2015 Vol. 32, No. 1

2015, 32(1): .
Research progress on severe plastic deformation behaviors of discontinuously reinforced metal matrix composites
HAN Yuanfei, DUAN Hongqiang, LYU Weijie, WANG Liqiang, ZHANG Di
2015, 32(1): 1-12. doi: 10.13801/j.cnki.fhclxb.20141204.004
Research progress was reviewed on the severe plastic deformation (SPD) behaviors of discontinuously reinforced metal matrix composites. Five kinds of SPD processing principle and methods, including equal channel angular pressing (ECAP), high pressure torsion (HRT), multiple forging (MF), accumulative roll bonding (ARB) and cyclic extrusion compression (CEC), were systematically described.The applications of these methods in aluminum matrix, magnesium matrix, copper matrix and titanium matrix composites, etc. were introduced intensively. The special attention was paid to the microstructure evolution and deformation mechanical behavior of metal matrix composites by SPD, and the SPD mechanism and formation mechanism in the preparation of ultrafine-grain composites were also discussed in details. Moreover, the existing problems and developing trend of metal matrix composites in SPD process were stated briefly, and the application of SPD method for preparing discontinuously reinforced metal matrix composites with ultrafine-grain was prospected.
Research progress on preparation of flame retardant natural cellulosic fiber fabric via layer-by-layer assembly method
ZHANG Tao, YAN Hongqiang, WANG Lili, FANG Zhengping
2015, 32(1): 13-20. doi: 10.13801/j.cnki.fhclxb.201501.005
Layer-by-layer assembly (LBL) is a new kind of method for preparing flame retardant natural cellulosic fiber fabric, which is based on the physical adsorption of oppositely charged polyelectrolytes and multilayer film is formed through alternate deposition on surface of fabric. Compared with traditional methods, LBL method can construct flame retardant multilayer films between the substrate and external environment, so as to inhibit the combustion process directly. In particular, adjusting the assembly conditions and process can change the mass, thickness and elementary composition of the multilayer films conveniently, so as to control the flame retardant properties effectively. Herein, the recent developments in the preparation of nanomaterials-nanomaterials, nanomaterials-polyelectrolyte, polyelectrolyte-polyelectrolyte flame retardant natural cellulosic fiber fabric via LBL method were summarized, and the related works for constructing amino-carbon nanotubes-polyphosphate and polyethyleneimine-polyphosphate intumescent flame retardant coatings on surface of ramie fabric in our lab were also introduced. Furthermore, the outlooks of future developments were discussed.
Cryogenic mechanical properties of epoxy composites synergistically reinforced by graphene-multi-walled carbon nanotubes
SHEN Xiaojun, MENG Lingxuan, FU Shaoyun
2015, 32(1): 21-26. doi: 10.13801/j.cnki.fhclxb.20140502.002
In order to enhance the cryogenic mechanical properties of epoxy, graphene and multi-walled carbon nanotubes (MWCNTs) were used to modify epoxy synergistically. Room temperature (RT) and cryogenic (77 K) mechanical properties of graphene-MWCNTs/epoxy composites were systematically studied. The results show that simultaneous enhancements in cryogenic tensile strength, elastic modulus and impact strength can be achieved with 0.1wt% graphene and 0.5wt% MWCNTs. At this optimal formulation, the tensile strength of graphene-MWCNTs/epoxy composites reaches the highest value at both RT and 77 K, and is increased by 11.04% and 43.78% respectively, compared to pure epoxy. The cryogenic mechanical properties of epoxy can be synergistically enhanced by graphene and MWCNTs.
Preparation and accelerated-aging properties of barium sulfate nanoparticles/polyethylene composites
ZHANG Han, CHEN Minfang
2015, 32(1): 27-31. doi: 10.13801/j.cnki.fhclxb.20140502.001
X-ray developing barium sulfate nanoparticles (n-BaSO4)/polyethylene (PE) composites were prepared by melt-blending. The dispersibility of aluminum coupling agent modified n-BaSO4 (Al-n-BaSO4) in PE matrix, mechanical properties and accelerated-aging properties of composites were investigated. The morphology, structure, mechanical properties and filler distribution of the products were characterized by XRD, FTIR, SEM and universal tensile testing machine. The results indicate that chemical bonding occurs between aluminum coupling agent and surface groups of n-BaSO4. The Al-n-BaSO4 nanoparticles disperse well in Al-n-BaSO4/PE system, and the average portical size is less than 100 nm. The maximum tensile strength of Al-n-BaSO4/PE composites is 11.87 MPa, flexural strength is 6.61 MPa, and elongation rate is 66.78%. After 14 weeks accelerated-aging experiment of Al-n-BaSO4/PE composites in simulated uterine solution, the tensile strength of composites only decreases by 5%-15%. The Al-n-BaSO4/PE composites are expected to use in human bodies for over 10 years.
Mechanical property characterization of halloysite nanotubes/epoxy composites based on nanoindentation method
FU Kunkun, ZHENG Bailin, ZHANG Jianing, XU Zhenzhong
2015, 32(1): 32-38. doi: 10.13801/j.cnki.fhclxb.20141222.002
Halloysite nanotubes (HNTs) with different mass fractions, i.e. 0, 5wt% and 10wt%, were dispersed in epoxy using ball milling homogenization. And HNTs/epoxy composites were prepared using piperidine hardner. The elastic modulus, hardness and creep properties of HNTs/epoxy composites were determined using nanoindentation method. SEM and TEM observations show that HNTs are well dispersed in epoxy. Nanoindentation test results show that there is a significant increase in anti-creep properties of the epoxy matrix composites without sacrificing other properties such as elastic modulus, hardness and glass transition temperature of HNTs/epoxy composites. This is because the new network caused by interfacial bonding between HNTs and epoxy matrix chains could increase the cross linking density of materials, and the rigid nanoparticles restrict the mobility of the epoxy matrix chains.
