COMPOSITES SCIENCE AND ENGINEERING

Research on bidirectional control method of tension force in additive manufacturing of continuous fiber reinforced composite

LIU Xiao-jun, SHAN Zhong-de, WANG Shao-zong, ZHAN Li, ZOU Ai-ling, LIU Xiao-hang

2021, 0(7): 5-10. DOI: 10.19936/j.cnki.2096-8000.20210728.001

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Aiming at the problem that the continuous fiber reinforced composite material has no tension or the tension can only be adjusted in one direction during the additive manufacturing process, a bidirectional control method for the tension in continuous fiber additive manufacturing was proposed. A bidirectional PID closed-loop control experiment platform for continuous fiber additive manufacturing with Siemens 1200-1217 PLC controller as the core, servo motor as the execution element and tension sensor as the detection element was built. The irregular movement of the printing nozzle of continuous fiber additive manufacturing was equivalently simulated by the forward and reverse movement of the fiber roller driven by the stepper motor. Through automatic adjustment and manual tuning of PID parameters, PID parameters that can stably control the tension within a certain range were obtained. Without the gravity stable module, the control accuracy of the tension control system at different take-up speeds and different tension setting values, as well as the control ability of the system when the take-up roller under the conditions of forward acceleration, reverse acceleration, and forward/reverse mixed speed change were studied. After adding the gravity stabilization module, its effect on stabilizing tension when the take-up speed switches instantaneously between forward and reverse was studied. The research results show that the control accuracy of the system can reach up to ±0.22 N, and it has a rapid adjustment function when the take-up roller is switched between forward and reverse at a certain speed. The addition of gravity stabilization device can reduce the sudden change of tension caused by the instantaneous excessive speed change, and has a stabilizing effect on the tension control system.

Research on torsional stiffness of fastener joints in GFRP supporting structure

QIAN Qing-feng, DENG An-zhong, LI Fei, LUO Sheng, GAO Xun-peng, SHI Lin

2021, 0(7): 11-16. DOI: 10.19936/j.cnki.2096-8000.20210427.001

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The torsional stiffness of GFRP support structure joints is an important parameter to study the stability of GFRP support structure, but it has not been studied. In this paper, the torsional stiffness of fastener joints of GFRP support structure under different tightening torques is studied through experiments, and the bending moment-rotation angle curve is established to obtain the torsional stiffness of joints under different tightening torques. Then the finite element model is established to analyze how the tightening torque affects the torsional stiffness of the fastener joint. Finally, the influence mechanism of different tightening torques on the rotational stiffness of the joint is obtained. The research shows that the GFRP tube fastener connection node is a semi-rigid node. With the increase of the tightening torque of the node, the rotational stiffness of the node increases with the increase of the tightening torque. The torsional stiffness of GFRP fastener joints obtained in this paper can provide a theoretical basis for the research and calculation of the overall stability bearing capacity of GFRP fastener support structure.

Fatigue study on bolt connection of carbon fiber reinforced plastics at low temperature

LI Hua, ZHENG Hui, WANG Gong-dong, LIU Yue, YAO Song-yang

2021, 0(7): 17-21. DOI: 10.19936/j.cnki.2096-8000.20210728.003

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The tensile fatigue of bolted connections at low temperature is studied, mainly aiming to solve the tension-tension fatigue problems of Carbon Fiber Reinforced Plastics (CFRP) and 2024Al. Firstly the tensile experiments under different environment were performed to get the maximum static load. Then the damage process of the heterogeneous material laminated plate connected joints under the different temperature was explored through the static load damage curve. Then the delamination and tear degree of the composite laminated plates were compared by the observation of different temperature tensile failure phenomenon. Moreover, based on the above analysis, the influence of the low temperature environment on the bolt connection fatigue of heterogeneous material was explored. Then the different temperature grouping of laminated plates joint in their respective 85%, 80% and 75% respectively were chosen to undergo room temperature and low temperature fatigue experiments under the maximum static load condition. The experimental results were used to fit S-N curve of normal temperature and low temperature. The results demonstrated that the tensile failure strength of the lower bonding plate joints in low temperature environment was stronger than that in normal temperature environment under the same experimental conditions. Fatigue curve analysis showed that the laminated plates under low temperature environment offered stronger fatigue loading ability.

