with the increase of CMC. When CMC content is 0.9wt% and 1.2wt%, respectively, the conductive ink writing is normal, the resistance of the writing lines are 14.9 kΩ/cm, 15.6 kΩ/cm, and the resistance increases by 8.7% and 7.8% after 100 times of folding. The conductive ink of 1.5wt% CMC content is broken when writing, the resistance after writing is 28.3 kΩ/cm, and the resistance increases by 9.5% after 100 times of folding. Compared with CG, conductive ink of 1.2wt% CMC has similar stable performance, rheological performance, and writing performance. In addition, conductive ink of 1.2wt% CMC has electrical conductivity and can light up LED lights.
Thetraditional neutral ink is mostly made of acrylic resin as thickener, and does not have the ability to conduct electricity. Therefore, this study explored the mixing of carboxymethyl cellulose (CMC) and multi-wall carbon nanotubes (MWCNT) to make the prepared ink conductive after writing. CMC-MWCNT conductive ink was prepared by ultrasonic and written on paper with a neutral pen. The stability, rheological property, writing property, corrosion resistance, electrical conductivity, and folding stability of the prepared conductive ink were analyzed, and compared with Chenguang neutral ink (CG) on the market. When the amount of CMC is 0.3wt% and 0.6wt% respectively, the Zeta potential, yield stress and yield viscosity of conductive ink are all low, ink leakage occurred during writing. And the line resistance of writing is small, but the resistance increases a lot after 100 times of folding, increasing by 32.3% and 17.9%, respectively. When CMC is added at 0.9wt%, 1.2wt% and 1.5wt%, respectively, the absolute value of Zeta potential of conductive ink is greater than 30 mV, and the system is in a stable state. The yield stress and viscosity increased with the increase of CMC. When CMC content is 0.9wt% and 1.2wt%, respectively, the conductive ink writing is normal, the resistance of the writing lines are 14.9 kΩ/cm, 15.6 kΩ/cm, and the resistance increases by 8.7% and 7.8% after 100 times of folding. The conductive ink of 1.5wt% CMC content is broken when writing, the resistance after writing is 28.3 kΩ/cm, and the resistance increases by 9.5% after 100 times of folding. Compared with CG, conductive ink of 1.2wt% CMC has similar stable performance, rheological performance, and writing performance. In addition, conductive ink of 1.2wt% CMC has electrical conductivity and can light up LED lights.
2021, 38(11): 3808-3817.
doi: 10.13801/j.cnki.fhclxb.20210210.006
Abstract:
As a new generation of antibacterial agent, silver nanoparticles are expected to be a substitute for traditional antibacterial agents in the future. Developing a new stable, efficient and eco-friendly nano-silver antibacterial agent has become the hot spot of current research. In this study, the grape seeds extract was used as an reducing and stabilizing agent, and polyvinyl alcohol (PVA) was used as the carrier, the silver nanoparticles/polyvinyl alcohol (AgNPs/PVA) composites were prepared by a facile, green, “one-pot” biological method. The asprepared AgNPs/PVA composites were characterized by UV absorption spectroscopy (UV-Vis), transmission electron transmission electron microscopy (TEM) and X ray diffraction (XRD). The results indicate that the silver ions are successfully reduced by the grade seeds extract and the produced AgNPs are decorated on the surface of PVA. The AgNPs are uniform and monodisperse, the particle size is small with mean diameter about 14 nm. The AgNPs/PVA composites show superior antibacterial effects against six tipical aquatic pathogens, such as Vibrio splendidus, V. harveyi, V. anguillarum, V. alginolyticus, V. parahaemolyticus and Aeromonas punctata. They have a minimum inhibitory concentration (MIC) of 1.1 μg/mL and a minimum inhibitory concentration (MBC) of 2.2 μg/mL against V. alginolyticus. The Zeta potential of AgNPs/PVA is found to be −24.1 mV, indicating that the strong repulsion between the nanoparticles, which provide guarantee for stable dispersion. The subsequent experiments prove that the prepared AgNPs/PVA has good stability and thermostability. The above research results indicate that AgNPs/PVA composites have a great application prospect in the control of aquaculture diseases.
As a new generation of antibacterial agent, silver nanoparticles are expected to be a substitute for traditional antibacterial agents in the future. Developing a new stable, efficient and eco-friendly nano-silver antibacterial agent has become the hot spot of current research. In this study, the grape seeds extract was used as an reducing and stabilizing agent, and polyvinyl alcohol (PVA) was used as the carrier, the silver nanoparticles/polyvinyl alcohol (AgNPs/PVA) composites were prepared by a facile, green, “one-pot” biological method. The asprepared AgNPs/PVA composites were characterized by UV absorption spectroscopy (UV-Vis), transmission electron transmission electron microscopy (TEM) and X ray diffraction (XRD). The results indicate that the silver ions are successfully reduced by the grade seeds extract and the produced AgNPs are decorated on the surface of PVA. The AgNPs are uniform and monodisperse, the particle size is small with mean diameter about 14 nm. The AgNPs/PVA composites show superior antibacterial effects against six tipical aquatic pathogens, such as Vibrio splendidus, V. harveyi, V. anguillarum, V. alginolyticus, V. parahaemolyticus and Aeromonas punctata. They have a minimum inhibitory concentration (MIC) of 1.1 μg/mL and a minimum inhibitory concentration (MBC) of 2.2 μg/mL against V. alginolyticus. The Zeta potential of AgNPs/PVA is found to be −24.1 mV, indicating that the strong repulsion between the nanoparticles, which provide guarantee for stable dispersion. The subsequent experiments prove that the prepared AgNPs/PVA has good stability and thermostability. The above research results indicate that AgNPs/PVA composites have a great application prospect in the control of aquaculture diseases.
2021, 38(11): 3818-3826.
doi: 10.13801/j.cnki.fhclxb.20210119.002
Abstract:
The 1-stage FeCl3-intercalated graphite intercalation compound (FeCl3-GIC) were prepared by a molten salt method using FeCl3 and natural flake graphite as raw materials. Subsequently, a conductive layer of polypyrrole (PPy) were uniformly coated on the surface of the FeCl3-GIC particles by in-situ polymerization to form a core-shell structured (FeCl3-GIC)@PPy composite material. Various characterization methods were employed to study the surface morphology and microstructure evolution of FeCl3-GIC before and after polypyrrole coating. The results show that a uniform and dense polypyrrole layer with a thickness of 35 nm is tightly coated on the surface of the micro-sized FeCl3-GIC particles. After coating, the conductivity of the (FeCl3-GIC)@PPy composite is significantly improved for the powder resistivity is reduced from 3.1×10−3 Ω·cm of FeCl3-GIC to 2.3×10−3 Ω·cm of (FeCl3-GIC)@PPy. As an anode material for sodium ion storage, it is found that the (FeCl3-GIC)@PPy anode exhibits the improved reversible capacitiy, rate capability and cycling stability compared with the naked FeCl3-GIC anode. Specially, the specific capacity of (FeCl3-GIC)@PPy remains steady with a high sodium storage value of 281 mA·h·g−1 after 100 cycles at the current density of 0.1 A·g−1, while the FeCl3-GIC anode shows a continuous capacity decay with a low value of 157 mA·h·g−1 after 100 cycles. Additionally, even at a high current density of 1.0 A·g−1, the (FeCl3-GIC)@PPy anode delivers a remained sodium storage capacity of 181 mA·h·g−1 after 500 cycles, accompanying with a fascinating capacity retention ratio of 89%.
The 1-stage FeCl3-intercalated graphite intercalation compound (FeCl3-GIC) were prepared by a molten salt method using FeCl3 and natural flake graphite as raw materials. Subsequently, a conductive layer of polypyrrole (PPy) were uniformly coated on the surface of the FeCl3-GIC particles by in-situ polymerization to form a core-shell structured (FeCl3-GIC)@PPy composite material. Various characterization methods were employed to study the surface morphology and microstructure evolution of FeCl3-GIC before and after polypyrrole coating. The results show that a uniform and dense polypyrrole layer with a thickness of 35 nm is tightly coated on the surface of the micro-sized FeCl3-GIC particles. After coating, the conductivity of the (FeCl3-GIC)@PPy composite is significantly improved for the powder resistivity is reduced from 3.1×10−3 Ω·cm of FeCl3-GIC to 2.3×10−3 Ω·cm of (FeCl3-GIC)@PPy. As an anode material for sodium ion storage, it is found that the (FeCl3-GIC)@PPy anode exhibits the improved reversible capacitiy, rate capability and cycling stability compared with the naked FeCl3-GIC anode. Specially, the specific capacity of (FeCl3-GIC)@PPy remains steady with a high sodium storage value of 281 mA·h·g−1 after 100 cycles at the current density of 0.1 A·g−1, while the FeCl3-GIC anode shows a continuous capacity decay with a low value of 157 mA·h·g−1 after 100 cycles. Additionally, even at a high current density of 1.0 A·g−1, the (FeCl3-GIC)@PPy anode delivers a remained sodium storage capacity of 181 mA·h·g−1 after 500 cycles, accompanying with a fascinating capacity retention ratio of 89%.
2021, 38(11): 3827-3837.
doi: 10.13801/j.cnki.fhclxb.20210115.005
Abstract:
Steel fiber can reinforce the compressive strength of ultra-high performance fiber reinforced concrete (UHPFRC), but it will reduce the flowability of fresh UHPFRC, thus weaken this reinforcement effect and the work performance of UHPFRC. In order to study this adverse effect, two sets of tests A and B were carried out with steel fiber volume fraction and aspect ratio as variables. In the A series test, the fixed water-to-binder ratio was 0.18 and didn’t control the flowability. It mainly studied the effect of steel fiber on flowability and compressive strength. The test results show that the flowability of fresh UHPFRC decreases with the increase of the volume fraction or aspect ratio of steel fiber; when the volume fraction of steel fiber exceeds a certain value (2.00vol%), the expansion degree decreases significantly, and the corresponding compressive strength enhancement effect also decreases. The X-ray CT scan test finds that the incorporation of steel fiber weaken the self-compacting ability of the fresh slurry, increasing in the internal pore size and porosity of the hardened matrix, thereby weakening the compressive strength. Comprehensively considering the positive and negative effects of steel fiber incorporation into compressive strength, a semi-empirical prediction formula for compressive strength was proposed. In the B series test, the water-binder ratio was changed and the expansion degree was controlled to 240 mm. Through comparative analysis of the A series test results, the effect of the volume fraction and aspect ratio of the steel fiber on the compressive strength after the control of the flowability was studied. The results show that when the volume fraction of steel fiber is large, the water-binder ratio should be increased to ensure a certain flowability, which can effectively improve the reinforcement effect of the fiber; when the volume fraction of fiber is small, the water-binder ratio should be decreased on the premise of meeting the flowability requirements, which can further improve the compressive strength. In the design of the UHPFRC mix ratio, in order to improve the reinforcing effect of steel fiber and ensure that UHPFRC has good working performance, the adverse effect of incorporating steel fiber on the flowability of UHPFRC should be considered.
