COMPOSITES SCIENCE AND ENGINEERING

ANALYSIS ON KEY FACTORS FOR NUMERICAL SIMULATION OF AXIAL COMPRESSION PROCESS OF PASSIVE CONFINED CONCRETE COLUMNS

KANG Chao-yi, OUYANG Li-jun, DING Bin, ZHEN Bin

2018, 0(11): 5-14.

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Axial compression failure of the fiber reinforced composite confined concrete columns involves issues of passive confined concrete and nonlinear problems. In order to further study axial compression failure process of the FRP-confined concrete columns, based on numerical simulation and analysis of existing experimental data, six key factors affecting numerical analysis results of FRP-confined concrete columns during axial compression are presented, including peak stress models and peak strain models for concrete under axial compression and active constant confining pressure, dilation function for concrete under passive confinement, concrete constitutive model, FRP-concrete contact types, types of boundary modeling and termination conditions for calculation. Applicability and limitation of each key factor in numerical simulation of axial compression process of FRP-confined concrete columns are pointed out.

MICROSTRUCTURE MECHANISM OF CARBON NANOTUBES TO IMPROVE ELASTIC MODULUS OF EPOXY RESIN:A MOLECULAR DYNAMICS SIMULATION AND EXPERIMENTAL VERIFICATION

ZHANG Wen-qing, LI Hao, SUI Gang

2018, 0(11): 15-20.

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According to the corresponding relationships between microstructure parameter and macro performance in high-low temperature of polymer composites, the predication of the structure-performance relationship need to be concerned in engineering application. In this paper, the effects of single-walled carbon nanotubes (SWCNTs) on elastic modulus of epoxy resin matrix from low temperature (100 K) until their T_g were investigated through molecular dynamics simulation. Then mechanisms of microstructure parameter were investigated in depth. The results show that with the increase of temperature, the ever-reduced cohesive energy density (E_coh) and ever-increasing free volume fraction (V_f) result in the decreasing of elastic modulus. Molecular simulation reveales that E_coh and radial distribution function (F_radial) of epoxy matrix are significantly increased as the addition of SWCNTs. Compared to the neat epoxy matrix, the inhibitory effect of SWCNT on the ascent of the V_f of the matrix at high temperatures was also more pronounced with increasing temperature. Elastic modulus in experiments verifies simulation results, which proves that molecular simulation was reliability to predict the macroscopic properties of polymer composites.

STRAIN HISTORY IN FAST AND CONVENTIONAL CURING EPOXY MATRIX COMPOSITES INVESTIGATED BY FBGs

QI Yi-xin, JU Su, JIANG Da-zhi

2018, 0(11): 21-26.

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Cure residual strain, which is generated by curing shrinkage of resin and mismatch of the coefficient of thermal expansion of the resin and the fiber in curing process of fiber reinforced resin matrix composite, is essential to allow better design and control of properties of the resin matrix composite. In this paper, nondestructive and destructive testing of the cure residual strain were introduced. Fiber Bragg grating sensors (FBGs) were located in ten-ply unidirectional carbon-fiber fabrics reinforced fast and conventional curing epoxy matrix composites manufactured by wet lay-up to measure strain history. The result show that the peak temperature due to curing exothermal reaction was 133.7 ℃ in the 5th ply in the fast curing composite when the cure temperature profile was settled at 80 ℃, while it was 106.3 ℃ in the conventional curing composite. Cure residual strain in the 5th ply in the fast and conventional curing composites were -4074.7 με and -2660.8 με, respectively.

EFFECT OF ALCOHOLS ON THE RHEOLOGICAL AND CURING BEHAVIOR OF EPOXY RESIN SYSTEM

LI Zhao-chen, ZHANG Wen-qing, YANG Xiao-ping, SUI Gang

2018, 0(11): 27-30.

