2014 Vol. 31, No. 5

2014, 31(5): .
Formation mechanism of T-slotting machining defects of carbon fiber reinforced plastics
SU Fei, YUAN Juntang, CHENG Yu
2014, 31(5): 1127-1133.
In view of the T-slotting defects on the outermost layer at the cut-out side on plain-woven carbon fiber reinforced plastics (CFRP), the cutting models on the outermost layer of fibers at the cut-out side were established.The slotting tests, using a T-slot cutter, were carried out to study the formation mechanism of the T-slotting defects.In the cutting process of the outermost layer at the cut-out side, there are Case A and Case B, for respectively the cutting of fill fibers with the support of warp fibers and the cutting of fill fibers without the support of warp fibers.The results show that when the feed per tooth increases, the residual factor of the outermost layer at the cut-out side basically decreases while the delamination factor increases.And residual factor mainly experiences 2 times of decreasing in succession, including the reducing of residual fill fibers of Case A and the reducing of residual warp fibers.Residual fill fibers of Case B are ubiquitous in each test, but some of them can be removed effectively when the feed per tooth region is appropriate, in which Case A fibers are removed.Using a fine grain cemented carbide cutter for slotting, the appropriate feed per tooth region is between 11.22 μm/z and 15.62 μm/z.The changing rules reflected by the theoretical derivations are in good agreement with the test results.The study has guiding significance for the selection of feed per tooth and the inhibition on the T-slotting defects.
Preparation and properties of continuous glass fiber reinforced anionic polyamide-6 composites via in situ anionic ring-opening polymerization
YAN Chun, FAN Xinyu, YU Liping, ZHANG Xiaoqing, LI Hongzhou
2014, 31(5): 1134-1141.
Continuous glass fiber (GF) reinforced anionic polyamide-6 (APA6) composites were prepared via in situ anionic ring-opening polymerization.The effects of catalyst ratio and polymerization temperature on the conversion and molecular weight of APA6 resin were studied.The effects of polymerization temperature and time on the degree of crystallinity of continuous GF/APA6 composites were investigated using DSC and TGA, and the effects of polymerization temperature and time on mechanical properties of continuous GF/APA6 composites were further discussed.The morphologies of tensile fracture surfaces of continuous GF/APA6 composites were observed by SEM.Results show that, when the polymerization temperature is 150 ℃ and the polymerization time is 45 min, the continuous GF/APA6 composites reach the highest values of mechanical properties, which the tensile strength is 538.1 MPa, bending strength is 497.2 MPa and interlaminar shear strength is 52.5 MPa.The SEM analysis shows that there is a good bonding quality between the glass fiber and APA6 resin matrix.
Preparation and properties of Al2O3 nanosheets/epoxy composites
ZHOU Hong, ZHANG Yuxia, FAN Yong, CHEN Hao
2014, 31(5): 1142-1147.
Al2O3 nanosheets were successfully synthesized by hydrothermal process.After modified with coupling agent, Al2O3 nanosheets/epoxy composites with different contents of Al2O3 nanosheets were prepared by solution mixing.The effects of Al2O3 nanosheet content on the dielectric and thermal properties of Al2O3 nanosheets/epoxy composites were discussed.The fracture morphology of composites was characterized by SEM.The results show that Al2O3 nanosheets uniformly disperse in epoxy matrix.With the increase of Al2O3 nanosheet content, the initial thermal decomposition temperature and the dielectric strength of Al2O3 nanosheets/epoxy composites increase.Dielectric strength of composites is 29.58 kV/mm with 7wt% Al2O3 adding, which is increased by 30% than that of the pure epoxy.Dielectric constant (3.8-4.5) and dielectric loss (0.015) of Al2O3 nanosheets/epoxy composites increase slightly than pure epoxy's, but the dielectric properties still remain at a good level.
Preparation of submicron SiO2 PMMA GMA composite particles and their modification for epoxy
HUANG Zengfang, QU Xiaoyue, CHEN Zheng
2014, 31(5): 1148-1153.
Based on the sol-gel method, the submicron SiO2 particles with the polymerizable group on the surface were prepared.The SiO2-poly(methyl methacrylate)(PMMA)-glycidyl methacrylate (GMA) composite particles with the core-shell structure were successfully prepared by emulsion polymerization on the surface of SiO2, the structure of the composite particles was characterized by TEM, FTIR and TGA.In succession, the SiO2-PMMA-GMA/epoxy composite materials were prepared and SEM was used to observe the fracture morphology, then the toughness mechanism of composite particles to epoxy was also put forward.The results indicate that SiO2 is the core in the composite particles with about 180 nm diameter, the surface of SiO2 is encapsulated by PMMA-GMA polymer with about 20 nm thickness.The mass ratio of PMMA-GMA polymer to original SiO2 is 87.4%, the grafting ratio of PMMA-GMA polymer to original SiO2 and effective grafting ratio of PMMA-GMA polymer are 77.0% and 88.1%, respectively.The impact strength of epoxy after curing increases to 42.0 kJ/m2 from 19.2 kJ/m2 when the content of the SiO2-PMMA-GMA composite particles is 4wt% in the epoxy matrix.
Preparation and properties of graphene/cyanate ester-epoxy composites
LI Jinhuan, WANG Ruihai, WANG Tangyang, GU Shanqun, LYU Zhaoping, CHEN Tian
2014, 31(5): 1154-1159.
