COMPOSITES SCIENCE AND ENGINEERING

RESEARCH ON AXIAL COMPRESSION PERFORMANCE OF
FIBER-REINFORCED FOAMED URETHANE SHORT COLUMNS

CHENG Jie, QI Yu-jun

2021, 0(2): 5-10.

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Fiber-reinforced Foamed Urethane (FFU) short columns are made of rigid polyurethane resin foam reinforced with glass fiber yarn bundles and manufactured by pultrusion. In order to study the axial compression performance of FFU short columns with different densities, three groups of FFU short columns with different densities were subjected to static axial compression tests and compared with ordinary concrete columns and steel columns. The test results show that the high- and low-density FFU short columns have different axial compression failure modes. As the density increases, the ultimate bearing capacity, initial stiffness and resistance to deformation will increase. However, the ductility of the specimen will decrease. FFU column has the characteristics of light weight and high strength. Under the same bearing capacity, the mass of FFU short columns is only 1/7 of reinforced concrete columns and 1/3 of I-shaped steel columns.

SIZE EFFECT STUDY OF TENSILE STRENGTH OF BAMBOO
FIBER COMPOSITES ON THE BASIS OF FRACTURE THEORY

NCHAMA Javier, LIU Wen, MENG Xin-miao, ZHANG Han-zheng, LI Kang-ning

2021, 0(2): 11-18.

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As a fibrous bio-composite material with quasi-brittle fracture property, bamboo fiber composites represented by bamboo scrimber has the size effect problem in its material strength, which would influence the design theory of its components. In order to solve the size effect problem of bamboo scrimber in its material strength, especially the longitudinal tensile strength, the three-point-bending test and direct tensile test were carried out to measure the size effect behavior. Meanwhile, the calculating methods of material defect and size effect were analysed by the tensile strength models on the basis of fracture theory. The test results show that the tensile strength of bamboo scrimber has obvious size effect phenomenon. However, by the tensile strength model on the basis of fracture theory, the theoretical plastic tensile strength of bamboo scrimber in its fiber direction, which considered the influence of material surface defect, was independent from size effect. Therefore, the influence of size effect can be determined by the theoretical plastic tensile strength and the defect size.

DETECTION OF ICE ACCRETION ON WIND TURINE BLADE ON MODAL FREQUENCY

LI Fei-yu, CUI Hong-mei, SU Hong-jie, WANG Nian-fu, MA Zhi-peng

2021, 0(2): 19-23.

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At present, the wind turbine blades are usually de-iced using a heating system after ice coating, and the energy consumption is about 1%~4% of the annual power generation of the generator set. In this paper, the finite element model is adjusted by experimental modal results, and the equations of the corresponding relationship between the thickness of the ice coating and the natural frequency at different positions are obtained by the simulation modes of the finite element model. These equations are used to generate random samples to train the BP neural network model. The frequency is the input, and the thickness of the ice is the nonlinear relationship of the output to realize the detection of the ice status. The research shows that through the results of the modal test of the blade′s force hammer excitation, the parameters of the blade model are adjusted, and the error between the first three-order natural frequency and the test value of the optimized three-dimensional model of the bladed iced hollow solid is within 2%. Through BP neural network modeling and training, the average error rate of the results of the model detection ice thickness and the actual value is 8.83%, the error at the blade tip is the smallest, and the error at the blade root is the largest, the relative error rate decreased with the increase of the ice thickness. The trained BP neural network model can basically realize the detection of ice coating position and thickness information, and provide a theoretical basis for the precise heating position and heating time of the heating system and reducing energy consumption.

RESEARCH ON INTERLAYER SLIP BEHAVIOR OF CONTINUOUS CARBON FIBER
REINFORCED POLYPHENYLENE SULFIDE PREPREG

LI Lin-xiu, YUE Guang-quan, YANG Yang, LI Zhe-fu, PAN LI-jian, LIU Wei-ping, LIU Fu

2021, 0(2): 24-31.

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Interlayer slip is an important forming mechanism for the thermal deformation process of thermoplastic composite parts. The study of the interlayer slip behavior of prepreg is the basis for the prediction and control of wrinkle defects in hot deformed composite parts. In this paper, the sliding behavior of continuous carbon fiber reinforced polyphenylene sulfide prepreg during hot deformation molding is studied. Using a self-designed test system, the sliding behavior of satin fabric prepreg and unidirectional prepreg is characterized. And the influence of temperature, normal pressure and speed on the slip behavior are considered. The results show that increasing the test temperature, lowering the pulling speed and normal pressure are conducive to the movement of the fibers and promote the interlayer slip deformation of the prepreg. The Stribeck model is used to predict the interlayer friction coefficient of continuous carbon fiber reinforced polyphenylene sulfide prepreg and compare it with the experimental results. The results show that there is a linear relationship between the Hersey number and the friction coefficient.

