COMPOSITES SCIENCE AND ENGINEERING

EXPERIMENTAL STUDY AND DESIGN METHOD OF CARBON FIBER CLOTH CONFINED PEC COLUMN

DENG Yu, GAN De-li, ZHANG Peng, YANG Xi-tao

2018, 0(1): 5-11.

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This paper presents the structure of H-beam partially packed concrete column (PEC column). Based on the axial and eccentric compression tests of 18 PEC column specimens, the effects of different carbon fiber sheet adhesive layers, different carbon fiber cloth paste spacing and different eccentricity on PEC column bearing capacity and failure mode were studied. It was found that the PEC column with carbon fiber cloth was larger than the PEC column with no carbon fiber cloth. Under the same carbon fiber cloth paste spacing, the bearing capacity of the two layers of cloth was larger than that of the single layer of PEC column. The smaller the bonding distance of the carbon fiber cloth, the greater the ultimate bearing capacity of the PEC column. The ultimate bearing capacity of all the test pieces decreases with the increase of eccentricity.Based on the test data, the calculation formula of bearing capacity is put forward.

STUDY ON THE STABILITY OF WIND TURBINE BLADE TRAILING EDGE STRCTURE

YUAN Wei-hua, WU Yu-guo, WANG Guo-fu, QIN Zhi-wen

2018, 0(1): 12-17.

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Local buckling of trailing edge near the maximum chord length is one of the main failure modes of wind turbine blades. The finite element method is used to simulate the buckling mode and the enhancement of the trailing edge with different relative thickness airfoils. Three blade sections with relative thickness of 19%, 24% and 35% are simulated to study the effects of laminates, filling of foam or balsa on the trailing edge buckling. The buckling analysis with finite element eigenvalue shows that the overlay of the blade shell at trailing edge can effectively inhibit the displacement and improve the stability of the trailing edge. Moreover, the effect of overlay increases with the decrease of airfoil thickness. But, the mass grows quickly with layers. On the other hand, filling of PVC foam with appropriate length at the trailing egde can also obviously improve the structure stability but rarely increase the mass. Compared with PVC foam, balsa has similar effects.

FINITE ELEMENT SIMULATION OF G_Ⅰ FRACTURE TOUGHNESS OF TOUGHENED COMPOSITES

TIAN Da, FU Hong-jun, WU Li-wei, WANG Qing-tao

2018, 0(1): 18-22.

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The two-dimensional shell element model and cohesive force model were established by using abqaus finite element simulation software and the brittle constitutive model. Besides, the second nominal stress criterion were also used to simulate the fracture toughness of G_Ⅰ fracture with polyimide as the toughening layer. The influences of the normal phase stiffness, energy release rate and other parameters on the properties of the composites were discussed. The above experimental results, indicate that the simulation results are consistent with the actual situation in the curve trend. With the increase of the energy release rate, the interlaminar toughness increases with the increase of the energy release rate, which is mainly caused by the absorption of energy by plastic buckling such as pumping and breaking of fibers. In addition, the normal phase stiffness has a significant effect on the brittle fracture after interlaminar failure. Larger normal phase stiffness leads to the fluctuation of the load-displacement curve, which shows the interlaminar brittleness.

ANALYSIS ON THE STABILITY OF VERTICAL BURIED GLASS FIBER REINFORCED PLASTIC CYLINDRICAL SHELL

CHEN Jian-zhong, LOU Yao-sheng, LV Yong, ZHANG Xiao-yu

2018, 0(1): 23-28.

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In order to determine the stability of vertical buried FRP cylindrical shells, several traditional formulas for stability calculation are introduced. Then, based on engineering practice, and by using the rod model without pressure bearing to solve the problem between the buried structure and the surrounding soil, the material parameter expression between the rod element and the soil is deduced, and the basic finite element calculation model is established. Compared with the traditional formula, the traditional stability formula can not be used to calculate the vertical buried structure. The influence of parameters on structural stability shows that the thickness of the structure, the elastic modulus and the elastic modulus of the surrounding soil can improve the stability and the influence of the thickness is more obvious. The structural stability decreases with the increase of shell length.In engineering application, by using the reinforcement structure to reduce the calculation length and choose the appropriate back-fill material and back-fill method to improve the elastic modulus of soil, the stability and security can effectively be improved, and has less impact on economy.

