2013 Vol. 30, No. 6

Preparation and conductivity property of graphene aerogel/epoxy composites
WANG Xuebao, LI Jinqing, LUO Yunjun
2013, 30(6): 1-6.
Graphene aerogel (GA) was prepared by sol-gel chemistry, and then GA/epoxy (EP) composites were prepared by sonicate-mixing method. The structure of GA was characterized by SEM, N2 nitrogen sorption tests, XPS and XRD. In addition, the effects of GA mass fraction on the thermal property and the conductivity property of the GA/EP composites were also investigated. The results indicate that the GA shows a three-dimensional network of randomly oriented graphene sheets with wrinkled texture, and is rich in pores. After thermal reduction, the specific surface area of GA increases to 731.84 m2 ·g-1, the interlayer spacing of the graphene decreases to 0.347 nm, and the oxygen-containing functional groups are almost all removed. DMA and electrical conductivity testing results show that with the increase of GA content, Tg of GA/EP composites increases first and then decreases, and the electrical conductivity increases with the percolation threshold of 0.05%-0.3%.
Influence of in-situ grown carbon nanotubes on carbon fiber on the flexural properties of C/C composites
WEN Shiqi, LI Kezhi, SONG Qiang
2013, 30(6): 7-13.
The carbon nanotubes (CNTs) were in-situ grown on carbon fiber felts and the hybrid felts were densified by chemical vapor infiltration (CVI) to prepare CNTs-C/C composites.The effects of catalyst content on the growth of CNTs and the effects of CNT content on the flexural properties of CNTs-C/C composites were investigated. The results show that catalyst content has a great influence on the yield of CNTs. More CNTs were obtained with the catalyst content increasing. The catalysts used for CNT growing deteriorate the flexural properties of C/C composites. The CNTs changes the infiltration behaviors of pyrocarbons and induces the formation of abundant small-sized spherical or cone-shaped pyrocarbons, which inhibits the formation of annular cracks in pyrocarbon matrix. The CNTs with a suitable content can increase the flexural strength and modulus and improve the fracture behavior of C/C composites.
Preparation and properties of graphene nanoplatelets/PP thermal conductive composites
WANG Wen, DING Hongliang, ZHANG Zikuan, SHEN Lie
2013, 30(6): 14-20.
Two kinds of GNPs/PP thermally conductive composites were prepared with KNG180 GNPs or KNG150 GNPs via melt blending, and their thermal conductivity, density, crystallization behavior and thermal stability were investigated. The results show that the density of KNG180 GNPs/PP composite is higher than that of KNG150 GNPs/PP, and the crystallization degree improvement of PP is higher when filled with KNG180 than KNG150. The thermal conductivity of composites was dramatically improved along with the increase of GNPs content, and the improvement of KNG180 GNPs/PP is much higher than KNG150 GPNs/PP. The composites contained 60% mass fraction of KNG180 has a thermal conductivity of 1.32 W/(m·K) which was more than 14 times as that of the pure PP(0.087 W/(m·K)). As the GNPs incorporated, thermal stability of the GNPs/PP composites is enhanced. When the mass fraction of KNG180 and KNG150 was 10%, the maximum mass loss rate temperature is increased from 345.1 ℃ to 374.6 ℃ and 397.9 ℃, respectively. But when the contents of KNG180 or KNG150 reach to a certain content, the thermal stability begins to decrease.
Rapid curing epoxy resin and the properties of carbon fiber/epoxy composite
ZHANG Kaomin, GU Yizhuo, LI Min, WANG Chaoran, ZHANG Zuoguang
2013, 30(6): 21-27.
A rapid curing resin system made from diglycidyl ether of bisphenol A (DGEBA) epoxy, modified imidazole (MIM) and modified aliphatic amine (MAA) was developed. The curing behavior and rheological characteristic of the resin were evaluated by DSC and rheological analysis respectively. The optimum ratio of the blending of curing agents was selected. The carbon fiber/epoxy resin composite laminates using this resin system were manufactured through vacuum assisted resin injection molding (VARIM) under short-term curing schedule. The processing quality and mechanical properties of the laminates were studied and compared with the properties of the laminates under traditional curing schedule. The results show that the curing time of the resin system is 5 min with 95% curing degree, and the cure time of the laminates using the studied resin can be controlled within 13 min under 120 ℃ with more than 95% curing degree and few defects. Compared with the laminates cured in traditional curing schedule (curing time more than 2 h), the laminates manufactured under short-term curing schedule exhibits slight decreases in the flexural property and thermal stability.
Effect of hydrothermal treatment on properties of reversibly thermochromic bamboo/plastic composite
WU Qiuning, YANG Wenbin, YU Fangbing, CHEN Lihong
2013, 30(6): 28-36.