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In order to study the effect of micromolecule alcohol on the epoxy/amine system, DSC, rheological and mechanics testing of the epoxy/amine system, epoxy/amine/micromolecule alcohol system, and epoxy/amine/imidazole/small molecule alcohol system were studied in this experiment. The overall performance of the three systems was compared. It is found that the addition of the micromolecular alcohol C₄H₁₀O₂ as an functional additive into the epoxy resin system has a significant promoting effect. In the presence of the imidazole accelerator 2-ethyl-4-methyl imidazole, the promotion effect of C₄H₁₀O₂ is better, and both two systems have good mechanical properties.

STUDY OF MECHANICAL PROPERTIES AND CURING KINETICS OF IPN SYSTEM BASED ON EPOXY RESIN/BISPHENOL A-BASED BENZOXAZINE RESIN

LV Jun-wei, WANG Bin, LI Hui

2018, 0(11): 31-36.

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This article applied Interpenetrating Polymer Network(IPN)technology to prepare complete epoxy resin/benzoxazine IPN system. The obtained composite material were processed to testing specimens and the mechanical properties were measured. Differential scanning calorimeter (DSC) was used to characterize the thermodynamic behaviors of the composite. The data obtained from DSC results was used in Kissinger, Ozawa and Crane equation to calculate the average activation energy, reaction order in the curing reaction of the composite. Research results showed that the toughness of the composite increased with the adding of epoxy resin. When the content of epoxy resin increased to 40%, the bending strength and bending modulus were changed to 98.2 MPa and 4.04 MPa, respectively. Compared with the bending strength and bending modulus of pure polybenzoxazine with the value of 79.31 MPa and 4.71 MPa, respectively, the IPN system showed a tendency to change from hard to soft. The analysis of curing kinetics indicated that the curing reaction had much lower apparent activation energy than before, and it was always a simple first-order reaction.

FIBERGLASS HOLLOW SANDWICH PIPE AND ANALYSIS OF MECHANICAL PROPERTIES

ZHU Yang-xuan, CHEN Jian-zhong, LV Yong, LIU Ju-fang

2018, 0(11): 37-42.

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In order to further improve the performance of FRP pipe and reduce the cost, fiberglass hollow sandwich pipe was designed. Compared with traditional fiberglass pipe, the new fiberglass hollow sandwich pipe has many advantages, such as light weight, low cost, and good impact resistance under the same ring stiffness. The strength and ring stiffness of the hollow sandwich pipe were analyzed using the theory of mechanics of materials and composite materials. The Euler formula was used to analyze the stability of the core material. At the same time, ANSYS software was used to establish the finite element model of the pipe ring and cell unit, and the strength, ring stiffness and core material stability of the pipe were analyzed. The results of the theoretical calculation and the finite element analysis are in close agreement, which verify the reliability of the theoretical calculation methods of strength, ring stiffness and stability.

STUDY ON PULL-OUT PERFORMANCE OF BOLTED JOINTS ON PULTRUDED FRP WITH PUNCHING HOLE

MA Zhi-zhou, QI Yu-jun, LIU Wei-qing

2018, 0(11): 43-49.

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In this paper, the pull-out performance of pultruded FRP (PFRP) with punching hole were studied. Parameters such as different resin matrix and fiber directions were investigated. The results indicate that the pull-out performance of bolted joints of polyurethane-based PFRP is better than the unsaturated polyester resin-based ones. And, the bearing capacity of the bolted joint on multi axial PFRP is better than the specimens with uniaxial fibers for the reason that multi axial fiber can effectively prevent the PFRP from longitudinal splitting. To numerically investigate the mechanical behavior of PFRP bolted joints, a progressive damage analysis material model integrating Hashin failure criteria was used. The 3D finite element models were established in Abaqus.

STUDY ON FIBER DISTRIBUTION IN INJECTION-MOLDED LGF/PA COMPOSITE WHEEL

ZHU Han-rui, GU Yi-zhuo, MENG Qing-yu, ZHANG Zuo-guang

2018, 0(11): 50-57.