Numerical simulation of influence of filler content on tribological properties of Cu/PTFE composites
XIE Ting, YANG Huaping, JIANG Kai
2015, 32(1): 39-46. doi: 10.13801/j.cnki.fhclxb.20140521.001
In order to investigate the influence of filler content on the tribological properties of Cu/polytetrafluoroethene (PTFE) composites, the Particle Flow Code in 2 Dimensions (PFC2D) was employed to simulate and analysis the processes of the friction and wear of PTFE-based composites with different Cu contents sliding against 45# steel. The friction transfer and wear of Cu/PTFE composites were mainly studied. The simulation results show that the transferred particle layer is formed on the surface of 45# steel when Cu/PTFE composites form friction pair with 45# steel. The wear of PTFE-based composites can be reduced effectively by the formation of transferred particle layer. On one hand, the addition of Cu particles can promote the formation of transferred particle layer by "pinning" effect of self-transition. On the other hand, due to the improvement of composite integrated strength, the addition of Cu particles produces an inhibition to the formation of transferred particle layer. Therefore, the moderate addition of Cu is beneficial to the formation of transferred particle layer. However, this effect will be reduced when the content of Cu is too high. Meanwhile, the wear of PTFE-based composites is reduced effectively due to the addition of Cu particles, and antifriction effect becomes better along with the increasing of Cu content. When the mass fraction of Cu particles is 50%, the number of the wear particles of PTFE-based composites is decreased to nearly half of the pure PTFE.
Preparation and characterization of functionalized nano-graphene sheet/PP-PP-g-MAH composites
HE Feixiong, BIAN Jun, LIN Hailan, YANG Feng, ZHOU Qiang, WANG Gang
2015, 32(1): 47-53. doi: 10.13801/j.cnki.fhclxb.20140410.001
Ethylenediamine functionalized graphene sheet/polypropylene-maleic anhydride grafted polypropylene (GS-EDA/PP-PP-g-MAH) composites were prepared by using solution compounding method. The structure and properties of graphite oxide (GO), GS-EDA and the composites were characterized by using FTIR, XRD, DSC, SEM and tensile test. The results indicate that the ethylenediamine (EDA) has been successfully grafted onto the surface of graphene sheet (GS), and hydrogen bond interactions which help GS-EDA disperse well in matrix happens between GS-EDA and PP-g-MAH during the compounding. DSC test shows that the crystallization peaks of GS-EDA/PP-PP-g-MAH composites move to higher temperatures due to the incorporation of GS-EDA.Tensile strength of GS-EDA/PP-PP-g-MAH composites increases and then decreases with increasing GS-EDA contents. With 0.5wt% mass fraction of GS-EDA, the tensile strength of composites approaches the ultimate value. Comparing to pure PP-PP-g-MAH and PP, the tensile strength increases by 24.7% and 17.5%, respectively. SEM observations show that GS-EDA disperses uniformly in matrix at low content but aggregates at higher incorporation.
Hydrolysis behaviors of ramie fiber/polylactic acid composites under different pH conditions
WEN Bianying, LI Xiaoyuan, ZHANG Yang
2015, 32(1): 54-60. doi: 10.13801/j.cnki.fhclxb.20140421.003
By using bio-based resin polylactic acid as matrix and plant fiber ramie as reinforcing agent, ramie fiber/polylactic acid (RF/PLA) composites were prepared by melting mixing method. The hydrolysis behaviors of RF/PLA composites in different pH environments were investigated and its degradable properties were evaluated by mechanical properties testing, SEM, DSC and Vicat softening temperature measurement. The results indicate that RF/PLA composites degrade faster in alkaline (pH=12.0) environment than in acid (pH=2.0) or neutral (pH=7.0) environments. The performance deterioration is mainly because the erosion and cavitation of the interface. The addition of RF improves the crystallinity and the Vicat softening temperature of PLA, and accelerates the degradation velocity of PLA. Then the degradation leads to the decline of the mechanical strength of the material. The crystallinity and Vicat softening temperature of RF/PLA composites show a gradual descending with the aggravating of degradation due to the generation of defect in the material. But the crystallinity of pure PLA resin increases and the Vicat softening temperature changes slightly along with the extension of alkali solution treatment time.
Fabrication and bone regenerability of chitosan/polylactic acid composite scaffolds with hierarchical porous structure
LIN Yanhuan, LI Na, ZENG Qinghui, LI Zhizhong, SUN Guodong, DING Shan, LI Lihua
2015, 32(1): 61-67. doi: 10.13801/j.cnki.fhclxb.20140424.003
To mimic the internal large pore structure of lotus, chitosan (CS) which has good biocompatibility was used as matrix material, and three molding methods, including porogen ice, wax molding and ice molding, were used to fabricate the hierarchical porous CS scaffold materials. Then the materials were combined with polylactic acid (PLLA) which has good mechanical intensity to form CS/PLLA composite scaffolds with interpenetrating network. SEM, compressive strength test and rabbit femoral bone defect model were used to characterize the morphology, mechanical strength and bone regenerability of CS/PLLA composites. The results show that the CS/PLLA composite scaffolds fabricated by ice mould can be produced controllably in batch, and possess micron-millimeter hierarchical porous structure. The diameter of macropores is about 2 mm, micropores whose diameter is about 60 μm distribute uniformly internally, and PLLA floc network structure is formed in the micropores. Compressive strength and modulus of dry composite are improved 6 times and 15 times respectively than that of pure CS scaffolds. Implant test results show that CS/PLLA composites can promote the healing of bone defects, and the composites is gradually absorbed with the formation of new bone.