FAILURE MODE ANALYSIS AND DESIGN PARAMETERS SELECTION OF REPAIRED COMPOSITE LAMINATES

DENG Zhi-kang, CHANG Lei, ZHU Qi-feng, ZHOU Zheng-gen

2018, 0(1): 29-37.

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Zinoviev theory is one of the most popular stiffness degradation when performing progressive damage analysis of laminates, but it introduces many parameters which makes it difficult to understand and to be applied. Whereas, Zinoviev theory can only be used for 2D model. But, after being simplified and improved, Zinoviev theory can be less parameterd and suitable for 3D model. Based on this improved Zinoviev theory, combined with improved three-dimensional Hashin criterion, simulated the adhesive layers with INTER 205 element, progressive damage analysis of repaired composite laminates with a circular hole, which bears tensile load, have been conducted by ANSYS based on three-dimensional finite element. The results of three-dimensional finite element are in good agreement with those of experiments, and hence proved that the simplified and improved Zinoviev theory and the three-dimensional finite element is capable of simulating the progressive damage analysis of repaired composite laminates. The main failure mode of the repaired composite laminates and the impact of patch parameters on the strength of repaired laminates are discussed, and find out the main failure mode is fiber failure around the hole, which accelerates the failure of fiber in laminates. Increasing the size of patch can imporve the strength of repaired composites, and higher strength can be achieved by designing the stiffness of patch as same as laminates. The repair can be most effective when the patch thickness is half of laminates thickness.

NUMERICAL AND THEORETICAL ANALYSIS OF FLEXURAL BEHAVIOR OF HYBRID FRP-STEEL REINFORCED CONCRETE BEAMS

KONG Xiang-qing, YU Yang, GAO Hua-dong, LIU Hua-xin

2018, 0(1): 38-44.

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Recently, the reinforced concrete structure with a hybrid combination of FRP and steel bars has already become a hot topic of research in civil engineering community. In this paper, a 3D finite element model of the hybrid FRP/steel reinforced concrete beams was set up using the software ANSYS based on the test data. The whole bending process of the hybrid FRP/steel reinforced concrete beams was analyzed. Then the concept of a nominal reinforcement area of the hybrid FRP/steel reinforced concrete beams was proposed and used to set up a theoretical model combining with the technical code for infrastructure application of FRP composites. The load capacity and deflection of the hybrid FRP/steel reinforced concrete beams were estimated by using the theoretical model. The comparisons between numerical/analytical results and experimental date demonstrate the reliability of both the proposed FE model and the theoretical model.

FLEXURAL TESTS OF RC BEAMS STRENGTHENED WITH NEAR SURFACE MOUNTED MIXED FRP RODS

WANG Xing-guo, DAI Bo, ZHANG Peng-fei

2018, 0(1): 45-49.

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Reinforced concrete beams were strengthened with near surface mounted (NSM) fiber reinforced polymer (FRP) rods into pre-cut grooves at the flexural zone and negative moment zone for simple supported beams and continuous RC beams. Flexural tests were monotonically carried out with NSM CFRP/BFRP hybrid rods under various initial loading. Experimental phenomena were recorded under loading levels such as crack width, typical loads, strains of steel bar/FRP rods and deformation. Test results show that flexural performances are increased for simple-supported and continuous RC beams strengthened with NSM hybrid FRP rods, especially for flexural capacity and normal stage performance. In comparison with RC beams with NSM single FRP rods, similar crack development and displacement ductility are better for beams with NSM hybrid rods. For test beams under initial loading, strengthen effect is slightly worse than beams without initial loading. External load is suggested to be removed as much as possible in field structure member.

