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Table of Content

    28 March 2022, Volume 0 Issue 3
    BASIC STUDY
    Progressive damage study of composite countersunk head bolt lap structures under thermal mechanical coupling
    YU Fen, LIU Guo-feng, HE Zhen-peng, JIN Wei, LI Bai-chun, SUN Ai-jun, QIAN Jun-ze, ZHANG Gui-chang
    2022, 0(3):  5-14.  DOI: 10.19936/j.cnki.2096-8000.20220328.001
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    This paper presents a numerical study of the damage expansion process and strength of composite laminates with countersunk head bolted connections. A new three-dimensional progressive damage model is developed to predict the load carrying capacity and damage extension of composite countersunk bolt lap structures under the combined effects of temperature and bolt torque. The model integrates the composite constitutive equations considering thermal strain, failure and material degradation criteria, temperature-induced stiffness and strength correction parameters into the VUMAT subroutine, and quasi-static simulations using a thermal mechanical coupling approach. The results show that the progressive damage model can accurately predict the influence of temperature and bolt torque on the ultimate load carrying capacity of the lap joint structure, and can clearly reflect the failure mechanism and damage extension process. As the temperature rises, the ultimate load bearing strength of the lap structure decreases when the torque exceeds 15 N·m. The laminate fibre damage is mainly influenced by the 0° directional load, the laminate matrix damage is mainly influenced by the 90° directional load, and the failure unit extends along the applied load direction to the free boundary failure.
    Thickness effects of composite during curing process in different thermal environments
    CHEN Shu-xian, BAO Zheng-tao, ZHANG Xiao-long, YAN Deng-jie
    2022, 0(3):  15-23.  DOI: 10.19936/j.cnki.2096-8000.20220328.002
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    Three-dimensional unsteady finite element model and a numerical method for thermo-curing of resin matrix composite laminates were established by taking the time-dependent properties of materials into consideration in order to study the thickness effects on the thermo-curing process. And the validity of the mathematical model and calculation method was verified by the experimental results. The temperature, degree of cure and the residual stress in the laminates with different thicknesses under different thermal boundary conditions were numerically calculated. The effects of thickness parameters on the distributions of temperature and thermal stress in the laminates during curing as well as the curing time were studied. The results show that under the first and second types of thermal boundary conditions, with the increase of the thickness of the laminates, the maximum temperature and the residual stress in the laminates increase, while the curing time of the laminates is close. Under the third type of thermal boundary condition, with the increase of the thickness of the laminates in a certain range, the maximum temperature and the residual stress in the laminates increase, and the curing time of the laminates is prolonged. With the further increase of the thickness of the laminate, the curing time is shortened. For large thickness laminates considered in the article, compared with other two types of thermal boundary conditions, the application of the first type of thermal boundary conditions can not only greatly reduce the maximum temperature and residual stress in the laminates, but also shorten the curing time.
    Application of Abaqus secondary development in buckling analysis of variable stiffness laminates
    DONG Ming-jun, CAO Zhong-liang, HAN Zhen-hua, FAN Guang-hong
    2022, 0(3):  24-28.  DOI: 10.19936/j.cnki.2096-8000.20220328.003
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    The buckling performance of variable stiffness laminates is one of the main criteria for analyzing its mechanical properties. This article is based on the Python language for the secondary development of Abaqus, and establishes a Python interactive interface. By establishing a finite element model of variable stiffness perforated/non-perforated laminates, the purpose of rapid modeling, automatic submission of analysis and collection of required data can be achieved. Finally, the call of the secondary development model, the reading of data and the output of the results are discussed through a calculation example, which verifies the feasibility of the secondary development. This study provides a reference for the subsequent development and application of Python's buckling simulation of variable stiffness laminates, and has certain guiding significance.
    Optimization and lightweight design of fretting fatigue performance of riveting holes in fiber metal laminates
    ZENG Xin, WANG Xiao-xiao, PING Xue-cheng, GUO Qian, HUANG Qi-heng
    2022, 0(3):  29-37.  DOI: 10.19936/j.cnki.2096-8000.20220328.004
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    In order to improve the fretting fatigue performance of the riveted structure of FMLs, the Smith-Waston-Topper (SWT) model based on the critical plane method was constructed to predict the crack initiation location and life of a riveted hole. The effects of design variables such as plate width W/D, end distance E/D, preload P and friction coefficient f on the SWT fretting damage are analyzed. The research results show that the fatigue damage parameter is the largest at the contact edge of the rivet and the FML. As the plate width and end distance increase, SWT fatigue damage parameters decrease. The increase of preload and friction coefficient contributes to the reduction of SWT fatigue damage parameters and the increase of specific load. A four-factor three-level quadratic orthogonal combination test design is carried out, and the SWT fatigue damage parameter is reduced by 47% compared to that without optimization. Finally, given the critical SWT damage parameters, lightweight design is carried out according to factors such as weight and critical load, and a reasonable Glare laminate method is selected.