Effects of seawater immersing on interlaminate shear properties of unidirectional T700/epoxy composites
HU Zhaohui, GAO Hongcheng, HUANG Qizhong, PENG Yugang
2015, 32(1): 68-75. doi: 10.13801/j.cnki.fhclxb.20140424.001
The factors that seriously affect the interlaminate shear properties of unidirectional T700/epoxy composites in seawater environment were studied, as well as the variation of interlaminate shear properties and water adsorption ratio of unidirectional T700/epoxy composites immersing in seawater and distilled water after five immersing periods(15, 40, 70, 165 and 400 d). The shear fracture microstructures of unidirectional T700/epoxy composites were observed by SEM to reveal the mechanism of propertiy decline. The experimental results show that the water adsorption ratio of unidirectional T700/epoxy composite increases with the extending of immersion time, and agrees well with the Fick's law on the whole. There is a significant decline in interlaminate shear properties of unidirectional T700/epoxy composite by almost 10% after immersing for 400 d, and the variation trend of interlaminate shear properties is similar to that of water adsorption ratio. The sensitivity of interlaminate shear properties of unidirectional T700/epoxy composite to seawater is greater than that to distilled water. The cross-sectional microstructure of sample shows that the degradation of the interface between resin and fiber caused by the absorbed seawater is the main reason for the decline in interlaminate shear properties. Therefore, more attention should be paid on the interlaminate shear properties while employing the unidirectional T700/epoxy composite in seawater.
Crystallization morphology and electrical tree resistance characteristics of montmorillonite/polypropylene composites
CHI Xiaohong, YU Li, ZHENG Jie, GAO Junguo, ZHANG Xiaohong
2015, 32(1): 76-84. doi: 10.13801/j.cnki.fhclxb.201501.003
In order to improve the electrical tree resistance of polypropylene (PP), montmorillonite (MMT)/PP composites were prepared by one-step and two-step melting intercalation processes, in which the organic MMT as the nanophase and the maleic anhydride grafted polypropylene (PP-g-MAH) as the compatibilizer. The crystallization morphology and crystallization process of PP and MMT/PP composites were studied by polarizing microscopy (PLM) and differential scanning calorimetry (DSC) curves. SEM was used to observe the dispersion state of MMT in composites. The influence of preparation process and crystallization morphology on property of electrical tree resistance was investigated by electrical tree initiating test. The test results indicate that the inorganic phase disperses more uniformly, crystallization size decreases and the spherulites become into lamellar crystallization stacks in MMT/PP composites which was prepared by two-step melting intercalation process, and the degree of crystallinity increases about 2.7%. The length of electrical trees are longer and it has less divarication in PP specimen, and characteristics of shorter and denser shape with more divarication are found in PP/MMT samples.
Effect of montmorillonite modified by poly (oxypropylene) amine hydrochlorides on microstructure of nano-montmorillonite/polypropylene composites
WANG Xiaoqun, MA Jun, LI Hai
2015, 32(1): 85-93. doi: 10.13801/j.cnki.fhclxb.201501.006
Two kinds of self-prepared montmorillonite (MMT) modified by poly (oxypropylene) amine hydrochlorides (POP) with large basal spacing, O-MMT1 and O-MMT2 (the basal spacing is 6.72 nm and 8.66 nm, respectively), were added into polypropylene-grafted-maleic anhydride (PP-g-MAH) or polypropylene (PP) by blending methods. The effects of blending methods, blending time, basal spacing of the POP modified MMT and PP-g-MAH on the microstructure of MMT/PP-g-MAH and MMT/PP composites were investigated. The results show that O-MMT1 with large basal spacing benefits the exfoliation of MMT in PP-g-MAH matrix during the solution blending and melt blending process. With the extension of blending time, O-MMT1 turns to the exfoliated state through transitional state from inserted layer type and MMT/PP-g-MAH composites with completely exfoliated state are obtained finally. A lot of MMT layers with "bilayer structure" are found at the transitional state in the solution blending process. In addition, the addition of O-MMT2 with larger basal spacing and PP-g-MAH, both facilitate the exfoliation of MMT in PP matrix so that the completely exfoliated nano-MMT/PP composites are obtained.
Effects of nano-ZnO and nano-montmorillonte on dielectric properties of low density polyethylene
CHENG Yujia, GUO Ning, WANG Ruoshi, ZHANG Xiaohong
2015, 32(1): 94-100. doi: 10.13801/j.cnki.fhclxb.20140609.001
Nano-ZnO and nano-montmorillonite (MMT) particles were added to improve the dielectric performance of low density polyethylene (LDPE). And the coupling agent was used in surface modification of nanoparticles. The composites of nano-ZnO/LDPE and nano-MMT/LDPE were prepared by melt blending method. The sample was characterized by XRD, FTIR and DSC. The alternating current breakdown properties of composites were investigated. The space charge tests were performed for the sample. Results show that the interface binding between nano-particles modified by coupling agent and polymer is improved, and the dispersion of nano-particles in matrix is more uniform, the crystallization rate of composites increases and crystalline structure becomes more perfect. Adding nanoparticles can increase the breakdown field strength of LDPE in different degrees. When the mass fraction of nano-ZnO and nano-MMT is 3wt%, respectively, the breakdown field strength of composites appear the highest values, which are 11.0% and 10.3% higher than those of origin LDPE, respectively. Both nano-ZnO and nano-MMT play an important role in inhibiting space charge, and the effect of nano-ZnO seems more obvious.
Preparation of DOPOMPC-APP-MWCNTs intumescent flame-retardant epoxy resin
LU Lingang, CHEN Yinghui, ZHAO Jin, YANG Shousheng
2015, 32(1): 101-107. doi: 10.13801/j.cnki.fhclxb.20140507.001
Epoxy resin (EP) was flame retarded with halogen-free intumescent flame retardant six-(4-DOPO hydroxymethyl phenoxy) cyclotriphosphazene (DOPOMPC), polyphosphate (APP) and multi-walled carbon nanotubes (MWCNTs) to prepare new flame retardant composites DOPOMPC-APP-MWCNTs/EP. The flame retardant property of the composites was analyzed by limit oxygen index (LOI), horizontal vertical combustion, and cone calorimetry. The result demonstrates that the addition of MWCNTs increases the flame retardant property and mechanical property of intumescent flame retardant system, and improves the dense smoke phenomenon to a certain extent when system is burning. When the total mass fraction of flame retardant system is 20% and the mass fraction of MWCNTs is 2%, optimal properties of materials can be obtained. The LOI of the composites is 36.8%, the peak heat release rate, average effective heat of combustion, average specific extinction area, average CO release rate are respectively reduced by 83.5%, 31.5%, 47.6%, 50.0% compared with the non-flame retardant EP, and reduced by 83.5%, 77.7%, 83.7%, 68.9% compared with DOPOMPC-APP/EP. SEM analysis reveal that a dense, cross-linked network charred layer is formed in DOPOMPC-APP-MWCNTs/EP after the addition of MWCNTs.