STUDY ON AXIAL COMPRESSION PERFORMANCE OF FRP CONFINED CONCRETE CYLINDER COLUMNS BASED ON NUMERICAL EXPERIEMNTS

ZHANG Bing, SUN Yun-lou, QI Yu-jun

2018, 0(1): 50-59.

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Fiber-reinforced Polymer (FRP) Confined Concrete Column (FCCC) have superior axial compressive capacity and ductility. It is difficult to make a comprehensive study about key parameters such as sectional dimension, concrete strength and number of FRP layer, due to the common approach, specimens experiment. Firstly, FCCC′s axial compressive test and simulation were reviewed. Then, a Finite Element (FE) model was created based on Drucker-Prager Constitutive and the validity of the FE model was verified based on the existing experimental results. Then, the axial compressive performance of FRP confined concrete column with different parameters was investigated using the verified FE model. Diameter of section, concrete strength grade and number of FRP layer were selected as key parameters and their ranges were 150 mm~750 mm, C30~C80 and 1~5, respectively. The results show that when the layers of FRP are constant, as the strength level of concrete increase, axial strength and ductility increase and decrease, respectively. When the concrete strength are constant, the axial bearing capacity and ductility of FCCC increases with increasing layers of FRP. When constraint amount of FRP and concrete strength are constant, confinement effect of FRP for inner concrete decreases with increasing diameter of section. The comprehensive studies about the effects of different parameters on the axial compression performance of FCCCs in this paper can provide a reference for further research and design of FCCCs.

INFLUENCE OF ELECTROPHORETIC DEPOSITION TIME ON SiC_f/SiC COMPOSITES PROPERTIES

HOU Hui-ning, ZHOU Xin-gui, LI Ming-yuan

2018, 0(1): 60-67.

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This paper pays attention to the hybrid method of Electrophoretic Deposition (EPD) and Precursor Infiltration and Pyrolysis (PIP) for fabricating the SiC_f/SiC composites. Influence of deposition time on SiC_f/SiC composites is analyzed. It is concluded that SiC fibers would be gradually corroded with EPD time prolonged, and the fibers′ peak strength would decrease as well. While, the existence of PyC interphases in front of the SiC fibers would effectively protect the SiC fibers. Because of the electric power of EPD suspension, interfacial strength between PyC interphases and SiC fibers would drop slightly. Therefore, the peak strength of SiC fibers would increase at first then decrease with EPD time. 5 min EPD and 9 cycles PIP result in a maximum bending strength of 731 MPa for SiC_f/SiC composites. After that, its mechanical property first dropped then grew a little with EPD time. Thermal conductivity of SiC_f/SiC composites rose first and then fell with EPD time. With 10 min EPD, thermal conductivity of SiC_f/SiC composites in room temperature reaches the maximum of 4.658 W/(m·K).

EXPERIMENTAL STUDY ON HIGH PRESSURE MICROWAVE CURING PROCESS OF ADVANCED RESIN MATRIX COMPOSITES

DING Xing-xing, ZHAN Li-hua, LI Shu-jian, CHANG Teng-fei

2018, 0(1): 68-72.

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Advanced resin-based composite materials have been widely applied in the field of aerospace. And the way to obtain satisfactory curing quality components with high efficiency, low energy consumption of microwave curing process has gradually attracted the attention of scholars. The high pressure was introducted in advanced resin-based composite materials curing process in this article. The quality of high-pressure microwave curing composite materials were studied based on defect analysis, microstructure observation and mechanical properties testing, respectively. The result indicates that high pressure microwave curing technology can effectively achieve the curing of resin matrix composites. Compared with the autoclave process, high-pressure microwave curing process can achieve low porosity, less defects, fiber/resin interface with better micro-quality. The mechanical properties of high pressure microwave composites have been improved. The material tensile strength can be increased by 4.82% and the interlayer shear strength can be increased by 10.32%. The results provide the basis for the popularization and application of high pressure microwave curing technology in composites. Through the analysis of the experimental results, it can be concluded that the high-pressure microwave curing process improves the transverse tensile properties and interlaminar shear properties of the components. The interal quality of the components is better, and the phenomenon of debonding does not occur on the interface.