Steel fiber can reinforce the compressive strength of ultra-high performance fiber reinforced concrete (UHPFRC), but it will reduce the flowability of fresh UHPFRC, thus weaken this reinforcement effect and the work performance of UHPFRC. In order to study this adverse effect, two sets of tests A and B were carried out with steel fiber volume fraction and aspect ratio as variables. In the A series test, the fixed water-to-binder ratio was 0.18 and didn’t control the flowability. It mainly studied the effect of steel fiber on flowability and compressive strength. The test results show that the flowability of fresh UHPFRC decreases with the increase of the volume fraction or aspect ratio of steel fiber; when the volume fraction of steel fiber exceeds a certain value (2.00vol%), the expansion degree decreases significantly, and the corresponding compressive strength enhancement effect also decreases. The X-ray CT scan test finds that the incorporation of steel fiber weaken the self-compacting ability of the fresh slurry, increasing in the internal pore size and porosity of the hardened matrix, thereby weakening the compressive strength. Comprehensively considering the positive and negative effects of steel fiber incorporation into compressive strength, a semi-empirical prediction formula for compressive strength was proposed. In the B series test, the water-binder ratio was changed and the expansion degree was controlled to 240 mm. Through comparative analysis of the A series test results, the effect of the volume fraction and aspect ratio of the steel fiber on the compressive strength after the control of the flowability was studied. The results show that when the volume fraction of steel fiber is large, the water-binder ratio should be increased to ensure a certain flowability, which can effectively improve the reinforcement effect of the fiber; when the volume fraction of fiber is small, the water-binder ratio should be decreased on the premise of meeting the flowability requirements, which can further improve the compressive strength. In the design of the UHPFRC mix ratio, in order to improve the reinforcing effect of steel fiber and ensure that UHPFRC has good working performance, the adverse effect of incorporating steel fiber on the flowability of UHPFRC should be considered.
2021, 38(11): 3838-3849.
doi: 10.13801/j.cnki.fhclxb.20210118.001
Abstract:
The effects of length to diameter ratio and mixing amount of polyester fiber on the mechanical properties of concrete, such as compressive strength, flexural strength, splitting tensile strength, fracture toughness and impact load, were studied. The mechanism of toughening and cracking resistance of polyester fiber concrete was studied by composite material theory and fiber spacing theory. The microscopic morphology observed by SEM was used to analyze the influence of fiber length-diameter ratio and content on the mechanism of toughening and cracking resistance. Orthogonal experimental design method and laser scanning confocal microscope (LSCM) were used to study the influence of impact height, specimen thickness, aspect ratio and content on the impact resistance of fiber/concrete. The results show that the polyester fibers with ratio of length to diameter of 300 and ratio of length to diameter of 600 would reduce the compressive strength of concrete, the low content of polyester fibers with ratio of length to diameter of 150 increases the compressive strength of concrete by increasing the density of concrete. In terms of tensile strength, the polyester fibers with ratio of length to diameter of 150 mainly exist in the form of defects, the polyester fibers with ratio of length to diameter of 150 have the most significant effect on improving the concrete internal pulling, the addition of 3% (volume ratio to cementitious materials) polyester fiber is the most significant to improve the flexbility of concrete. For the fracture toughness of concrete, the fracture toughness of polyester fiber/concrete with ratio of length to diameter of 300 and 600 is significantly improved. According to the SEM microscopic morphology, it is found that the micro-cracks generated by fiber pulling action would improve the energy dissipation capacity of concrete, thus increasing the ultimate load and central deflection of concrete during failure, and the variation of tensile strength of polyester fibers with ratio of length to diameter of 300 reinforced concrete is in good agreement with the composite material theory and fiber spacing theory. Impact height is the main factor affecting the impact load, and the fiber length and diameter have greater influence than fiber content. Through LSCM analysis of three-dimensional damage morphology, it is concluded that the damage improvement effect of polyester fibers with ratio of length to diameter of 150 on concrete material is relatively significant, and at the same dosage, the small spacing of polyester fibers with ratio of length to diameter of 150 results in the improvement of local mechanical properties of concrete, thus improving the impact resistance of concrete.
The effects of length to diameter ratio and mixing amount of polyester fiber on the mechanical properties of concrete, such as compressive strength, flexural strength, splitting tensile strength, fracture toughness and impact load, were studied. The mechanism of toughening and cracking resistance of polyester fiber concrete was studied by composite material theory and fiber spacing theory. The microscopic morphology observed by SEM was used to analyze the influence of fiber length-diameter ratio and content on the mechanism of toughening and cracking resistance. Orthogonal experimental design method and laser scanning confocal microscope (LSCM) were used to study the influence of impact height, specimen thickness, aspect ratio and content on the impact resistance of fiber/concrete. The results show that the polyester fibers with ratio of length to diameter of 300 and ratio of length to diameter of 600 would reduce the compressive strength of concrete, the low content of polyester fibers with ratio of length to diameter of 150 increases the compressive strength of concrete by increasing the density of concrete. In terms of tensile strength, the polyester fibers with ratio of length to diameter of 150 mainly exist in the form of defects, the polyester fibers with ratio of length to diameter of 150 have the most significant effect on improving the concrete internal pulling, the addition of 3% (volume ratio to cementitious materials) polyester fiber is the most significant to improve the flexbility of concrete. For the fracture toughness of concrete, the fracture toughness of polyester fiber/concrete with ratio of length to diameter of 300 and 600 is significantly improved. According to the SEM microscopic morphology, it is found that the micro-cracks generated by fiber pulling action would improve the energy dissipation capacity of concrete, thus increasing the ultimate load and central deflection of concrete during failure, and the variation of tensile strength of polyester fibers with ratio of length to diameter of 300 reinforced concrete is in good agreement with the composite material theory and fiber spacing theory. Impact height is the main factor affecting the impact load, and the fiber length and diameter have greater influence than fiber content. Through LSCM analysis of three-dimensional damage morphology, it is concluded that the damage improvement effect of polyester fibers with ratio of length to diameter of 150 on concrete material is relatively significant, and at the same dosage, the small spacing of polyester fibers with ratio of length to diameter of 150 results in the improvement of local mechanical properties of concrete, thus improving the impact resistance of concrete.
2021, 38(11): 3850-3860.
doi: 10.13801/j.cnki.fhclxb.20210107.001
Abstract:
In order to reduce the influence of microcracks and other damages caused by environmental factors such as force and heat on the performance and service life of polymeric bonded explosives (PBX), an intrinsic self-repairing polymer binder containing DA bonds was designed and synthesized to realize autonomous healing of PBX internal damage according to the structural characteristic of particle filled polymer composites. The research results show that using TAPE-DAPU containing reversible DA covalent bonds as binder, the designed and prepared PBX material has good damage-healing ability. When the damage in PBX is slight, the strength recovery rate of the PBX exceeds 95%, while the repair efficiency is also above 65% for relatively severe penetrating damage.
In order to reduce the influence of microcracks and other damages caused by environmental factors such as force and heat on the performance and service life of polymeric bonded explosives (PBX), an intrinsic self-repairing polymer binder containing DA bonds was designed and synthesized to realize autonomous healing of PBX internal damage according to the structural characteristic of particle filled polymer composites. The research results show that using TAPE-DAPU containing reversible DA covalent bonds as binder, the designed and prepared PBX material has good damage-healing ability. When the damage in PBX is slight, the strength recovery rate of the PBX exceeds 95%, while the repair efficiency is also above 65% for relatively severe penetrating damage.
2021, 38(11): 3861-3871.
doi: 10.13801/j.cnki.fhclxb.20210306.001
Abstract:
The heterojunction photocatalytic material constructed with g-C3N4 as the matrix shows excellent effects in degrading toxic and harmful pollutants. In this study, a series of x-CS/g-C3N4 (x=4wt%, 5wt% and 7wt%) composite photocatalysts with different addition amounts of carbon nanospheres (CS) were prepared by hydrothermal method, and the photocatalytic degradation performance of x-CS/g-C3N4 on acid orange II were explored when a xenon lamp was used as a visible light source. The results show that the photocatalytic activity of 5wt% CS/g-C3N4 is the highest, and the degradation rate of acid orange II reaches 95% when the photocatalytic reaction is 150 min. The characterization results show that g-C3N4 and CS have a similar π-π conjugate structure, and π-π stacking interaction is prone to occur, which is beneficial to electronic transition. The combination of g-C3N4 and CS can effectively enhance the absorption efficiency of g-C3N4 for visible light, reduce the charge transfer resistance at the surface/interface, and significantly enhance the transport capacity of carriers. x-CS/g-C3N4 can be used as an effective visible light catalyst for the degradation of organic dyes and has application prospects.
The heterojunction photocatalytic material constructed with g-C3N4 as the matrix shows excellent effects in degrading toxic and harmful pollutants. In this study, a series of x-CS/g-C3N4 (x=4wt%, 5wt% and 7wt%) composite photocatalysts with different addition amounts of carbon nanospheres (CS) were prepared by hydrothermal method, and the photocatalytic degradation performance of x-CS/g-C3N4 on acid orange II were explored when a xenon lamp was used as a visible light source. The results show that the photocatalytic activity of 5wt% CS/g-C3N4 is the highest, and the degradation rate of acid orange II reaches 95% when the photocatalytic reaction is 150 min. The characterization results show that g-C3N4 and CS have a similar π-π conjugate structure, and π-π stacking interaction is prone to occur, which is beneficial to electronic transition. The combination of g-C3N4 and CS can effectively enhance the absorption efficiency of g-C3N4 for visible light, reduce the charge transfer resistance at the surface/interface, and significantly enhance the transport capacity of carriers. x-CS/g-C3N4 can be used as an effective visible light catalyst for the degradation of organic dyes and has application prospects.
2021, 38(11): 3872-3883.
doi: 10.13801/j.cnki.fhclxb.20210425.003
Abstract:
The two-dimensional Ti3C2Tx was modified by sulfonic acid group grafting (abbreviated as Ti3C2Tx—SO3H), and its microstructure before and after the modification was characterized. The adsorption behavior and mechanism of heavy metal Pb2+ by the Ti3C2Tx—SO3H were also investigated. XRD, FTIR and EDS analyses indicate that sulfonic acid group is successfully grafted on the surface of the Ti3C2Tx, while SEM shows that the Ti3C2Tx—SO3H has a lighter and thinner layered structure than the Ti3C2Tx. Pb2+ adsorption by the Ti3C2Tx—SO3H reaches equilibrium within 20 minutes. The maximum adsorption capacity of the Ti3C2Tx—SO3H is 733.6 mg·g−1, which is 23% higher than the Ti3C2Tx. And Pb2+ adsorption capacity by the Ti3C2Tx—SO3H gradually increases with the increase of pH (2-6). Under the interference of coexisting ions such as Mg2+, Ca2+, Co2+ and Zn2+, the Ti3C2Tx-SO3H still maintains a high level of Pb2+ adsorption. Pb2+ adsorption processes by both the Ti3C2Tx and the Ti3C2Tx—SO3H fit well the pseudo second kinetic model and Langmuir isotherm model, suggesting that the adsorption processes are monolayer chemisorption. The Ti3C2Tx—SO3H shows more excellent adsorption performance towards Pb2+ after adsorption mainly due to the more active sites provided by sulfonic acid group and the enhanced dispersion in aqueous solution.
The two-dimensional Ti3C2Tx was modified by sulfonic acid group grafting (abbreviated as Ti3C2Tx—SO3H), and its microstructure before and after the modification was characterized. The adsorption behavior and mechanism of heavy metal Pb2+ by the Ti3C2Tx—SO3H were also investigated. XRD, FTIR and EDS analyses indicate that sulfonic acid group is successfully grafted on the surface of the Ti3C2Tx, while SEM shows that the Ti3C2Tx—SO3H has a lighter and thinner layered structure than the Ti3C2Tx. Pb2+ adsorption by the Ti3C2Tx—SO3H reaches equilibrium within 20 minutes. The maximum adsorption capacity of the Ti3C2Tx—SO3H is 733.6 mg·g−1, which is 23% higher than the Ti3C2Tx. And Pb2+ adsorption capacity by the Ti3C2Tx—SO3H gradually increases with the increase of pH (2-6). Under the interference of coexisting ions such as Mg2+, Ca2+, Co2+ and Zn2+, the Ti3C2Tx-SO3H still maintains a high level of Pb2+ adsorption. Pb2+ adsorption processes by both the Ti3C2Tx and the Ti3C2Tx—SO3H fit well the pseudo second kinetic model and Langmuir isotherm model, suggesting that the adsorption processes are monolayer chemisorption. The Ti3C2Tx—SO3H shows more excellent adsorption performance towards Pb2+ after adsorption mainly due to the more active sites provided by sulfonic acid group and the enhanced dispersion in aqueous solution.