The effect of hydrothermal treatment on the color and mechanical properties of reversibly thermochromic bamboo flour/plastic composites was studied. ESEM observation was used to explain surface microstructure of reverisibly thermochromic bamboo/plastic composites. Surface chemical composition and crystallinity were determined by FTIR and DSC respectively. The results show that hydrothermal treatment has a great influence on the properties of bamboo/plastic composites with the order of hydro-thermal treatment at 80 ℃ >water-bath treatment >heat treatment at 80 ℃. There are many cracks appearing on the surface, contact angles and mechanical properties decrease obviously, and the color of samples changes greatly after hydro-thermal treatment at 80 ℃. There are some small cracks appearing on the surface, and contact angles decrease a little after water-bath treatment at room temperature. The mechanical properties of the bamboo flour/plastic composites presents firstly increasing then decreasing and then increasing again, and the color of samples change more obviously after water-bath treatment. The surface is smooth and the color change a little, the contact angles turn bigger after heat treatment at 80 ℃. The results of FTIR and DSC indicate that the bamboo fibre and high density polyethelene (HDPE) molecular chain lead to degradation in some extent, and recrystallization of HDPE is found after heat treatment at 80 ℃, water-bath treatment and hydro-thermal treatment at 80 ℃.
Laser ablation behaviors of C/SiC composites in air
SU Meng, CHENG Laifei, LUAN Xingang, ZHANG Litong
2013, 30(6): 37-47.
Ablation behaviors of silicon carbide (SiC) coated 2D carbon fiber reinforced silicon carbide matrix (designated as 2D C/SiC) composites prepared by chemical vapor infiltration (CVI) were investigated by a continuous wave CO2 laser. The 2D C/SiC specimens were exposed under laser for 0.5 s in ambient air, and the laser powers varied from 500 W to 1500 W. A 3D finite element model was established to calculate the temperature distribution in the laser ablation process. The ablation depth, width and profile were measured by Laser Confocal Microscope (LCM). The results indicate that the increase of ablation depth follows a linear relation with the increase of laser power, and the increase of ablation width follows a similar trend with the increase of the isotherm diameter of 1712 ℃. The ablated surface can be distinguished into three different regions by scanning electron microscope (SEM) observation, including ablation center, transition zone and ablation fringe. The ablation behaviors of carbon fibers and SiC matrices in different regions were presented and discussed in the study.
Preparation and characterization of ferrocenyl-terminated hyperbranched polyesters/epoxy resin composite
ZHANG Ya, CHAI Chunpeng, LUO Yunjun, LU Mingming, LI Guoping, WANG Lu
2013, 30(6): 48-53.
Ferrocenyl-terminated hyperbranched polyesters/epoxy resin (HBPE-Fc/E-51) composites with mechanical and electromagnetic performance were prepared with the third generation of epoxidized hyperbranched polyesters (EHBP) toughened epoxy resin as matrix material, and ferrocenyl-terminated hyperbranched polyesters (HBPE-Fc) as microwave-absorber. The mechanics and electromagnetic properties of the composites were investigated by mechanics performance tests, SEM and the vector network analyzer. The results indicate that lower content of HBPE-Fc can improve the tensile and impact performance of epoxy resin. Compared with base curing system. When the mass fraction of G4 HBPE-Fc is 2%, the tensile strength, tensile rupture elongation and impact strength increase by 21.81%, 34.32% and 15.41%, respectively. The analysis of tensile fracture surfaces shows that the composites with HBPE-Fc were judged for ductile fracture with the glass transition temperatures for the composites of 105.29-130.27 ℃, and the composites also possess certain electromagnetic properties.
Alignment of Fe3O4-MWCNTs in epoxy resin
CHEN Wei, ZHENG Yaping
2013, 30(6): 54-59.
Nanoparticles Fe3O4 were synthesized with co-precipitation method and coated on the surface of multi-walled carbon nanotubes (MWCNTs) to prepare the magnetic Fe3O4-MWCNTs hybrid. The magnetic Fe3O4-MWCNTs hybrid was aligned in the epoxy resin under weak magnetic field (0.6 T). Alignment and dispersion of Fe3O4-MWCNTs were studied by transmission electron microscope (TEM). Dynamic mechanical analysis (DMA), differential scanning calorimetry (DSC) and thermal conductivity were tested. As a result, nanoparticles Fe3O4 are coated on the surface of MWCNTs, hybrids are aligned end-to-up under 0.6 T magnetic field. Thermal conductivity is anisotropy, with lower thermal conductivity in vertical direction, while Fe3O4-MWCNTs hybrid has little effect on the parallel thermal conductivity. With adding Fe3O4-MWCNTs hybrid into epoxy resin, storage modulus decreases and loss modulus increases. In the meantime, loss factors of nano Fe3O4-MWCNTs/epoxy composites are higher than those of the pure epoxy resin exihibiting good damping property. When the mass ratio of Fe3O4-MWCNTs hybrid to epxy resin is 0.3%, loss factor is more than 0.7 and up to 1.16 at about 20 ℃.
Resistance of polyvinyl alcohol fiber reinforced cementitious composites to sulfate attack under long-term immersion
LIU Shuguang, ZHAO Xiaoming, ZHANG Ju, YANG Changwang
2013, 30(6): 60-66.
In order to research the effect of fiber and fly ash on resistance of polyvinyl alcohol fiber reinforced cementitious composites(PVA fiber/cement composites)to sulfate attack under long-term immersion, the research was done by analyzing morphology change, quality change, volume change, compressive strength and microstructure of the samples tested after several experimental periods. The results of the experiments show that the fiber incorporation with good distribution forming excellent network distribution structure in matrix slows down the erosion rate of PVA fiber/cement composites in sodium sulfate solution, but there is the best content for the fiber incorporation. The fly ash corporation solids PVA fiber/cement composites, and obviously improves resistance of PVA fiber/cement composites to sulfate attack with increasing doping content under mass fraction of 50%.
