COMPOSITES SCIENCE AND ENGINEERING

FLEXURAL BEHAVIOUR OF STEEL FIBER-REINFORCED RECYCLED AGGREGATE CONCRETE BEAMS REINFORCED WITH BFRP REBARS

KONG Xiang-qing, HAN Fei, XING Li-li, WANG Xue-zhi

2019, 0(11): 5-11.

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In order to investigated the influence of the different volume fraction of steel fibers v_sf (0.5%, 1%, 1.5%, 2%), longitudinal reinforcement ratio ρ and recycled aggregate replacement rate R (0, 50%, 100%) on the bending behaviour of steel fiber reinforced recycled concrete beams reinforced with BFRP bars (BFRP-SFRAC) beams, the bending performance tests of nine BFRP-SFRAC beams and one steel fiber reinforced recycled concrete beams reinforced with steel bars (control beam) were carried out. The failure mode, flexural capacity and deflection deformation, etc., were analyzed. The results show that the section strain of BFRP-SFRAC beams meets the plane section assumption, and the descending branch of the load-deflection curve of the BFRP-SFRAC beam has a smooth drop, which indicates that the post-peak behaviours of the BFRP-SFRAC beams show better ductility characteristics. The flexural capacity of BFRP-SFRAC beams is greatly affected by reinforcement ratio ρ and volume fraction of steel fiber v_sf, and less affected by replacement ratio of recycled aggregate. Both the initial cracking load and the ultimate load increase with the increase of the volume fraction of steel fiber v_sf, but it does not always increase linearly, while the deflection deformation decreases. It is also found that the initial cracking load of the BFRP-SFRAC beam is slightly lower than that of the control beam, but the ultimate load is obviously improved.

STIFFNESS OPTIMIZATION OF VARIABLE ANGLE FIBER LAMINATES BASED ON DIFFERENTIAL EVOLUTION ALGORITHM

WU Shuang-hua, CHEN Tong, YIN Guan-sheng

2019, 0(11): 12-17.

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The starting angle of the variable angle fiber, the ending angle and the lamination order of the laminate are the design variables, and the bending stiffness is the design goal to optimize the variable angle fiber laminate. In the optimization process, the design variables corresponding to the layering order are converted into integer variables by real coding and replacement strategies to realize the conversion between discrete space and continuous space. Due to the difference of optimization process between discrete variables and continuous variables, Improved Adaptive Differential Evolution Algorithm is proposed in this paper, and different adaptive mutation operators are adopted for different types of optimization variables. The calculation results of related examples show that, regardless of the local optimization and global optimization of the laminate, Improved Adaptive Differential Evolution Algorithm is more accurate than Differential Evolution Algorithm and Adaptive Differential Evolution Algorithm, and can effectively avoid "Premature" phenomenon. For the optimization of the bending stiffness of variable angle fiber laminates, Improved Adaptive Differential Evolution Algorithm proposed in this paper is a relatively efficient and feasible method.

PRESTRESSED CFRP BENDING REINFORCEMENT DESIGN METHOD BASED ON EARLY WARNING WIRE CONCEPT

GUO Rong, WANG Ming-hao, PENG Zhi-hui, ZHAO Shao-wei

2019, 0(11): 18-23.

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In recent years, the prestressed CFRP plate reinforcement technology has been widely used in building reinforcement. The bearing capacity, crack resistance, stiffness and material utilization rate of the strengthened members have been significantly improved. However, the ductility of the members after reinforcement is significantly reduced, and the failure mode becomes brittle failure, and there is no obvious sign before the damage. In order to solve this problem, based on the prestressed CFRP plate bending reinforcement design method and the early warning wire theory, the theory of using the breaking point of the warning wire as the yield point of the component is proposed. In this paper, the bending performance tests of four prestressed CFRP plates reinforced concrete beams were carried out. The research results showed that the steel bars, the warning wires and the carbon fiber plates can work in coordination, which verified the feasibility of the design method based on the early warning wire theory. The far method verified that the breakpoint of the warning wire is the actual yield point of the reinforcement member. The design method successfully solved the problem of insufficient ductility of the reinforcement member.

FORECASTING METHOD OF THERMAL RESPONSE FOR GLASS FIBER VINYL ESTER RESIN COMPOSITE MATERIAL

FENG Zhen-yu, WANG Na-si-dan, FAN Mao-hua, FAN Bao-xin

2019, 0(11): 24-29.