2021, 38(11): 3884-3895.
doi: 10.13801/j.cnki.fhclxb.20210302.001
Abstract:
As an important application scenario of proton exchange membrane fuel cell (PEMFC), the development of low-temperature proton exchange membrane fuel cell (LT-PEMFC) for drones is attracting attention. The operating conditions of the PEMFC used by drones are relatively special. The hydrogen and air used as raw materials are dry gas without humidification. To meet this requirement, it is necessary to develop a proton exchange membrane with water retention capacity. We first synthesized a polymer with high water retention (PAAAM), used the solution casting method to form composite membranes, blended it into Nafion solution, and studied the content of PAAAM. Subsequently, we characterized each composite membrane by FT-IR, SEM, proton conductivity, water uptake, swelling ratio and other properties. Then we tested the battery output performance. The final results show that the optimum operating temperature range of Nafion proton exchange membrane is 50-55℃ when the raw material is dry air and dry hydrogen. When the amount of PAAAM added is 1.0wt%, the Nafion-based composite membrane (NFPAM1) has better battery performance. When the battery temperature is 55℃, the dry hydrogen gas, and the dry air flow rate are 0.1 L·min−1 and 0.55 L·min−1, respectively, the highest power density of PEMFC using NFPAM1 composite membrane is 691 mW·cm−2.
As an important application scenario of proton exchange membrane fuel cell (PEMFC), the development of low-temperature proton exchange membrane fuel cell (LT-PEMFC) for drones is attracting attention. The operating conditions of the PEMFC used by drones are relatively special. The hydrogen and air used as raw materials are dry gas without humidification. To meet this requirement, it is necessary to develop a proton exchange membrane with water retention capacity. We first synthesized a polymer with high water retention (PAAAM), used the solution casting method to form composite membranes, blended it into Nafion solution, and studied the content of PAAAM. Subsequently, we characterized each composite membrane by FT-IR, SEM, proton conductivity, water uptake, swelling ratio and other properties. Then we tested the battery output performance. The final results show that the optimum operating temperature range of Nafion proton exchange membrane is 50-55℃ when the raw material is dry air and dry hydrogen. When the amount of PAAAM added is 1.0wt%, the Nafion-based composite membrane (NFPAM1) has better battery performance. When the battery temperature is 55℃, the dry hydrogen gas, and the dry air flow rate are 0.1 L·min−1 and 0.55 L·min−1, respectively, the highest power density of PEMFC using NFPAM1 composite membrane is 691 mW·cm−2.
2021, 38(11): 3896-3903.
doi: 10.13801/j.cnki.fhclxb.20210113.001
Abstract:
A novel strategy based on Metal-organic frameworks nanoparticles (MOFs NPs)-stabilized suspension polymerization has been achieved for the fabrication of multifunctional ZIF-8/P(TDA-co-HDA) and PB/P(TDA-co-HDA) composites. By using this technique, functional nanoparticles can be immobilized on the surface of polymer. In this paper, ZIF-8 and PB nanoparticles (NPs) were used as stabilizer for the suspension polymerization in water and ZIF-8/P(TDA-co-HDA) and PB/P(TDA-co-HDA) composites are successfully synthesized. ZIF-8/P(TDA-co-HDA) and PB/P(TDA-co-HDA) absorbed heat at 37.5℃, 39.1℃ and released it at 8.4℃, 10.1℃ with a heat storage capacity of 63 J/g, 68 J/g, respectively. The material retains its shape without any leakage at 60℃, which is much higher than that of the melting temperature of P(TDA-co-HDA). The ZIF-8/P(TDA-co-HDA) and PB/P(TDA-co-HDA) composites exhibit good crystallization behaviors and excellent thermal reliabilities after 1000 thermal cycles. The thermal properties of the ZIF-8/P(TDA-co-HDA) and PB/P(TDA-co-HDA) composites were also investigated. The novel shape-stabilized PCMs fabricated in this study have potential uses in thermal energy storage applications.
A novel strategy based on Metal-organic frameworks nanoparticles (MOFs NPs)-stabilized suspension polymerization has been achieved for the fabrication of multifunctional ZIF-8/P(TDA-co-HDA) and PB/P(TDA-co-HDA) composites. By using this technique, functional nanoparticles can be immobilized on the surface of polymer. In this paper, ZIF-8 and PB nanoparticles (NPs) were used as stabilizer for the suspension polymerization in water and ZIF-8/P(TDA-co-HDA) and PB/P(TDA-co-HDA) composites are successfully synthesized. ZIF-8/P(TDA-co-HDA) and PB/P(TDA-co-HDA) absorbed heat at 37.5℃, 39.1℃ and released it at 8.4℃, 10.1℃ with a heat storage capacity of 63 J/g, 68 J/g, respectively. The material retains its shape without any leakage at 60℃, which is much higher than that of the melting temperature of P(TDA-co-HDA). The ZIF-8/P(TDA-co-HDA) and PB/P(TDA-co-HDA) composites exhibit good crystallization behaviors and excellent thermal reliabilities after 1000 thermal cycles. The thermal properties of the ZIF-8/P(TDA-co-HDA) and PB/P(TDA-co-HDA) composites were also investigated. The novel shape-stabilized PCMs fabricated in this study have potential uses in thermal energy storage applications.
2021, 38(11): 3904-3911.
doi: 10.13801/j.cnki.fhclxb.20201225.002
Abstract:
The compressive performance of new composite material “concrete confined with high-strength stainless steel stranded wire meshes/ECC” (hereinafter referred to as HSE confined concrete) was studied by considering the effects of parameters: concrete strength, strength of engineered cementitious composites (ECC) and reinforcement ratio of lateral high-strength stainless steel stranded wires. The axial compression test of HSE confined concrete shows that vertical cracks about 0.01 mm appears on ECC in constraint layer at about 30% of the peak load. When the applied load reaches about 85% and 100% of the peak load, the maximum crack width on the surfaces is about 0.07 mm, 0.20 mm, respectively. These phenomena show that the new composite material has excellent crack dispersion and crack-controlling ability. When the applied load decreases to 75% of the peak load, the first lateral steel stranded wires rupture for the first time. The HSE confined concrete specimens are cracked without breaking when completely destroyed, and maintain a good bond between the constraint layer and core concrete, which has a good integrity. Compared with the plain concrete column, the cracking stress, axial compressive strength, the axial compressive strain and ultimate compressive strain of HSE confined concrete are increased by 88%-116%, 21%-49%, 45%, 106%-175%, respectively. The increases of ECC strength, concrete strength grade and the reinforcement ratio of lateral steel stranded wires have improved the cracking load, peak load and ultimate compressive strain of HSE confined concrete.
The compressive performance of new composite material “concrete confined with high-strength stainless steel stranded wire meshes/ECC” (hereinafter referred to as HSE confined concrete) was studied by considering the effects of parameters: concrete strength, strength of engineered cementitious composites (ECC) and reinforcement ratio of lateral high-strength stainless steel stranded wires. The axial compression test of HSE confined concrete shows that vertical cracks about 0.01 mm appears on ECC in constraint layer at about 30% of the peak load. When the applied load reaches about 85% and 100% of the peak load, the maximum crack width on the surfaces is about 0.07 mm, 0.20 mm, respectively. These phenomena show that the new composite material has excellent crack dispersion and crack-controlling ability. When the applied load decreases to 75% of the peak load, the first lateral steel stranded wires rupture for the first time. The HSE confined concrete specimens are cracked without breaking when completely destroyed, and maintain a good bond between the constraint layer and core concrete, which has a good integrity. Compared with the plain concrete column, the cracking stress, axial compressive strength, the axial compressive strain and ultimate compressive strain of HSE confined concrete are increased by 88%-116%, 21%-49%, 45%, 106%-175%, respectively. The increases of ECC strength, concrete strength grade and the reinforcement ratio of lateral steel stranded wires have improved the cracking load, peak load and ultimate compressive strain of HSE confined concrete.
2021, 38(11): 3912-3924.
doi: 10.13801/j.cnki.fhclxb.20201229.006
Abstract:
Ultra high performance concrete (UHPC) is a kind of cement-based material with high strength, high toughness and high durability. To study the lap-spliced bond performance of steel bars in UHPC, 21 groups of lap-spliced specimens were tested considering the parameters of lap length, fibers content and stirrups ratio. 3 groups of pull-out specimens considering a parameter of anchorage length were conducted to be control groups. Two failure modes, those are splitting-pull-out failure and steel-bar-rupture failure appear. The average bond strength decreases with the increase of embedded length and increases with the increase of stirrup ratio. The steel fibers enhance the confinement for UHPC. Increasing the stirrup ratio and fiber content can reduce the lap-spliced length of the steel bars in UHPC. Combining with the previous research, average bond strength and development length as well as splice length formulas were fitted. Simplified algorithms of development length and splice length were proposed according to the Code for Design of Concrete Stuctures, and the results agree well with the test results.
Ultra high performance concrete (UHPC) is a kind of cement-based material with high strength, high toughness and high durability. To study the lap-spliced bond performance of steel bars in UHPC, 21 groups of lap-spliced specimens were tested considering the parameters of lap length, fibers content and stirrups ratio. 3 groups of pull-out specimens considering a parameter of anchorage length were conducted to be control groups. Two failure modes, those are splitting-pull-out failure and steel-bar-rupture failure appear. The average bond strength decreases with the increase of embedded length and increases with the increase of stirrup ratio. The steel fibers enhance the confinement for UHPC. Increasing the stirrup ratio and fiber content can reduce the lap-spliced length of the steel bars in UHPC. Combining with the previous research, average bond strength and development length as well as splice length formulas were fitted. Simplified algorithms of development length and splice length were proposed according to the Code for Design of Concrete Stuctures, and the results agree well with the test results.
2021, 38(11): 3925-3938.
doi: 10.13801/j.cnki.fhclxb.20201218.002
Abstract:
The direct tensile tests under monotonic and cyclic loading were conducted on the ultra high performance concrete (UHPC) with different tensile strain characteristics (strain hardening and strain softening). The test results reflect that the strain hardening UHPC enters the stage of strain hardening with multi-point microcrack distribution after the cracking of UHPC matrix, and it enters the strain softening section with single seam cracking after reaching the ultimate tensile strength. The strain softening UHPC enters the strain softening stage with single seam crack after the cracking of UHPC matrix. The envelope of axial tensile stress-strain curves of the two types UHPC under cyclic load are generally consistent with that curves under monotonic load. Based on the stiffness degradation process, the axial tensile damage evolution equations of two types of UHPC were established. Based on the measured stress-strain curves and the crack distribution of the specimens, the axial tensile constitutive relation models of the two UHPCs were established. The test data are satisfactorily approximate to the proposed models. The equivalent method for the strain hardening UHPC with two-stage axial tensile constitutive relation in numerical calculation was studied by using energy method. Finally, the proposed axial tensile constitutive relation model and damage evolution equation of strain hardening UHPC were verified according to the numerical simulation of unreinforced strain strengthened UHPC flexural test beam. The results reveal that the proposed axial tensile constitutive model could precisely predict the ultimate bearing capacity of UHPC flexural-tensile members, and the axial tensile damage variables could generally reflect the crack distribution of the specimens.
The direct tensile tests under monotonic and cyclic loading were conducted on the ultra high performance concrete (UHPC) with different tensile strain characteristics (strain hardening and strain softening). The test results reflect that the strain hardening UHPC enters the stage of strain hardening with multi-point microcrack distribution after the cracking of UHPC matrix, and it enters the strain softening section with single seam cracking after reaching the ultimate tensile strength. The strain softening UHPC enters the strain softening stage with single seam crack after the cracking of UHPC matrix. The envelope of axial tensile stress-strain curves of the two types UHPC under cyclic load are generally consistent with that curves under monotonic load. Based on the stiffness degradation process, the axial tensile damage evolution equations of two types of UHPC were established. Based on the measured stress-strain curves and the crack distribution of the specimens, the axial tensile constitutive relation models of the two UHPCs were established. The test data are satisfactorily approximate to the proposed models. The equivalent method for the strain hardening UHPC with two-stage axial tensile constitutive relation in numerical calculation was studied by using energy method. Finally, the proposed axial tensile constitutive relation model and damage evolution equation of strain hardening UHPC were verified according to the numerical simulation of unreinforced strain strengthened UHPC flexural test beam. The results reveal that the proposed axial tensile constitutive model could precisely predict the ultimate bearing capacity of UHPC flexural-tensile members, and the axial tensile damage variables could generally reflect the crack distribution of the specimens.
