COMPOSITES SCIENCE AND ENGINEERING

EXPERIMENTAL INVESTIGATION ON FLEXURAL BEHAVIOR OF REINFORCED FOAMSANDWICH BEAMS WITH TWO-WAY LATTICE-WEB

CHEN Ji-ye, FANG Hai, ZHUANG Yong, LIU Wei-qing

2017, 0(10): 5-10.

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Composite sandwich structure has the characteristics of high specific strength, high specific stiffness, good designability and corrosion resistance etc. Two-way lattice-web reinforced foam core sandwich beams are prepared through vacuum assisted resin infusion, with polyurethane foam as the core, Glass Fiber Reinforced Polymer (GFRP) as the panels and lattice webs. In order to study the failure mode and mechanism, a series of three point bending tests were performed on the common foam sandwich beams and the lattice-web reinforced foam sandwich beams with different web height and web space. Based on the equivalent cross model of foam filled with rectangular honeycomb shape, the bending stiffness and the deflection of the specimens are predicted, and the calculated values agree well with the experimental values.

NUMERICAL SIMULATION ON THE EFFECT OF INTERFACE PERMEABILITY ONTHE FLOW AND COMPACTION OF THICK COMPOSITE LAMINATES

QIAO Yan-liang, ZHANG Mei, ZHANG Jiang-tao, LIU Li-sheng

2017, 0(10): 11-16.

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Based on the effective stress theory and Darcy′s flow theory, a multi-field coupled numerical model is developed to simulate the flow and compaction of thick composite laminates. The model is verified by comparing the prediction with the experiment result of a thick unidirectional laminate. A thick cross ply composite laminate model with an interface layer is built, and is used to analyze the effect of the interface permeability on the flow and compaction process of the thick cross ply composite laminate. The calculating results of the thick cross ply composite laminate model are compared with those of the unidirectional laminate model with the same thickness. The results show that, the thick cross ply composite laminate with high interface permeability has the similar flow and compaction process with that of the thick unidirectional laminate. An interface layer with low permeability impedes the flow of the resin in the interior of the thick cross ply composite laminate, and causes a slow increase of fiber content with curing time as compared with that in a unidirectional laminate. The effect of interface layer with low permeability is more obvious in the interior of the thick cross ply composite laminate, and causes a jump in the distribution of fiber content across the interface layer at the end of the flow and compaction process.

THE INFLUENCE OF SPECIAL MICRO-CARBON FIBER COMPOSITEMATERIAL ON MECHANICAL PROPERTIES OF CONCRETE

DAI Hui-ping, CHEN Qiu-fei, GUO Peng-zong, WU Hao

2017, 0(10): 17-22.

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This article studies the influence of concrete′s mechanical properties of four kind of special micro-carbon fiber composites under rod, flake(wide and narrow), wave and so on by axis tensile test. Experiments show that the addition of carbon fiber composite materials can be effective and largely improve the tensile strength, strength and flexural strength of concrete. The tensile strength of special micro-carbon fiber composite materials can maximum increase 64% compared with the reference concrete. The grades of reinforced concrete can be increased from C40~C45 to C60; As the increase of the sum of specific surface area of carbon fiber composites, the strength and flexural strength of concrete can both maximum increase 45.6% and 50.6% respectively. Besides, flake carbon fiber concrete is more likely to be broken than wavy under the same size and specific surface area. All of above prove PAN-based carbon fiber composite materials have a better increase of concrete′s toughness.

MECHANICAL PROPERTIES OF CARBON FIBER REINFORCED PLASTIC STRUCTURESWITH DIFFERENT FORMING PROCESS

WU Wen-yan, LIU Qiang, WU Liang-jun

2017, 0(10): 23-28.