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In order to study the thermal response of glass fiber vinyl ester resin composites in fire, considering the pyrolysis process in fire, the thermal response equations were established, and a finite difference method was used to calculate and analyze the material′s internal time-dependent temperature progressions and carbonization subjected to one-sided heat flux. The theoretical results from the established nonlinear thermal response equations were validated against experimental data and a good agreement is observed. As the heating time increases, the material is completely carbonized, the temperature changes tend to be stable, and the distribution of material temperature with depth position changes from nonlinear to linear. With the increase of the depth, the time for the glass fiber vinyl ester resin composites reaching the pyrolysis temperature increased and the carbonization process slowed down. The residual mass fraction of materials at different depth in the pyrolysis reaction zone is slightly different at the same temperature, the residual mass fraction decreased and the degree of carbonization increased as the depth of the position rose.

CALCULATION OF LOCAL BUCKLING LOAD OF COMPOSITE THIN RECTANGULAR TUBE BASED ON THIN PLATE DEFLECTION THEORY

ZHU Xiu-jie, XIONG Chao, YIN De-jun, YIN Jun-hui

2019, 0(11): 30-36.

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A calculation method for the local buckling load of a composite rectangular thin-walled tube is proposed. The wall plate of the composite rectangular thin-walled tube under the axial compression load is regarded as the one-way compression anisotropic plate, and the elastic embedded coefficient is introduced into the solution of the equilibrium differential equation, and the rectangular thin-walled tube of the composite material is obtained, as well as the analytical formula of the buckling load. Compared with the experimental data in the literature and the finite element results of this paper, the correctness of the computational model is verified. The applicable range of the calculation model is analyzed by quantitative calculation of the equivalent stiffness coefficients of four kinds of laminated composite rectangular thin-walled tubes. Combined with the calculation formula of Euler′s buckling load of composite members, the calculation formula of buckling load considering the overall instability and local instability is obtained. It is found that when the layup parameters are constant, there is a critical aspect ratio that distinguishes between local buckling and Euler buckling.

NUMERICAL ANALYSIS OF BENDING CHARACTERISTICS OF CFRP/DC04 STEEL BONDING JOINTS

DONG Bo-yan, MA Qi-hua

2019, 0(11): 37-44.

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The finite element model of the bonded specimens was established based on the quasi-static three-point bending test of CFRP/DC04 steel bonded joints and the simulation results calculated by ABAQUS/Explicit have good consistency with the test results, which proves that the model reproduces the mechanical response of the bonded joint under load. Based on the simulation results, the stress distribution law and damage failure mechanism of the adhesive layer are analyzed. The results show that the stress distribution of the adhesive layer is obviously different under the bending load. The normal stress σ is mainly concentrated at both ends; the shear stress τ₁₃ is symmetrically distributed along the length of the adhesive; the shear stress τ₂₃ is distributed at the four corners of the adhesive. Due to the different stiffness and relative position of the bonding plates, the adhesive at one end first is peeled off due to large normal stress, and gradually expands to the other end. Based on this, the influence of the relative position of the bonded plates on the bending resistance of the bonded joints was analyzed. It was found that the CFRP plate at bottom has a better joint tenacity and higher bending strength than the plate at the top.

COMPOSITE CYLINDER STRENGTHENED WITH GFRP LATTICES UNDER LATERAL IMPACT LOAD

ZONG Li-na, FANG Hai, ZHOU Hui

2019, 0(11): 45-49.

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In this paper, lateral impact resistance of lattice-reinforced composite bridge anti-collision device is studied by experimental method. The spacing of transverse lattice effects of the impact ultimate load, maximum displacement and energy dissipation performance of composite cylinders are analyzed. Numerical fitting is carried out according to the test data. The fitting curves of lattice spacing to ultimate load are obtained. The results show that the tighter the transverse lattice in the test, the greater the ultimate compressive load or ultimate impact load.

EXPERIMENTAL STUDY ON FLEXURAL BEHAVIOR OF REINFORCED BEAMS AFFECTED BY THE DIFFERENT MATERIALS AND METHODS OF REINFORCEMENT

XU Ping, DAI Jun-feng, DING Ya-hong, MA Jin-yi

2019, 0(11): 50-57.