Research on the post-buckling bearing capacity of T-type composite stiffened panel

CUI Yong-jiang, WANG Bin-tuan, ZHAO Zhan-wen

2021, 0(7): 22-27. DOI: 10.19936/j.cnki.2096-8000.20210728.004

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In order to study the post-buckling bearing capacity of T-type composite stiffened panel under compression load, calculation of engineering algorithm, finite element method and compression test are used for composite stiffened panel. The buckling load and failure load, load-displacement curve and damage evolution of composite stiffened panel are obtained. By comparing the two methods and test results, some conclusions can be obtained. There is a strong post-buckling bearing capacity after buckling. Compared with the finite element method, the error of engineering algorithm is larger. The quasi-static method can effectively simulate the buckling and post-buckling behavior of stiffened panel, but the calculation cost is relatively large.

Test and theoretical method for coefficients of thermal expansion of carbon fiber reinforced composite laminate

QIU Xue-qiong, CHEN Lin

2021, 0(7): 28-32. DOI: 10.19936/j.cnki.2096-8000.20210728.005

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With the increase of applications of composites in airplane structures, the thermally-induced stresses become unneglected issues in composite-metal hybrid structures due to the coefficients of thermal expansion (CTE) differences of metal and composites. In order to analyze thermally-induced structural stresses, the CTEs of materials is necessary. Due to the anisotropy of CTEs of composites, which is dependent on the layer and structure of laminates, and the low CTEs along fiber direction, it results in difficulties in evaluation of CTEs for composites. Based on the ASTM E831 and ASTM E289, the CTEs of the T800 carbon fiber reinforced composites with different stack styles were tested through thermomechanical analysis (TMA) and speckle interferometry method, respectively. The CTEs for laminates in different stack sequences were studied, and the theory of in-plane CTEs for composite laminates was proposed. This work provided a fast approach for evaluation of CTEs for carbon fiber reinforced laminated composites for aircraft.

Electrical performance optimization design of the radome with composite material in the top region

SONG Xiao-jie, ZHANG Li-song

2021, 0(7): 33-38. DOI: 10.19936/j.cnki.2096-8000.20210728.006

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Radome is an important part of missiles and other aircraft, and its electrical performance directly determines the guidance accuracy and distance of action of missiles. In this paper, the cone radome which is the typical shape is designed for simulation and optimization of the top region. The geometric model of the cone radome is built and the key dimensions parameters are determined. According to the relevant electrical performance parameters and the incidence angle distribution of composite materials, the radome is designed with the half-wave thickness initially. Based on the FEKO simulation platform, MOM is used to simulate the model with MLFMM, and the transmission coefficient of radome in different scan angle states in pitching direction is obtained with the change of the top region's thickness. The analysis found that the transmission coefficient of the radome showed a cyclical downward trend with the increase of the thickness of the top region. Changing the outer diameter of the ball head of the radome and the angle of the cone, the law of electrical performance change is basically consistent in general. However, the larger the increase of the outer diameter of the ball head, the larger the scanning angle range affected by the thickness of the top region. The change of the cone angle affects the range of the top region thickness with optimal transmission coefficient. Based on the law of electrical performance change, the top region of cone radome is optimized. By analyzing the law of electrical performance change, the optimization direction is proposed and the technical support is provided. The paper is of some reference and guiding significance in radome design field.