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Two carbon fiber reinforced plastic (CFRP) structures were prepared by hand lay-up process, vacuum bag pressure process and compression molding process. The effects of forming process on the mechanical properties and forming quality of CFRP structures were investigated based on tests and cross-section morphology observation. For the application of CFRP in the electric vehicle, two typical kinds of structures, laminated plates and double-cap tubes, were designed and prepared by different process. The tensile and three point bending tests were carried out, and the mechanical properties, surface qualities, microstructures and failure modes of structures were compared. The results indicate that the composite structures made by compression molding process have better quality with fewer bubbles and smaller porosity. The tensile strength of CFRP laminated plate made by compression molding process is about 14.39% higher than hand lay-up laminated plate. The bending strength of tubes is twice of hand lay-up tubes, and is 47.58% higher than vacuum bag pressure tubes. It is concluded that the CFRP structures prepared via the compressing molding process have higher mechanical properties and better consistency than the other process, it is more suitable for the application on the electric vehicle and other lightweight structures.

THE STRUCTURAL DESIGN OF NANCHANG BRIDGE PIER ANTI-FLOATING PIPE SECTIONIMPACT COMPOSITES ANTI-COLLISION SYSTEM

DENG Guo-liang, XING Yong-hui, HUA Peng, ZHU Lu

2017, 0(10): 29-33.

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In this paper, the Nanchang Honggu tunnel section of the pipe floating near the bridge pier, through the Nanchang Bridge 17#, 18# pier in the impact by the floating pipe, calculate the internal force generated at the most dangerous cross section of the pier. According to the "Code for Design of Highway Reinforced Concrete and Prestressed Concrete-Bridges and Culverts" to calculate the pier can withstand the maximum level of impact force. Using the finite element software ANSYS/LS-DYNA, considering the influence of impact angle and the water level, the impact force of the floating pipe hit the pier was analyzed and the anti-collision ability of the pier was evaluated according to the simulation results. Based on the characteristics of the waters of the bridge and the anti-collision ability of the pier, the flexible composite anti-collision facilities are designed. The numerical simulation results show that the horizontal impact force of the pier is obviously reduced after installation the composite anti-collision system, effectively protect the safe use of the pier structure and avoids collision damage from the floating pipe section.

LIGHTWEIGHT RESEARCH ON BUMPER BEAM OF FIBER REINFORCED COMPOSITE

ZHANG Hai-yang, MO Fu-hao, XIAO Zhi, LI Bei

2017, 0(10): 34-40.

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Two kinds of fiber reinforced composite materials-Long Glass Fiber Reinforced Thermoplastics (LGFT) and Carbon Fiber Reinforced Plastic (CFRP) have been studied regarding their lightweight application on vehicle bumper beam. Mechanical properties tests of the LGFT and CFRP materials have been carried out to obtain their simulation parameters. The aluminum alloy of the original bumper beam is replaced by these composite materials with the method of equivalent stiffness to evaluate the performance of crashworthiness and lightweight according to the rules of low-speed impact. The results show that, for satisfying the requirements of the crashworthiness performance, the LGFT can decrease the bumper mass by 11.2% and the CFRP can decrease the bumper mass by 46.1%, so the lightweight effect of both composite materials is evident. Therefore, on the method of equivalent stiffness design, fiber reinforced composite materials are more favorable to meet lightweight requirements of the bumper beam.

THE INFLUENCE OF NANO-Al₂O₃ ON THE PROPERTIES OF PHOSPHORUS-CONTAININGFLAME RETARDED EPOXY RESINS

LI Dao-cheng, WANG Jun, HUO Si-qi, ZHANG Bin

2017, 0(10): 41-45.