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To study the influence of different materials, reinforcement amounts, and reinforcement methods on the carrying capacity, deflection change, failure modes and crack propagation of reinforced beams, 11 experimental beams were subjected to the four-point loading test. The results show that the cracking load, yield load, ultimate load and load-deflection curve of the test beams were directly affected by the materials and methods of reinforcement. The promotion of cracking load was mainly affected by the reinforcement method, and the cracking loads of the reinforced beams embedded spiral ribbed steel wires with fishtail and grille were increased obviously, which was up to 182% higher than that of the reinforced beams by the straight embedded reinforcement method. The yield load and ultimate load of the reinforced beams used the end anchorage method were increased most obviously with the same amount. The ultimate load of reinforced beams with embedded Carbon Fiber Reinforced Polymer/Plastic (CFRP) bars was the largest, which is increased by 113.68%. The reinforced materials had obvious influence on the flexural rigidity of the reinforced beams, and the flexural rigidity of beams with CFRP bars was optimum. The flexural rigidity of cross-embedded, fishtail-embedded, grille, and end-anchorage reinforced beams was significantly better than that of the straight-embedded reinforced beams.

EXPERIMENTAL STUDY ON LOW SPEED IMPACT PROPERTIES OF PLAIN FABRIC HYBRID FIBER-REINFORCED PLASTICS

SU bo, ZHANG tuan, YU Guo-jun, GE jing

2019, 0(11): 58-63.

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In this paper, four kinds of plain weave fibre reinforced laminates with different hybrid modes are prepared by vacuum induction process with glass fibre, carbon fibre, aramid fibre and vinyl ester resin. A pendulum impact experiment is carried out and compared with the simulation results by finite element simulation software Abaqus. The results show that pure glass fiber specimens suffer the greatest impact force and have the worst energy absorption effect under low-speed impact load. When carbon fiber/aramid fiber is mixed, the impact force and energy absorption effect are improved. Among them, G₂/A₄/G₂ sample has the best cushioning effect, and the impact force is reduced by 54.4%. C₂/G₄/C₂ sample has the best energy absorption effect, and the energy absorption is increased by 34.1%. Abaqus simulation results are close to the experimental results, which can better reflect the damage process of composite materials.

EXPERIMENTAL RESEARCH ON AXIAL COMPRESSIVE PERFORMANCE OF COMPOSITE SHORT COLUMN WITH WOOD CORE REINFORCED BY GFRP WEBS

ZHU Xiao-xiong, FANG Hai, ZOU Fang, YANG Lai-yun

2019, 0(11): 64-68.

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The composite short column with paulownia wood core reinforced by GFRP webs is prepared through vacuum assisted resin infusion. The composite column has the characteristics of high specific strength, high specific stiffness, good corrosion resistance and ductility etc.. Composite columns were tested under axial compression, the mechanical properties of the composite columns with different lattice forms and different fiber layers are studied. Based on the elastic analysis method, the theoretical value is calculated, which is consistent with test result.

STUDY ON FLEXURAL PROPERTIES OF CFRP LAMINATED PLATE REINFORCED BY EMBEDDED CARBON CNTS BUCKYPAPER

WANG Meng, WANG Gong-dong

2019, 0(11): 69-73.

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In order to study the bending properties of carbon fiber reinforced composites, CFRP laminates were prepared by pre-buried carbon nanosheets. The static experiments under three-point bending loading were carried out. The bending stress-strain curves and bending limits of the specimens were analyzed to study the effect of carbon nanopaper and curing pressure on CFRP bending properties. The results show that the pre-embedded CNTs buckypaper can effectively enhance the CFRP bending strength and ultimate bending load-bearing capacity. The curing pressure can enhance the mechanical properties of the pre-embedded CNTs buckypaper CFRP, and the best strengthening effect is achieved when the curing pressure is 2 MPa.

ANALYSIS OF BURST PRESSURE FOR LARGE VOLUME STEEL LINER COMPOSITE CYLINDERS WITH WINDING LAYER DEFECTS

WANG Hao, DENG Gui-de, ZHANG Xing-fang, JIANG Yong-shan

2019, 0(11): 74-80.

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In the process of production and manufacturing, collision and friction would inevitably occur in the large-volume steel liner composite cylinder, which would cause damage on surface of the winding layer and reduce safety of cylinder. Because of the high cost of cylinder, it would cause great economic loss if cylinder with surface defect of winding layer was scrapped. Therefore, it was necessary to conduct finite element analysis on cylinders with winding layer defects. The finite element software was used to construct a large volume hoop-wrapped composite cylinder model, and three volume defects were established on surface of the winding layer. The process of numerical model and defect establishment were described in detail. Stress distribution and size of cylinder liner and winding layer with different winding layer surface defects were analyzed under the design burst pressure (50 MPa), and cylinder burst pressure in each case was predicted by maximum stress criterion. Then, the simulation results were compared with data of cylinder hydraulic burst testing. Critical size of winding layer that has no effect on burst pressure was studied base on the above discussion. Simulation results show that defects of winding layer had little effect on liner stress, but stress of winding layer would increase sharply, and burst pressure would obviously decrease and depth had a greater influence on it. For cylinder discussed in this paper, the critical size was that the area was 200 mm×200 mm and depth was 1 mm.