Microstructure and properties of new type Ti3AlC2-Al2O3/TiAl3 composites
LI Xiaomei, XIAO Huaqiang, ZENG Yong, CHEN Weiping
2015, 32(1): 108-116. doi: 10.13801/j.cnki.fhclxb.20140424.002
The TiAl3 matrix intermetallic composites reinforced by in-situ synthesized two phases of Ti3AlC2 and Al2O3 were produced by mechanically ball-milled and hot pressing of Al-TiO2-TiC system. The reaction mechanism, microstructure, mechanical properties and oxidation-resistance properties of the composites were investigated using DSC, XRD, SEM and TEM. The results indicate that dense Ti3AlC2-Al2O3/TiAl3 composites with homogeneous and pyknotic microstructure can be obtained by sintering 50 h ball-milled power mixture at 1 250 ℃/50 MPa for 10 min. The density, Vickers hardness, three-point bending strength, fracture toughness and compressive strength at room temperature of Ti3AlC2-Al2O3/TiAl3 composites reach 3.8 g/cm3, 8.4 GPa, 658.9 MPa, 7.9 MPa·m1/2 and 1 742.0 MPa, respectively, and the elevated-temperature compressive strength at 1 000 ℃ reaches 604.1 MPa. The toughening mechanism of Ti3AlC2-Al2O3/TiAl3 composites is primarily attributed to the pull-out of Ti3AlC2 and Al2O3 particles, crack deflection and crack bridging by Ti3AlC2 phase, and the deformation and delamination of Ti3AlC2 particles. Tough the oxidation scales generated in the temperature range from 700 to 1 000 ℃ are not dense, the Ti3AlC2-Al2O3/TiAl3 composites still exhibit excellent cyclic oxidation resistance.
Hot deformation and dynamic recrystallization of TiC(30vol%)/Cu-Al2O3 composites
YANG Zhiqiang, LIU Yong, TIAN Baohong, ZHANG Yi
2015, 32(1): 117-124. doi: 10.13801/j.cnki.fhclxb.201501.009
The TiC(30vol%)/Cu-Al2O3 composites were successfully prepared by vacuum thermal pressed-internal oxidation sintering process. The basic properties and microstructure of the composites were tested and observed. The hot compression deformation tests of TiC(30vol%)/Cu-Al2O3 composites were conducted at deformation temperature of 450-850 ℃, strain rate of 0.001-1 s-1 and deformation amount of 50% by Gleeble-1500D simulator. By analyzing and caculating the flow stress, constitutive equation and model of dynamic recrystallization critical strain were constructed. By the inflection point of work hardening rate-strain curves and the minimum value criterion of corresponding partial derivative curves, the function relationship between dynamic recrystallization critical strain and Zener-Hollomon parameter was constructed. The results show that the softening mechanism of dynamic recrystallization is a feature of true stress-true strain curves of TiC(30vol%)/Cu-Al2O3 composites, and the peak stress increases with the decrease of deformation temperature or the increase of strain rate. The calculating thermal deformation activation energy is 211.384 kJ/mol.
High temperature tensile damage behavior of ZrB2-based ultra-high temperature ceramic composites
WANG Lingling, FANG Guodong, LIANG Jun
2015, 32(1): 125-130. doi: 10.13801/j.cnki.fbclxb.201501.002
The tensile property tests of SiC(20vol%)-graphite(15vol%)/ZrB2 composites were carried out at room and high temperatures. The reduction of tensile strength and elastic modulus, and the obvious nonlinear behavior for composites were observed at high temperatures. The attenuation law of elastic modulus with temperature was characterized by introducing thermal damage. The mechanical damage evolution equation under the uniaxial stress was determined through the statistical analysis of strength, and then a high temperature tensile damage nonlinear constitutive model was presented under the thermal-mechanical coupling conditions. The results show that, with the increase of temperature, the thermal and mechanical damage of SiC-graphite/ZrB2 composites increase as well as the ductility, and the transition temperature which range from brittle fracture to ductile fracture is 1 250-1 350 ℃.
Microstructure of attapulgite-goethite modified woodceramics from wheat straw
WU Wentao, LI Yanyan, LU Maoji, CAI Chuanlun
2015, 32(1): 131-137. doi: 10.13801/j.cnki.fhclxb.20140523.001
Attapulgite, goethite and wheat straw were used as raw materials, and little amount of epoxy was added as adhesive. The models were sintered under proper temperature and atmosphere, then biomass carbonization, attapulgite thermal activation and goethite deoxidation were achieved simultaneously, so as to acquire attapulgite-goethite modified woodceramics from wheat straw with the property of high porosity and strong magnetism. The effects of mass ratios of raw materials and sintering temperature on the phase and microstructure of the composites were analyzed by XRD and SEM. The results show that the attapulgite-goethite modified woodceramics from wheat straw is a kind of amorphous and porous carbon material, mass ratio of raw materials has almost no influence on phases under the same temperature. With the increase of sintering temperature, characteristic diffraction peaks of attapulgite disappeare gradually, new phase appears in attapulgite-goethite modified woodceramics from wheat straw.