AGING RESISTANCE OF MICROWAVE ABSORBING SANDWICH STRUCTURE

HE Xiang, LI Yong-qing, ZHU Xi, CHEN Ke-meng

2018, 0(1): 73-78.

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In this study, the accelerated aging test of microwave absorbing sandwich structures is carried out, under the typical marine environmental factors such as wet hot and salt fog. The aging resistance of microwave absorbing sandwich structure and absorbing patch is also compared. Several conclusions have been drawn at last after ultraviolet aging for 15 days. The decline of Q-GFRP′s dielectric constant is most obvious, which lead to the effective bandwidth of microwave absorbing sandwich structure being reduced by 0.41 GHz. Salt-fog aging 30 days later, the oxide rust of microwave absorbing patch is most serious. At the same time, the absorption peak and effective bandwidth are reduced by -6.59 dB and 2.40 GHz, respectively. Besides, due to the protection of Q-GFRP, the aging resistance of microwave absorbing sandwich structure is superior to absorbing patch. And, after accelerated aging treatment, it can still meet the radar stealth requirements of warship in X-band and Ku-band.

STUDY ON LAMINATING PROCESS OF CONTINUOUS FIBER REINFORCED POLYPROPYLENE PREPARED BY HYBRID YARN FABRIC

ZENG Zheng, GUO Bing-bing, SUN Tian-shu, HONG Cheng

2018, 0(1): 79-84.

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In this paper, two different forms of hybrid yarn fabric were used as raw material to prepare the continuous glass fiber (GF) reinforced polypropylene (PP) laminated composites by the laminating process. To prepare the laminate with excellent mechanical property, the influences of molding temperature, molding pressure, molding time and the form of fabrics on the flexural property and interlaminar shear strength (ILSS) of the laminated composites were investigated to get the optimal process parameters. The results show that the laminated composites with optimal mechanical property were prepared at hot pressing temperature of 230 ℃, hot pressing pressure of 8.5 MPa, molding time of 30 min and cooling rate of 0.5 ℃/min. The optimal mechanical properties of the laminate are as follows: flexural strength reaches 352.58 MPa, flexural modulus reaches 23.09 GPa, ILSS reaches 27.37 MPa. At this time, the fiber content and the porosity content of the laminate is 72.25% and 2.03%, respectively. The flexural strength and flexural modulus and ILSS of laminated composites prepared by two different forms fabric under the optimal processing conditions: 2/2 twill fabric＞plain fabric. In addition, the porosity content of the two different laminates prepared by two different forms fabric: 2/2 twill fabric＜plain fabric.

MATCHING PERFORMANCE RESEARCH OF P2352W-19 PREPREG AND PEEL PLY

CHEN Lu-yuan, GU Ling-cong, WANG Xu, CHEN Ping

2018, 0(1): 85-88.

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To further understand the effect of peel-ply on bond quality of P2352W-19 prepreg, mode Ⅰ DCB fracture toughness testing and double lap shear strength were used to analyze the samples prepared using dry peel-ply and wet peel-ply removal as surface preparation technique. Then, the results were correlated to specimen failure mode for evaluating mechanical performance of bonding surface. Laminates were co-bonded and second bonded with 2 film adhesives. Through those tests, the compatibility of different peel ply with P2352W-19 prepreg systems was studied.

STUDY ON THERMAL PROPERTIES OF GRAPHENE OXIDE MODIFIED THERMOSETTING PHENOLIC RESIN

SUN Yi,TU Chen-cheng,TAN Juan-juan, GAO Hong-cheng

2018, 0(1): 89-93.