2021, 38(11): 3939-3949.
doi: 10.13801/j.cnki.fhclxb.20210115.004
Abstract:
This paper focuses on the mode Ⅱ fracture behaviors of concrete with different coarse aggregate volume fractions by laboratory experiments. Based on the maximum paste thickness (MPT) theory, the empirical relationship between the fracture toughness KⅡ C and the coarse aggregate volume fraction Va was proposed. The mode Ⅱ fracture parameters including peak load, fracture toughness and energy release rate were determined by the compression on half part of the non-notched specimen with different coarse aggregate volume fractions of 19%, 25%, 31% and 37%. The crack distribution on the surface of the fracture ligaments was analyzed. The results show that both mode Ⅱ fracture toughness KⅡ C and the critical energy release rate GⅡ C enhance with the increase of coarse aggregate volume fraction from 19% to 37% while the crack paths become more tortuous and longer with the increase of coarse aggregate volume fraction. The fracture patterns of all specimens are basically identical, even if the coarse aggregate volume fractions are different. It is found that the shear crack propagation is mainly around the middle ligaments. Additionally, the technique of digital image correlation (DIC) was employed during the tests to track the fracture evolution and characterize the strain localization regions as well as fracture process zone (FPZ). It is also observed by the DIC technique that there are more branches in FPZ and their shapes are more irregular as the coarse aggregate volume fraction increases.
This paper focuses on the mode Ⅱ fracture behaviors of concrete with different coarse aggregate volume fractions by laboratory experiments. Based on the maximum paste thickness (MPT) theory, the empirical relationship between the fracture toughness KⅡ C and the coarse aggregate volume fraction Va was proposed. The mode Ⅱ fracture parameters including peak load, fracture toughness and energy release rate were determined by the compression on half part of the non-notched specimen with different coarse aggregate volume fractions of 19%, 25%, 31% and 37%. The crack distribution on the surface of the fracture ligaments was analyzed. The results show that both mode Ⅱ fracture toughness KⅡ C and the critical energy release rate GⅡ C enhance with the increase of coarse aggregate volume fraction from 19% to 37% while the crack paths become more tortuous and longer with the increase of coarse aggregate volume fraction. The fracture patterns of all specimens are basically identical, even if the coarse aggregate volume fractions are different. It is found that the shear crack propagation is mainly around the middle ligaments. Additionally, the technique of digital image correlation (DIC) was employed during the tests to track the fracture evolution and characterize the strain localization regions as well as fracture process zone (FPZ). It is also observed by the DIC technique that there are more branches in FPZ and their shapes are more irregular as the coarse aggregate volume fraction increases.
2021, 38(11): 3950-3961.
doi: 10.13801/j.cnki.fhclxb.20210129.005
Abstract:
In order to ensure the accuracy and convergence of the calculation results, the mesh size of the adhesive layer should be less than 1 mm for the failure analysis of composite adhesive layer using the cohesive zone model. However, when the cohesive zone model is used to analysis a large composite material structure in the aircraft, the model will generate millions of finite elements, which will consume numerous computing resources. Based on the research of the influence of the adhesive properties on the adhesive layer failure analysis, by inversion of the adhesive properties with different mesh sizes, the method that can accurately describe the failure behavior of the adhesive layer by changing the parameters of the adhesive layer to adapt to different mesh sizes was proposed. This method was used to simulate the mixed-mode-bending (MMB) model and composite cylindrical shell model with different mesh sizes. The results show that the method proposed can greatly reduce the number of meshes in the model and the calculation scale, and quickly and accurately calculate the damage evolution and failure of the adhesive layer under mixed loading conditions.
In order to ensure the accuracy and convergence of the calculation results, the mesh size of the adhesive layer should be less than 1 mm for the failure analysis of composite adhesive layer using the cohesive zone model. However, when the cohesive zone model is used to analysis a large composite material structure in the aircraft, the model will generate millions of finite elements, which will consume numerous computing resources. Based on the research of the influence of the adhesive properties on the adhesive layer failure analysis, by inversion of the adhesive properties with different mesh sizes, the method that can accurately describe the failure behavior of the adhesive layer by changing the parameters of the adhesive layer to adapt to different mesh sizes was proposed. This method was used to simulate the mixed-mode-bending (MMB) model and composite cylindrical shell model with different mesh sizes. The results show that the method proposed can greatly reduce the number of meshes in the model and the calculation scale, and quickly and accurately calculate the damage evolution and failure of the adhesive layer under mixed loading conditions.
2021, 38(11): 3962-3970.
doi: 10.13801/j.cnki.fhclxb.20210122.001
Abstract:
In order to study the effect of replacement rate of recycled aggregate concrete (RAC) on the direct shear performance of concrete, 75cubic specimens incorporating different replacement rates of RCA were fabricated. The direct shear test, compressive strength test and splitting tensile strength test were carried out. The failure mechanism of direct shear and the conversion rule between different strength indexes of RAC were revealed. The results show that RAC is obviously brittle failure under direct shear and both the coarse aggregate and cement matrix are sheared. With the increase of the replacement rate, the direct shear strength of RAC has little change compared with the ordinary concrete, and shows a decreasing trend in general. However, the direct shear strength of RAC increases when the replacement rate is 50% (by mass). The peak shear deformation generally increases by 18.85% and the initial shear deformation modulus decreases by 8.97% on average. Finally, based on experimental data, the conversion relationship of RAC between the shear and the compressive and split tensile strength was proposed. The calculated results are in good agreement with the experimental values.
In order to study the effect of replacement rate of recycled aggregate concrete (RAC) on the direct shear performance of concrete, 75cubic specimens incorporating different replacement rates of RCA were fabricated. The direct shear test, compressive strength test and splitting tensile strength test were carried out. The failure mechanism of direct shear and the conversion rule between different strength indexes of RAC were revealed. The results show that RAC is obviously brittle failure under direct shear and both the coarse aggregate and cement matrix are sheared. With the increase of the replacement rate, the direct shear strength of RAC has little change compared with the ordinary concrete, and shows a decreasing trend in general. However, the direct shear strength of RAC increases when the replacement rate is 50% (by mass). The peak shear deformation generally increases by 18.85% and the initial shear deformation modulus decreases by 8.97% on average. Finally, based on experimental data, the conversion relationship of RAC between the shear and the compressive and split tensile strength was proposed. The calculated results are in good agreement with the experimental values.
2021, 38(11): 3563-3577.
doi: 10.13801/j.cnki.fhclxb.20210105.002
Abstract:
To investigate the damage in self-piercing riveting (SPR) of carbon fiber reinforced polymer (CFRP) and aluminum alloy, three groups of SPR joints with typical ply angles were prepared, and the effects of ply angles on the macroscopic damage morphology of joints were studied. The effects of temperature on the mechanical properties and failure of CFRP were studied. Based on the thermal mechanical properties of CFRP, the warm self-piercing riveting (WSPR) process for CFRP and aluminum alloy was innovatively proposed for the purpose of reducing joint damage. The damage difference of CFRP in the joint obtained by two riveting processes was compared. The effect of ply angle on mechanical properties and failure process of WSPR joints in CFRP and aluminum alloy was investigated. The results show that macro-cracks tend to appear in the area near the rivet head at room riveting temperature, mainly in the form of matrix cracks parallel to the fiber direction and fiber cracks perpendicular to the fiber direction. At the glass transition temperature of the resin matrix, the ductility of CFRP in transverse and shear directions is greatly improved, resulting in no macro-cracks on the surface of CFRP sheet, and the delamination area is reduced in the WSPR joints. The ply angle affects the tensile-shear properties and failure process of the joint and the joint with [0/90/0]s laminated structure has the optimist mechanical properties.
To investigate the damage in self-piercing riveting (SPR) of carbon fiber reinforced polymer (CFRP) and aluminum alloy, three groups of SPR joints with typical ply angles were prepared, and the effects of ply angles on the macroscopic damage morphology of joints were studied. The effects of temperature on the mechanical properties and failure of CFRP were studied. Based on the thermal mechanical properties of CFRP, the warm self-piercing riveting (WSPR) process for CFRP and aluminum alloy was innovatively proposed for the purpose of reducing joint damage. The damage difference of CFRP in the joint obtained by two riveting processes was compared. The effect of ply angle on mechanical properties and failure process of WSPR joints in CFRP and aluminum alloy was investigated. The results show that macro-cracks tend to appear in the area near the rivet head at room riveting temperature, mainly in the form of matrix cracks parallel to the fiber direction and fiber cracks perpendicular to the fiber direction. At the glass transition temperature of the resin matrix, the ductility of CFRP in transverse and shear directions is greatly improved, resulting in no macro-cracks on the surface of CFRP sheet, and the delamination area is reduced in the WSPR joints. The ply angle affects the tensile-shear properties and failure process of the joint and the joint with [0/90/0]s laminated structure has the optimist mechanical properties.
2021, 38(11): 3578-3585.
doi: 10.13801/j.cnki.fhclxb.20210129.003
Abstract:
With the rapid development of electronic products, electric vehicles and smart grids, lithium-ion batteries (LIBs) are required to not only possess superior lithium storage performance, but also be low-cost, abundant resources, and foremost sustainable. Based on the advantages of carbon anode materials, a smart strategy to convert the used bamboo chopsticks into uniform carbon fibers (CFs) by using the abundant natural fibers in chopsticks after a simple hydrothermal treatment was proposed. Compared with graphite electrodes, bamboo-based CFs exhibits excellent electrochemical performance as a sustainable anode of LIBs. Moreover, the lithium storage performance of CFs can be further upgraded by integrating nanostructured molybdenum disulfide (MoS2) onto their surface by hydrothermal method to form the CFs/MoS2 composite with a core-shell structure. The electro-chemical results show that the CFs electrode cycled 500 times at a current density of 200 mA/g, has a specific discharge capacity of 381.1 mA·h/g. And the CFs/MoS2 composite electrode still maintains a specific discharge capacity of 843 mA·h/g at a high current density of 1000 mA/g for 1000 cycles.
With the rapid development of electronic products, electric vehicles and smart grids, lithium-ion batteries (LIBs) are required to not only possess superior lithium storage performance, but also be low-cost, abundant resources, and foremost sustainable. Based on the advantages of carbon anode materials, a smart strategy to convert the used bamboo chopsticks into uniform carbon fibers (CFs) by using the abundant natural fibers in chopsticks after a simple hydrothermal treatment was proposed. Compared with graphite electrodes, bamboo-based CFs exhibits excellent electrochemical performance as a sustainable anode of LIBs. Moreover, the lithium storage performance of CFs can be further upgraded by integrating nanostructured molybdenum disulfide (MoS2) onto their surface by hydrothermal method to form the CFs/MoS2 composite with a core-shell structure. The electro-chemical results show that the CFs electrode cycled 500 times at a current density of 200 mA/g, has a specific discharge capacity of 381.1 mA·h/g. And the CFs/MoS2 composite electrode still maintains a specific discharge capacity of 843 mA·h/g at a high current density of 1000 mA/g for 1000 cycles.