Experimental study on tensile properties of GFRP rebars under different stress levels as exposed to alkaline solution
XUE Weichen, WANG Wei, FU Kai
2013, 30(6): 67-75.
According to the ACI440.3R-04, the tests consisting of 90 glass fiber reinforced plastic (GFRP) rebars in 60 ℃ of the alkaline solution for 3.65, 18, 36.5, 92 and 183 d, were conducted to evaluate the tensile properties of GFRP rebars at different stress levels(0, 25%, 45%). The micro-formation of the GFRP rebars surface was surveyed by SEM. It indicates that the bonds between fibers and resin of GFRP rebars in the corrosion region becomes loose, and with the stress levels increase, the interfacial debonding between fiber and resin of GFRP rebars becomes more significant. After being exposed to alkaline solution for 183 d, tensile strength of GFRP rebars at stress level of 0 and 25% decreases by 48.81% and 55.56%, while tensile elastic modulus of GFRP rebars decreases by 5.47% and 5.73%, respectively, and GFRP rebars at 45% stress level have been already destroyed. The results of moisture absorption test show that the absorption kinetics is satisfactorily described by Fick's law. In addition, based on the Fick's law, the tensile strength prediction degradation model of GFRP rebars under alkaline solution was proposed.
Properties of low loss ZrTi2O6 filled PTFE composite substrates
WU Kaituo, YUAN Ying, ZHANG Shuren, YAN Xiangyu, CUI Yuren
2013, 30(6): 76-81.
A new kind of low loss ZrTi2O6 filled polytetrafluoroethylene (PTFE) microwave composite substrates were fabricated through the hot-pressing process. The microwave dielectric properties of the composites were measured using dielectric resonator method (18-12 GHz). The relative permittivity (εr) and loss tangent (tanδ) of the composites increase with an increase of the volume fraction of ZrTi2O6 ceramic (0-46%). The experimental dielectric constants of the composites match well with the theoretically predicted values using Lichtenecker model. As the volume fraction of ZrTi2O6 ceramic increases, the thermal expansion coefficient and the temperature coefficient of dielectric constant decrease. The ZrTi2O6/PTFE composites exhibit a dielectric constant of 7.42 with a loss tangent of 0.0022 (10 GHz) at an optimum filler volume fraction of 46% ZrTi2O6.
Investigation of resin flowing and infiltration behavior during z direction flowing RTM process
LI Weidong, LIU Gang, AN Xuefeng, YI Xiaosu
2013, 30(6): 82-89.
The flowing and infiltration behaviors of the equivalent fluid (resin), which passed through the thickness direction (z direction) of large thickness un-toughened and "ex-situ" toughened preforms were studied. The pressure variation of inlet and outlet pot were monitored respectively by pressure transducers during z direction flowing RTM (z-RTM) process. Based on the pressure curves, the macro-flowing and micro-infiltrition behaviors of the "resin" inside the "ex-situ"toughened preforms and untoughened preforms were deduced. The results show that the resin flow along the z direction between the gap of fiber bundles and at the same time infiltrated the intra fiber bundles during the injection stage of z-RTM process. The "ex-situ" toughener will delay the resin macro-flowing, however the resin flow front will be smoothed by the interlaminar toughener. Compared with the un-toughened preform, the introducing of interlaminar toughening agent reduces the z-direction permeability of the preform from 2.9×10-14m2 to 3.5×10-15m2.
Key factors on the thickness and volume fraction of fiber reinforced resin composite laminates molded via VARI technology
LIU Qiang, ZHAO Long, CAO Zhenghua
2013, 30(6): 90-95.
The key factors on the fiber volume fraction and thickness uniformity of the composite molded via vacuum assisted resin infusion(VARI) technology were analyzed, i.e. resin flow control, state of preform, state of fabric and viscosity of resin. The effects of the key factors on the thickness and the fiber volume fraction of the composite molded via VARI technology were verified individually by process test. The results of the tests show that the fiber volume fraction and thickness uniformity of the fiber reinforced resin composite laminates are comparable with those of the composite article molded via prepreg/autoclave process, wherein the fiber reinforced resin composite laminates were molded by HFVI (high fiber-volume vacuum infusion) process and BA9914 resin and vacuum treated U3160 unidirectional woven fabrics are used.
Degradable performance and bio-mineralization function of bioglass/PLA-PEG-PLA/poly(Lactic acid) tissue engineering scaffold in SBF
GE Jianhua, WANG Yingjun, CHEN Xiaofeng, ZHENG Yudong
2013, 30(6): 96-100.