STUDY ON CURING BEHAVIOR OF X850 COMPOSITE MATERIAL DURING AUTOCLAVE PROCESS

WANG Min, LUAN Ying-wei, XU Peng, GAO Long-fei, WANG Shi-jie, LI Zhen-you

2021, 0(2): 32-37.

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The exothermic effects of the resin curing at 100 ℃, 110 ℃, 120 ℃ and 130 ℃ were studied by means of constant temperature DSC experiments. The curing behavior of the resin was nonlinear fitted based on the autocatalytic reaction model. The specific form of curing kinetics equation is as follows: dα/dt=7.76×10⁸exp(-10352.8/T)α^0.5928(1-α)^1.4628. With the help of secondary development technology, the curing kinetics equation was embedded into FLUENT software to simulate X850 laminates curing process. Comparison between experiment and simulation results show that the established curing kinetic model can accurately reflect the exothermic effect of resin during the autoclave curing process. The exothermic effect of resin curing is the main reason for the phenomenon of "temperature overshoot" in the actual production process, and with the increase of the laminate thickness, the exothermic effect of resin is intensified. It is difficult to transfer the heat from inside to outside effectively. In the actual preparation of parts, heat dissipation should be done well.

THEORETICAL BENDING COMPUTATIONAL ANALYSIS OF
SANDWICH BEAM UNDER EXTERNAL LOADS

WU Xiao, LIU Qi-yuan

2021, 0(2): 38-42.

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Using the geometric equations of shear strain and displacement of elastomer, the bending differential equations of sandwich beam are derived, and the bending deflection calculation of sandwich beam is studied. The bending deflection of sandwich beam under external load can be calculated by using the bending differential equation. However, the bending calculation of sandwich beams under external load in elastic theory has a disadvantage that only obtaining one problem in one solution. The method proposed in this paper overcomes this defects of the elasticity theory. The experimental results show that the proposed method in this paper has higher computational accuracy.

RESEARCH ON EXPERIMENT AND MANUFACTURING PROCESS OF CARBON/GLASS
FIBER REINFORCED PLASTIC COMPRESSION SPRINGS

LIU Yu-chen, HUA Jun, NING Li-jia

2021, 0(2): 43-48.

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Carbon/glass fiber reinforced plastic (C/GFRP) compression springs have the advantages of high mechanical property efficiency and low cost, compared with carbon fiber reinforced plastic (CFRP) compression springs that are mainly used in vehicle suspension system. Based on the mechanics of composite laminate theory, the calculation method of static stiffness and maximum working load of C/GFRP springs with PU inner core has been put forward, and the structural parameters are calculated. A new method of manufacturing process of C/GFRP compression springs is presented and specimens are made. By testing the quasi-static mechanical properties of specimens, the static stiffness and maximum working load are obtained, the error of them are 6.92% and 4.43%, respectively, which verifies that this manufacturing method can be applied to the customized production of C/GFRP compression springs, and C/GFRP springs can be a low-cost substitute for CFRP springs.

STRENGTH ANALYSIS MODEL CONSIDERING IN-SITU EFFECT
AND EXPERIMENT OF COMPOSITE

YE Ti, YUE Yuan, MA Ming-ze

2021, 0(2): 49-53.

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A numerical analysis model is established to predict the strength of composite. The 3-d PUCK criterion is used as the failure criterion, and the degradation criterion based on the continuum damage mechanics (CDM) is adopted in the model. Meanwhile, the in-situ effect is taken into account. The analysis model is implemented by the user material subroutine (UMAT) embedded in ABAQUS. The accuracy of the model is verified by tensile test of carbon fiber composites with open hole. The results show that the model can predict the strength of the test and the damage development process,the in-situ effect should be considered in the strength analysis of composite materials.

EFFECT OF HYGROTHERMAL ENVIRONMENT ON NATURAL FREQUENCY OF COMPOSITE
HONEYCOMB STRUCTURE WITH FACESHEET/CORE DEBONDING

WANG Yu-xin, HAO Tong-xing, SONG Hao, LU Xiang

2021, 0(2): 54-64.