Preparation and performance evaluation of ultra-thin carbon fiber composite structure battery

YANG Xiang-tao, WANG Chao-yang, ZHANG Jin-na, ZHU Shi-jie, GUO Hai-wei, WU Hai-hong, TONG Li-yong

2021, 0(7): 39-47. DOI: 10.19936/j.cnki.2096-8000.20210728.007

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With the continuous development of intelligent systems, driverless vehicles and other modern transportation, the lightweight, safety, payload and cycle life of traditional batteries have been faced with new challenges. In this paper, three different electrodes of carbon material were prepared by mixing activated carbon, mesoporous carbon and hybrid activated and mesoporous carbons. The microstructures and electrochemical properties of all three electrodes were compared and analyzed. A structural battery was fabricated by selecting the electrode presenting the best electrochemical performance integrated with ultra-thin carbon fiber reinforced polymer composite (UTCFRP). The mechanical properties were tested by a universal testing machine. The experimental results show that the electrode made of hybrid activated carbon and mesoporous carbon has a surface morphology that is more suitable for ions to migrate. The structural battery presents good charge and discharge characteristics. Under load conditions, the fluctuate of its specific capacitance and energy density is below 15% as the unit mass load of tensile test is less than 240 kN/kg; the specific capacitance and energy density increase by 39.5% as the unit mass load of compression test reaches 58 kN/kg, and the retention rate of the specific capacitance and energy density is 89% as the unit mass load of bending test reaches 41 kN/kg. As one kind of energy storage composite material, the structural battery with UTCFRP has great potential in improving the battery performance and realizing miniaturization and lightweight.

Research on filament winding line path and technology of unequal pole hole

ZU Lei, XIAO Kang, ZHANG Qian, ZHANG Gui-ming, WU Qiao-guo, LI De-bao

2021, 0(7): 48-54. DOI: 10.19936/j.cnki.2096-8000.20210728.008

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In this paper, the design and process research of uniform filling linear trajectory for filament wound vessel with unequal polar holes are carried out. Firstly, the winding angle of left and right heads is smoothly and continuously transited in the cylinder by optimizing the slip coefficient. The necessary conditions for realizing the central angle of uniform filling are studied, and the tangent points of the line are calculated by using the continuous fraction principle. At the same time, the slip coefficient of the left and right ends of the stable winding and uniform covering is satisfied. Based on the equal contour constraint conditions, the motion trajectory equation of the four axis winding machine is analyzed and converted into the corresponding machine code for actual winding. The experimental results show that the stable winding of the fiber on the surface of the unequal polar hole mandrel is realized, and the uniform filling and winding effect are achieved after winding a certain number of cycles. The simulation results show that the design parameters and optimization algorithm are feasible.

Numerical simulation of projectile oblique penetration into damping composite armor

WANG De-pan, LIANG Sen, ZHOU Yue-song, LIU Long

2021, 0(7): 55-62. DOI: 10.19936/j.cnki.2096-8000.20210728.009

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The process of 12.7 mm penetrating alumina/damping layer/UHMWPE composite bulletproof armor was simulated by ANSYS/LS-DYNA finite element software. The energy absorption of tungsten alloy core penetrating the target plate at different angles and speeds was calculated, and the effect of damping layer thickness on the energy absorption of composite armor was investigated. The calculation results show that the energy absorbed by the composite target increases with the increase of the oblique angle of the composite target. By simulating the oblique penetration process of the penetrating projectile with different speeds into the composite armor, it is found that the composite armor shows the best energy absorption effect in the range of 700 m/s~850 m/s velocity, and the thickness of the damping layer at different positions in the composite armor to achieve the best energy absorption effect is different. This work provides a reference for the follow-up study of the medium and high-speed impact resistance of damped composite structures.