To optimize the preparation process of graphene/cyanate ester (CE) composites and improve their toughness, p-phenylenediamine functionalized graphene oxide (GO-PPD) was prepared from graphene oxide (GO).GO/CE-epoxy and GO-PPD/CE-epoxy composites were prepared using CE and epoxy blends (mass ratio is 7:3) as matrix resin and GO, GO-PPD as addition filler.The chemical structure of GO and GO-PPD were characterized by FTIR and Raman spectroscopy.The solubility of GO and GO-PPD was also checked.GO-PPD can steadily dissolve in such solvents as alcohol with low boiling point and hypotoxicity.Compared with GO, GO-PPD greatly improves the preparation process of its composites.The property investigation shows that both of the introduction of GO and GO-PPD decrease the curing temperature, dramatically increase the mechanical and thermal properties, and increase the dielectric constant and the dielectric loss of the matrix resin obviously.However, the good hot-wet and corrosion resistance are maintained.The properties of graphene/CE-epoxy composites change with the surface chemical property of graphene.Compared with GO, GO-PPD more greatly contributes to the improvement of the mechanical and thermal properties of composites.
Preparation and properties of chitin nanofibers/montmorillonite composites
DENG Qiaoyun, LI Dagang, WANG Ru, YANG Jingyun
2014, 31(5): 1160-1166.
The chitin nanofibers(CNF)/montmorillonite(MMT) intercalated composites were prepared by using the method of ultrasonic miscibility-vacuum filtration.The structure of CNF/MMT was characterized by FE-SEM and FTIR, and the effects of MMT content on the mechanical properties, water absorption performance, coefficient of thermal expansion(CTE) and thermal stability of the composites were investigated.The results show that, when the content of MMT is low, the bonding state of CNF and MMT is relatively good, CNF are more evenly dispersed in lamellar MMT interlayer, which forms CNF/MMT composites.The mechanical properties and water absorption of the composites decrease with the increasing of MMT content.CTE of the composites reduces with the the increasing of CNF because CNF could suppress the thermal expansion of MMT.The thermal stability of CNF/MMT composites can be effectively improved through adding MMT since it can reduce the mass loss rate of composites and improve the initial degradation temperature.
Effects of Mg(OH)2 on flame retardant of benzoxazine epoxy composites
YU Yang, LIU Lizhu, WENG Ling, CUI Weiwei, ZHU Xingsong
2014, 31(5): 1167-1172.
Mg(OH)2-glass fiber fabric/benzoxazine (BZ)-epoxy (EP) laminate was prepared by thermo-compression formation using Mg(OH)2 as the flame retardant, BZ-EP as the matrix.The flame retardant of the laminate was tested by the vertical flame and the limited oxygen index method.The effects of Mg(OH)2 powder amount, particle size and compound addition of powder with different sizes on flame retardant of composites were analyzed.SEM was used to characterize the dispersion structure of Mg(OH)2 powder in impregnation resin.The results indicate that the flame retardant of the laminates is influenced by the particle size and the amount of Mg(OH)2 powder.The compound addition of powders with different particle sizes makes a flame-retardant net in composites, leading to the best flame retardant effect.And the negative impact of inorganic particle on the mechanical and electrical properties of the laminates is reduced.When the content of Mg(OH)2 is 30wt% of total mass of BZ-EP and the mass ratio of Mg(OH)2 powder with 2 μm (YX-105) and 4 μm (YX-110) is 1:2, the limited oxygen index of the laminates is 34%.The shortest self-extinguishing time of single sample in vertical burning test is 7.52 s, and the total self-extinguishing time of the five samples is 49.81 s, which reaches the ranking of UL-94V-0.The bending strength and the relative dielectric constant of the composite is 399.84 MPa and 3.848, respectively.
Absorption behavior of glass fiber reinforced unsaturated polyester composites subjected to chloride ion environment and sustained load
WANG Jun, LIU Weiqing, ZHAO Huimin, FANG Yuan
2014, 31(5): 1173-1178.
Loaded by weights, glass fiber reinforced unsaturated polyester (GFRP) composites were immersed in chloride ion environment at regular intervals, the moisture absorption rate of GFRP was tested to study the moisture absorption law under different stress levels.The results show that the moisture absorption rate of GFRP increases quickly with time in the initial immersion stage, then the moisture absorption rate becomes slow.Moreover, the increasing of the immersion time beyond 180 d causes a gradual decrease of the moisture absorption rate.With the increase of the load, the moisture absorption rate of GFRP decreases.And the change law of moisture absorption rate with varying time is the same for GFRP specimens under different load levels.The moisture absorption behavior of GFRP immersed in chloride ion environment has been demonstrated to show non-Fickian feature.Based on Langmuir model and taking moisture absorption feature of materials mass loss due to materials hydrolysis into accounts, a moisture absorption model was proposed to describe the increase and down trend of mositure absorption curve of composites, which can predict the moisture absorption amounts of GFRP well.
Structure and properties of hyperbranched polyester/poly composites
LI Chunxia, WANG Wang, LIU Jingru, YU Qiang
2014, 31(5): 1179-1185.