Microscopic structure model and finite element simulation of mechanical properties of fiber-bar composites reinforced by three dimensional weaving
SHAN Zhongde, KANG Huairong, ZANG Yong, LIU Feng
2015, 32(1): 138-149. doi: 10.13801/j.cnki.fhclxb.20140408.002
Aiming at the requirement of interlaminar reinforcing of composites, the geometrical structure of fiber-bar composites reinforced by three dimensional weaving was proposed. Three single-cell finite element models based on 0°/90°, 45°/135° and 0°/90°/45°/135° weaving schemes were presented respectively, which can really reflect the mutual squeezing of fiber bundles and fiber-bars in weaving fabrics. Coupled with the periodical displacement boundary condition, the equivalent elastic property parameters of composites based on three different weaving schemes were predicted by the single-cell finite element model. The relationship of elastic properties of composites with weaving scheme and yarn packing factor were studied. The microscopic stress field distributions of single cell based on three different weaving schemes under uniaxial tensile load were analyzed. Several qualified models were made and relevant tests were performed. Results indicate that simulation results obtained by single-cell finite element model make well agreement with the experimental results. The yarn packing factor makes different effect on the elastic constants of the weaving composites. The mechanical properties of composites also vary as the difference of weaving schemes, which mainly result from the arrangement of fiber bundles inside fabrics based on different weaving schemes. The stress field distributions of three weaving single-cell models were exhibited, which provide basis for the fabrics optimization of the fiber-bar composites reinforced by three dimensional weaving.
Experiment and numerical simulation on compressive properties of 2.5D woven fabric composites
LU Zixing, ZHOU Yuan, FENG Zhihai, YANG Yunhua, JI Gaoning
2015, 32(1): 150-159. doi: 10.13801/j.cnki.fhclxb.20140331.002
To investigate the damage and failure mechanisms of 2.5D woven fabric composites under compression, and verify the effectiveness of the finite element numerical simulation method with a two-scale, progressive damage model, quasi-static compression experiments were conducted on both warp and weft directional specimens to obtain the corresponding stress-strain curves. And the initial elastic modulus and ultimate strength of materials were measured. On this basis, the compressive stress-strain responses and the damage evolution behavior were simulated using the two-scale, progressive damage finite element numerical method. The results from both experiment and simulation show good agreements, and indicate that the main failure mode of 2.5D woven fabric composites in weft directional compression is the axial crush and fracture of weft yarns, from which relatively higher strength is obtained. Meanwhile, additional bending moment is added to the warp yarn under warp directional compression due to bending, which causes extrusion on surrounding matrix. Therefore, matrix fracture and delamination cracking between neighboring warp yarns easily occur before the axial fracture of warp yarns, which are not conducive to utilize the advantage of fibers in bearing load, and result in relatively lower strength.
Flexural properties of stitched sandwich structure beam with different modulus in tension and compression
WEI Jing, SHI Duoqi, SUN Yantao, YANG Xiaoguang, CAO Feng
2015, 32(1): 160-166. doi: 10.13801/j.cnki.fhclxb.201501.007
In order to establish a theoretical prediction method of position of neutral plane and flexural stiffness for stitched sandwich structure beam with characteristics of different elastic modulus in tension and compression, and verify the effectiveness of the method through related experiment. Firstly, the stitched sandwich structure beam was looked as a quasi-layered structure, taking the characteristics of different modulus in tension and compression as well as different geometry on the top and bottom panel of materials into consideration, a modified Reissner plate theory was developed to evaluate the flexural stiffness and neutral plane position. Secondly, three-point flexural test of stitched sandwich structure beam was carried out, and digital image correlated (DIC) method was also adopted to measure the position of neutral plane. Finally, theoretical predictions were performed for flexural stiffness and position of neutral plane. The results show that theoretical prediction values are in good agreement with experimental data, which demonstrate the validity of the theoretical prediction method.
Multi-field coupled numerical simulation for curing process of composites with time-dependent properties of materials
YUAN Zhenyi, WANG Yongjun, ZHANG Yue, YANG Xuanhong, WANG Junbiao, WEI Shengmin
2015, 32(1): 167-175. doi: 10.13801/j.cnki.fhclxb.20140328.001
According to the interrelationship of the complex physical and chemical processes during the curing process of thermoset resin composites, a multi-field coupled two-dimensional model based on the time-dependent properties of materials during the curing process of composites was established. The model incorporated three typical existing sub models for curing process of composites: thermo-chemical model, resin viscosity model and resin flow model. On the basis, the time-dependent properties of material performances during the curing process were introduced into multi-field coupled calculation model. According to the comparison with experiment data in reference, the model established was proved to possess relative superior reliability. The curing process of AS4/3501-6 composite laminates were numerical simulated. The effects of the variation of fiber volume fraction and time-dependent properties of material performances on the temperature, the degree of cure, the pressure of resin and other parameters during curing process was studied attentively. The results show that when taking the changes of fiber volume fraction and time-dependent properties of material parameters into consideration, the peak value of temperature at the center of composite laminate decreases significantly, and the change of resin pressure verses time lags.
An improved GBJM method and its application in bolt load distribution and load capacity analysis of composite structures with bolt group
LI Nian, REN Feixiang, CHEN Puhui, YE Qiang, SUN Yanpeng
2015, 32(1): 176-181. doi: 10.13801/j.cnki.fhclxb.20140611.001
In order to analyze the bolt load distribution and load capacity of composite structures with bolt group, an improved global bolted joint model (GBJM) method was developed firstly, and then the method was applied to predict the bolt load distribution and load capacity of multi-bolt composite joint structures. The prediction values and test results were compared. Results show that the predicted multi-bolt load distribution coincides well with the test results before the onset of composite hole-edge damage; as for the prediction of the load capacity of structures, this method seems to be conservative with 15% lower than the test results. Meanwhile the improved model has two significant advantages: one is high computational efficiency with a 75% rise compared to the three-dimensional finite element models for the calculations of bolt load distribution; the other is that this method is effective for the prediction of failure loads of composite structures with bolt group.