2021, 38(11): 3586-3600.
doi: 10.13801/j.cnki.fhclxb.20210126.002
Abstract:
The fiber angles of the winding tubes were changed by controlling the winding lines to realize the gradual change of the stiffness along the axial direction, and then the collapse-stable carbon fiber/epoxy resin composite thin-walled tubes with variable stiffness were fabricated. Finally, the axial quasi-static crushing tests were carried out for three types of winding tubes with variable stiffness, [±45°]n and [90°]n structures. Combined with digital image correlation (DSC) technology and finite element analysis results, the initial strain modes, damage evolution and stress states were compared to study the crushing response and failure mechanism of variable stiffness structures. The results show that the initial failure and damage evolution of the tubes with different fiber angles are different due to the various axial stiffness, so the different crushing response and failure modes are generated respectively, and the continuously changing circular fibers in the variable stiffness zone can effectively cause the delaminated and “flowering” mode mixed damage to release the strain energy slowly. Therefore, the energy absorption effect of the variable stiffness structure is obviously better than that of other two structures. Its peak load is 66.97 kN, crushing efficiency is 50.8%, and specific energy absorption is 10.1 kJ/kg. Compared with the [±45°]n structure, the specific energy absorption increases by 156.35%, and the crushing efficiency increases by 518.76%. Compared with the [90°]n structure, the specific energy absorption increases by 16.9%, and the crushing efficiency reduces by 27.3%.
The fiber angles of the winding tubes were changed by controlling the winding lines to realize the gradual change of the stiffness along the axial direction, and then the collapse-stable carbon fiber/epoxy resin composite thin-walled tubes with variable stiffness were fabricated. Finally, the axial quasi-static crushing tests were carried out for three types of winding tubes with variable stiffness, [±45°]n and [90°]n structures. Combined with digital image correlation (DSC) technology and finite element analysis results, the initial strain modes, damage evolution and stress states were compared to study the crushing response and failure mechanism of variable stiffness structures. The results show that the initial failure and damage evolution of the tubes with different fiber angles are different due to the various axial stiffness, so the different crushing response and failure modes are generated respectively, and the continuously changing circular fibers in the variable stiffness zone can effectively cause the delaminated and “flowering” mode mixed damage to release the strain energy slowly. Therefore, the energy absorption effect of the variable stiffness structure is obviously better than that of other two structures. Its peak load is 66.97 kN, crushing efficiency is 50.8%, and specific energy absorption is 10.1 kJ/kg. Compared with the [±45°]n structure, the specific energy absorption increases by 156.35%, and the crushing efficiency increases by 518.76%. Compared with the [90°]n structure, the specific energy absorption increases by 16.9%, and the crushing efficiency reduces by 27.3%.
2021, 38(11): 3601-3609.
doi: 10.13801/j.cnki.fhclxb.20210210.008
Abstract:
The picosecond laser processing thresholds and morphology characteristics of polyacrylonitrile-based high modulus carbon fiber reinforced cyanate ester composite (M55/BS-4) and an asphalt-based high thermal conductivity carbon fiber reinforced plastic (K600/5418) were studied. Diameter-regression method was used to test and compare the ablation threshold, threshold incubation effect, and single-pulse thresholds for each composite were predicted. The influence of incident energy fluence (0.7-25 J/cm2) and beam scanning velocity (0.2-5 m/s) on the incision quality was analyzed. The results show that the great difference in the fiber thermal conductivity leads to significant quantitative difference in processing threshold and morphology. Using the highest scanning speed (5 m/s) available and fluence equivalent to 3.2 times the single-pulse threshold (i.e., about 8 J/cm2), carbon fiber and resin can be almost synergically removed, characterized by uniform slit inlet widths and neat cutting edge. The use of higher scanning speeds coupled with appropriate processing energy is expected to further improve the quality of processing.
The picosecond laser processing thresholds and morphology characteristics of polyacrylonitrile-based high modulus carbon fiber reinforced cyanate ester composite (M55/BS-4) and an asphalt-based high thermal conductivity carbon fiber reinforced plastic (K600/5418) were studied. Diameter-regression method was used to test and compare the ablation threshold, threshold incubation effect, and single-pulse thresholds for each composite were predicted. The influence of incident energy fluence (0.7-25 J/cm2) and beam scanning velocity (0.2-5 m/s) on the incision quality was analyzed. The results show that the great difference in the fiber thermal conductivity leads to significant quantitative difference in processing threshold and morphology. Using the highest scanning speed (5 m/s) available and fluence equivalent to 3.2 times the single-pulse threshold (i.e., about 8 J/cm2), carbon fiber and resin can be almost synergically removed, characterized by uniform slit inlet widths and neat cutting edge. The use of higher scanning speeds coupled with appropriate processing energy is expected to further improve the quality of processing.
2021, 38(11): 3610-3619.
doi: 10.13801/j.cnki.fhclxb.20210122.002
Abstract:
Aiming at the large brittleness of resin adhesive layer, structural defect of carbon fiber layer, prone to peeling and delamination, etc. the carbon fiber reinforced plastics (CFRP) with aramid pulp (AP) toughening were prepared by compression molding via using AP with high strength and toughness as interface enhancer. The effects of AP with different interface densities on the compressive strength, impact resistance and compressive strength after damages of CFRP were studied. The compressive strengths of directly testing, testing after impact, drill and drill-impact are improved by 37.3%, 41.0% and 41.8% correspondingly for longitudinal CFRP with AP interface density of 6 g/m2. AP improves brittleness of resin, eliminates interlayer resin-rich region, toughens the interlayer toughness and suppressed cracks generation. The formed AP fiber-bridging structure throughout resin layer and carbon fiber layer not only remove the bonding interface defect, but also build quasi-Z fiber distribution to achieve tightly connected structure, which prevent cracks expanding along interlayer and delamination failure, thereby to achieve structure reinforced.
Aiming at the large brittleness of resin adhesive layer, structural defect of carbon fiber layer, prone to peeling and delamination, etc. the carbon fiber reinforced plastics (CFRP) with aramid pulp (AP) toughening were prepared by compression molding via using AP with high strength and toughness as interface enhancer. The effects of AP with different interface densities on the compressive strength, impact resistance and compressive strength after damages of CFRP were studied. The compressive strengths of directly testing, testing after impact, drill and drill-impact are improved by 37.3%, 41.0% and 41.8% correspondingly for longitudinal CFRP with AP interface density of 6 g/m2. AP improves brittleness of resin, eliminates interlayer resin-rich region, toughens the interlayer toughness and suppressed cracks generation. The formed AP fiber-bridging structure throughout resin layer and carbon fiber layer not only remove the bonding interface defect, but also build quasi-Z fiber distribution to achieve tightly connected structure, which prevent cracks expanding along interlayer and delamination failure, thereby to achieve structure reinforced.
2021, 38(11): 3620-3628.
doi: 10.13801/j.cnki.fhclxb.20210207.002
Abstract:
One of the most important deformation modes in resin transfer molding (RTM) of manufacturing processes is compression along thickness direction, which reduces the thickness of the textile preform and causes the change of the fabric structure, causing the nesting effect. Nesting reduces the laminate thickness, increases the fibre volume fraction, and changes the porosity pattern. The effect of adjacent fabric layer nesting has a certain spatial dispersion. This makes the fabric permeability variable. In this work, an experimental device was designed to measure the spatial dispersion of local permeability for low viscosity resins. Then, a random nested monocyte model was established, ANSYS/CFX finite element software was used to realize the numerical simulation of single cell, and the local permeability was obtained by flow analysis. The statistical distribution of permeability was then studied. The experimental results were compared with the numerical simulation results. The reliability of the numerical simulation results was verified. Finally, the random permeability field was established based on the statistical distribution of permeability, and the numerical simulation of resin filling was carried out. The results show that this method is more advanced than traditional method based on constant permeability. The results can provide a basis for the robustness optimization of RTM process in the future.
One of the most important deformation modes in resin transfer molding (RTM) of manufacturing processes is compression along thickness direction, which reduces the thickness of the textile preform and causes the change of the fabric structure, causing the nesting effect. Nesting reduces the laminate thickness, increases the fibre volume fraction, and changes the porosity pattern. The effect of adjacent fabric layer nesting has a certain spatial dispersion. This makes the fabric permeability variable. In this work, an experimental device was designed to measure the spatial dispersion of local permeability for low viscosity resins. Then, a random nested monocyte model was established, ANSYS/CFX finite element software was used to realize the numerical simulation of single cell, and the local permeability was obtained by flow analysis. The statistical distribution of permeability was then studied. The experimental results were compared with the numerical simulation results. The reliability of the numerical simulation results was verified. Finally, the random permeability field was established based on the statistical distribution of permeability, and the numerical simulation of resin filling was carried out. The results show that this method is more advanced than traditional method based on constant permeability. The results can provide a basis for the robustness optimization of RTM process in the future.
2021, 38(11): 3629-3639.
doi: 10.13801/j.cnki.fhclxb.20210210.009
Abstract:
In order to satisfy the requirement of high-temperature resistant wave-transparent composite in project field, a quartz fiber (QF) reinforced novel silicon-containing polyarylacetylene (PSA) resin based composite (QF/PSA) was researched and characterized. Firstly, viscosity prediction model of different temperature and time was established based on the viscosity-time curves of the resin, the model indicates that the resin can be injected between 70~100℃ for resin transfer molding (RTM) process. The curing heat, FT-IR spectra and rheological behavior of the resin were analysized, then the curing temperature and process were revealed. The results show that the resin can be curved at 250℃. Based on the above research, the high-quality preparation of the composite was achieved. Furthermore, the micro-morphology, mechanical properties, thermal expansion performance, dielectric properties as well as high temperature resistant performance of the composite were investigated and verified by experiments. The composite exhibits excellent thermal stability with Tg above 500℃ and T5% up to 625℃, and quartz lamp experiment further indicates that the high temperature resistant ability is up to 520℃/1000 s. The dielectric constant is 3.1~3.2 and dielectric loss is less than 0.003. In addition, the mechanical property is enough for functional composite. The above research indicates that the novel silicon-containing polyarylacetylene resin based wave-transparent composite has high potentials in the fields of aeronautics and astronautics.
In order to satisfy the requirement of high-temperature resistant wave-transparent composite in project field, a quartz fiber (QF) reinforced novel silicon-containing polyarylacetylene (PSA) resin based composite (QF/PSA) was researched and characterized. Firstly, viscosity prediction model of different temperature and time was established based on the viscosity-time curves of the resin, the model indicates that the resin can be injected between 70~100℃ for resin transfer molding (RTM) process. The curing heat, FT-IR spectra and rheological behavior of the resin were analysized, then the curing temperature and process were revealed. The results show that the resin can be curved at 250℃. Based on the above research, the high-quality preparation of the composite was achieved. Furthermore, the micro-morphology, mechanical properties, thermal expansion performance, dielectric properties as well as high temperature resistant performance of the composite were investigated and verified by experiments. The composite exhibits excellent thermal stability with Tg above 500℃ and T5% up to 625℃, and quartz lamp experiment further indicates that the high temperature resistant ability is up to 520℃/1000 s. The dielectric constant is 3.1~3.2 and dielectric loss is less than 0.003. In addition, the mechanical property is enough for functional composite. The above research indicates that the novel silicon-containing polyarylacetylene resin based wave-transparent composite has high potentials in the fields of aeronautics and astronautics.
2021, 38(11): 3640-3651.
doi: 10.13801/j.cnki.fhclxb.20210129.004
Abstract:
Drop hammer impact test was used to study the failure mechanism and the compression after impact (CAI) of carbon fiber reinforced epoxy composite shaft tubes when subjected to different impact energy levels to simulate the low-velocity impact (LVI) process. ABQUAS finite element analysis technology and X-ray tomography (CT) techniques were used to investigate the internal failure mechanisms. Results show that, with the increase of impact energy, the deformation resistance of the composite tubes first increases and then decreases, and reaches a maximum value when the impact energy falls between 10 J and 20 J. The accuracy of the test results is confirmed by the fact that the energy absorption rates of the shaft tube with different energy levels differ little. CT results show that the composite shaft tube after LVI mainly fails in forms of delamination and resin cracking. Fiber fracture mainly occurs at the impact location, and the fiber fracture becomes more and more significant with the increase of impact energy. The finite element simulation results show that the fiber failure of composite shaft tube in the tensile direction is significantly less than the compression failure. The compression failure mainly diffuses along the fiber layout direction. The tensile failure mainly spreads along the axial direction and transverse direction, and the axial failure degree is greater than the transverse failure degree. The compression failure of the resin mainly diffuses from the impact position to the transverse along the axial direction. The diffusion shape is nearly round, the closer to the center, the failure is more obvious. The stretching failure range is a cross; the overall failure diffuses along the cross edge.