Poly(ethylene terephthalate) (PET) was modified by blending with hyperbranched polyester (HBP) with terminal groups of hydroxyl, hexadecyl and phenyl.The effects of types and dosage of terminal groups of HBP on tensile strength, impact strength, crystallization and dynamic viscoelastic properties of HBP/PET composites were studied.The results show that when the mass fraction of phenyl-terminated HBP (HBP-Bz), hexadecyl-terminated HBP (HBP-C16) and hydroxyl-terminated HBP (HBP-OH) are 0.1%, 0.4% and 0.2%, respectively, the tensile strength and impact strength of HBP/PET composites reach the maximum.HBP improves the degree of crystallinity when the mass fraction of HBP is in the range of 0.1%-0.4%.Compared with HBP-C16 and HBP-OH, HBP-Bz dramatically accelerates the crystallization rate of PET.The lower mass fraction (0.1%-0.4%) of HBP plays a tackifying role in the blended systems of PET.HBP/PET composite melt exhibits the rheological behavior of typical pseudoplastic fluids.To some extent, the addition of HBP increases the macromolecular chain entanglement and physical junction of PET, and the tensile strength, impact strength and melt viscosity of HBP/PET composites are improved.
Mechanical property of UV curable glass fiber fabric/EP PBMA resin composites
ZHAO Peizhong, DAI Jingtao, JI Bolin, HU Fangyou
2014, 31(5): 1186-1191.
The epoxy-poly(butyl methacrylate) (EP-PBMA) resins which can be polymerized and cured by UV and thermal initiation were designed.Based on the EP-PBMA resin, UV curable glass fiber fabric/EP-PBMA composites were prepared.The tensile properties of the glass fiber fabric/EP-PBMA composite samples with different mass ratios of EP to PBMA were tested under different loading rates.According to the results, glass fiber fabric/EP-PBMA composites have a obvious strain rate effect.With the increase of loading rate, the tensile strength and elastic modulus increase.The composition of EP-PBMA resin matrix can affect the strain rate effect greatly.When the loading rate is low, glass fiber fabric/EP-PBMA composites perform better tensile strength than the composites of pure EP matrix.However, when the loading rate reaches 50 mm/min, the tensile strength of glass fiber fabric/EP-PBMA composites becomes lower.
Effects of graphene oxide SiO2 hybrid materials on tensile properties of epoxy
LI Jiani, YU Kejing, QIAN Kun, CAO Haijian, LU Xuefeng, SUN Jie
2014, 31(5): 1192-1197.
In order to improve the mechanical properties of epoxy, one-step synthesis method was used to obtain graphene oxide(GO)-SiO2 (GO-SiO2) hybrid materials.SEM confirmed that three dimensional GO-SiO2 hybrid materials were prepared successfully.GO, SiO2 and GO-SiO2 with the same content of 0.1% mass fraction were added into epoxy to prepare composites.Universal strength tester was used to test the tensile performance of the composites, and the effects of three types of fillers on tensile performance of the resin matrix composites were compared.Then different contents with 0.1%, 0.3% and 0.5% mass fraction of the GO-SiO2 were added into epoxy to prepare GO-SiO2 /epoxidation composites, and the effects of different contents of GO-SiO2 on the tensile perpormance of resin matrix composites were compared.SEM was used to test the fracture cross-section of tensile specimen, and the reinforcing and toughening effect of different kinds and contents of fillers on the resin matrix composites were analyzed, and the reinforcing and toughening mechanism was analyzed.Results show that the reinforcing and toughening effect of GO-SiO2 is much better than GO and SiO2 particles, and when the mass fraction of GO-SiO2 is 0.3%, the reinforcing and toughening effect is the best.
Degradation behavior of straw/SPI modified urea formaldehyde resin composite flowerpots in different surroundings
SUN Enhui, HUANG Hongying, WU Guofeng, CHANG Zhizhou
2014, 31(5): 1198-1205.
In order to study the degradability of flowerpot made from straw/soy protein isolate (SPI) modified urea formaldehyde resin composites in different surroundings, the specimens were treated by soil burial (SB) and outdoor exposure(OE)methods.Structure and performance of flowerpots were investigated through mechanical properties, mass loss rate and water absorption test, TG-FTIR, SEM and EDS.Results show that, compared with control group (US), after treated with SB and OE for 12 months, respectively, the tensile strength of flowerpots decreases by 36.51% and 19.92%, elastic modulus decreases by 9.38% and 3.92%, the elongation at break decreases by 41.36% and 36.61%, respectively.The mass loss rates of the two composites are 13.74% and 4.69%, respectively, and the water absorption of specimens enhance.TG-FTIR results show that degassing condition of pyrolytic reaction of flowerpot after degradation process becomes milder, and the maximum pyrolysis peaks lag.SEM shows the degree of surface corrosion and morphology changes of flowerpots after treated with SB are markedly greater than that of flowerpots after treated with OE, and the content of carbon and nitrogen significantly drops.These results indicate that the straw/SPI modified urea formaldehyde resin composite flowerpots treated with SB and OE have been degraded in different extents and degradation rate of flowerpots treated with SB is faster than that of flowerpots treated with OE.
Interfacial shear strength and microstructure of carbon nanotube fiber/epoxy composites
REN Yunhui, WANG Yang, ZHANG Boming
2014, 31(5): 1206-1211.