The degradable performance and bio-mineralization function of bioglass/poly(lactic acid)-poly(ethylene glycol)-poly(lactic acid) block copolymer (PLA-PEG-PLA)/poly(lactic acid) tissue engineering scaffolds were systematically studied in the simulated body fluid (SBF) by measuring pH value of SBF, the mass loss ratio of the scaffolds and analyzing SEM pictures, XRD and FTIR spectra of scaffolds' surface. The results show that in SBF, the pH value of SBF with tissue engineering scaffolds and the mass of scaffolds decrease with the prolongation of time. At the same time, the present of bioglass makes pH value of SBF increase and the present of PLA-PEG-PLA makes pH value of SBF decrease. SEM pictures, XRD and FTIR spectra show that there appears the deposition of carbonate hydroxyl apatite on the surface of the bioglass/PLA-PEG-PLA/poly(lactic acid) tissue engineering scaffolds, and the degradation rate of PLA-PEG-PLA is quicker than that of PLA in SBF, because the present of PLA-PEG-PLA in the sample immersed in SBF for 7 d could not be detected by FTIR.
Characterization and cytocompatibility of tourmaline/chitosan composite fiber
ZHAO Kai, XIAO Jiangang, LI Junfeng, LI Yubao, ZOU Qin
2013, 30(6): 101-107.
Tourmaline/chitosan(Tur/CS) composite fibers were prepared with Chitosan as the matrix and tourmaline as the dispersed phase by solution spinning, and characterized by optical microscope, SEM and FTIR. MG63 cells were co-cultured with Tur/CS composite fibers to assess the cytocompatibility. The results show that the tourmaline particles were wrapped by chitosan and fully dispersed in the composite fiber. There were no bare tourmaline particles on the surface. Cytocompatibility test using MG63 revealed positive cell viability and proliferation over a period in vitro. And materials appeared no apparent toxicity. These results indicate that the material can be a kind of good wound repair dressing.
Fabrication and thermal expansion behavior of SiO2-TiO2 ceramic filled PTFE composites
YAN Xiangyu, YUAN Ying, ZHANG Shuren, WU Kaituo, CUI Yuren
2013, 30(6): 108-113.
To match the thermal expansion coefficient of copper foil, the thermal expansion properties of SiO2-TiO2 ceramic filled PTFE microwave substrate composites were investigated. SiO2 together with TiO2 were added to PTFE matrix by the wet process. The influences of the SiO2-TiO2/PTFE composite density, ceramic particle size and volume fraction of ceramic filler on the thermal expansion coefficient(CTE)of the SiO2-TiO2/PTFE composites were investigated. The results show that as the volume fraction of SiO2 increases from 0 to 40%(TiO2: 34%-26%), the linear expansion coefficient of the composites decreases from 50.13×10-6K-1 to 10.03×10-6 K-1. The decrease of ceramic particle size and density of composites results in the decrease of the CTE. According to the calculation of CTE with ROM, Turner and Kerner models, the experimental values show better matching with the theoretically predicted values using ROM and Kerner models. Whereas, promotion of the difference between experimental value and the predicted value by Turner model is along with PTFE volume fraction increasing.
Condition and criterion for TiC particles getting into molten steel
BIN Shibo, XING Shuming, GUO Lijun, BAO Peiwei, GUO Honggang
2013, 30(6): 114-120.
The composites of 20%TiC/ZG270-500 were made by means of squeeze casting, and it's realizable for TiC particles getting into molten steel with the action of foam carrier. Then TiC particles motion behaviors in air gap and conditions for TiC particles getting into molten steel were investigated during the gasification and extinction of foam carrier. The experimental results show that TiC particle motion velocity increases with the increase of pouring temperature, filling velocity and cross-section ratio of exhaust orifice to metal cavity. There is a critical velocity that the TiC particle should exceed for getting into molten steel. The greater of TiC particle motion velocity, the easier for them getting into molten steel, and the more uniform distribution of TiC particles in steel matrix.
Effects of microstructures of Ti anode coating with two constituents and three constituent (RuO2-SnO2-TiO2) on the electrochemical properties
HAN Zhaohui, ZHU Peixian, GUO Jiaxin, MA Huiyu
2013, 30(6): 121-126.
RuO2-TiO2 coating and RuO2-SnO2-TiO2 coating of titanium(Ti) anode were obtained by thermal decomposition. The microstructure and the electrochemical performance of these Ti anode coating were examined by means of SEM, XRD and polarization curves. The results show that RuO2-SnO2-TiO2 coating of titanium anode has high performance with 1.128 V and 1.674 V of tomography potential of chlorine and oxyen respectively at drying temperature of 130 ℃, sintering temperature of 500 ℃, holding time of 15 min and annealing time of 1 h. Adding Sn to RuO2-TiO2 coating of titanium anode will reduce Ru usage and decrease the costs for titanium anode. The presence of SnO2 can improve catalytic activity, and reduce tomography chlorine and oxygen potential of coating surface for titanium anode, which will increase the lifetime of titanium anode.
Two-step hot-pressing sintering of composite WC-40%Al2O3 compacts
PEI Yang, ZHU Shigen, QU Haixia
2013, 30(6): 127-134.