Drop hammer impact test was used to study the failure mechanism and the compression after impact (CAI) of carbon fiber reinforced epoxy composite shaft tubes when subjected to different impact energy levels to simulate the low-velocity impact (LVI) process. ABQUAS finite element analysis technology and X-ray tomography (CT) techniques were used to investigate the internal failure mechanisms. Results show that, with the increase of impact energy, the deformation resistance of the composite tubes first increases and then decreases, and reaches a maximum value when the impact energy falls between 10 J and 20 J. The accuracy of the test results is confirmed by the fact that the energy absorption rates of the shaft tube with different energy levels differ little. CT results show that the composite shaft tube after LVI mainly fails in forms of delamination and resin cracking. Fiber fracture mainly occurs at the impact location, and the fiber fracture becomes more and more significant with the increase of impact energy. The finite element simulation results show that the fiber failure of composite shaft tube in the tensile direction is significantly less than the compression failure. The compression failure mainly diffuses along the fiber layout direction. The tensile failure mainly spreads along the axial direction and transverse direction, and the axial failure degree is greater than the transverse failure degree. The compression failure of the resin mainly diffuses from the impact position to the transverse along the axial direction. The diffusion shape is nearly round, the closer to the center, the failure is more obvious. The stretching failure range is a cross; the overall failure diffuses along the cross edge.
2021, 38(11): 3652-3660.
doi: 10.13801/j.cnki.fhclxb.20210114.003
Abstract:
Bisphenol A-type phthalonitrile/poly (dimethylsilane-m-diacetylenyl phenyl) resin (PBA) was prepared by modifying Poly (dimethylsilane-m-diacetylenyl phenyl) resin (PDMP) with bisphenol A-type phthalonitrile prepolymer (BAPh-P). The curing behavior, viscosity and heat resistance were analyzed by DSC, FTIR, rheological analysis and TGA. The results show that the curing peak temperature of PBA resin is higher than that of PDMP; the curing reaction is mainly Diels alder and addition reaction of alkynyl group, triazine ring and phthalocyanine ring formed by cyano further crosslinking; heat resistance of PDMP in air is improved by the addition of BAPh-P, and temperature with mass loss of 5% (Td5) of PBA-1 (PDMP: BAPh-P mass ratio of 5∶1) in N2 and air is 640.6℃ and 591℃, respectively, and mass retention rates at 1000℃ is 89.0% and 26.9%; with the increase of BAPh-P mass, the Td5 of PBA resin curing compound decreases, but the Td5 in air is higher than that of PDMP; The bending strength of quartz fiber reinforced PBA resin matrix (QF/PBA) composites increases gradually at room temperature with the increase of BAPh-P mass, and then decreases at high temperature; flexural strength of QF/PBA-2 composite at room temperature and 400℃ is 363 MPa and 330 MPa, respectively, which is higher than that of PDMP, interlaminar shear strength (ILSS) at room temperature and 400℃ is 37.5 MPa and 22.2 MPa, respectively.
Bisphenol A-type phthalonitrile/poly (dimethylsilane-m-diacetylenyl phenyl) resin (PBA) was prepared by modifying Poly (dimethylsilane-m-diacetylenyl phenyl) resin (PDMP) with bisphenol A-type phthalonitrile prepolymer (BAPh-P). The curing behavior, viscosity and heat resistance were analyzed by DSC, FTIR, rheological analysis and TGA. The results show that the curing peak temperature of PBA resin is higher than that of PDMP; the curing reaction is mainly Diels alder and addition reaction of alkynyl group, triazine ring and phthalocyanine ring formed by cyano further crosslinking; heat resistance of PDMP in air is improved by the addition of BAPh-P, and temperature with mass loss of 5% (Td5) of PBA-1 (PDMP: BAPh-P mass ratio of 5∶1) in N2 and air is 640.6℃ and 591℃, respectively, and mass retention rates at 1000℃ is 89.0% and 26.9%; with the increase of BAPh-P mass, the Td5 of PBA resin curing compound decreases, but the Td5 in air is higher than that of PDMP; The bending strength of quartz fiber reinforced PBA resin matrix (QF/PBA) composites increases gradually at room temperature with the increase of BAPh-P mass, and then decreases at high temperature; flexural strength of QF/PBA-2 composite at room temperature and 400℃ is 363 MPa and 330 MPa, respectively, which is higher than that of PDMP, interlaminar shear strength (ILSS) at room temperature and 400℃ is 37.5 MPa and 22.2 MPa, respectively.
2021, 38(11): 3661-3671.
doi: 10.13801/j.cnki.fhclxb.20210126.001
Abstract:
To improve the transverse mechanical heterogeneity of conventional uni-directional corrugated sandwich structures, a new type of bi-directional composite corrugated sandwich structure was designed. Considering the difficulty of manufacturing the bi-directional corrugated sandwich structure, a procese based on vacuum assistant resin infusion (VARI) was proposed for high efficiency and quality preparation. The prepared structures were subjected to compression, bending and shear tests. The failure modes and mechanism of the bi-directional composite sandwich structures were analyzed, the strength and modulus of the structure under different load conditions were obtained, and the comparison between the bi-directional and uni-directional corrugated sandwich structure was made. The results show that the glass fiber/epoxy resin core is the main bearing part under the compression load, and the failure of the structure is mainly reflected in the buckling, fracture and delamination of the core. Under the bending load, caused by the lower compressive strength than its tensile strength of fiber, the upper panel first reaches the failure load under the pressure head. The bending failure modes of the structure are mainly the fracture and debonding of upper panel. The shear failure of the structure is mainly caused by the debonding of the foam and the panel and the collapse of the foam, but the core and the panel are not obviously destroyed. Compared with uni-directional corrugated sandwich structure, the mechanical properties of bi-directional corrugated sandwich structure are significantly improved.
To improve the transverse mechanical heterogeneity of conventional uni-directional corrugated sandwich structures, a new type of bi-directional composite corrugated sandwich structure was designed. Considering the difficulty of manufacturing the bi-directional corrugated sandwich structure, a procese based on vacuum assistant resin infusion (VARI) was proposed for high efficiency and quality preparation. The prepared structures were subjected to compression, bending and shear tests. The failure modes and mechanism of the bi-directional composite sandwich structures were analyzed, the strength and modulus of the structure under different load conditions were obtained, and the comparison between the bi-directional and uni-directional corrugated sandwich structure was made. The results show that the glass fiber/epoxy resin core is the main bearing part under the compression load, and the failure of the structure is mainly reflected in the buckling, fracture and delamination of the core. Under the bending load, caused by the lower compressive strength than its tensile strength of fiber, the upper panel first reaches the failure load under the pressure head. The bending failure modes of the structure are mainly the fracture and debonding of upper panel. The shear failure of the structure is mainly caused by the debonding of the foam and the panel and the collapse of the foam, but the core and the panel are not obviously destroyed. Compared with uni-directional corrugated sandwich structure, the mechanical properties of bi-directional corrugated sandwich structure are significantly improved.
2021, 38(11): 3672-3681.
doi: 10.13801/j.cnki.fhclxb.20201016.003
Abstract:
To clarify the wave propagation behavior in the radii of carbon fiber reinforced plastics (CFRP) components with complex geometry, the elastic property characterization, finite element modeling, wave field calculation and experimental verification were carried out for phased array ultrasonic testing (PAUT). Based on a back-reflection ultrasonic immersion method and a simulated annealing algorithm, the stiffness matrix of a unidirectional CFRP plate was inversely solved, and the elastic property in the radii was described quantitatively by Bond transformation. The material and geometric characteristics of the radii for multidirectional laminates were analyzed, and a finite element model of PAUT was proposed by considering the curved surface, layered structure and elastic anisotropy simultaneously. Furthermore, the A-scan and B-scan of PAUT were calculated and compared with the experimental results. A certain degree of structural noise is observed between surface echo and defect echo, and there are strong pseudo defects on the left and right sides. The transient wave field was compared with those in a CFRP plate, a unidirectional CFRP radii and an elastically isotropic radii. It is found that the coupling of the elastic anisotropy and the curved laminated structure are the main reasons for the above phenomena. When an ultrasonic wave is incident obliquely into the radii part, the mismatched acoustic properties of different layers result in the structural noise. When the wave runs into the ribbed plate, the echo is received by the probe after twice reflections and forms an image of the pseudo defects. The refraction part propagates along with the fiber rapidly into the radii, overlapping with the defect echo, and directly contributes to the structural noise. It is indicated that the high-quality reorganization of the defects in CFRP radii has been influenced by the coupling of the material and geometric factors.
To clarify the wave propagation behavior in the radii of carbon fiber reinforced plastics (CFRP) components with complex geometry, the elastic property characterization, finite element modeling, wave field calculation and experimental verification were carried out for phased array ultrasonic testing (PAUT). Based on a back-reflection ultrasonic immersion method and a simulated annealing algorithm, the stiffness matrix of a unidirectional CFRP plate was inversely solved, and the elastic property in the radii was described quantitatively by Bond transformation. The material and geometric characteristics of the radii for multidirectional laminates were analyzed, and a finite element model of PAUT was proposed by considering the curved surface, layered structure and elastic anisotropy simultaneously. Furthermore, the A-scan and B-scan of PAUT were calculated and compared with the experimental results. A certain degree of structural noise is observed between surface echo and defect echo, and there are strong pseudo defects on the left and right sides. The transient wave field was compared with those in a CFRP plate, a unidirectional CFRP radii and an elastically isotropic radii. It is found that the coupling of the elastic anisotropy and the curved laminated structure are the main reasons for the above phenomena. When an ultrasonic wave is incident obliquely into the radii part, the mismatched acoustic properties of different layers result in the structural noise. When the wave runs into the ribbed plate, the echo is received by the probe after twice reflections and forms an image of the pseudo defects. The refraction part propagates along with the fiber rapidly into the radii, overlapping with the defect echo, and directly contributes to the structural noise. It is indicated that the high-quality reorganization of the defects in CFRP radii has been influenced by the coupling of the material and geometric factors.
2021, 38(11): 3682-3692.
doi: 10.13801/j.cnki.fhclxb.20210119.001
Abstract:
A unit cell model of creep mixing rate containing interface for glass fiber/resin composite (GFRP) was established to analyze the long-term creep property of GFRP. The experimental results of bending creep of GFRP under loads with the stress level of 20% of the initial bending strength were compared. The effects of interfacial modulus, interfacial thickness, fiber continuity, morphology and orientation on the long-term creep properties of composites were analyzed. The results show that this model is more accurate and more consistent with the experimental results compared with the mixing rate model without considering the interface effect. Interfacial modulus reflects the degree of binding between fiber and matrix, and affects the creep property of composite. The creep compliance decreases with the increase of interface modulus. The creep compliance of the composite increases slightly with the increase of the interfacial thickness. Compared with continuous fiber reinforced resin composites, the creep properties of chopped strand mat reinforced resin composite are more easily affected by interfacial effects. The fiber direction has a significant influence on the creep performance of composite materials. With the increase of fiber direction angle, the creep compliance of composite increases. However, when the fiber direction angle reaches 60°, the fiber has basically lost the load transfer and reinforcing ability, and the creep compliance of composite materials no longer increases with the increase of fiber direction angle.