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In this study, polyamide 6,6 (PA66)with 50wt% of long glass fibers (LFT)was processed using injection molding to prepare composite plate and composite wheel. Glass fiber content, glass fiber length and glass fiber orientation in the plate and the wheel were analyzed and compared to provide data for the development of composite wheel. Moreover, through wheel radial fatigue test, it is found that as the length of fiber in wheel increases, radial fatigue performance of the wheel is significantly improved.

CRASHWORTHINESS ANALYSIS OF CARBON FIBER AUTOMOBILE B-PILLAR BASED ON EQUAL STIFFNESS PRINCIPLE

SUN Dong-ming, MA Qi-hua,SUN Jia-rui

2018, 0(11): 58-63.

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The use of carbon fiber reinforced composites (CFRP) with higher energy absorption ratio to replace the original metal automobile B-pillar is a useful exploration to realize the lightweight of the whole vehicle, and is of great significance for the replacement of automobile structural parts. The carbon fiber reinforced composite material B-pillar was designed based on the principle of equal stiffness, and the finite element collision model of B-pillar and moving column was established. By comparing and analyzing the intrusion amount and the intrusion speed difference of the moving column at different impact points of the B-pillar at the impact velocity of 7.2 km/h. The results show that compared with the original high-strength steel B-pillar, the carbon fiber composite B-pillar has less deformation at low speed impact, more energy absorption and better crashworthiness. At the same time, compared with the high-strength steel B-pillar, a mass reduction of 26.27% is realized, which could better meet the automotive B-pillar lightweight requirements.

MODELING STUDY ON THERMOMECHANICAL PROPERTIES OF WOVEN QUARTZ/PHENOLIC COMPOSITES

YANG Tao, DING Jie, LUO Hai-tao, HUANG Zhi-xiong

2018, 0(11): 64-67.

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In this paper, 2.5D quartz fiber/phenolic composites were thermally treated at 800 ℃ for different time. The longest thermal treatment time was 20 min. Then the residual mechanical properties were tested. Mouritz-Mathys model was used to calculate the theoretical values after thermal treatment. The results show that the mechanical properties of the composites decrease sharply with the increase of the thermal treatment time. In all tests, the consistency between measurement and theoretical residual mechanical properties was less than 15%. Using this model, the variation of mechanical properties and time after thermal treatment can be obtained quickly.

PERFORMANCE OF FRP HOLLOW BRIDGE DECK AFTER FATIGUE LOADING AND NATURAL AGING

WU Yu-wei, FENG Peng, LIU Xing

2018, 0(11): 68-72.

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This paper presents results from an experimental study of an innovative Glass Fiber Reinforced Polymer (GFRP) bridge deck composed of GFRP pultruded panels, GFRP filament-wound square core-tubes, and Outside Filament-wound Reinforcement (OFR). One specimen was tested by four-point bending test and point load test after fatigue loading for 2000000 times and natural aging for 10 years. Bending stiffness and shear stiffness were analyzed in four-bending test. Point load test simulated vehicle load. Failure mode and ultimate strength were tested in point load test. Specimen was not damaged in four point bending test, during which it remained intact and elastic. Ultimate strength of point load test was 764.57 kN. The failure mode was punching damage near load point. The test results revealed that the long-term performance of GFRP bridge deck was able to satisfy the engineering requirement. Furthermore, GFRP bridge deck had excellent durability.

STUDY ON THE CERAMICS OF POLY (M-DIETHYNYLBENZENE- METHYLSILANE-PHENYLSILANE)

LU Dan, ZHOU Quan, GENG Jie, SONG Ning

2018, 0(11): 73-77.

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In this paper, the cured poly (m-diethynylbenzene-methylsilane-phenylsilane) resin (PDMP) was used to study cracking and ceramics under high temperature. The composition, structure and morphology of pyrolysis products were characterized by X-ray diffraction (XRD), energy dispersive spectroscopy (EDS) and scanning electron microscope (SEM). The results showed that many bulging balls were found on the surface of the pyrolysis products and distributed uniformly. It showed that ceramic of SiC structure crystals was formed, and the ceramic yield of the cured resin was 80.83%.