The effect of corner radius and strain rate on the compressive strength of FRP weakly confined square concrete

MA Chen-yu, JI Yu-peng, LIU Da-wei, LIU Hao-yuan, CAO Yu-gui

2021, 0(7): 63-67. DOI: 10.19936/j.cnki.2096-8000.20210728.010

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Fiber-reinforced polymer (FRP) has been widely used in repair or confinement concrete column. However, most of research has been conducted on the mechanical behavior of FRP strong confined circular concrete. Few studies had focused on the mechanical behavior of FRP weakly confined square cylinder. In order to study the influence of the corner radius ratio and strain rate on the compression mechanical properties of FRP weakly confined square cylinder, an experiment of 20 specimens with different corner radius was carried out under different strain rates. The typical stress-strain curves were drawn based on the test data. The test results show that the compressive strength of FRP weakly confined square cylinder increased with the increase of both corner radius ratio and strain rate. The test results are used to evaluate the existing compressive strength model, and it was found that the existing compressive strength model can be used to predict the compressive strength of FRP weakly confined square concrete under different loading rates.

Analysis of falling performance of composite skid landing gear

WU Yu-gen, MAO Chun-jian, ZHOU Zhong-bin, ZHONG Mao-ping

2021, 0(7): 68-75. DOI: 10.19936/j.cnki.2096-8000.20210728.011

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Composite materials have good mechanical properties and have been widely used in aviation field. Compared with the traditional metal landing gear, the composite skid landing gear has the advantages of light weight, corrosion resistance and designability. In order to ensure the safety of composite landing gear in use, it is necessary to study the mechanical properties of composite landing gear. For composite skid landing gear, a falling platform test system is designed and tested. Based on ABAQUS/Explict analysis module, the material user subroutine VUMAT is redeveloped and defined, damage criterion and material stiffness reduction scheme are introduced, and a progressive damage analysis method for composite skid landing gear is established. The numerical results agree well with the test results, which verifies the validity of the model. The results show that the stress and strain of the fuselage-skid connection and the variable thickness area of the composite layers are higher during the falling of the composite skid landing gear. In condition Ⅱ, composite skid landing gear may cause certain matrix damage at the clamp connection after landing.

Research on axial compression performance of carbon fiber composite tube based on AE

LI Qian-qian, ZHANG Jia-shun, TUO Xiao-qing, GAO Yan-tao, LI Wei

2021, 0(7): 76-83. DOI: 10.19936/j.cnki.2096-8000.20210728.012

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Acoustic emission(AE) technology is used to monitor and record the axial compression loading process of a carbon fiber composite tube. And acoustic emission characteristic parameters including Cumulative Event Count, Energy, Peak Frequency and Amplitude during the compression process are analyzed. Combined with the compression load curve, the damage process and failure modes of the carbon fiber composite tube under axial compression load are studied. The results show that the typical characteristic parameters of AE can correspond well to the change of the time-load curve. The change of acoustic emission signals can reflect the damage form at different failure stages and the damage characteristics of different types of samples. It has reference value for studying the axial compression performance of carbon fiber composite tube.

Influences of assembly process on bending performance of composite assemblies

GE En-de, SHANG Yan-wei, LIU Xue-shu, LI Ru-peng

2021, 0(7): 84-92. DOI: 10.19936/j.cnki.2096-8000.20210728.013

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In order to study the influence of different assembly process on bending performance of carbon fiber reinforced resin plastics (CFRP), experimental studies were carried out on the DNS100 electronic universal testing machine. By comparing the ultimate load, assembly stiffness and failure time, the influence of assembly process such as pitch of holes, gap size and shimming material on the bending performance of composite assemblies is analyzed. The results show that, within a certain range, increasing pitch of holes can effectively improve the stiffness of the assembly. The effect of assembly gap on the bending performance is closely related to the thickness of the assembly. In some cases the liquid shim is better than the glass fiber.

The effect of cross-linked structure of epoxy resin on curing kinetics

ZHANG Dai-jun, XING Yu, BAO Jian-wen, ZHONG Xiang-yu, LIU Wei

2021, 0(7): 93-98. DOI: 10.19936/j.cnki.2096-8000.20210728.014

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The epoxy resin E54 was added with different proportions of the trifunctional meta-aminophenol epoxy resin S500M and was used to prepare the epoxy resins which has different cross-linked structures with the DDS curing agent. The non-isothermal DSC method was used to analyze the curing process of epoxy resin, and the curing degree versus temperature curve was drawn according to the curing reaction heat. The activation energy and kinetic parameters of the epoxy resin systems were obtained by using Kissinger and Crane equations. With the increase of crosslinking density, the results showed that the starting temperature, peak temperature and termination temperature of the curing reaction moved forward, the curing time was shortened, and the activation energy of curing reaction was decreased, but the frequency factor and reaction order were basically unchanged.