A unit cell model of creep mixing rate containing interface for glass fiber/resin composite (GFRP) was established to analyze the long-term creep property of GFRP. The experimental results of bending creep of GFRP under loads with the stress level of 20% of the initial bending strength were compared. The effects of interfacial modulus, interfacial thickness, fiber continuity, morphology and orientation on the long-term creep properties of composites were analyzed. The results show that this model is more accurate and more consistent with the experimental results compared with the mixing rate model without considering the interface effect. Interfacial modulus reflects the degree of binding between fiber and matrix, and affects the creep property of composite. The creep compliance decreases with the increase of interface modulus. The creep compliance of the composite increases slightly with the increase of the interfacial thickness. Compared with continuous fiber reinforced resin composites, the creep properties of chopped strand mat reinforced resin composite are more easily affected by interfacial effects. The fiber direction has a significant influence on the creep performance of composite materials. With the increase of fiber direction angle, the creep compliance of composite increases. However, when the fiber direction angle reaches 60°, the fiber has basically lost the load transfer and reinforcing ability, and the creep compliance of composite materials no longer increases with the increase of fiber direction angle.
2021, 38(11): 3693-3703.
doi: 10.13801/j.cnki.fhclxb.20210301.001
Abstract:
With the development of automated fiber placement technology, it is possible to lay complex curves which greatly increase the freedom of angle design. In this paper, with the purpose of improving the dynamic characteristics of composite laminates, the vibration damping performance of variable angle laminates was studied and analyzed. Firstly, the free attenuation experiment was carried out to study the relationship between the change of fiber angle and damping ratio of variable angle laminates. Then, the vibration response of variable angle laminates under random excitation was studied by random experiments. The transition function (TF) at the formant and the root mean square (RMS) of the acceleration at the pick-up point of vibration were used to evaluate the effect of vibration reduction. The results show that the damping ratio of laminates is the largest when the fiber angle is ±<45|60> and the least when the fiber angle is ±<73|88>. Based on the vibration reduction evaluation index of RMS, the vibration reduction performance of ±<45|60> sandwich laminate is 27.13% higher than the traditional linear laminate; Based on the formant vibration reduction evaluation index of TF, the vibration reduction effect of different formants is obviously different with the fiber change. The results show that the vibration reduction performance of the variable angle laminates is obviously better than that of the traditional linear laminates. The relevant experimental results will be helpful for the design and optimization of vibration reduction of variable angle laminates.
With the development of automated fiber placement technology, it is possible to lay complex curves which greatly increase the freedom of angle design. In this paper, with the purpose of improving the dynamic characteristics of composite laminates, the vibration damping performance of variable angle laminates was studied and analyzed. Firstly, the free attenuation experiment was carried out to study the relationship between the change of fiber angle and damping ratio of variable angle laminates. Then, the vibration response of variable angle laminates under random excitation was studied by random experiments. The transition function (TF) at the formant and the root mean square (RMS) of the acceleration at the pick-up point of vibration were used to evaluate the effect of vibration reduction. The results show that the damping ratio of laminates is the largest when the fiber angle is ±<45|60> and the least when the fiber angle is ±<73|88>. Based on the vibration reduction evaluation index of RMS, the vibration reduction performance of ±<45|60> sandwich laminate is 27.13% higher than the traditional linear laminate; Based on the formant vibration reduction evaluation index of TF, the vibration reduction effect of different formants is obviously different with the fiber change. The results show that the vibration reduction performance of the variable angle laminates is obviously better than that of the traditional linear laminates. The relevant experimental results will be helpful for the design and optimization of vibration reduction of variable angle laminates.
2021, 38(11): 3704-3713.
doi: 10.13801/j.cnki.fhclxb.20210122.003
Abstract:
To accurately predict the macroscopic elastic properties of 3D angle-interlock woven composites, interior and surface unit-cells mesoscopic solid models were established for numerical analysis based on the geometric parameters measured in CT images, and surface unit-cells were modeled in the form of integrated surface unit-cells. Then a tensile test in warp direction was conducted for 3D angle-interlock woven ultra-high molecular weight polyethylene (UHMWPE) fiber/polyurethane composites. The results show that the predicted macroscopic elastic modulus values of the composites based on two unit-cells models are in good agreement with the experimental values. The tensile modulus in the warp direction of the integrated surface unit-cells is smaller than that of the interior unit-cells. During the tensile test in the warp direction, stress concentration tends to occur at the interface among warp yarns, the end of weft yarns along the width and the interface between warp yarns and matrix. When the number of weft layers is less than 30, the effect of surface region on the overall mechanical properties of the composites should be considered.
To accurately predict the macroscopic elastic properties of 3D angle-interlock woven composites, interior and surface unit-cells mesoscopic solid models were established for numerical analysis based on the geometric parameters measured in CT images, and surface unit-cells were modeled in the form of integrated surface unit-cells. Then a tensile test in warp direction was conducted for 3D angle-interlock woven ultra-high molecular weight polyethylene (UHMWPE) fiber/polyurethane composites. The results show that the predicted macroscopic elastic modulus values of the composites based on two unit-cells models are in good agreement with the experimental values. The tensile modulus in the warp direction of the integrated surface unit-cells is smaller than that of the interior unit-cells. During the tensile test in the warp direction, stress concentration tends to occur at the interface among warp yarns, the end of weft yarns along the width and the interface between warp yarns and matrix. When the number of weft layers is less than 30, the effect of surface region on the overall mechanical properties of the composites should be considered.
2021, 38(11): 3714-3725.
doi: 10.13801/j.cnki.fhclxb.20210119.003
Abstract:
Experimental study has shown that the interfacial bonding between fibers and matrix can be significantly improved by introducing nanophases into fiber reinforced polymer composites. The reinforcing effects of various nanophases on the obtained multi-scale composites were found different, which were associated with the shape and dimension of the nanophases. In this paper, a multiscale model was proposed based on the cohesive energy model to explore the source of the difference in reinforcing efficiency introduced by the three kinds of typical nanophases, i.e., carbon nanotubes, spherical fullerene nanoparticles and graphene nanoplates. The model elucidates how the shape and quantity of nanophases influence the strength of interfacial bonding in multiscale composites. The proposed model was verified according to the experimental results obtained through transverse tension tests of fiber bundle composites. The theoretical prediction shows a good agreement with the measured data.
Experimental study has shown that the interfacial bonding between fibers and matrix can be significantly improved by introducing nanophases into fiber reinforced polymer composites. The reinforcing effects of various nanophases on the obtained multi-scale composites were found different, which were associated with the shape and dimension of the nanophases. In this paper, a multiscale model was proposed based on the cohesive energy model to explore the source of the difference in reinforcing efficiency introduced by the three kinds of typical nanophases, i.e., carbon nanotubes, spherical fullerene nanoparticles and graphene nanoplates. The model elucidates how the shape and quantity of nanophases influence the strength of interfacial bonding in multiscale composites. The proposed model was verified according to the experimental results obtained through transverse tension tests of fiber bundle composites. The theoretical prediction shows a good agreement with the measured data.
2021, 38(11): 3726-3736.
doi: 10.13801/j.cnki.fhclxb.20210202.003
Abstract:
Aiming at the on-line diagnosis and prognosis of composite structures, a method for structural delamination diagnosis and remaining useful life (RUL) prediction was proposed based on structural health monitoring (SHM) and the Bayesian theory. Within the Bayesian probabilistic framework, an exponential model was adopted to describe the prior progression of the fatigue delamination in the composite structure. Then, on-line SHM data were incorporated for diagnosing the delamination state, as well as parameters of the damage area progression model. The posterior estimations denoted the diagnosis result, based on which the progression of the delamination area in the future was predicted, giving the RUL of the current composite structure. The proposed method was validated on the simulated fatigue delamination growth in a stiffened composite structure through the finite element method. The result shows the accuracy of this method for on-line diagnosing the delamination damage, as well as predicting the RUL of the structure.
Aiming at the on-line diagnosis and prognosis of composite structures, a method for structural delamination diagnosis and remaining useful life (RUL) prediction was proposed based on structural health monitoring (SHM) and the Bayesian theory. Within the Bayesian probabilistic framework, an exponential model was adopted to describe the prior progression of the fatigue delamination in the composite structure. Then, on-line SHM data were incorporated for diagnosing the delamination state, as well as parameters of the damage area progression model. The posterior estimations denoted the diagnosis result, based on which the progression of the delamination area in the future was predicted, giving the RUL of the current composite structure. The proposed method was validated on the simulated fatigue delamination growth in a stiffened composite structure through the finite element method. The result shows the accuracy of this method for on-line diagnosing the delamination damage, as well as predicting the RUL of the structure.
2021, 38(11): 3737-3746.
doi: 10.13801/j.cnki.fhclxb.20210115.003
Abstract:
Numerical simulation based on finite element method was carried out for the air-coupled ultrasonic testing of C/SiC composites with high porosity. The elastic stiffness matrix was calculated based on mechanical and acoustical analysis. Finite element models with random void morphology were established, of which the porosity was 5%, 10%, and 15%, respectively. The characteristics of ultrasonic propagation and the response to typical defects were studied in the transmission testing profile. Results indicate that the longitudinal wave velocity in the direction vertical to laminate is about 2830 m/s, and five independent elastic constants of transverse isotropy are 158.149, 88.589, 34.141, 15.288 and 13.793 GPa. The voids are strip-like, and the ratio of width to wavelength is between 0.05~0.22. It is found that the ultrasonic attenuation gradually increases with the increasing porosity, which is mainly in Rayleigh scattering regime. Meanwhile, the directivity pattern of ultrasonic field under some conditions is also changed due to the high porosity and complex morphology. As the length of delamination increases from 0 to 25 mm, the attenuation of received signal increases, and the maximum is about 33.9 dB compared with that without delamination. It is of similarity for the evolution of the ultrasonic field with the increasing thickness of laminate, mainly owing to the combined effects of the delamination and voids. The simulation results show a good consistency with experiments and provide support for high-quality non-destructive testing on C/SiC composites.
Numerical simulation based on finite element method was carried out for the air-coupled ultrasonic testing of C/SiC composites with high porosity. The elastic stiffness matrix was calculated based on mechanical and acoustical analysis. Finite element models with random void morphology were established, of which the porosity was 5%, 10%, and 15%, respectively. The characteristics of ultrasonic propagation and the response to typical defects were studied in the transmission testing profile. Results indicate that the longitudinal wave velocity in the direction vertical to laminate is about 2830 m/s, and five independent elastic constants of transverse isotropy are 158.149, 88.589, 34.141, 15.288 and 13.793 GPa. The voids are strip-like, and the ratio of width to wavelength is between 0.05~0.22. It is found that the ultrasonic attenuation gradually increases with the increasing porosity, which is mainly in Rayleigh scattering regime. Meanwhile, the directivity pattern of ultrasonic field under some conditions is also changed due to the high porosity and complex morphology. As the length of delamination increases from 0 to 25 mm, the attenuation of received signal increases, and the maximum is about 33.9 dB compared with that without delamination. It is of similarity for the evolution of the ultrasonic field with the increasing thickness of laminate, mainly owing to the combined effects of the delamination and voids. The simulation results show a good consistency with experiments and provide support for high-quality non-destructive testing on C/SiC composites.