STUDY ON SAFETY OF SHALLOW BURIAL FRPM PIPE CULVERT UNDER HEAVY VEHICLE DRIVING DURING CONSTRUCTION PERIOD

CHEN Zhao-nan, PEI Ya-nan, WEI Lian-yu, JIANG Ke-lin

2019, 0(11): 81-85.

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FRPM pipe has the advantages of light weight, high strength, short construction period and good durability. It can be used as a substitute for traditional reinforced concrete road pipe culvert materials, and has a wider application prospect in highway engineering. In order to study the influence of the engineering transport vehicle during the construction period on the bearing characteristics of the buried glass fiber reinforced plastic pipe culvert and the thickness of the pipe top cover to ensure the safety of the pipe culvert, the dynamic load test and the load of the heavy soil are analyzed. The dynamic strain change characteristics of the glass fiber reinforced plastic sand pipe under driving are investigated. The results show that the top of the culvert pipe of the FRP sand pipe is the control point during construction, the maximum stress is 0.6 MPa, which is much smaller than the compressive strength of the pipe culvert. The thickness of the cover soil is 50 cm, which can allow heavy-duty engineering transport vehicles to pass, and the safety of the glass-reinforced plastic pipe culvert during highway construction. Sex control points have important guiding significance and engineering application value.

RESEARCH ON THE TECHNOLOGY OF SINGLE-SIDED CURVED NEEDLE STITCHING EQUIPMENT OF THE COMPOSITES PREFORM

FENG Qiao-qiao, WEN Li-wei, XIAO Jun, WANG Yu

2019, 0(11): 86-94.

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Three-dimensional stitching technology can not only significantly improve the inter-laminar properties of composite materials, the delamination resistance and impact damage tolerance, but also combine the liquid forming process to realize the integrated structure of composite materials. In this paper, the single-sided stitching technology of composite materials was taken as the research background, and the study on stitching equipment for single-sided curved needle of composite materials was carried out. By analyzing the functional requirements of the stitching equipment, the overall planning scheme of the equipment was proposed, and a single-sided curved needle stitching head was designed and developed. Subsequently, the stabilizing forming factors of the stitches were discussed and analyzed. The displacement-time relationship between the end effector of the stitching head in a stitching cycle was determined, and the optimal loop shape and the expression of the balance of supply and demand of the thread was derrmined. Finally, the trial sewing test proved that the stitching equipment can form a smooth and stable chain stitch on the fiber preform, and achieve good stitching effect.

PREPARATION AND SALT SPRAY ATMOSPHERIC CORROSION BEHAVIOR OF GLASS FIBER/VINYL ESTER COMPOSITES

QU Li, KANG Shao-fu, LI Jin, CHENG Xuan

2019, 0(11): 95-99.

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Limestone wet desulfurization has been mainstream during practical process of coal-fired generating units built in China. However, salt spray take a significant role in detachment of chimney lining materials caused by wet flue gas. In this paper, glass fiber/vinyl ester composites was fabricated based on the low-costing process of vacuum assisted molding (VARTM) process and its mechanical properties was investigated in natural salt spray environment simulated by salt spray testing chamber for 4 days, 14 days, 28 days and 60 days to evaluate corrosion resistance. Meanwhile, cross-reference of corrosion was observed with the help of SEM to reveal the microscopic mechanism and evolution law of surface morphology. The results show that the mechanical properties of the composites are increased and then decreased with the increase of the days of salt spray corrosion. After 60 days of salt spray corrosion, tensile strength, bending strength and interlaminar shear strength respectively decreased by 5.6%, 12.71% and 13.61%. The morphological characterization showed that the resin matrix exploded and cracked after salt spray corrosion, and defects were formed at the fiber-resin interface, which led to a decrease in mechanical properties.

STUDY ON THE EFFECT OF OPENING HOLE ON THE RECIPROCATING IMPACT RESISTANCE OF THERMOPLASTIC COMPOSITE LAMINATES

PENG Pi, WANG Ji-hui, CHEN Hong-da, LUO Chuan-long

2019, 0(11): 100-104.