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In this paper, the thermosetting phenolic resin modified by graphene oxide (GO) was prepared by in situ polymerization and solution blending. The influence of the addition content of GO and the adding way on the thermal properties of phenolic resin was analyzed. For the modified resin prepared by in situ polymerization, the T_g decreased slightly with the addition of GO. Besides, the residual carbon rate and the thermal decomposition temperature of the first stage increased firstly and then decreased. Compared with the resin prepared by in situ polymerization, the resin prepared by solution blending had a better heat resistance and a narrower GO dispersion scale.

VOLUME POROSITY MEASUREMENT OF CFRP BASED ON MICRO-CT TECHNOLOGY

XIAO Peng, LIU Kui

2018, 0(1): 94-97.

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A new method was proposed for volume porosity measurement based on micro-CT technology. The principle of micro-CT technology was analyzed, picture processing of results was done, and volume porosity was quantitated. The results show that micro-CT technology can be effectivly used on CFRP volume porosity measurement, and matrix and voids distinguish. In order to obtain accurate porosity result, large volume of representative specimen is necessary.

THE FINITE ELEMENT STRUCTURE ANALYSIS OF THE THREE DIMENSIONAL HOLLOW SANDWICH COMPOSITES RADOME

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

2018, 0(1): 98-102.

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The radome requires large external dimensions and the weight saving. The hollow sandwich composite material can meet the requirements of transmitting wave and light high-strength. Based on the above requirement and actual condition, this paper puts forward the choice of glass fiber reinforced epoxy resin composite material for skin, and three-dimensional hollow fabric composite material for the core material of A sandwich structure radome. This article uses finite element analysis software to establish the three-dimensional finite element model of hollow sandwich radome, and the radome stiffness, strength and stability under the operating conditions are analyzed. The calculation results meet the requirements of stiffness, strength and stability. And, the pressure test verifies that the deformation of hollow sandwich radome is consistent with the results of finite element analysis, which provides guidance for the layer design, material selection and optimization of the radome.

RESEARCH PROGRESS IN BOND PERFORMANCES OF MASONRY STRUCTURES STRENGTHENED BY FRP SHEETS

WANG Zuo-hu, YANG Wen-xiong, LIU Du

2018, 0(1): 103-107.

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Strengthening masonry structures is of great significance because of the low bearing capacity, poor seismic capacity and other problems of the masonry structures. In recent years, the rise of fiber reinforced plastic (FRP) abroad and at home provides a new direction to strengthen masonry structures by virtue of FRP′s good performances, including low weight, high strength, fine durability and easy construction. The bond performance between the FRP and the masonry structure is one of the key factors that influences the effect of strengthened structures. This paper summarizes the current research progress, made by both domestic and foreign scholars, in bond performance for masonry structures strengthened by FRP sheets and finds that there are fewer researches on bond performance for masonry structures strengthened by FRP sheets under a multiple-corrosive environment. We verifie the calculation formulas of the FRP′s ultimate load in strengthened masonry structure according to collected experimental data and chooses one formula which has less error. At the end of the paper, some suggestions are put forward for the future research work.

RESEARCH PROGRESS ON COMPOSITE INTERFACE DESIGN OF GRAFTING CARBON NANOMATERIALS ONTO CARBON FIBERS

LI Jun, JIAO Wei-cheng, YAN Mei-ling, LIU Zhen-xiang

2018, 0(1): 108-113.

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Interface, as an important component of composite materials, acts as a transfer load, and affects the overall properties of composites. The surface of carbon fiber belongs to graphite disordered structure, and the crystallite is orderly and inert. Therefore, it is difficult for it to combine with the resin matrix. Increasing the specific surface area, the roughness of the fiber or introducing active functional groups to the fiber can improve the surface wettability, mechanical and chemical combination and improve the interface properties of composite materials. The grafting of carbon nanomaterials onto the surface of carbon fibers is one of the effective methods to improve the interfacial properties. In this paper, the preparation methods of grafting carbon nanotubes and graphene oxide onto carbon fibers, interface design and interface enhancement mechanism were reviewed and analyzed. The development trends and prospects of grafting carbon nanomaterials onto carbon fibers and interface performance evaluation methods also were discussed.

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