2021, 38(11): 3747-3756.
doi: 10.13801/j.cnki.fhclxb.20210129.002
Abstract:
Multiphase Mo-12Si-8.5B alloy is a promising high-temperature structural material. In order to further simultaneously improve the strength and toughness of the Mo-12Si-8.5B alloy, the method of strengthening and toughening the bimodal grain size Mo-12Si-8.5B alloy with adding nano-ZrO2 (Y2O3) particles was put out. Nanometer Mo-ZrO2 (Y2O3) composite powders were successfully prepared by sol-gel and high-temperature hydrogen reduction method, and a series of Mo-12Si-8.5B-ZrO2 (Y2O3) composites with a bimodal grain size distribution were fabricated via spark plasma sintering (SPS) using nanometer Mo-ZrO2 (Y2O3) and micrometer Mo powders as raw materials. The results show that the particle size of Mo powders and the relative density of the sintered body decrease with the increase of the ZrO2 (Y2O3) content. When the ZrO2 (Y2O3) content is less than 2.5wt%, the relative density is above 98.1%. As the content of ZrO2 (Y2O3) are 1.5wt% and 2.5wt%, the composites exhibit the high hardness (9.76-9.98 GPa), flexural strength (672-678 MPa) and fracture toughness (12.68-12.82 MPa·m1/2). Grain refinement of the Mo, grain boundary strengthening of the nanometer/micrometer Mo grains and the second-phase strengthening of the nano-ZrO2(Y2O3) particles attribute to the increase of the hardness and flexural strength. The coarse grain Mo and nanometer ZrO2 (Y2O3) in the composites contribute to the improvement of the fracture toughness. The toughening mechanisms of the Mo-12Si-8.5B-ZrO2 (Y2O3) composites are crack deflection and crack bridging.
Multiphase Mo-12Si-8.5B alloy is a promising high-temperature structural material. In order to further simultaneously improve the strength and toughness of the Mo-12Si-8.5B alloy, the method of strengthening and toughening the bimodal grain size Mo-12Si-8.5B alloy with adding nano-ZrO2 (Y2O3) particles was put out. Nanometer Mo-ZrO2 (Y2O3) composite powders were successfully prepared by sol-gel and high-temperature hydrogen reduction method, and a series of Mo-12Si-8.5B-ZrO2 (Y2O3) composites with a bimodal grain size distribution were fabricated via spark plasma sintering (SPS) using nanometer Mo-ZrO2 (Y2O3) and micrometer Mo powders as raw materials. The results show that the particle size of Mo powders and the relative density of the sintered body decrease with the increase of the ZrO2 (Y2O3) content. When the ZrO2 (Y2O3) content is less than 2.5wt%, the relative density is above 98.1%. As the content of ZrO2 (Y2O3) are 1.5wt% and 2.5wt%, the composites exhibit the high hardness (9.76-9.98 GPa), flexural strength (672-678 MPa) and fracture toughness (12.68-12.82 MPa·m1/2). Grain refinement of the Mo, grain boundary strengthening of the nanometer/micrometer Mo grains and the second-phase strengthening of the nano-ZrO2(Y2O3) particles attribute to the increase of the hardness and flexural strength. The coarse grain Mo and nanometer ZrO2 (Y2O3) in the composites contribute to the improvement of the fracture toughness. The toughening mechanisms of the Mo-12Si-8.5B-ZrO2 (Y2O3) composites are crack deflection and crack bridging.
2021, 38(11): 3757-3763.
doi: 10.13801/j.cnki.fhclxb.20210128.001
Abstract:
The Ca0.7La0.2TiO3 ceramic with excellent dielectric properties was filled into cyanate ester (CE) resin to prepare Ca0.7La0.2TiO3/CE composite by a melt pouring technique. The results show that dense microstructure is observed in the composites with different filler volume fractions. The Ca0.7La0.2TiO3/CE composite with a high dielectric constant (ε) and low dielectric loss (tanδ) (ε=25.7, tanδ=0.0055, at 10 GHz) is obtained when the filler volume fraction reaches 40%. Meanwhile, the bending strength reaches 130 MPa. And the thermal conductivity increases to 0.8601 W/(m·K), which can effectively dissipate heat. TGA results show that compared with CE resin, the composites have higher thermal stability and have good application prospects in high-frequency communications, integrated circuits and other fields.
The Ca0.7La0.2TiO3 ceramic with excellent dielectric properties was filled into cyanate ester (CE) resin to prepare Ca0.7La0.2TiO3/CE composite by a melt pouring technique. The results show that dense microstructure is observed in the composites with different filler volume fractions. The Ca0.7La0.2TiO3/CE composite with a high dielectric constant (ε) and low dielectric loss (tanδ) (ε=25.7, tanδ=0.0055, at 10 GHz) is obtained when the filler volume fraction reaches 40%. Meanwhile, the bending strength reaches 130 MPa. And the thermal conductivity increases to 0.8601 W/(m·K), which can effectively dissipate heat. TGA results show that compared with CE resin, the composites have higher thermal stability and have good application prospects in high-frequency communications, integrated circuits and other fields.
2021, 38(11): 3764-3774.
doi: 10.13801/j.cnki.fhclxb.20210223.005
Abstract:
Electrolytic water includes hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), because OER is a complex 4-electron transfer process, developing highly active non-precious OER electrocatalysts with superior durability is crucial to electrolytic water. In order to reduce the cost, 304 stainless steel mesh (SS) was selected as the matrix, Co-Ni double hydroxides was prepared by electrodeposition, Co-Ni oxides were produced by vacuum calcination. The crystal structure, morphology and electrocatalytic OER performance of Co2Ni1O4/ SS composite were studied by XRD, SEM, TEM, XPS and electrochemical workstation. As a result, the Co-Ni double hydroxides prepared by electrodeposition are transformed into Co-Ni oxides with spinel structure after vacuum calcination; successfully synthesized a large number of dense layered structures on the surface of stainless steel;the Co2Ni1O4/SS electrode exhibits an outstanding OER catalytic activity with an overpotentials of 240 mV at 10 mA·cm−2 and a Tafel slop as low as 53.92 mV·dec−1 in 1.0 mol/L KOH. In addition, the Co2Ni1O4/SS composites shows excellent stability in the alkaline electrolyte.
Electrolytic water includes hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), because OER is a complex 4-electron transfer process, developing highly active non-precious OER electrocatalysts with superior durability is crucial to electrolytic water. In order to reduce the cost, 304 stainless steel mesh (SS) was selected as the matrix, Co-Ni double hydroxides was prepared by electrodeposition, Co-Ni oxides were produced by vacuum calcination. The crystal structure, morphology and electrocatalytic OER performance of Co2Ni1O4/ SS composite were studied by XRD, SEM, TEM, XPS and electrochemical workstation. As a result, the Co-Ni double hydroxides prepared by electrodeposition are transformed into Co-Ni oxides with spinel structure after vacuum calcination; successfully synthesized a large number of dense layered structures on the surface of stainless steel;the Co2Ni1O4/SS electrode exhibits an outstanding OER catalytic activity with an overpotentials of 240 mV at 10 mA·cm−2 and a Tafel slop as low as 53.92 mV·dec−1 in 1.0 mol/L KOH. In addition, the Co2Ni1O4/SS composites shows excellent stability in the alkaline electrolyte.
2021, 38(11): 3775-3784.
doi: 10.13801/j.cnki.fhclxb.20210121.001
Abstract:
Using electrolytic copper powder and graphite powder as raw materials, anionic emulsified asphalt as binder, the Cu-graphite-emulsified asphalt composites were prepared by powder metallurgy technology, and XRD, EDS and SEM were used to characterize the microstructure of Cu-graphite-emulsified asphalt composites with graphite content of 2wt%-8wt%. The friction and wear properties, mechanical and electrical properties of Cu-graphite-emulsified asphalt composites were studied, and compared with those of Cu-graphite composites without emulsified asphalt. The results show that emulsified asphalt can effectively prevent the aggregation of graphite particles and has a bonding effect on the graphite and Cu matrix; At the interface of the two phases, there is almost no gap and layered graphite being produced; The sample with 4wt% graphite has minimum wear loss of only 0.0049 g, and the friction coefficient is about 0.025; Increasing the load and graphite content will increase the wear loss, but it can reduce the friction coefficients; During sliding friction, cracks, chutes, depressions, small particles and lamellar structures will appear on the worn surface, but the extent is lower than that of composites without emulsified asphalt.
Using electrolytic copper powder and graphite powder as raw materials, anionic emulsified asphalt as binder, the Cu-graphite-emulsified asphalt composites were prepared by powder metallurgy technology, and XRD, EDS and SEM were used to characterize the microstructure of Cu-graphite-emulsified asphalt composites with graphite content of 2wt%-8wt%. The friction and wear properties, mechanical and electrical properties of Cu-graphite-emulsified asphalt composites were studied, and compared with those of Cu-graphite composites without emulsified asphalt. The results show that emulsified asphalt can effectively prevent the aggregation of graphite particles and has a bonding effect on the graphite and Cu matrix; At the interface of the two phases, there is almost no gap and layered graphite being produced; The sample with 4wt% graphite has minimum wear loss of only 0.0049 g, and the friction coefficient is about 0.025; Increasing the load and graphite content will increase the wear loss, but it can reduce the friction coefficients; During sliding friction, cracks, chutes, depressions, small particles and lamellar structures will appear on the worn surface, but the extent is lower than that of composites without emulsified asphalt.
2021, 38(11): 3785-3798.
doi: 10.13801/j.cnki.fhclxb.20210202.001
Abstract:
This paper presents a strength criterion and fatigue life prediction method for 2D braided alumina matrix composites under a complex in-plane stress state. The static strength of the material was obtained by in-plane tensile, compression, and pure shear tests. Considering the difference between tensile and compressive properties of materials and the influence mechanism of in-plane tensile and shear coupling on material strength, a revised Hoffman strength theory was proposed. The predicted off-axis tensile strength is consistent with the test results, and the deviation is not more than 10%. Tensile fatigue tests were carried out with the off-axis angle θ=0°, 15°, 30°, 45°, the stress ratio R=0.1, and frequency f=10 Hz. The test results show that the fatigue life decreases with the increase of off-axis angle. Due to the in-plane shear stress component, the fatigue failure is gradually changed from fiber-dominated to fiber-matrix dominated mode. Based on a combination of the uniaxial tensile fatigue life curve, the Broutman-Sahu residual strength model, which is used to characterize the variation of the residual strength with the fatigue cycles, and the modified Hoffman strength theory, the paper proposes a fatigue life prediction model under complex in-plane loading conditions. The fatigue shear damage factor is defined to characterize the effect of the normal and shear stress interaction on fatigue life. The fatigue life prediction model is used to predict the fatigue life of specimens in the off-axis tensile fatigue tests. The predicted result agrees with the test result, and the deviation is within the 1-time life span. The results indicate that the proposed fatigue life prediction model can be used to predict the fatigue life of 2D braided alumina matrix composites under the complex in-plane stress condition with the given stress ratio, temperature, and fatigue load frequency.
This paper presents a strength criterion and fatigue life prediction method for 2D braided alumina matrix composites under a complex in-plane stress state. The static strength of the material was obtained by in-plane tensile, compression, and pure shear tests. Considering the difference between tensile and compressive properties of materials and the influence mechanism of in-plane tensile and shear coupling on material strength, a revised Hoffman strength theory was proposed. The predicted off-axis tensile strength is consistent with the test results, and the deviation is not more than 10%. Tensile fatigue tests were carried out with the off-axis angle θ=0°, 15°, 30°, 45°, the stress ratio R=0.1, and frequency f=10 Hz. The test results show that the fatigue life decreases with the increase of off-axis angle. Due to the in-plane shear stress component, the fatigue failure is gradually changed from fiber-dominated to fiber-matrix dominated mode. Based on a combination of the uniaxial tensile fatigue life curve, the Broutman-Sahu residual strength model, which is used to characterize the variation of the residual strength with the fatigue cycles, and the modified Hoffman strength theory, the paper proposes a fatigue life prediction model under complex in-plane loading conditions. The fatigue shear damage factor is defined to characterize the effect of the normal and shear stress interaction on fatigue life. The fatigue life prediction model is used to predict the fatigue life of specimens in the off-axis tensile fatigue tests. The predicted result agrees with the test result, and the deviation is within the 1-time life span. The results indicate that the proposed fatigue life prediction model can be used to predict the fatigue life of 2D braided alumina matrix composites under the complex in-plane stress condition with the given stress ratio, temperature, and fatigue load frequency.