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In this paper, the effect of the distance between the hole and the impact point on the repeated impact resistance of the glass fiber reinforced polypropylene composite (GFRPP) laminate is studied. GFRPP laminates were prepared by hot press forming. Repeated impact on laminates were performed by drop hammer impact tester. Until it is completely penetrated, the relevant data of the impact response is obtained. The results show that the distance d between the hole and the impact point has a significant effect on the repeated impact resistance of the GFRPP laminate. For a single impact, the larger the distance is, the larger the maximum contact force of the impact response, and the smaller the displacement and the absorption energy. Compared with non-hole laminates, the number of times of d=5 mm, 10 mm, 15 mm, 20 mm perforated plates against repeated impacts decreased by 88.1%, 57.6%, 20.3%, and 3.3%, respectively. During the repeated impact process, the maximum contact force of the d=5 mm and d=10 mm aperture plates has a peak point, which promotes the absorption energy of the laminate, and the absorption energy of each impact increases slowly with the increase of the number of impacts.

APPLICATION OF DARK CHANNEL IMAGE ENHANCEMENT TECHNOLOGY IN DIGITAL RADIOGRAPHIC DETECTION

ZHENG Jin-hua, SHENG Tao, FENG Jun-wei, QIAN Yun-xiang

2019, 0(11): 105-110.

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This paper refers to the dark channel dehazing image enhancement technology. Combining the characteristics of CFRP molded parts DR digital ray image, and analyzing the image enhancement effects under different filter radius and defogging coefficient, and obtaining reasonable image enhancement parameters, the product is successfully applied to the DR digital imaging detection. The results show that the method can effectively reduce the contrast change caused by the thickness difference of the workpiece in the DR image, reduce the background noise in the workpiece, and highlight the defect information in the workpiece, so that the enhanced image has better visual effect. This makes it possible to basically unify the evaluation window for different types of defects. It reduces the number of times that the traditional DR image evaluation needs to adjust the window, effectively improves the work efficiency and the accuracy of the film reviewer, and has great reference value and guiding significance in practical engineering applications.

INFLUENCE OF FILAMENT WINDING TENSION ON THE QUALITY OF FRP PRODUCT AND ITS CONTROL MEASURES

ZHANG Zhi-jian, SONG Chang-jiu, ZHANG Jian-zhong, FEI Qi-feng

2019, 0(11): 111-114.

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The tension control in FRP filament winding process is a key technology which affects the performance and quality of FRP products. By analyzing filament winding tension, this paper tries to find out how it occurs and what factors will influence it. At the end of the paper we give three suggestions on how to control the tension to get higher quality products.

STUDY ON THE EFFECT OF ELECTROPHORETIC COATING ON THE PROPERTIES OF COMPOSITES IN AUTOMOTIVE

XIAO Yun-jian, HUANG Zi-yu, XIN Chao-bo, HE Peng

2019, 0(11): 115-118.

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With the continuous development of the automobile industry, people′s requirements for automobiles are becoming more and more strict. On the one hand, traditional fuel vehicles will face the stringent requirements of fuel consumption of 100 kilometers; on the other hand, new energy vehicles will also bear battery life. The mileage challenge, both of which are closely related to the weight of cars. Therefore, the demand for lightweight vehicles is very urgent and has become an important development trend in the automotive industry in the future. The choice of materials is the key to lightweighting. Carbon fiber has excellent specific strength, specific stiffness and other properties, and has excellent lightweight performance. Carbon fiber composites are used on body structural components, which not only reduce the weight of the car, but also provide reliable pedestrian protection and safety. Therefore, the discussion of the interaction between electrophoretic coating and composite materials has important research significance in the development of lightweight automotive structural parts. In this paper, the interaction between composite materials and electrophoresis bath was studied by electrophoretic coating of composite samples. The study on the influence of composite materials on electric swimming pool bath and the effect of electrophoretic coating on the properties of composite materials. Thus, at the material level, the applicability of carbon fiber composite materials in the field of lightweight automotive structural parts is demonstrated.

CRITICAL CONTROL TECHNOLOGY OF LARGE SEGMENT WIND TURBINE BLADE MOULD ASSEMBLYP ROCESS

LI Yi-quan, WU Jian-dan, FAN Hu, LIU Xiao-bin

2019, 0(11): 119-122.

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Sectionalized molding of large-scale wind turbine blade mold is an effective way to solve the transportation difficulty and reduce transportation cost, and is also the trend of producing large-scale wind turbine blade mold. In this paper, three key technologies, including geometry accuracy control, pre-expanded air tightness and temperature uniformity control, are described. Taking the test results after the assembling of a certain model of sectionalized wind turbine blade mold as an example, the geometry accuracy, air tightness and temperature uniformity of the mold all meet the requirements of producing the blade. And the feasibility of sectionalized molding of large-scale wind turbine blade mold is proved.

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