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For the honeycomb structure with facesheet/core debonding composed by composite laminate and Nomex core, numerical analysis under different hygrothermal environment was carried out to investigate the influence of facesheet/core debonding on the natural frequency of composite honeycomb structure. Based on the piecewise shear deformation theory, considering the displacement difference between the upper facesheet and the core in the debonding area after deformation, the governing equation of motion of honeycomb structure was solved by using the equivalence of hygrothermal expansion. Finite element model of composite honeycomb structure with facesheet/core debonding by four-edge clamped support was established. The effects of temperature, humidity and combined humidity and temperature on the natural frequencies of honeycomb structure with different facesheet/core debonding area were discussed, respectively. The results of the example show that when the moisture concentration is between 0.5% and 0.75%, the honeycomb structure with 25% debonding area first appears buckling effect. Under the same hygrothermal environment, with the expansion of debonding area, the first three natural frequencies of composite honeycomb structure decrease gradually, and the influence on the first natural frequency is the greatest. When the hygrothermal stress reaches a certain degree, the increase of debonding area will cause the honeycomb structure to reach the state of hygrothermal buckling earlier, and the effect of buckling will gradually extend from low-order frequency to high-order frequency. Under the combined effect of temperature and humidity, the natural frequency of honeycomb structure with 18% debonding area is most seriously affected by the environment.

THE INFLUENCE OF END INDUCED HOLES ON AXIAL COMPRESSION
PERFORMANCE OF Al-CFRP COMPOSITE THIN-WALLED TUBE

WANG Kai, MA Qi-hua, ZHA Yi-bin

2021, 0(2): 65-71.

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In order to study the axial compression performance and fracture mode of Al-CFRP tubes with different end induced holes, this paper based on initial peak value, total energy absorption and crushing efficiency, the quasi-static axial compression tests were carried out for aluminum-carbon fiber composite tubes (Al-CFRP tubes) with different end induced holes, and the contrast tests for aluminum tubes (Al tubes) and carbon fiber reinforced resin matrix plastic tubes (CFRP tubes) were also carried out, and comprehensive evaluation of axial compression performance of thin-walled tube by using the evaluation index W of the weighted combination form combining crushing efficiency and total energy absorption. The results show that the Al-CFRP tubes have a more stable failure mode; compared with pure Al tubes and pure CFRP tubes with no improvement in axial compression performance, the end induced holes improve the crushing efficiency of Al-CFRP tubes, and the total energy absorption decreases first and then increases with the increase of the number of holes, among which the four holes have the most obvious effect on the axial compression performance of the Al-CFRP tubes; compared with the Al-CFRP tubes without holes, its total energy absorption and crushing efficiency are increased by 4.2% and 28.3%, respectively, and its weighted evaluation index W_AC4 is 1.16, which is also significantly higher than the reference value.

STUDY ON PROPERTIES OF ARAMID/FLAME RETARDANT EPOXY RESIN COMPOSITES

LIU Ji-kai, PAN Li-jian

2021, 0(2): 72-76.

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Kevlar/epoxy composite laminates were prepared by molding process using halogen free flame retardant epoxy preg reinforced with para aramid fiber. The thickness, fiber volume fraction and mechanical properties of the composite laminates under different forming pressures were measured, the cross section of the samples under different forming pressures was characterized by metallographic microscope, and the flame retardancy of the laminates was tested. The results show that the thickness and fiber volume fraction of laminates do not change when the curing temperature (160 ℃) and the curing time (90 min) are constant and the curing pressure is 0.8 MPa. The thickness of the laminate and the volume content of the fiber basically no longer change, the interlayer bonding is tight, the comprehensive mechanical properties are optimal, and the molding quality is the best. The laminate has a limiting oxygen index of 44.57%, a vertical combustion rating of V-0, and excellent heat resistance and flame retardancy.

THE INFLUENCE ANALYSIS OF TEMPERATURE AND CIRCULAR-HOLE DEFECT
ON THE LINEAR BUCKLING OF LAMINATED PLATE

SU Jun, KONG Lin, XIA Zhi-ping

2021, 0(2): 77-83.