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In this work, nano-Al₂O₃ was used as the synergistic flame retardant to study its influence on the flame retardancy of the EP/DOPO and EP/HPCTP thermosets. The thermal stability and flame retardancy of the neat EP and flame retarded EP thermosets were studied by thermogravimetric analysis (TGA), dynamic thermomechanical analysis (DMA), limiting oxygen index (LOI) and UL-94 vertical burning test. The results indicated that the phosphorus-containing flame retardant (DOPO or HPCTP) contributed to improving the flame retardancy of the cured EP resins. However, it will result in the decrease of the T_g of the cured EP resins. Nevertheless, Nano-Al₂O₃ not only increased the char yield at 800 ℃ and LOI of the cured EP resins, but also improved the T_g and onset decomposition temperature of the cured EP resins to some extent. When the content of nano-Al₂O₃ was 4% in the cured EP resins, the LOI of EP-DOPO-Al₂O₃-4phr and EP-HPCTP-Al₂O₃-4phr achieved 36.4% and 41.0%, and UL-94 V-0 rating was obtained, which indicated that nano-Al₂O₃ was an effective synergistic flame retardant to improve the flame retardancy of the EP/DOPO and EP/HPCTP thermosets.

MECHANICAL PERFORMANCE OF STITCHED FOAM CORE SANDWICH COMPOSITES

QIU Yan-hui,XU Qing-lin,YIN Chang-ping,ZHANG Jian-wei

2017, 0(10): 46-52.

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The stitched foam core sandwich structure preforms were prepared by new type of stitched machine. Then the vacuum infusion molding process (VIMP) was used to fabricate the stitched foam core sandwich composites. Then the influences of fiber panel layers, fiber panel penetrating layers, stitched angles, stitched step length, the numbers of yarns on the bending and the compression performance were carefully studied. The results show that, compared with the unstitched structure, stitching can significantly improve the bending and compression properties of the composites. The bending stiffness of the structure increased by 4.66 times and the breaking load increased by 13.8 times at most. Simultaneously, the compression strength and compression modulus increased by 26.2 times and 15.2 times at most.

THE EFFECT OF FOLDING ON THE FATIGUE PROPERTIES OFGLASS FIBER REINFORCED PLASTICS

HE Cheng-zhi, MA Xiao-jun, LI Yang-yang, Wang Xiao-min

2017, 0(10): 53-57.

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AS the layer of glass fabric increases, the fold is more likely to be produced in the manufacturing process of blade girder. Due to the existence of fold, the fatigue performance of blade becomes worse and the operation life will be drastically declined. By designing different types of fold system and manufacturing different samples, the influence of different fold ratio, different fold offset angle and fold width ratio on the fatigue performance of blade girder was studied in detail in this article. The results show that the fatigue performance of GFRP declined sharply with the increase of ratio between height and width of the fold. And no obvious difference was found in the fatigue performance when the samples with different angular offset were tested under the conditions of same fold. Within the certain range of ratio between fold width, the fatigue performance declined slowly. But, when it is above the certain range, the performance began to drop sharply.

INITIAL STUDY OF EFFECTS ON STRENGTH OF WIND TURBINEBLADE WITH TYPICAL ROOT WAVINESS

GAO Kang, TAO Wei-wen, LIU Qi-xing, BU Ji-ling

2017, 0(10): 58-61.

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In this article, large composite wind turbine blade is chosen as research object, and effects of typical root waviness on performance of wind turbine blade are initially studied with the finite element method. First, the plate samples which contain waviness are used to discuss sample′s strength influenced by different waviness positions. At last, the finite model of root of 2 MW wind turbine blade is established. When the root blade is pressed, its strength is influenced by many features, such as the number of layer, width and aspect ratio, etc. The results of calculation show that when the sample with waviness is thinner, its strength is lower. With the number of layers, width or aspect ratio increasing, the blade which contains waviness loses its strength apparently. The results of this article provide some reference for dealing with root blades which contain waviness and can be applied for further study.

EFFECT OF FIBER VOLUME DENSITY HETEROGENEITY ON RESINFLOW IN RTM MOLDING PROCESS

ZHAN Dong, YANG Rui, SUN Shi-yong

2017, 0(10): 62-67.