The WC-40%Al2O3 composite powder synthesized by high-energy ball milling was used as raw material followed by two-step hot-pressing sintering (TSS).The first step sintering at a constant heating rate with a higher temperature T1 to obtain an initial high density and guarantees the disappearance of supercritical pores, while the other pores become unstable. The second step was held at lower temperature T2 by isothermal for a period of hours to increase bulk density with a limited grain size. The phase and microstructure of the composite were characterized by XRD, SEM and SPM technology. The present work dealt with the influence of deliberate temperature and holding time at second step, which had been well documented by orthogonal analysis, on microstructure and mechanical properties of WC-40%Al2O3 nanocomposite. The results show that when the sample sintered at 1600 ℃(T1) and holding 6 h at 1450 ℃(T2) obtains a relative density of 99.03%, Vickers hardness of 18.36 GPa, a fracture toughness of 10.4 MPa·m1/2 and a bending strength of 1162.1 MPa.
Evaluation of thermal properties of SiO2/polyurethane acrylate-epoxy acrylate as coating for fiber Bragg grating sensor
YANG Zehui, NI Aiqing, YIN Yanzi, WANG Jihui
2013, 30(6): 135-138.
Compared with polyurethane acrylate (PUA)-epoxy acrylate (EA), the SiO2/PUA-EA shows better thermal properties by thermogravimetry analysis (TGA) and differential scanning calorimetry (DSC). The initial decomposition temperature is 143.8 ℃, and the most mass loss occur at 320 ℃ for SiO2/PUA-EA, both of which are higher than those of pure resin. The SiO2/PUA-EA can be used as coating for FBG monitoring for curing of composites accurately. The residual stress for hybrid materials is 128 kPa, lower than that reported previously. SEM shows that no delamination occurs between the SiO2/PUA-EA and the core of optical fibers indicating their good binding.
Experimental study on dual-fluid-grout composite materials with slag steel modified Portland cement and sodium silicate
CHEN Feng, HUANG Beili, BA Mingfang, BAO Xudong
2013, 30(6): 139-145.
The effects of mass fraction of steel slag, water to binder ratio of single cemented paste, and volume ratio of double slurry on the working capability of dual-fluid gout were investigated. The optimum water to binder ratio of slag-modified Portland cement slurry is 0.6-0.8, and the optimal mass percentage range of steel slag with 20.4 μm average particle size in steel slag modified Portland cement slurry of 50%-80%. There exits an appropriate volume ratio of 4:1-6:1 between slag-modified cement slurry and sodium. According to above parameters the steel slag modified cement-silicate dual fluid gout was prepared and cured in water for 3 days after demolding, whose early average compressive strength and corresponding softening coefficient are over 40 MPa and 0.80 respectively.
Low-frequency magnetoelectric coupling of Tb1-xDyxFe2-y-BaTi0.99Mn0.01O3+δ layered composites
CAO Hongxia, LIU Qingquan, WANG Youbao
2013, 30(6): 146-152.
A elastic mechanics model was introduced to derive the magnetoelectric voltage coefficients of magnetostrictive-piezoelectric bilayer according to the constitutive equations. The transverse magnetoelectric coupling of Tb1-xDyxFe2-y-BaTiO3 layered composites were calculated by using the corresponding material parameters of individual phases. 1.0%(mole fraction) Mn doped BaTiO3 (BaTi0.99Mn0.01O3+δ) was synthesized with sol-gel technique. Layered composites were fabricated by binding discs of rare earth alloy Tb1-xDyxFe2-y and Mn doped BaTiO3, and the transverse magnetoelectric was investigated. XRD and DSC analysis show that Mn doped BaTiO3 keeps the tetragonal structure at room temperature, and the phase transition temperature and the latent heat of ferroelectric to paraelectric are a little less than those of BaTiO3. The peak values of transverse magnetoelectric voltage coefficients for Tb1-xDyxFe2-y-BaTi0.99Mn0.01O3+δ and Tb1-xDyxFe2-y-BaTi0.99Mn0.01O3+δ-Tb1-xDyxFe2-y reach 529.4 mV/A and 1659.5 mV/A under a bias magnetic field of about 33 kA/m, which are 1.48 and 1.45 times of Tb1-xDyxFe2-y-BaTiO3 and Tb1-xDyxFe2-y-BaTiO3-Tb1-xDyxFe2-y, respectively. The transverse magnetoelectric voltage coefficient of trilayer composites is about three times as large as those for bilayers of the same kind.
Fabrication of Fe78Si13B9 magnetic materials by spark plasma sintering technology
WANG Xinghua, WANG Ge, LI Qiang
2013, 30(6): 153-158.
Fe78Si13B9 magnetic amorphous powder was prepared by high-energy ball-milling and then was consolidated in several solid sample at different sintering temperature by spark plasma sintering technology. The phase composition, glass transition temperature (Tg), onset crystallization temperature (Tx) and peak temperature (Tp) of Fe78Si13B9 amorphous alloy powders were analyzed by XRD and DSC. The phase transition, microstructure, mechanical properties and magnetic performance of the bulk alloys in different sintering temperature were discussed by XRD, SEM, and vibration sample magnetometer, etc. It is found that with the increase of the sintering temperature at the pressure of 500 MPa, the amorphous phase begins to crystallization gradually and the density, compressive strength, micro-hardness and saturation magnetization of the sintering sample improve significantly. The desirable amorphous nanocrystalline magnetic material at the sintering temperature of 823.15 K and under the pressure of 500 MPa has a density of 6.6 g/cm3, compressive strength of 1500 MPa and a saturation magnetization of 1.3864 T.