FRP DURABILITY EVALUATION METHOD BASED ON ELASTIC MODULUS

GUO Ao, YANG Yong-xin, JIA Bin, YU Jian-wei

2018, 0(11): 78-82.

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In order to study the durability of FRP, the non-failure test method is presented. The modulus of elasticity was used as the durability evaluation index, and two methods of the non-failure test and the failure test were tested and analyzed. The factors influencing FRP performance test results were discussed. Elastic modulus tests of 20 non-failure test specimens and 21 failure test specimens at different aging times were completed. The experimental data indicate that there is a significant positive correlation between the elastic modulus of the non-failure test and the failure test. This correlation can convert the failure test data into the data of the non-failure test and find the same benchmark. Similar relationship exists between the non-failure test and the failure test data under different preparation processes and different test conditions. The durability of FRP has the same benchmark, and it is more reasonable and scientific to evaluate the durability of FRP by elastic modulus.

INFLUENCE OF LAMINATED STRUCTURE(THICKNESS) ON GLASS FIBER REINFORCED PLASTIC FLUE GAS PIPE′S TENSILE PROPERTIES

WANG Jun, LI Chen-song, WANG Tao, HOU Rui-gang

2018, 0(11): 83-86.

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Fiber reinforced resin matrix composites are highly configurable. In this paper, the influence of the glass fiber fabric/vinyl ester resin composite laminate structure on the tensile properties of the fiber reinforced plastic exhaust cylinder of coal-fired power plants was studied. A variety of ply structures were designed, and the plywood was prepared by a winding forming method. The tensile properties were tested according to the corresponding national standards. The results show that the tensile properties of the laminate are related to the basic layup structure and the number of cycles (thickness). When designing the glass fiber reinforced plastic exhaust pipe, the mechanical properties and comprehensive cost should be considered comprehensively.

TENSILE PROPERTIES OF CARBON FIBER WEFT INLAY KNITTED FABRIC REINFORCED COMPOSITES

LIANG Jia-yu, QIN Zhi-gang

2018, 0(11): 87-91.

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The tensile properties of epoxy composites reinforced with carbon fiber weft inlay knitted fabrics were studied. In the experiment, the reinforcement ground structure is composed of double rib. By changing the number of lining yarn and the depth of the yarn in the weft lining, weft inlay knitted fabric with 4 different structures and parameters is knitted. Finally, the composite plate is prepared by hydraulic technology. The tensile strength and circle strength of carbon fiber were tested by universal strength testing machine. The tensile properties of composites at 0 degrees, 45 degrees and 90 degrees were tested. The results show that the strength of the composite material and the tensile modulus of elasticity are obviously enhanced in the direction of 90 degree after being inserted into the weft yarn, and the tensile curve is linear. The strength of 0 and 45 directions is decreased slightly, but the effect is not obvious. Moreover, as compared to the strength of composite material with different weft lining yarn numbers, the more the number of weft yarns inserted per unit length, the greater the strength at the 90 degree direction. The influence of different sinking depth on the properties of the composite is compared. The strength of the plate in the direction of 45 and 90 degree is reduced, and the strength in the direction of 0 degree increases with the sinking depth depter.

STRUCTURE SCHEME OF THE ELLIPSOIDAL SHELL ADVANCED COMPOSITE REAR PRESSURE BULKHEAD

CAI Qi-yang, ZHOU Shi-gang

2018, 0(11): 92-98.

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In this paper, nonlinear finite element method is used to analyze the buckling and post-buckling behaviors of different positions and regions of advanced composite ellipsoidal shells under uniform external pressure.The effects of the base diameter, radius of curvature, boundary conditions and bending stiffness on the buckling and post-buckling behaviors were investigated. The range of different shell positions with upper critical load and lower critical load during buckling is determined. Base on this, a grid stiffened structure scheme of the composite rear pressure bulkhead was proposed and optimized. Finally, a method for the reinforcement scheme of the ellipsoidal shell grid structure is determined, and the corresponding grid structure ellipsoid shell has a higher lower critical load. The grid structure determining method thus formed can also be applied to the determination of the reinforcement scheme of the shell-like grid structure.