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In this paper, the influence law of permeability change caused by local fiber volume density on the resin flow front has been investigated. Effects of the local permeability on the flow front and the time of resin filling the local region have been simulated using the commercial software RTM-Worx, respectively. For further verification, the corresponding experiments are designed. In the verification experiments, spacers with different thicknesses have been adopted to change the local fiber volume density. And, good agreements between the simulated and the experimental results can be observed. Both simulation and experimental results show that the time of resin filling the local region increases sharply when the local fiber volume density increases to a certain value. And, if the volume density continues increasing, the region will appear incomplete resin filling, resulting in the phenomenon of the final parts with dry spot defects.

THE STUDY OF ELECTRICAL AND MECHANICAL PROPERTIES OF 3D COMPOSITES

QI Hong-qiang, ZHOU Zheng-liang, ZHANG Shou-yu, ZHAO Da-juan

2017, 0(10): 68-71.

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For studying the electrical and mechanical properties of 3D composites, three kinds of 3D composites were prepared via vacuum assistant resin infusion process (VARI). Their permittivity (ε_r) and loss angle tangent (tanδ) were tested by resonance cavity perturbation method. In addition, their transmission coefficient, flatwise tension strength and flatwise compression properties were investigated. The results of experiments have shown that with the increase of thickness, the ε_r and tanδ decrease. The permittivity of 5 mm, 6 mm and 8 mm are 1.93, 1.77 and 1.62, and the loss angle tangent of 5 mm, 6 mm and 8 mm are 0.0083, 0.0078 and 0.0065. Besides, their transmission coefficients are all below 0.2 dB between 1 GHz and 12 GHz. What′s more, the results indicate that the compression strengths of the 5 mm, 6 mm and 8 mm are 5.8 MPa, 4.6 MPa and 3.8 MPa, respectively. The flatwise tension strengths of the 5 mm, 6 mm and 8 mm are 7.8 MPa, 6.4 MPa and 5.2 MPa, respectively, which indicates that the 3D composites have excellent mechanical properties.

EFFECT OF WATER ABSORPTION ON MECHANICAL PROPERTIES OF CONTINUOUSGLASS FIBER REINFORCED POLYPROPYLENE COMPOSITES

TAN Yi-bei, NI Ai-qing, CHEN Hong-da, WANG Ji-hui

2017, 0(10): 72-78.

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Continuous glass fiber reinforced polypropylene (PP) prepreg is used to fabricate composite laminates. Continuous glass fiber reinforced PP composites are subjected to normal temperature, 60 ℃ and 80 ℃ brine immersion experiments by artificial accelerated aging method. The flexural strength and performance degradation of the composite are investigated with aging time, aging temperature and other coefficients. The results show that the trend of moisture absorption was in accordance with Fick′s spreads at the beginning of aging, and the degree of aging was proportional to time and temperature. The aging degree of the samples under different environmental conditions were examined by scanning electron microscopy (SEM). With the increase of aging temperature and time, the interface corrosion increases between the reinforcing fiber and the resin matrix.

STUDY ON HYDROTHERMAL AGING OF TWO KINDS OFGLASS FIBER REINFORCED COMPOSITE

YUAN Ying-li, WANG Ji-hui

2017, 0(10): 79-84.

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The degradation of glass fiber reinforced composite materials (GFRP) in hydrothermal environment is a problem to be solved in the engineering research. Artificial accelerated aging method is a good and common way to study hydrothermal aging. In this paper, two different systems of glass fiber/resin were investigated by artificial accelerated aging method combined with open water storage environment, which reinforced composite materials in the environment of 35 ℃ water immersion, 65 ℃ water immersion and salt spray. The properties of mechanical, water absorption, hardness, bending strength were investigated and the service life were predicted by two models. The study shows that the hardness of the material changes obviously in the early period, and tends to be stable in the later stage. The water absorption rate almost fit the Fick law. The temperature has a significant effect on the retention rate of the flexural strength, and the salt spray is the second factor. The median aging formula has a higher fitting degree than the empirical formula, which even exceed by 7.6%.