The microstructure and tensile properties of the carbon nanotube fibers were studied, and then the interfacial shear strength and microstructure of the interface between carbon nanotube fibers and epoxy matrix were analyzed.The single fiber fragmentation test was used to test the interfacial shear strength of the carbon nanotube fiber/epoxy composites.Combined with the polarized light micrographs during single fiber fragmentation test, Raman spectroscope images of the composites and scanning electron microscope images of fracture surface, the interface microstructure of the carbon nanotube fiber/epoxy composites was studied.The results show that the interfacial shear strength of the carbon nanotube fiber/epoxy composites is about 14 MPa.During the formation of the interface between carbon nanotube fibers and epoxy matrix, epoxy can permeate into the carbon nanotube fibers and form a compound phase with a certain thickness, and this infiltration process and formation of the compound phase are beneficial to the bonding between the carbon nanotube fibers and matrix.
Modified epoxy with monodispersed solvent-free nano SiO2 fluid
ZHENG Yaping, FAN Wendi, YANG Ruilu, LI Dewang, WU Fei
2014, 31(5): 1212-1218.
The solvent-free nano SiO2 fluid was prepared with nanoparticle SiO2 as the core, N,N-didecyl-N-methyl-N-(3-trimethoxysilylpropyl) ammonium chloride (SID3392) as the necklayer and poly(ethylene glycol) 4-nonylphenyl3-sulfopropyl ether potassium salt (PEGS) as the canopy.The solvent-free nano SiO2 fluid is a Newtonian fluid with low viscosity at room temperature, and its viscosity is 4.3 Pa·s at 26.5 ℃.The mass fraction of SiO2 in the solvent-free nano SiO2 fluid is 13.65%.The solvent-free nano SiO2 fluid is loaded in the epoxy matrix to prepare solvent-free nano SiO2 fluid/epoxy composites.The TEM results confirm that the solvent-free nano SiO2 fluid disperses well in the epoxy matrix.DSC test shows that the solvent-free nano SiO2 fluid can decrease the curing temperature of the epoxy.When the content of solvent-free nano SiO2 fluid in the composites reaches up to 2.5wt%, the impact properties of the epoxy is improved up to 164.7%.The glass transition temperature is improved by 15.4 ℃.The SEM results of fracture surface also confirm that solvent-free nano SiO2 fluid can improve the toughness of epoxy.
Preparation and property of graphene-like/chlorinated polyethylene-polyvinyl chloride composites
LI Kanshe, LI Shuliang, CHEN Chuangqian, KANG Jie
2014, 31(5): 1219-1227.
The expanded graphite (EG) was prepared by microwave irradiation, through solid state shear milling (S3M) with EG, chlorinated polyethylene (CPE) and polyvinyl chloride (PVC), EG-CPE-PVC co-powders were prepared.The co-powders were then mixed homogeneous with PVC, thermal stabilizer and plasticizer.And the graphene-like/CPE-PVC composites were obtained by plastification and molding.Structure and properties of co-powders and composites were characterized by analysis of particle size and distribution, XRD, AFM, SEM and TEM.Results show that S3M can realize pulverizing, dispersion, exfoliation of EG layer and nano-compounding of EG-CPE-PVC.Further more, the addition of CPE realizes the further exfoliation of EG, which makes the EG thickness reaches to 1-3 layers and achieves the goal of transforming EG to graphene.When the EG mass fraction reaches 3%, compared with PVC, the conductivity of graphene-like/CPE-PVC composites shows exponential rise and increases 8 orders of magnitude, while EG mass fraction is over 4%, the conductivity surges again and appears the percolation phenomenon.When the EG mass fraction reaches 5%, the conductivity is up to 0.01 S/m, and the composites show good antistatic property.
Development challenge and opportunity of metal matrix composites
WU Gaohui
2014, 31(5): 1228-1237.
The technical upgrading and transforming of equipments bring a great challenge to the materials investigation.Metal matrix composites (MMCs) show excellent designability to meet this challenge.Using various inorganic nonmetal materials and carbon with different properties, shapes and size as the reinforcements, MMCs can obtain versatile properties and functions, which is the trend and opportunity of the development of MMCs.Several attempts of the author on the research and design of MMCs are briefly introduced, including the design of self-lubricating interface, non-ablation functional materials, materials with constant stiffness at high temperatures, structural and functional integration of geomagnetic shielding materials, solid solution interface with high strength and ductility, to prove that the property and function design of MMCs are valid.
Plasma ablation properties of C/C-Cu composites
CHEN Yingbo, LI Hong, SUN Le, REN Musu, SUN Jinliang, YANG Min
2014, 31(5): 1238-1243.
In order to study the ablation properties of C/C composites influenced by copper infiltration, C/C-Cu composites were prepared by chemical vapor infiltration (CVI) and liquid pressure infiltration processes.The ablation properties of C/C-Cu composites were verified using a plasma ablation device.The results show that the preparation period is significantly shortened with the addition of Cu in C/C composites.Cu uniformly distributes in C/C composites and forms a continuous network structure.The linear ablation rate of C/C-Cu composites is lower than that of C/C composites in the initial stage within 30 s of ablation, because the melting of Cu could absorb a lot of energy and reduce the heating rate.With the ablation time increases, Cu on surface of C/C-Cu composites is blowing away by plasma flames, the sample surface of C/C-Cu composites becomes a lower density porous C/C framework.Therefore, the linear ablation rate of C/C-Cu composites increases violently, and becomes higher than C/C composites', the ablation resistance of C/C-Cu composites decreases evidently.
Preparation of Al2Cu/Al composites by mechanical alloying and spark plasma sintering
PU Shaoling, QIAO Zhijia, MOU Yang, XUE Lihong, YAN Youwei, WU Shusen
2014, 31(5): 1244-1249.