Investigation on the manufacturing process of large-scale nacelles with double curved honeycomb sandwich structure

WANG Ying, XIAO Guang-ming, HE Wei

2021, 0(7): 99-104. DOI: 10.19936/j.cnki.2096-8000.20210728.015

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The large hyperbolic honeycomb sandwich structure is a kind of complex structure form in composite materials, it has the charecteristics of large size and complex profile. But its mechanical bearing performance is good, light weight, and has strong resistance to deformation. Sandwich nacelles are studied, the structure characteristics and processing technology are discussed in detail. The honeycomb core is easy to shrink and hard to fix, and the assembly area requires high technical difficulties. The experimental scheme, experimental data, and engineering differences are analyzed and compared. Finally, a set of effective forming methods were obtained.

Development of an anti-bird impact test piece of aramid fiber reinforced composite

SU Zhen-yu, QIU Qi-yan

2021, 0(7): 105-110. DOI: 10.19936/j.cnki.2096-8000.20210728.016

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An anti-bird impact test piece was manufactured by a domestic novel aramid fabric reinforced prepreg 044B/BA9918. By means of simulation analysis, the entire development cycle was greatly shortened. The part passed the bird impact test, which showed that the anti-bird impact test piece made by 044B/BA9918 aramid fabric prepreg had excellent impact resistance performance. Furthermore, surface profile, weight as well as thickness of the test piece met the design requirements well.

Fabrication technologies and mechanical properties of composite foam sandwich structure with a reinforcement between face sheets and core

DU Yun-tong, XIONG Jian, ZHANG Rui, LIU Hui-bin, ZHANG Chao, ZHU Ye, ZHONG Hai-gang, WANG Ji-hui, LI Xu

2021, 0(7): 111-120. DOI: 10.19936/j.cnki.2096-8000.20210728.017

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Lightweight structure is an eternal theme in the development of aerospace, vehicles, ships and other fields. Composite foam sandwich panels are an important structural form in lightweight structures. Generally, high-strength, high-modulus composites panels were used as the face sheets and lightweight porous foam were used as the sandwich cores in the middle. However, the failure of debonding between the face sheets and foam core of the sandwich structure has become the essence of its engineering application. This paper summarizes the latest researches about composite foam sandwich structure with a reinforcement between face sheets and core in terms of design, fabrication and mechanical properties, focusing on the reinforcement methods of stitching, tufting and Z-pin about design and preparation process. The improvements of mechanical performance after the reinforcement between the face sheets and core is characterized from comparisons of the experimental results between the foam sandwich structures with and without reinforcement.

Research progress of fatigue performance of RC beams strengthened with externally bonded FRP

ZHANG Zhi-mei, YANG Ming

2021, 0(7): 121-128. DOI: 10.19936/j.cnki.2096-8000.20210728.018

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Fiber reinforced polymer (FRP) is widely used in reinforcement engineering because of its light weight, high strength and good fatigue resistance. Under the action of fatigue load, the properties of various materials and the interface bond between FRP and concrete are deteriorating, and the existing damage is accumulating, which greatly reduces the safety of reinforced concrete beams. In this paper, the experimental research, numerical simulation and theoretical analysis of the flexural fatigue performance of reinforced concrete beams strengthened with externally bonded FRP are summarized in detail, and the fatigue performance of FRP-concrete bonding interface and corroded reinforced concrete strengthened beams are introduced. The shortcomings of existing research are analyzed, and some suggestions for the direction of future research are put forward.

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