Prediction on mechanical behavior of carbon black filled rubber composites based on periodic boundary conditions
LI Qing, YANG Xiaoxiang
2013, 30(6): 159-167.
Based on the relation of macroscopic and microscopic characteristics of carbon black filled rubber composites, representative volume element with random distribution pattern has been proposed, the boundary conditions for the periodic microstructures has been discussed, and three dimensional multi-particles RVE numerical model has been established to study and analyze the macro mechanical properties of the carbon black filled rubber composites by the micromechanical finite element method. The research shows that the compatibility of the deformation field and stress field in macrostructure are ensured by the periodic boundary conditions, the modulus of the rubber composite is increased considerably with the introduction of carbon black filler particles, and the effective elastic modulus of the rubber composite is increased with the increase of the carbon black particle volume fraction. In the simultaneous, the results of the prediction on the effective elastic modulus of the rubber composite made with this numerical model are consistent with the experimental results, and better than the predictions of the model proposed by Bergstrom, which demonstrate that this model can be used for simulation analysis of effective properties of the carbon black filler particle reinforced rubber matrix composites.
Phase change and plasticity analysis for metal honeycomb sandwich structure under high temperature load
JI Zhanling, LI Yunze, LI Yunhua
2013, 30(6): 168-176.
To analyze the influence of phase change and plastic deformation under high temperature on inherent properties of metal honeycomb sandwich structure, a nonlinear coupling analysis was implemented to honeycomb sandwich structure equipped with heating elements by the finite element numerical solution method, which was based on transient heat transfer theory of multilayer panel with phase change and thermal elastoplastic theory. By means of the analysis on the temperature field, the solid-liquid and gas-liquid phase change occurred in outer glue, and the occurring time, location, severity, and development trends can be quickly determined. Combining with the computation results of temperature field and stress field, the plastic deformation produced in the outer skin can be easily confirmed, and its dynamic evolution laws versus loaded time can also be predicted.
Numerical investigation of the effective thermal conductivity of polymer composite filled by TATB
WEI Xingwen, ZHOU Xiaoyu, HUANG Zhong, LI Ming, LI Jingming
2013, 30(6): 177-184.
At microscopic scale, the 1, 3, 5-triamino-2, 4, 6-trinitrobenzene(TATB)/polymer bonded explosive (PBX) was regarded as a three-phase composite, consisting of TATB particles, polymer matrix and voids. Based on the microstructure of PBX, a representative volume element (RVE) model was developed by the Monte Carlo method. The finite element model (FEM) was built considering the fraction and distribution of the fillers and pores based on the RVE model. The effect of filler fraction, porosity and pore distribution on the effective thermal conduction of TATB/PBX was studied. The results show that the effective thermal conductivity of TATB/PBX increases with TATB volume fraction increasing. At the same TATB volume fraction, the increase of porosity leads to the exponentially reduction in thermal conductivity of TATB/PBX, but the pore spatial distribution has little effect. The good consistence between simulation and experimental results proves that the model can be used to predict the effective thermal conductivity of TATB/PBX by comparing the predicted and the experimental results.
Fracture behavior of carbon fiber T-joints under tensile load
SHENG Yi, XIONG Ke, BIAN Kan, XIONG Xuan, CHEN Hong, HAO Yinfeng
2013, 30(6): 185-190.
The numerical mode of carbon fiber T-joints was built by finite element analysis software, and its cohesive mode technique. The damage formation, extension and failing process of T-joints under tensile load were investigated. Then the static tension test was carried out on the carbon fiber T-joints. The test results demonstrate that the initial damage load was between 9.8 kN and 12.0 kN, and after the damage appeared, the bearing value on the T-joints descends sharply (approximately by 27%-38%). The ultimate damage load is between 8.0 kN and 8.6 kN, which is slightly lower than the initial one, because the filling area was destroyed. Both of the numerical and test results confirm that the filling area is the weakest part of the T-joints where the damage first appears. The crack then rapidly spreads to the glue film around the filling area. It was the peeling off of the glue film that accounts mostly for the failure of T-joints.
Experimental and numerical simulation of composite laminates bolted joints with local reinforcement
ZHANG Jifeng, XIE Yonggang, ZHANG Lu
2013, 30(6): 191-196.
Four different composite laminates specimens of bolted joints with local reinforcement were prepared by vacuum assisted resin injection molding (VARI). The mechanical behavior of the composite bolted joints specimens was experimental and numerical investigated. In the numerical study, the bolted of static tensile was deemed to a quasi static problem. An explicit dynamic solver and ABAQUS user subroutine VUMAT were implemented to simulate the 3D progressive failure process of composite bolted joints. Interface delamination was simulationed using a cohesive element layer between laminates and reinforcement layer. The numerical results are in good correlation with the experimental results, which demonstrate that the simulation is feasible. The research results show that bolted joints with different local reinforcement methods affect connection properties of laminates obviously, and the connection properties of laminates are significantly improved by [0/90/0/90]S internal fiber layer reinforcement.
Combined joint design and analysis at stringer run-outs in stiffened composite panels
ZHONG Xiaodan, CHEN Puhui
2013, 30(6): 197-202.