STUDY ON PREPARATION AND PROPERTIES OF BISMALEIMIDERESIN FOR RTM AND ITS COMPOSITES

DENG Hua, GAO Jun-peng, BAO Jian-wen

2017, 0(10): 85-88.

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The bismaleimide (BMI) resin, owing to its excellent thermal-oxidative stability and outstanding mechanical properties, has been successfully used for aerospace structure composites. The obvious shortcoming of the BMI resin is brittleness, therefore its application is limited. Resin transfer molding (RTM) process is suitable for the production of large, complex, thick-sectioned structures, which provides good surface quality and increases the parts integration. Traditional toughening methods such as thermoplastic toughening are not suitable for resin for RTM process due to viscosity increase. A kind of novel toughened bismaleimide resin for RTM was fabricated by introducing of an internal chain extension monomer, which presented good processability, such as low viscosity, long pot time (~3 h) and high toughness. The mechanical properties were characterized and indicated that the tensile strength and elongation was 115 MPa and 3.1%, respectively. The flexural strength was 159 MPa. The glass transition temperature of the cured resin was 270 ℃, characterized by DMA. Composites were prepared from carbon fiber and the BMI resin, which exhibited excellent mechanical properties and high retention rate at 230 ℃.

INVESTIGATION OF HYDROTHERMAL AGING MECHANICAL PROPERTIESOF GLASS FIBER-ALUMINUM LAMINATE

CUI Hai-chao, XIONG Lei, MA Hong-yi, ZHAI Quan-sheng

2017, 0(10): 89-93.

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The mechanism of hydrothermal aging of glass fiber-aluminum laminate was studied by analyzing their mechanical properties, IR spectra, morphology and elemental changes of aluminum alloy, as well as the hydrothermal aging include different aging cycles at 70 ℃ and 85%. The results show that under the condition of accelerating the hydrothermal aging, the inner matrix of the composite material will be hygroscopic and plasticized, and destroy the interface of resin-fiber and resin-aluminum, which will affect the internal stress transmission and the mechanical properties related to the interface and bridge stress. The aluminum alloys are oxidized with hydrothermal aging time, so that the plasticity of aluminum decreased, and the mechanical properties of the laminate are affected.

REVIEW ON THE EFFECTIVE ULTIMATE TENSILE STRAIN OF FRP FOR FRP-CONFINEDCONCRETE COLUMNS UNDER VARIOUS FACTORS

OUYANG Li-jun, XU Feng

2017, 0(10): 94-103.

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FRP confinement effects make concrete columns under the statement of triaxial compression,which improves the compressive strength and ductility of concrete columns. Effective ultimate tensile strain of FRP is essential for calculating the lateral restraint force, proposing peak stress models, peak strain models and stress-strain models of confined columns. In addition, the influence parameters are various. Researchers have obtained some meaningful but discrete and limited results on the effective ultimate tensile strain of FRP. In this paper, systematic analysis was conducted on various influence parameters based on the existing research results, and the remaining problems and key issues which need to be focused in future are pointed out.

PROGRESSINNG IN THE RESEARCH ON MECHANICAL PROPERTIESOF 3D BRAIDED COMPOSITES

SONG Yun-fei, DU Yu

2017, 0(10): 104-109.

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The research status of mechanical properties of three-dimensional braided composites is reviewed. The research methods can be summarized as follows: the study on the micro structures of fiber distribution, internal structure geometry and interfacial interaction, finite element analysis software to predict its mechanical properties and experimental study on mechanical properties. The study of the microscopic structure is mainly about the establishment of the single cell geometry model and the relationship between the braiding process and the cell structure model. The finite element method is mainly focused on the mechanical analysis and the stiffness strength performance prediction of the meso-structure model by finite element software and the equivalent elastic performance parameters of the material are obtained. The experimental study is to study the tensile properties, flexural properties and fatigue properties of the material. The effects of braided process parameters and temperature on the mechanical properties were analyzed. Finally, the problems existing in the current research and future development trends are prospected.

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