The bulk dense Al2Cu/Al composites were prepared in situ by mechanical alloying (MA) and spark plasma sintering (SPS), using Al and Cu powders as raw materials.The variation of morphology, size and phase structure of powders during the MA process was studied.The microstructure and the mechanical properties of composites after SPS process were investigated.The results show that with the increase of MA time in MA process, some amount of Cu atoms gradually diffuse into Al atomic lattice to form a homogeneous supersaturated Al (Cu) solid solution.During SPS process, Cu atoms precipitate from supersaturated solid solution and then react with Al to form Al2Cu particles uniformly distributed in Al matrix and Al2Cu/Al composites are formed.The density of Al2Cu/Al composites reaches up 98.7%.It exhibits good mechanical properties with high fracture strength (611.3 MPa) and large plastic strain (9.6%) at room temperature.
Preparation of Ag/low molecular weight chitosan composite colloids and their antibacterial activities
WANG Desong, ZHANG Yanyan, AN Jing, LUO Qingzhi, LI Xueyan
2014, 31(5): 1250-1257.
Silver/low molecular weight chitosan(Ag/LMWC) and Ag/LMWC-polypyrrole (PPy) composite colloids were prepared in situ by liquid chemical reduction method.The effects of various process conditions on the size and size distribution of Ag nanoparticles in composite colloids were investigated.And the appropriate synthetic conditions were determined.The component of the composite colloids and the morphological structure of Ag nanoparticles were characterized by UV-Vis, TEM, FTIR and XRD.The results show that the structure of Ag nanoparticles in the composite colloids is face-centered cubic with average particle size about 10-20 nm.The antibacterial tests reveal that the inhibitory of LMWC (viscosity-average molecular weight Mη=4.3×105) is stronger than that of the original chitosan (CS).Moreover, compared with the single LMWC, the antibacterial activities of Ag/LMWC and Ag/LMWC-PPy composite colloids to Escherichia coli and Staphylococcus aureus are very excellent due to the introduction of Ag nanoparticles.
Preparation and properties of TaC/Ti3SiC2 composites
YIN Hongfeng, YANG Yinuo
2014, 31(5): 1258-1263.
TaC/Ti3SiC2 composites were prepared by reactive hot-pressed sintering.Effects of TaC content on the phase composition, microstructure, mechanical properties and oxidation resistance of TaC/Ti3SiC2 composites were investigated by means of X-ray diffraction analysis, scanning electronic microscopy, energy disperse spectroscopy and thermogravimetry.The results show that dense TaC/Ti3SiC2 composites can be prepared by reactive hot-pressed sintering.The main phases are Ti3SiC2 and TaTiC2, minor phase is TiC.The bending strength and fracture toughness of TaC/Ti3SiC2 composites increase firstly and then decrease with TaC content increasing, and reach the maximum value when the content of TaC is 30wt%.The bending strength and fracture toughness of the composite are 404 MPa and 4.10 MPa·m1/2, respectively.The addition of TaC makes TaC/Ti3SiC2 composites possess superior oxidation resistance than Ti3SiC.
Preparation of 3D Cf/SiC anti-high temperature oxidation composites and engineering test of their members
CHEN Zhiyan, YANG Yi, ZOU Shiqin
2014, 31(5): 1264-1269.
3D Cf/SiC anti-high temperature oxidation composites were prepared with low-molecular polycarbosilane (PCS) via precursor infiltration and pyrolysis (PIP) process, chemical vapor deposition (CVD) and powder sintering technology.FTIR, 1H-NMR, gel permeation chromatography (GPC), TGA-DTA, XRD and TEM were used to research the structure and inorganic process of low-molecular weight PCS.Results show that the main structure of PCS may be [(-Si(CH3, H)-CH2-]n, the number average molecular weight of PCS is 420, its ceramic yield is approximately 70%, and PCS translates into β-SiC micro-crystal at 1 200 ℃.3D Cf/SiC composites and their members show good performance of anti-high temperature oxidation.
Effects of SiCW on porous Al2TiO5 SiCW composites by reaction sintering
LI Shuhai, CUI Hongzhi, ZHENG Wenlong, CUI Deyun
2014, 31(5): 1270-1276.
Porous Al2TiO5-SiCw composites were prepared by reaction sintering with γ-AlOOH, TiO2 and SiCw as raw materials.The effects of SiCw on phases, microstructures, porosity and compressive strength of Al2TiO5-SiCw composites were investigated.The results show that the main phases of the reaction products are Al2TiO5, Al6Si2O13, TiC and SiO2.SiCw reacts completely with TiO2 to form TiC and SiO2 because of the fast decomposition of slender SiCw.With the addition of SiCw, the microstructures of Al2TiO5 composites are significantly refined.The fine regular TiC grains and Al6Si2O13 grains which distribute between the grain boundaries of Al2TiO5 can impede the growth of Al2TiO5 grains and improve the compressive strength of the porous Al2TiO5 composites.Moreover, because SiCw changes the packing form of the raw materials and increases the pore size, its porosity increases notably.In addition, some SiO2 existing among the crystalline grains makes the walls of pores denser and increases the compressive strength of Al2TiO5 composites, but the compressive strength will decrease when the content of SiCw is excessive for the appearance of more glass phase.
Influence of pore geometry and porosity on elastic properties of porous materials
SHEN Ming, WEI Dasheng
2014, 31(5): 1277-1283.