A novel combined joint design principle at stringer run-outs in stiffened composite panels was studied with reducing bond-line configurations to improve the structural debond load. FEM verified by experiment results was used to analyze load transferred and failure mechanisms of combined joint at stringer run-outs, and research the influence of bond-line length to stringer terminations debond load. The results illustrate that normal constraint and shear load path provided by fasteners in the novel combined joint concept can improve structural debond load significantly, and enhance the capacity of arresting damage propagation at the bond-line tip. Moreover, the debond load increases with bond-line configurations reducing, interface failure can be avoided while the bond-line tip is beyond fasteners in the last row, and the failure load is determined by the strength of skin mechanically joints.
Effect of the rubber size on properties of rubber/epoxy composites filled with sub-micron or nano-sized rubber particles
SONG Pin, ZHANG Hui, ZHANG Zhong, PENG Zhijian
2013, 30(6): 203-208.
A comparative study was carried out on the rubber/epoxy composites filled with sub-micron or nano-sized rubber particles. The results show that the viscosities of uncured epoxy resins increase after adding nano-sized rubber particles, but decrease when mixed with sub-micron ones. The glass transition temperatures of the rubber/epoxy composites increase with the nano-sized rubber particles, but decrease with the sub-micron ones. All rubber particles result in decreasing the elastic modulus of the composites obviously, but increasing the elongations at break. At lower filler content, the nano-sized rubber can improve the tensile strength of epoxy. All rubber particles exhibite significant toughening effect. Based on the morphologies in micro-scale, rubber particle debonding is observed for both rubber particles, and this promotes local plastic deformation around crack tips.
Buckling resistance of advanced grid stiffened composite trapped conical shells under thermal and mechanical mixed loading
SHI Shanshan, SUN Zhi, REN Mingfa, CHEN Haoran
2013, 30(6): 209-214.
Based on homogenization approach, the thermal expansion coefficient and variable stiffness matrices along the longitudes were deduced, and according to pre-buckling membranes theory, the total potential energy for buckling analysis of advanced grid stiffened composite (AGS) conical shells under thermal and mechanical mixed loading was presented. Then, by minimum potential principle, the critical load of AGS conical shells under thermal and pressure loading was predicted. The good agreement between predicted results by provided method and FEA results for a typical example of buckling analysis of AGS conical shells validates the present method. Lastly, by some numerical results, the discussions of the influence of temperature and semi-cone angles on the thermo-mechanical buckling response of AGS trapped conical shells were carried out. It can be seen that the effect of temperature on buckling resistance of the shells increases with increasing the semi-cone angles.
Random disturbing model and experimental verification for thermal expansion property prediction of composite
RAN Zhiguo, YAN Ying, LI Jianfeng, CONG Qiang, CHEN Haifeng, YAN Liang
2013, 30(6): 215-220.
To study the thermal expansion property of long fibre reinforced unidirectional (UD) composite, a new method was developed to create fibre random distribution models. In all the models, the fibre distribution state and the real periodic boundary condition have been taken into account. For models with high fibre volume fraction, a method called RDM (random disturbing method) was developed, which can generate models with fibre volume fraction not less than 65%. Random models generated by RDM were used to forecast the thermal expansion coefficient of M40J/TDE-85, and the thermal expansion coefficients of this composite were tested with high precision. The predicted results agree well with the experimental data, which shows that this random model can be used to predict the thermal expansion coefficients of UD composite correctly. It is rapid and precise to adopt this random model to predict the thermal expansion property of composite, and it would be convenient for materials study and engineering application.
Continuum damage model and damage parameter identifications for composites considering the effect of shear nonlinearity
LIU Weixian, ZHOU Guangming, GAO Jun, QIAN Yuan
2013, 30(6): 221-226.
The strain based integrated continuous variables were introduced and used to describe the evolution of damage. The shear nonlinearity of the composite materials was taken into considerations by introducing a nonlinear damage factor in the constitutive equations. The proposed continuum damage model was then implemented into the ABAQUS via VUMAT. The method to determine the parameters was explained in detail. Damage parameters which cannot be obtained by experiment were identified by using the genetic algorithms. The individual fitness was defined by the difference between the experimental and simulated load displacement curves. The parameters inversion method was carried out by the developed MATLAB program to call ABAQUS to perform the finite element analysis. A common composite laminated plate with a hole was selected to identify parameters by using the proposed model. Numerical results reveal the feasibility of the proposed parameter identification method.
Simulation of progressive damage of 3D braided compositesusing domain superposition technique
ZHANG Fangfang, JIANG Wenguang, LIU Cai, YAN Lijuan
2013, 30(6): 227-236.
Domain superposition technique (DST) has been implemented for simulation of the progressive damage of braided composites in this paper. To establish the tow finite element mesh used for the DST analysis model, first of all, regular parametric geometric model for the tows were easily constructed using ANSYS parametric design language (APDL), and then a programmed automatic mesh trimming process has been carried out to trim the tow meshes established in the first step to establish new tow meshes which can fit exactly the space of the unit cell (UC) model used for the DST analysis. The element edges crossing the UC boundaries were cut by the UC boundaries to create new nodes. Some new elements were constructed using these newly created nodes and some original nodes to fit the boundary regions. Hashin and Von Mises damage criterions were used to predict damage initiations in tow phase and matrix respectively. Blackketter's degradation scheme for the elastic properties of the composites was adopted. A stiffness matching scheme suitable for damage analysis for DST implementation has been applied. A domain mapping method to ease the post-processing of the damage results of the matrix/resin-rich regions has been implemented. The numerical results predicted using the DST model correlate well with the traditional FEM predictions. And also, the strength and failure strain predictions are in good agreement with experimental results.