Load bearing capability of thread teeth of C/SiC composite bolts
LU Zixing, LIAO Qiang, YANG Zhenyu, FENG Xiang, ZHANG Zhongwei, FENG Zhihai
2015, 32(1): 182-187. doi: 10.13801/j.cnki.fhclxb.20140611.004
In order to evaluate the load bearing capability of thread teeth of C/SiC composite bolts, finite element method and stiffness degradation method were used to study the load bearing capability of the thread teeth of C/SiC composite bolts. The results show that when the number of teeth engaged is more than six, the initial pull-off load of thread teeth almost does not increase with the number of teeth engaged increasing, and it also can not be increased significantly by solely increasing the pitch of thread for this will decrease the initial pull-off strength of thread teeth; when the ratio of thread teeth to bolt diameter is constant, the initial pull-off load of thread teeth is proportional to the square of bolt diameter; however, the ultimate pull-off load of the thread teeth is nearly proportional to the number of teeth engaged, the pitch of thread and bolt diameter.
Effects of mechanics and interface parameters and volume fraction of shape memory alloys on toughening of bulk metallic matrix glass composites
ZHANG Ruyuan, KAN Qianhua, ZHANG Juan, KANG Guozheng
2015, 32(1): 188-195. doi: 10.13801/j.cnki.fhclxb.20140422.001
Using superelasticity material model taking plasticity into consideration and quasi-brittle material model based on damage plasticity, a three-dimensional finite element unit cell model was established, and the monotonic tensile behaviors of shape memory alloy particle toughening bulk metallic glass matrix composites were simulated. The effects of mechanics parameters and volume fraction of shape memory alloys, along with interface thickness and interface material parameters on the toughening of bulk metallic glass were discussed. Results show that the increasing of the phase transformation strain of shape memory alloys and martensite plastic yield stress can improve the tensile failure strain of shape memory alloy particle toughening bulk metallic glass matrix composites significantly; meantime, the tensile failure strain changes little when the elastic modulus of shape memory alloys is beyond 50.0 GPa and martensite plastic yield stress is over 1.8 GPa. The reasonable volume fraction of shape memory alloy in balance of failure strain and failure stress is about 15%. The increasing of composites interfacial elastic modulus and interfacial yield stress can improve the failure stress of composites; however, the failure strain does not change a lot with them. The increasing of the thickness of composites interface can improve the failure strain while decreases the failure stress of composites.
Impact tests and numerical simulation of composite waved-beam
MENG Xiangji, YAN Ying, LUO Haibo, HOU Kang, LIANG Zudian, GONG Shaobo
2015, 32(1): 196-203. doi: 10.13801/j.cnki.fhclxb.20140605.005
In order to investigate the energy absorption properties of composite waved-beams, the dynamic impact tests of three types of composite waved-beam specimens which have the stacking sequences of [(±45)3/(0,90)/(±45)3], [(±45)8] and [(±45)7], were conducted to obtain the energy absorption load-displacement curves and the failure morphology was analyzed subsequently. Based on the continuum damage mechanics, a stiffness degraded model that involved extended Hashin failure criterion and damage evolution law was proposed for analyzing the crashworthiness failure of waved-beams. The progressive failure user subroutine for composite waved-beams was developed on the basis of finite element software platform. The progressive failure numerical analysis was performed for three different types of waved-beams. The energy evaluative parameters including the special energy absorption (SEA) and average load value were acquired by simulation. The simulation and experimental results were compared and analyzed. The energy absorption capability of composite waved-beams with different triggers was compared. The result shows that the progressive crushing failure mode of waved-beam is observed under impact load. The relative error of average crushing load is less than 12%. It satisfies the precision of engineering application. And the property of composites and layup mode should be taken into account for setting the trigger.
Experimental-numerical hybrid method for measurement of cohesive zone model parameters of short fiber composites in both macro and micro scale
SHEN Min, ZHANG Xiaoxu, SUN Xiaoxiang
2015, 32(1): 204-216. doi: 10.13801/j.cnki.fhclxb.20140609.002
An improved experimental-numerical hybrid method was proposed. Compact tension experiment of the random short fiber reinforced composites was used in this method, and macroscopic cohesive zone model (CZM) of the material was obtained firstly, then the microscopic CZM parameters of the fiber/matrix interfaces of the material were obtained. The macroscopic CZM results were obtained by both finite element method and the inverse extraction based on field projection method. By comparing the results of the two methods, the fault tolerance of the inverse extraction method was found to be lower. Then the improved inverse extraction method was adopted, and the separation amount of macroscopic CZM was directly obtained by digital image correlation method (DIC), so that the amount of unknowns in the inverse extraction method was reduced, and the fault tolerance was also improved. The DIC and the improved inverse extraction method were combined, and the traction of macroscopic cohesive zone at the cracktip of the material was inverse extracted. The bilinear CZM was adopted, and the Mori-Tanaka method was used to link the macroscopic cohesive law obtained above and the microscopic cohesive law for fiber/matrix interfaces. The model parameters of microscale cohesive of fiber/matrix interfaces were also determined. This method and the results provide an experimental basis for the micromechanics analysis of the fiber/matrix interface of short fiber reinforced composites.
Effects of structural corner on permeability of fiber preform in VIMP
ZHONG Yong, XIAO Jiayu, YIN Dulin, YANG Jinshui
2015, 32(1): 217-226. doi: 10.13801/j.cnki.fhclxb.201501.001
In the manufacture of multi-walled composite structures with fiber reinforced polymer composites by the vacuum infusion molding process (VIMP), the local multi-walled permeability is changed at the corners of multi-walled structure due to the fiber bending deformation. The effects of corner on multi-walled permeability and resin flow behavior were investigated by the visual flow experiments. The results show that, regardless of the application of distribution medium, the resin molding flow rate and overall multi-walled apparent permeability would be decreased due to the corner effect. This behavior is ascribed to the local resistance effect of the corners applied to the resin in filling process of VIMP. The corner effect can be weakened through applying distribution medium to the corners. When the distance between the corner location and the injection gate becomes larger, the overall apparent permeability will decrease first, and then increase.