The generalized method of cells(GMC)was used to study the influence of pore geometry and porosity on equivalent elastic parameters of porous materials.2D models with square and circular pore geometry and 3D models with cubic and spherical pore geometry were used to simulate porous materials.The results of equivalent elastic parameters under different porosities show that different pore geometry affects the degradation of equivalent elastic parameters with increasing of porosity.The comparison of 2D and 3D models indicates that 2D models would underestimate equivalent elastic parameters of porous materials.Experimental data from existing literature were used to verify the accuracy of GMC prediction, and both are in good agreement.Finally, GMC results were compared with finite element and empirical model to obtain the limitation of GMC model.It can be summarized from all the calculations that GMC has certain accuracy and could be used in engineering analysis.
Out-of-plane compression performance of K cor sandwich structure
DUAN Mufeng, XIAO Jun, LI Yong, SHEN Yufeng
2014, 31(5): 1284-1291.
According to Euler buckling model, the end restraint coefficient μ was characterized to analysis the interfacial interaction of Z-pin in sandwich structures.And it is inversely proportional to the integration degree with factsheets and instability of Z-pin during compressive process.On this basis, compression tests of K/X-cor structures with different Z-pin configurations were performed, and the influence of Z-pin diameters and bending lengths on compression property were studied.With the use of microscopic observation and "mixture law", the enhance efficiency of Z-pin diameters on K-cor and X-cor structures were compared.With the consideration of mass loss, the influence of bending length on strength and stiffness ratio were analyzed.And the semi-analytical formulas for optimal bending length was given.The results reveal that large diameter pin in K-cor structure has better reinforcement efficiency and causes less structural damage compared with X-cor structure.With the increase of bending length, the strength and stiffness ratio increase first and then decrease.There exists the optimum bending length value on different circumstances.
Study on cutting force and machining quality of orbital drilling for CFRP
LIU Gang, ZHANG Heng, WANG Yafei, ZHOU Lan, GAO Kaiye, KE Yinglin, LU Dawei
2014, 31(5): 1292-1299.
Conventional drilling of composites always results in fiber delamination and tear, as a new borehole processing method, orbital drilling has many advantages for composites processing.Considering the practical processing condition in aircraft assembly site, one drilling system including robot as moving carrier, orbital drilling terminal actuators as processing unit and orbital drilling tool was established.The orbital drilling parameters orthogonal test of carbon fiber reinforced plastics (CFRP) was carried out based on this system, and the effects of tool spindle speed, feed per tooth and axial feed depth on cutting force were deeply analyzed.With the defects inspection results, the relationship between cutting force and defects, such as delamination and tear, were investigated.At last, the optimal set of process parameters was obtained.It is verified that thrust force decreases more than 26% after optimation and there are hardly tear and burr formation around the hole exit and entrance, which indicates a better machining quality.
Tensile performance with bending of CFRP tendons used in civil engineering
ZHUGE Ping, ZHANG Zihua, DING Yong, LU Pengzhen
2014, 31(5): 1300-1305.
For the tensile performance with bending of carbon fiber reinforced polymer (CFRP) tendons in the process of civil engineering, a new tensile strength test method was developed for CFRP tendons, and the actual tensile strength with bending of CFRP tendons was tested through model testing corresponding to several bending angles.The tensile strength reduction factors of CFRP tendon used for civil engineering corresponding to bending states were obtained, and an empirical formula of the reduction factor was fitted at last.Results show that tensile strength of CFRP tendons tested by the new method is more than 9% higher than the results based on ordinary method.The empirical formula presented in the paper can effectively predict the tensile strength reduction factor with bending.When the bending angle is 3°, the tensile strength with bending drops by 18.9%.Therefore, even if a small bending angle exists, the reduction of tensile strength should not be ignored during the application.
Impact properties of warp knitted spacer fabric reinforced flexible composites
LU Zhenqian, WU Liwei, SUN Baozhong, GU Bohong
2014, 31(5): 1306-1311.
According to the problem of rigid and restricted physical activity of the personnel protection material, two kinds of flexible composites with shear thickening fluid (STF) and silicon rubber filling warp knitted spacer fabric (WKSF) were designed, and the impact properties of composites were studied.The WKSF has the upper and lower outer layers and spacer layer, the spacer layer was composed of spacer yarns.STF and the silicon rubber were filled into the spacer layer.STF was composed of nano-SiO2 suspended in polyethylene glycol (PEG) liquid, and silicon rubber was composed of silicone component and curing agent mixture components.The rheometrics was used to test the rheological behaviors of STF, and Instron drop tower impact tester was used to test the impact properties of the WKSF and the flexible composites.Results indicate that STF shows shear thickening transition after reaching the critical shear rate.The impact process of the pure fabric can be divided into three stages of elastic stage, plateau stage and densification stage.There is a plateau stage for the WKSF.The impact processes of the two kinds of flexible composites are different from pure fabric, the force-displacement curves are in linear way.The silicon rubber filled composites show higher stiffness and no strain rate effect.The STF filled composites show higher energy absorption capacity and obvious strain rate effect.
Manufacturing and testing verification for high temperature composite rudder
LUO Chuyang, WU Cuisheng, WEI Zhongwei, HE Hui, CAI Peipei, ZHAO Rong
2014, 31(5): 1312-1320.