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With the application environment of laminated plates becoming more and more complex, they are often in different temperature environment and often need to drill a circular-hole for mechanical connection, and the size of thickness direction is small, so they are prone to buckling when compressed. Therefore, it is of great significance to study the effects of different temperatures and circular-hole defects on the buckling characteristics of laminated plates. Firstly, the theory of Euler beam is reviewed, and the analytical solutions of the equilibrium load and deflection curve of the beam under the condition of hinged compression at both ends are derived. Furthermore, the finite element method is used to study the buckling problem of isotropic plates. The buckling load and buckling mode are compared with the analytical solution based on the Euler beam theory to determine the appropriate mesh density and verify the correctness of the model. Then, the buckling characteristics of quasi-isotropic laminated plates with different circular-hole sizes are analyzed at different temperature levels, and the first five buckling loads and modes are obtained respectively. Finally, the effect of the depth of the circular-hole on the buckling behavior of the laminated plate is studied. The results show that with the increment of temperature, the buckling load of laminated plates with the same hole size decreases linearly. With the increment of the circular-hole size at the same temperature, the buckling load decreases faster and faster; with the increment of the hole depth at the same circular-hole size, the buckling load decreases firstly and then increases, showing symmetry.

PREDICTION OF COMPOSITE MECHANICAL PROPERTIES BASED ON MATERIAL
PARAMETERS REVERSELY CALCULATED BY THE BRIDGING MODEL

YANG Wan-qing, WANG Yan-chao, LI Neng-wen, XU Xi-yu, YE Guo-rui

2021, 0(2): 84-88.

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Mechanical properties of a composite are the key to the simulation of a composite structure. A micromechanical model can predict the mechanical response of a composite from the properties of the fiber and matrix. However, it is frequently encountered that only a part of the mechanical properties of the fiber and the matrix are available in engineering applications, which directly affects the design accuracy of a composite structure. Thus, a reverse calculation process is presented in this work,with which the lacking mechanical parameters can be calculated from limit experimental data of the composite and the fiber and matrix. Firstly, all the available data of the unidirectional composite and the fiber and matrix are collected. Then the undetermined parameters into linear or nonlinear parts are clarified. Finally, the undetermined parameters by the micromechanical bridging model are calculated. The elastic parameters of a composite and the fiber and matrix are enough for the calculation of linear undetermined parameters, while stress-strain curves of a composite must be given for the calculation of nonlinear parameters. In order to validate the reverse calculation process, a series of off-axis tension tests of a T700/Epoxy UD composite are conducted. Only the elastic modulus of the composite, the longitudinal parameters of the fiber and the Young′s modulus of the matrix are available from the material provider. The other elastic parameters of the fiber and the matrix are obtained by the reverse calculation process. Then, the off-axis tensile strengths of the UD composite are predicted based on the bridging model with the reverse calculated parameters. For the cases of 10°, 15°, 60°, 75°, 90° off-axis tension, the predicted errors are less than 10%, which is accurate enough in engineering application. Thus, the reverse calculation process is validated. The presented reverse calculation process can increase the design efficiency and reduce the experimental cost in design.

FAILURE MECHANISM OF UNIDIRECTIONAL CARBON/CARBON
COMPOSITES AT HIGH TEMPERATURE

CHEN Bo, WENG Shao-dong, WEN Wei-dong, YANG Xing-lin

2021, 0(2): 89-94.

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Carbon/carbon composite material is a new type of composite material with high temperature and friction resistance. In order to investigate the damage and failure mechanism of carbon/carbon composites under tensile load at high temperature, axial tensile test of [0]₁₆ unidirectional laminate carbon/carbon composites with anti-oxidation coating(hereinafter referred to as coating) and [0]₁₆ unidirectional laminate carbon/carbon composites without coating were carried out at 700 ℃. The fracture of corresponding test parts was observed and analyzed under SEM. The fractures of specimens were analyzed by SEM. The tensile test results show that the stress-strain curves of unidirectional carbon/carbon composites with coating at 700 ℃ are linear, and the tensile strength and elastic modulus of unidirectional carbon/carbon composites with coating at 700 ℃ are enhanced compared with room temperature. The stress-strain curves of uncoated unidirectional carbon/carbon composites at 700 ℃ are highly nonlinear and the corresponding mechanical properties decrease obviously. The results of microscopic observation show that the damage forms of unidirectional carbon/carbon composite fiber bundle with coating at 700 ℃ include tensile failure, matrix crack and fiber pulling out. Fiber bundles become thin and distributed for carbon/carbon composite without coating at 700 ℃.

DESIGN AND ANALYSIS OF THE CARBON FIBRE REINFORCED COMPOSITES
SKIRT PLATE ON HIGH SPEED MAGLEV TRAINS

QIU Ya-ping, SHEN Zhen, CHEN Hai-jun, DONG Qing-qing, SHAN Yong-lin

2021, 0(2): 95-101.