Scanning imaging of composite plate using air-coupled Lamb waves based on probabilistic damage algorithm
LIU Zenghua, FAN Junwei, HE Cunfu, WU Bin
2015, 32(1): 227-235. doi: 10.13801/j.cnki.fhclxb.201501.004
Non-contact air-coupled ultrasonic transducers were used to generate pure Lamb wave mode in quasi-isotropic composite plate, the wave mode was used to scan for delamination inspection. In the scanning process, generating and receiving transducers were arranged on the same side of the plate oppositely and obliquely. They were linearly moved synchronously in two orthogonal directions in order to obtain different inspection signals at different positions. Wavelet coefficient envelope signals at certain generating frequency were extracted from the inspection signals in different scanning paths through continuous wavelet transform to image the delamination defects. Based on this, damage index was defined by using probabilistic damage algorithm and damage index of different directions were combined to realize the delamination imaging. Data fusion of imaging results acquired from two orthogonal directions was achieved by using full summation algorithm and full multiplication algorithm. The delamination defect can be well located and reconstructed. Furthermore, a threshold was introduced to the imaging algorithm to improve the location precision and reconstruction quality of the delamination defect.
Ply optimization of composite laminate with ply drop based on genetic algorithm
JIN Dafeng, LIU Zhe, FAN Zhirui
2015, 32(1): 236-242. doi: 10.13801/j.cnki.fhclxb.20140408.001
A hierarchy optimization model was proposed for carbon fiber reinforced polymer laminate with dramatic stress variation. An optimal design with minimal mass was obtained by dividing the structure into several sub-laminates and optimizing the location, size, number of plies and stacking sequences of each sub-laminate with the constraints of strength and manufacturability. The location and size of each sub-laminate were optimized by using the reference ply in the first and second level optimization and the number of plies and stacking sequences of each sub-laminate were optimized by introducing the parametric method of cubic spline interpolation in the third level optimization. The reference ply was designed to reduce the number of design variables and the problem of uncertainty of design variables number was solved by the parametric method of cubic spline interpolation, taking layer angle as design variable. Finite element method was used to analyze the structure mechanically whose strength was judged by Tsai-Wu criterion and genetic algorithm was used in the second and third level optimization to the optimization problem. The example calculation shows that the results of ply hierarchical optimization of ply drop are reasonable and the ply drop can considerably reduce the mass of structures compared with results of uniform layer method.
Energy absorption mechanism of circular-square irregular section composite tubes
MA Yan, YANG Yuqiu
2015, 32(1): 243-249. doi: 10.13801/j.cnki.fhclxb.20140425.001
The energy absorption properties of composite tubes with circle cross-section are found superior to tubes with square cross-section, while the square tubes with plane surfaces are easier to combine with other parts in the assembly process, which means square tubes have advantages in practical uses. The advantages of both circle and square tubes were combined, carbon fiber and epoxy resin were used as reinforcement and matrix, respectively. Three types of circular-square composite tubes code T15-15, T15-60 and T60-60 with different braiding angles including 15° and 60°, were manufactured with braiding technology and molded by Vacuum Assisted Resin Transfer Molding technology. After researching the properties of energy absorption through quasi-static compression test, it was found that through the reasonable design of braiding angle, circumferential fiber can prevent the spreading out of axial centre cracks, which could improve the energy absorption properties of fiber reinforced composite tubes for the fracture of extra fiber in the composits. The circular-square irregular fiber reinforced composite tubes with high energy absorption and easy-assemble properties were manufactured ultimately.
Experiment and electrical-thermal coupled simulation for lightning current damage of carbon fiber reinforced plastic
FU Shangchen, ZHOU Yinghui, SHI Lihua, SI Qing, WANG Dong, XU Jifeng
2015, 32(1): 250-259. doi: 10.13801/j.cnki.fhclxb.20140605.006
In order to study the damage law of carbon fiber reinforcement plastic (CFRP) caused by lightning current, direct effect experiment of lightning current and electrical-thermal coupled effect simulation for CFRP were carried out. At first, direct effect experiment of lightning current was implemented with the impulse current experiment apparatus. External damages subjected to currents with different peak-values were compared together, and internal damages were observed with C-scan. Experiment results show that damage range increases obviously with the increasing peak value of current, and the range of internal damage is much larger than that of the external damage. Then, electrical-thermal coupled finite element analysis of specimen was carried out, and the superimposed temperature field was approximately chosen to represent the range of internal damage. The comparison with the experiment results shows the effectiveness of this method. The results of thermal-electrical coupled analysis under impact currents with different types and action integrals show that the range of damage is greatly influenced by action integral.
Effects of different hand-made preparation methods on quality of prepreg radius fillers
HUANG Binyao, XIONG Meirong, DUAN Yuexin
2015, 32(1): 260-267. doi: 10.13801/j.cnki.fhclxb.201501.010
Radius filler is a kind of filling material used in triangle gap of composite beam and rib structure. To optimize the hand-made preparation method of radius fillers and provide the basis for engineering practice and automatic production, the prepreg radius fillers were prepared by rolled mode and laminated mode respectively. To investigate the influence of different hand-made preparation methods on quality of radius fillers, the boundary dimension, microstructure and mechanical property of prepreg radius fillers were characterized. The results show that there is little difference in boundary dimension of the prepreg radius fillers prepared by rolled mode and laminated mode. The fiber volume fraction is all around 60%, and the void content is all around 3%. But the form of inner defects and mechanical property of the radius fillers differ significantly. For the radius fillers obtained by rolled mode, the inner defects are small and scattered, fibers arrange in disorder and bending failure mode is fiber fracture. For the radius fillers obtained by laminated mode, the inner defects are large and continuous, fibers arrange neatly and collimated, the bending failure mode is delamination fracture.