The high temperature composite rudder consisted of skin and frame structure was designed and fabricated by press molding process.Then the test of natural modal of composite rudder under free and fixed state was conducted.Finally, the static strength test under bending load was completed.The finite element (FE) model for modal analysis of rudder was generated by using 3D solid element.The calculations of natural modal are consistent well with the test, demonstrating the validity of the FE model proposed in the paper.Based on this FE model, the failure mechanism of rudder under bending load was investigated.The test results show that debonding of resin initially arises at resin connected zone of the rudder, which is followed by inter-laminar delamination propagating along the interface between the composite skin and titanium alloy frame, and finally causes the failure of the rudder.The FE analysis results indicate that the mass distribution of sensors has significant effect on the frequency but slight effect on the mode.The stress analysis results show that the tensile stress causes the debonding of resin at the resin connected zone.The failure location of the rudder predicted by FE method agrees well with the test results.
Mechanical performance of Lyocell short fiber reinforced pneumatic wheel substrate
JI Shiming, ZHENG Mengxiang, JIN Mingsheng, ZHANG Li, ZENG Xi, LI Zhi'an, LI Xiao
2014, 31(5): 1321-1329.
In order to achieve efficient finishing processing of the mould free-form surface with high hardness and high abrasion resistance, a new method of Lyocell short fiber reinforced pneumatic wheel substrate was put forward, and the theory model of Lyocell short fiber reinforced rubber composites and the structure model of pneumatic wheel were analyzed.Tensile test of composite samples were carried out by Instron tensile testing machine and the ultimate strength was studied through error analysis.The test values and theoretical values of elastic modulus were contrasted and analyzed, and proved that the shear-lag model can predict the elastic modulus of pneumatic wheel substrate accurately.The pressure changing and the strain range of the pneumatic wheel with different short fiber contents during finishing process were simulated and analyzed, and the feasibility of short fiber reinforced pneumatic wheel substrate was verified.Ideal contact angle was obtained by analyzing the stress level and processing area when convex surface contacts with pneumatic wheel in different angles.The material removal tests of high hardness convex surface show the advisability of the theory of short fiber reinforced pneumatic wheel substrate and the simulation of pneumatic wheel test.
Theoretical prediction of elastic modulus of interpenetrating phase composites with open-cell foam skeleton
LU Zixing, XIE Fan, WANG Jianyue
2014, 31(5): 1330-1336.
Based on the microstructure of the interpenetrating phase composites (IPC) with open-cell foam skeleton, a tetrakaidecahedron mechanical model with elastic foundation beam was proposed, and the prediction formula of elastic modulus was deduced using the minimum potential energy principle.The example analysis of experimental material parameters given by the literature was conducted.The results show that the present results agree well with the experimental results, which confirms the validity of this model.The influences of the volume fraction of different skeleton materials and the strut cross-section shape on the elastic modulus of IPC were discussed furthermore.The present semi-empiric theoretical model provides a new way for characterizing the elastic properties of IPC with open-cell foam skeleton commendably and a basis for the prediction of strength and thermo-physical properties of IPC.
Dynamic compressive properties of 2D C/SiC composites' Z direction in low temperature
YE Longhai, DENG Qiong, TANG Zhongbin
2014, 31(5): 1337-1342.
The tests for dynamic compressive properties of 2D-C/SiC composites' Z -direction were performed in low temperature circumstance by using the SHPB system.The low temperature was made by controlling the ratio of coefficients between alcohol and liquid nitrogen to be obtained.The key issue to apply high strain rates to the 2D-C/SiC was to design the geometrical size of the shaper in the SHPB system.The test results of the dynamic loading were successful.Results indicate that 2D-C/SiC composite material show pseudo-plastic behavior at dynamic loading conditions in low temperature circumstance owing to a lot of internal microcracks in the initial composite material, so it does not exhibit typical brittle failure when the composites were destroyed, but it shows the strain softening phenomenon significantly when the stress reaches the compressive strength of the composites, and the specimens have experienced a large deformation before destruction.As the temperature decreases, the dynamic compressive strength of composites' Z -direction increases, but the failure strain decreases.At low temperatures, the interface between the internal fiber and matrix in the 2D-C/SiC composites enhances the binding force of the interface, and the more strength interfacial force can lead to a more strength high compression.
Load-bearing capacity analysis of composite case structure of solid rocket motor
HOU Xiao, QIN Yi, DING Wenhui
2014, 31(5): 1343-1349.
In order to improve the external load-bearing capacity of solid rocket motor (SRM), the failure mechanism of the composite case structure was studied, and the form of improved structure for composite case structure was put forward.The composite case structure was improved by increasing axial stiffness and lateral bending stiffness of the exterior layer.The axial deformations of interior and exterior layers were in concordance, and the axial load-bearing capacity distribution of exterior to interior layers was improved.The load-bearing capacity of the improved composite case structure was largely increased by about 124% and the structural mass was only increased by less than 10%.Results indicate that the stiffness matching design of the lap-joint interior and exterior layers is the key factor that affects the load-bearing capacity of the composite case structure of SRM.The composite case structure of SRM has the load-bearing capacity well only on condition of coordination of the stiffness match and deformation in lap-joint interior and exterior layers.
Electronic structure of phase interface diffusion reaction layer of Ti-Al laminar composites
HAN Zhaohui, ZHOU Shenggang, ZHU Peixian, GUO Jiaxin
2014, 31(5): 1350-1356.