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Based on designability and capability of one-time forming of complex structures of resin matrix composites, in this paper, the authors drew lessons from various composite aircraft design codes and compared analysis results from two structural forms developed in parallel. A carbon fibre reinforced composites skirt plate on high-speed maglev trains was finally developed. The structure realized integrated forming of a kind of cavity structure, typical gained advantages were up to 33% weight reduction while meeting all corresponding design requirements, better impact resistance and reduced production cost. Based on the development process of the new skirt plate, this paper presents a systematical discussion of the design ideas of resin matrix composites in the field of rail transit industry in terms of material selection, structure form selection, design specifications adaption, design values determination, structure simulation and final product verification.

STUDY ON TENSILE AND LOW VELOCITY IMPACT PERFORMANCE OF GLASS
AND CARBON FIBERS HYBRID COMPOSITES

WANG Hai-lei, DUAN Yue-xin, WANG Wei-wei, JIANG Jin-long

2021, 0(2): 102-109.

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In this paper, 0°/90° glass fiber non-crimp fabrics and 0°/90° carbon fiber non-crimp fabrics composite laminates with different hybrid ratios were formed by Vacuum Assisted Resin Infusion (VARI) process, and the effects of different hybrid ratios and hybrid ways on hybrid composite tensile and low velocity impact performance have been studied. The results are as follows: the tensile and low velocity impact properties of glass fiber composites are greatly improved when small amount of carbon fibers are added; glass fiber covered surface and inter-layer hybrid structure have the best tensile properties in the same kind of hybrid ratios; for the low-velocity impact properties of hybrid fiber composites, the impact energy, the expansion energy, the toughness index are decreased and the compressive residual strength properties of damaged composites are improved with the increase of carbon fiber content. Meanwhile, glass fiber covered surface and sandwich hybrid structure show the best performance of the low-velocity impact when the contents of carbon fibers and glass fibers are close. Otherwise, glass fiber covered surface and inter-layer hybrid structure have the better impact performance.

DESIGN AND ANALYSIS OF PULTRUSION-WINDING DEVICE
FOR COMPOSITE TUBULAR PRODUCTS

TIAN Hui-fang, CHEN Hai-qing, WU Ying-feng

2021, 0(2): 110-114.

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This article first introduces the characteristics of composite tubular products, and then explains the advantages of the combination of composite pultrusion-winding technology in the product production process, and then explains the pultrusion-winding process forming technology, and introduces the winding device and traction device in detail. The function and the requirements that should be met by each, as well as the movement relationship in the pultrusion-winding process, and then the structure design of the winding device and the traction device, the analysis of the movement sequence relationship of the traction device, and the clamping device in the traction device force analysis. Finally, the clamping device is imported into the workbench for static analysis to verify the rationality of the design.

RESEARCH PROGRESS IN IMPACT RESISTANCE OF COMPOSITE LAMINATED STRUCTURES

SHI Nan-nan, KANG Zhi-kuan, WANG Li-hui, WANG Xiao-juan, ZHAO Zhuo

2021, 0(2): 115-122.

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Laminated composite materials are widely used in industrial and civil, building bridges, military and other structures because of their good corrosion resistance, fatigue resistance, designability of materials and structures, and good comprehensive mechanical properties. However, when the laminated composite is impacted during installation and use, it will produce invisible internal damage, thus reducing its residual strength. In order to understand the impact resistance of laminated composites more systematically and comprehensively, the impact resistance of four kinds of composite laminated structures, including fiber-reinforced composites, hybrid fiber-reinforced composites, biomimetic composites and functional gradient composites, is reviewed by sorting out the relevant literature at home and abroad, and the characteristics of each kind of composite in impact resistance are summarized. This paper summarizes the research status of impact resistance of composite laminated structures at home and abroad, and analyzes the impact resistance of four kinds of common composite laminated structures. With the development of new structural forms and new materials in the field of composite materials, combined with the research progress of impact resistance of composite laminated structures, the future application of composite laminated structures is prospected in impact resistance.

PROGRESS OF RESIN-BASED ABLATIVE MATERIALS RESEARCH

XU Kong-li, XIA Yu, LI Li-ying, XU Xue-wei, WANG Dong, LI Zheng, XIE Yong-wang

2021, 0(2): 123-128.

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Resin-based ablation materials have been the most mature and widely used thermal protection material system. However, with the continuous development of aerospace technology, in order to meet the ever-increasing demand for aircraft thermal protection, a lot of research works have been carried out on resin-based ablation materials at home and abroad. This article focuses on the resin matrix, filler, reinforcing fiber, lightweight and ablation performance test of resin-based ablation materials, introduces the research progress and current status of resin-based ablation materials at home and abroad, and finally points out that the future research work of resin-based ablation materials will become more diversified and collaborative.

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