Effective thermal conductivity and heat dissipation performance of sandwich cylinder with cellular materials considering the active heat dissipation
ZHANG Kai, DENG Zichen, WANG Bo, ZHOU Jiaxi
2013, 30(6): 237-242.
For issues of active heat dissipation performance and effective thermal conductivity of the sandwich cylinder with cellular materials, the effective thermal conductivity including the effects of active heat dissipation of the sandwich cylinder was calculated, and its relationships with the relative density and the speed of the fluid were obtained by deriving the effective thermal conductivity and thermal governing equation under the heat convection boundary conditions. By considering the effective thermal conductivity of active heat dissipation, the transient temperature of the sandwich cylinder was calculated and compared with the result obtained by finite element method. Meanwhile, the relationship between the relative density and heat dissipation performance of the unit cells was obtained, and the optimal relative density and the optimal thickness corresponding to the maximum heat dissipation index in different dividing parts were also obtained. By comparing the transient temperature obtained by theoretical solutions using the effective thermal conductivity including the effects of active heat dissipation with FE simulations, the results are nearly the same, indicating the correct effective thermal conductivity and the accuracy to calculate the temperature of the structure. At the same time, the study demonstrates that the effective thermal conductivity increases with the decrease of the velocity of the fluid and the increase of the relative density of the structure. The Square and Hexagon have the best heat dissipation capability in the same mass quantity.
Combined effects and mechanism of interference fit and clamping force on composite mechanical joints
CHEN Kunkun, LIU Longquan, WANG Hai
2013, 30(6): 243-251.
In order to investigate the combined effects of bolt-hole interference fit condition and clamping force on the strength of the bolted mechanical composite joints and their mechanism, a finite element model validated by experiments was taken out. A three dimensional nonlinear finite element model agrees well with two sets of composite-to-titanium single-lap bolted joints tensile tests. Based on the finite element model, seven interference fit conditions combined with six clamping force conditions, altogether forty two different working conditions were studied. The results show that, although certain interference fit condition and clamping force may cause some pre-failure of the joints area, they can improve the contact condition and prevent failure evolution under bigger load, making the joints strength maximize. At the same time, there is interaction between interference fit and clamping forces on the joints strength, namely the optimal clamping force will be different under different interference fit conditions, vice versa. So the two factors on the interference fit and clamping force need to be considered at the same time in order to achieve the optimal structural design.
Structural acoustic optimization of hybrid metal composite structure based on material selection optimization approach
CHEN Luyun, ZHANG Yufang, LIU Yong
2013, 30(6): 252-257.
According to the stacking sequence hypothesis of metal, the corresponding material selection optimization mathematical model of hybrid metal-composite structure was established with the material property and layers number as design variables. Taking the hybrid steel-fiber reinforced composite structure as an example, the structural-acoustic radiation dynamic optimization design with multi-variables and multi-constraints problem was presented. In the end, by introducing genetic algorithm, the optimization problems were solved, and the structural material conversion was achieved. The numerical calculation shows that the vibration and acoustic radiation of the hybrid metal-composite structure can be reduced by using material selection optimization method. The paper provides an effective and feasible method to solve the problem for multi-material distribute optimization.
Design and optimization method for composite main shaft of aircraft engine
SUN Qingwei, LU Shan
2013, 30(6): 258-263.
A method was proposed for designing and optimizing composite shaft and a mathematical modal was established based on it. In the model, the quantity was set as objective, and the strength, critical speed and the outer diameter dimensions were set as restraint conditions. The design parameters consist of the thickness of the core, number of composite layers, thickness of single layer and the fiber's direction of each layer. A design and optimization platform was also established by ANSYS for optimizing both the discrete variables and the continuous variables. A low pressure turbine shaft was taken as a design example using metal matrix composite. It can save 36.16% mass compared with the metal one.
Baseline-free Lamb wave phased array imaging method for structural damage monitoring
SUN Yajie, ZHANG Yonghong, YUAN Shenfang, QIAN Chengshan, ZHANG Zijia
2013, 30(6): 264-269.
In the ultrasonic phased array structural health monitoring method, the damage scattering signal gotten by comparing the damage structural response signal with the health structural response signal can be affected easily by some external factors, such as, environment and the change of the structure. In order to solve this problem, the baseline-free phased array damage identification imaging method was proposed. The window function was used to get the damage scattering signal and to exclude the direct propagation wave and the reflection wave from the structural boundaries. Based on the phased array theory, the response signals travelling in the damage structure could be used to realize the damage recognition, and the health structural response signals no longer act as the reference signal in the calculation procedure. Experiments on the carbon composite structure show that the damage in the structure can be recognized precisely by using the baseline-free phased array method. The method does not need the baseline signal. It can greatly shorten the monitoring time and is not affected by the change of the environment and the structure. This research is the foundation of the engineering application for the method.