Adsorption characteristics and mechanism of hydroxyethyl cellulose/sodium alginate blend films for uranium(Ⅵ)
XIE Shuibo, LUO Jingyang, LIU Qing, LING Hui, DUAN Yi, WANG Jinsong
2015, 32(1): 268-275. doi: 10.13801/j.cnki.fhclxb.20140519.002
Hydroxyethyl cellulose/sodium alginate (HEC/SA) polymer composite porous films were made by blending HEC and SA together and crosslinked by glutaraldehyde, and its adsorption properties for uranium(Ⅵ) (U(Ⅵ)) in simulated wastewater containing uranium were studied. The effects of initial pH value, initial U(Ⅵ) ions concentration, temperature and adsorption time et al on the adsorption of HEC/SA blend films for U(Ⅵ) were investigated by static experiment. The process of adsorption was investigated by thermodynamic and kinetic analysis. The adsorption mechanism was investigated by FTIR, SEM, energy dispersive X-ray spectrum and so on. The experimental results show that there is a positive correlation between temperature and the U(Ⅵ) adsorption quantity, adsorption equilibrium time is about 90 min, and the optimal initial pH value is 5.0. The adsorption process conforms to the pseudo-second-order kinetics model, and mainly preforms particle internal diffusion. The isothermal adsorption process conforms to the Langmuir isothermal adsorption model, when the temperature is 45 ℃, the maximum adsorption capacity of HEC/SA blend films for U(Ⅵ) ions reaches 357.1 mg·g-1. The adsorption of HEC/SA blend films for U(Ⅵ) presents ion-exchange process, and the interaction groups with U(Ⅵ) is carboxyl.
An analytical solution for periodic multi-phase fibrous piezoelectric composites under antiplane deformation
XU Yaoling, XIAO Junhua, QIU Pengkai
2015, 32(1): 276-283. doi: 10.13801/j.cnki.fhclxb.20140617.003
The electro-elastic field of multi-phase fibrous piezoelectric composites with periodic microstructure under antiplane deformation was studied. By introducing non-uniform generalized eigen strain in each inhomogeneous phase, the original problem was replaced by a homogenous medium problem with the periodically distributed generalized eigen strains, the equivalent condition between the two problems was established. By use of the continuity conditions of generalized stress and the compatibility conditions of generalized displacement on the interfaces of each neighboring region in equivalent problem, together with doubly quasi-periodic Riemann boundary value problem theory and equivalent condition, the analytical solutions of the electro-elastic fields in each phase of composites were derived, and the effective piezoelectric coefficient of the composites was evaluated by using average field theorem. The differences of the effective piezoelectric coefficient of composites with hollow piezoelectric fibers, carbon core piezoelectric structural fibers and solid piezoelectric fibers were demonstrated under the same piezoelectric material volume fraction, and the effects of the stiffness of non-piezoelectric core in the piezoelectric structural fibers and coatings between piezoelectric structural fibers and matrix on the effective piezoelectric coefficient were discussed. The conclusions can provide valuable references for designing piezoelectric composites with high sensibility.
Damage zoning characteristics of composite laminates with different protections subjected to lightning strike
LIU Zhiqiang, YUE Zhufeng, WANG Fusheng, JI Yaoyao
2015, 32(1): 284-294. doi: 10.13801/j.cnki.fhclxb.20140605.004
Lightning strike tests of composite laminates with different protections were conducted based on the combining strikes of four standard waveforms A+B+C+D. The interaction procedure between the lightning channel and composite laminate surface was analyzed, and the surface damage area of composite was divided into initial attachment area, attached conduction area, attached expansion area, reattachment area and swept damage area with respect to the physical characteristics of lightning channel. And the damage characteristics were analyzed for four types of laminates: unprotected reference specimen, partial and full-scale spraying aluminum specimens, and copper grid specimen. The results show that the surface damage of composite is induced by the interactions of thermo-electrical physical properties of lightning channel, surface thermo-electrical properties of composites, and charge distribution in strong electromagnetic field. The characteristics of symmetry and zoning of damage area on surface of composites are affected by spraying shape, thickness and homogeneity of aluminum layer. The rough surface of composite laminates induced by copper grid protection leads to the complexity of surface damage zoning. The accumulation characteristic and homogeneity of distribution for the induced charge on surface of composite laminates are the direct reasons for distributions of reattachment area and swept damage area. The primary damage forms of composites subjected to the lightning strike include fiber sublimation, rupture and fuzzing, the matrix charring melting and ablation, the delamination and detaching of materials, and the melting, vaporization and breakdown of protective materials. The analysis results can be applied to the qualitative design for lightning protection of composites.
Numerical simulation and test on stability of composite grid stiffened cylinder
YANG Yanzhi, ZHENG Quan, LI Hao, LYU Rongxin, WANG Ruifeng
2015, 32(1): 295-300. doi: 10.13801/j.cnki.fhclxb.20140519.001
As a typical aerospace structure, the axial compression stability of composite grid stiffened cylinder determines the ultimate bearing capacity of the spacecraft structure. The homogenization equivalent method and beam-shell finite element method which have been researched are deficient. The local stress and stability of grids were taken into consideration, the grids were equivalent to shell elements, and the all-shell finite element method was put forward. Depending on the composite grid stiffened cylinder of certain aircraft, the three methods were used to study the axial compression stability respectively. Meanwhile, a full-size axial compression destruction test was also designed. Good agreement was achieved in the comparison between the numerical simulation and test results, which verified the rationality of the aircraft design. The deviation between the homogenization equivalent method, the beam-shell finite element method, the all-shell finite element method and test value are 14.9%, 9.5% and 5.2% respectively. The all-shell finite element method has the highest precision, and can predict the failure modes accurately. The research can also be regarded as a design reference for similar structures.