Ti-Al laminar composites were prepared by hot-pressing diffusion bonding method.Hot-pressing diffusion bonding was conducted under different bonding temperature conditions, and the reaction products and electronic structure features of the diffusion reaction layer of Ti-Al diffusion couple were texted by SEM, EDS, XRD and first-principle based on density functional theory (DFT).The results show that when the bonding temperature is not less than 560 ℃, the main reaction products of the phase interface diffusion reaction layer of Ti-Al diffusion couple are intermetallic compound Al3Ti.The pseudo gap of total density of state (TDOS) of Al3Ti is 2.8 eV, and the pseudo gap of partial density of state (PDOS) of adjacent Al and Ti atom is also 2.8 eV, the covalent bond of intermetallic compound Al3Ti is less, but the metal bond is more.Therefore, Al3Ti shows more metal characteristics, and it has good electrical conductivity, which is a basis as a novel electrode material for Ti-Al laminar composites.
Analytical solutions of mode-III lip-shape crack in piezoelectric composites
YU Jing, GUO Junhong, XING Yongming
2014, 31(5): 1357-1363.
Based on the complex variable function method and the technique of conformal mapping, an anti-plane problem of lip-shape crack in piezoelectric composites was investigated under the anti-plane loading at infinity and in-plane electric loads.By using the residue theorem and Cauchy integral formula, the analytical expressions of the field intensity factors and the mechanical strain energy release rate are obtained with the assumption that the crack surfaces were electrically impermeable and electrically permeable.When the height of lip-shape crack approaches to zero, the analytical solutions of an infinitely large piezoelectric solid with a Griffith crack was obtained.Ignoring the effect of the electric field the present results can be reduced to the well-known solutions of classic material.The numerical examples are provided to show the influences of geometrical parameters and applied mechanical/electric loads on the mechanical strain energy release rate.The results indicate that an increase of the height of the lip-shape crack will retard the crack propagation and mechanical loads always accelerate the crack propagation.The influences of electric loads on the crack propagation was about boundary conditions of the lip-shape crack.
First principle calculation of configuration evolution of Ti-Si-N islands affected by nitrogen particles
LIU Xuejie, WEI Huai, LU Feng, WU Shuai, REN Yuan, YIN Yongjie, ZHANG Suhui
2014, 31(5): 1364-1368.
In order to study the interface formation in the growth process of Ti-Si-N films, the first principle calculations were used to investigate the total energies and adsorption energies of 3N-2Ti-1Si, 4N-1Ti-1Si and 4N-2Ti-1Si island configurations on the TiN (001) surface.And the migration activation energies of these islands' configuration evolutions were investigated by nudged elastic band (NEB) method.The calculations results show that the configurations of Ti particle inside the islands are generally stable structures with low energy, which are formed by the separation of SiN phase from TiN phase.Among the configuration evolutions of 3N-2Ti-1Si, 4N-1Ti-1Si and 4N-2Ti-1Si islands, activation energy of 3N-2Ti-1Si island evolution is relative low, and it is easier to realize configuration evolution.With the increasing of the deposition ratio of N particles moderately, the activation energies of configuration evolutions decrease, which promotes the separation of SiN and TiN phase.When the proportion of N and Ti is 3:2, the interface is most likely to form.
Omni-directional impact localization method on composite structure using plum blossom array
ZHONG Yongteng, YUAN Shenfang, QIU Lei
2014, 31(5): 1369-1374.
Aiming at the problem of blind area using uniform linear array, impact localization method of 2D multiple signal classification (2D-MUSIC) using plum blossom array was investigated.The layout of plum blossom array consisted of one sensor in the center and M sensors uniformly spaced on circle with the radius R .First, the velocity of Lamb wave propagating was estimated by the time information of impact signal acquired by reference array element PZT0 and array element PZT1 which received impact signal firstly.Second, near-field 2D-MUSIC algorithm was applied to localize the distance and direction of impact source simultaneously.Finally, the experiment on the glass fiber composite laminates was established to verify the validity of the impact localization method.Experimental results show that plum blossom array based impact localization method could localize impact source from 0° to 360° accurately, whose maximum error of distance and direction error is 2.2 cm and 5° respectively.
Modeling and simulation of milling forces in side milling multi-layer CFRP with multitooth cutter
HAN Shengchao, CHEN Yan, XU Jiuhua, FU Yucan, ZHOU Jingwen
2014, 31(5): 1375-1381.
The milling machining process of carbon fiber reinforced plastic (CFRP) could generate undesirable defects such as delamination and burr under the cutting forces, due to low bonding strength between the layers.Therefore, the prediction and control of cutting forces can substantially improve the machining quality.The milling forces in side milling multi-layer CFRP with multitooth cutter were modeled and simulated by using an instantaneous rigid force model.And the influence of special tool geometry of multitooth cutter on milling forces was analyzed.Milling tests of unidirectional CFRP in typical directions (45°, 0°, -45°, 90°) were carried out at the same cutting speed but with different feed speeds.Thus milling force coefficients of each unidirectional CFRP were also calculated by the test data of cutting force.Based on vector superposition principle, the simplified expression for milling force coefficients of multi-directional CFRP was obtained.Finally, the caculated results were substituted into milling forces model and the simulated value of milling force at each moment were obtained.Furthermore, verification test of milling multi-directional CFRP was carried out under the same machining condition.The results show that the model can well predict the milling force that the maximum relative error is less than 9% and average relative error is less than 5%.Thus, the model can provide a theoretical basis for cutting parameter optimization and tool geometry optimization.