    Defect detection of wind turbine blade based on improved SSD
    ZHU Jia-wei, WEN Chuan-bo
    2022, 0(3):  38-44.  DOI: 10.19936/j.cnki.2096-8000.20220328.005
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    Aiming at the problems of low accuracy and time-consuming of traditional algorithm, this paper proposed a defect detection method of wind turbine(WT) blade based on improved SSD. Firstly, the inclined WT blades are corrected by Hough transform and trimmed to a uniform size to form a complete data set. Then, two kinds of residual networks (ResNet, ResNext) are used to replace the traditional VGG as the backbone of SSD algorithm for feature extraction. Finally, the prediction network is used to complete the prediction of defect category and boundary box location. The experimental results show that the improved SSD algorithm improves the value of mAP by 7% compared with the traditional SSD algorithm. At the same time, the detection efficiency has been greatly improved.
    APPLICATION RESEARCH
    Properties of color carbon fiber prepared by self-assembly deposition of chemically modified graphene oxide
    HOU Jing, YANG Chen, LIU Qin-qin, LEI Yan-ni, XU Pei-jun
    2022, 0(3):  45-50.  DOI: 10.19936/j.cnki.2096-8000.20220328.006
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    Carbon fiber has been widely used in aviation, aerospace, automotive, energy and other fields due to its high specific strength, high specific modulus and other excellent properties. How to maintain the excellent mechanical properties of carbon fiber composites while taking into consideration its functionality and intelligence has gradually become the future development direction of composites. Graphene oxide (GO) aqueous solution can form a structural color coating similar to one-dimensional photonic crystal through deposition and self-assembly on carbon fiber. However, there is only physical absorbing force between GO coating and carbon fiber, and the interface performance is insufficient. In this paper, GO is chemically modified with silane coupling agent (APTES). The modified GO (mGO) is also deposited on the surface of carbon fibers by self-assembly method to prepare color carbon fibers. The influence of APTES content on interfacial shear strength, tensile mechanical properties and coloring mechanism are investigated. The results show that the introduction of amino functional group in APTES can significantly improve the interfacial bonding property between carbon fiber and GO. mGO with multilayer structure can remedy the surface defects of carbon fiber and improve the strength of monofilament fiber. Compared with GO-CF, the monofilament tensile strength and interfacial shear strength of mGO-CF-15 are increased by 12.4% and 13.5% respectively.
    Force analysis of underwater solar composite floating body system under wave load
    XIA Guo-long, FANG Hai, HAN Juan, LI Xiao-long
    2022, 0(3):  51-55.  DOI: 10.19936/j.cnki.2096-8000.20220328.007
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    Aiming at the problems of low strength, poor durability, poor wind wave resistance and high maintenance cost of traditional floating structures such as polyethylene and polyvinyl chloride, a floating structure of composite materials for water solar photovoltaic power generation is proposed in this paper. The structure includes the main beam and secondary beam of the floating body made by vacuum induction molding process, and the vertical support made by pultrusion molding process. In this paper, static buoyancy, wind force analysis, wave buoyancy calculation and strength check of floating body system are carried out. The results show that when the maximum water depth of the river is less than 5.06 m, the maximum upward wave buoyancy pressure on the main beam of the floating body is 50 kPa, the main beam of the composite floating body system meets the requirements of the bearing capacity under the wave load, and the floating body system has the ability to resist the wave damage, which provides a reference for the future application of the composite floating body structure in the floating photovoltaic power station.
    Experimental study on the effect of damping coating on the vibration of GRP plate
    YANG Zhuo-yi, WANG Yi-bo, ZHOU Feng-lei, SONG Lei, OU Shu-bo, CHEN Shu-hu
    2022, 0(3):  56-59.  DOI: 10.19936/j.cnki.2096-8000.20220328.008
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    Coating technology refers to the application of coating materials on the surface of structural parts to achieve its anti-corrosion, anti-friction, and thermal barrier functions. In recent years, it has been discovered through continuous in-depth research on coating technology that the application of coating materials on structural parts coatings can achieve good vibration damping effects and have little effect on the overall quality of structural parts. At the same time, the coating layer has the advantages of high temperature resistance, corrosion resistance and high hardness. Therefore, it has gradually become an emerging vibration damping method. The vibration characteristics of FRP coated with damping coating and butyl rubber damping layer were studied, and the frequency and damping loss factor of FRP in each mode after applying the above two damping materials were compared and analyzed. The results show that applying damping paint on the GRP plate can achieve a better vibration damping effect.