THE PROPERTIES OF AMPHIPHILIC BLOCK COPOLYMER POLYCAPROLACTONE- POLYDIMETHYLSILOXANE-POLYCAPROLACTONE TOUGHENED CYANATE RESIN

LIU Qi, ZHOU Quan, SONG Ning, NI Li-zhong

2018, 0(11): 99-103.

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By the ring-opening polymerization of caprolactone, PCL-b-PDMS-b-PCL triblock amphiphilic polymer was obtained and added into the cyanate ester thermosetting resin, producing a mixture of self-assembled nanostructures. In the ester resin prepolymer, a cyanate resin/block modification mixture having a nanocomposite structure is obtained. The results of cyanate resin/block system SAXS and TEM confirm that the 50 nm~60 nm nanostructures were achieved by CE/PCL-b-PDMS-b-PCL system. The system also has a diverse morphology from particles to worm-like structures as the block polymer content increases. Meanwhile, the average distance between neighboring microdomains increases. The mechanism of the the CE/PCL-PDMS-PCL is self-assembling. By non-isothermal DSC curing and critical stress intensity factor (K_IC) value, the block-modified resin is 25 ℃~50 ℃ ahead of the exothermic peak of the unmodified CE resin, indicating that the reactivity of blends system is improved. The K_IC of the 20 wt% block content of CE/PCL-b-PDMS-b-PCL was 0.65, which was 97% higher than that of the unmodified CE system, demonstrating that the fracture toughness of the block-modified resin is improved.

STUDY IN PROGRESS OF INTERFACIALLY ENHANCEMENT OF PBO/EPOXY RESIN COMPOSITE

ZHANG Zhen, WANG Bin, LV Jun-wei, LI Hui

2018, 0(11): 104-108.

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This article reviews the study of interfacially enhancement of PBO/epoxy composite based on increasing the compatibility between PBO fiber and eposy resin. We analyzed the advantages and shortcomings of mentioned modification methods classfied by designing high energy surface or introducing plenty of chemical active spots. Finally, we did an outlook of this research direction.

RESEARCH PROGRESS OF ANTI-LEAKAGE OF CARBON FIBER REINFORCED RESIN COMPOSITES AT CRYOGENIC TANKS

CHEN Zhen-guo, JIAO Wei-cheng, YAN Mei-ling, YANG Fan

2018, 0(11): 109-116.

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Carbon fiber-reinforced resin matrix composites (CFRP) are lightweight, high-strength and can be applied to space vehicle tanks to significantly reduce the structural weight and geometric volume of the propulsion system. However, the leakage of CFRP tanks has seriously affected the tank application. This article first introduced the metal-lined CFRP tank, and then reviewed the research progress of anti-leakage of the non-metal-lined CFRP cryogenic tank, including the leakage mechanism, anti-leakage design, leakage detection methods, etc. The anti-leakage design methods for nanomaterial doping enhancement, resin matrix modification and toughening, and layered structure optimization design at home and abroad were summarized, and the research direction of non-metal-lined CFRP cryogenic tank anti-leakage research was prospected.

RESEARCH PROGRESS ON TRIAXIAL WOVEN FABRICS AND ITS COMPOSITES

RAO Yun-fei, ZHANG Chen, WANG Qing-tao, LI Wei

2018, 0(11): 117-121.

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A brief introduction on triaxial woven fabric and its composites was made in the paper, which focuses on the structure, fabrication, properties and simulation of triaxial woven fabrics and its composites. The mechanical properties of triaxial woven fabric and its composites were analyzed and summarized. Simulation models of triaxial woven fabric and its composites were highlighted. At last, the research trends and prospect of triaxial woven fabric and its composites were discussed.

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