    Compressive strength prediction model of civil aircraft panel based on fiber reinforced Metal
    LIU Jia, WANG Xue-hua, BAI Cheng-zheng
    2022, 0(3):  60-65.  DOI: 10.19936/j.cnki.2096-8000.20220328.009
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    Based on the moment distribution method, the buckling analysis theory of fiber-metal reinforced civil aircraft plate structure under axial compression load is studied, the compressive strength of the civil aircraft plate structure is analyzed and calculated, and a theoretical prediction model for the ultimate strength of the civil aircraft plate structure after buckling is proposed. By comparing with the compressive strength failure test results of fiber-metal reinforced plate structure of civil aircraft, the theoretical predicted values of the model are in good agreement with the experimental values, with a deviation of 3.01%. The accuracy of the strength prediction model established is verified. In addition, the buckling and post-buckling load-bearing capacities of fiber-metal reinforced civil aircraft plate structure were analyzed by using the finite element method, and the stress concentration area and failure process of the plate were simulated. The results show that the plate structure have ideal post-buckling load-bearing capacities after local buckling. This study can provide some theoretical basis and experimental data for the material selection of reinforced civil aircraft plate structure configuration, the improvement of technological performance and the prediction of the compression strength value of fiber metal reinforced civil aircraft plate structure, and can replace the compression test of large structural parts of the plate structure and reduce the cost and cycle of the pre-research experiment in the stage of civil aircraft pre-research and design.
    Research on electrical-heating activated healing of composite cracks by CNT/EMAA/epoxy film
    WANG Wei, OUYANG Qin, LIU Ling
    2022, 0(3):  66-72.  DOI: 10.19936/j.cnki.2096-8000.20220328.010
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    Brittle epoxy composites are easy to initiate cracks under external loads, thereby affecting the mechanical properties and integrity of the composites. If these cracks can be healed in time, the reliability and service lives of the composites can be improved. Therefore, in this paper, thermoplastic copolymer poly (ethylene-co-methacrylic acid) (EMAA) is used as a crack healing agent, and carbon nanotubes (CNT) are introduced into epoxy at the same time to prepare a CNT/EMAA/epoxy film, which has electrical-heating activated crack healing function. Firstly, EMAA films with ordered holes are prepared by hot-pressing and then sprayed with CNT. Next, the CNT/EMAA films are infiltrated with epoxy to prepare CNT/EMAA/epoxy adhesive films. Then, the healing efficiency of tensile strength is studied. Finally, the adhesive film is used as glue layers to bond composite T-joints, and the healing efficiency of T-joint peeling damage is studied. The results show that the healing efficiency of the CNT/EMAA/epoxy film on tensile strength is 73.8% by using the electrical-heating method. In addition, when the T-joints are completely peeling failed or start initial damage cracks, the electrical-heating healing efficiencies of the corresponding peeling load are 75.0% and 121.2%, respectively. The results indicate that the CNT/EMAA/epoxy adhesive film prepared in this paper has good crack healing properties, and the healing effect of electrical-heating is the same as traditional oven-heating.
    Calculation for maximum crack width of concrete beams reinforced with hybrid steel and FRP bars
    ZHOU Man-qing, ZHANG Zhi-mei, WEI Jiu-yi
    2022, 0(3):  73-80.  DOI: 10.19936/j.cnki.2096-8000.20220328.011
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    In order to study the crack calculation of concrete beams reinforced with hybrid (steel/FRP) bars, firstly, the applicability of the existing average crack spacing calculation formulas for hybrid reinforced concrete beams is analyzed using 55 crack relevant test data of hybrid reinforced beams at home and abroad. The multiple regression analysis of 55 test data is carried out using MATLAB, and the relevant undetermined coefficients in the existing formulas are modified. Then, the formula of the average crack spacing for hybrid reinforced concrete beams is established, and the value of the relative bonding characteristic coefficient vi is given. Secondly, the calculation method of the longitudinal bars strain non-uniform coefficient ψ and the value of the force characteristic coefficient αcr under short-term load are determined. At the same time, the maximum crack width correction coefficient k3 is introduced, and the value of k3 is determined based on the analysis of 45 crack width relevant test data. Then, the calculation formula of the maximum crack width is established. The comparative analysis with the test data shows that the formulas of the average crack spacing and the maximum crack width for the hybrid reinforced concrete beam have good applicability.
    Experimental study of the deformation performance of composite beams with SMA sheet actuators adhered on the surface
    LIN Zai-wei, YUAN Guo-qing
    2022, 0(3):  81-86.  DOI: 10.19936/j.cnki.2096-8000.20220328.012
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    Adhering SMA sheet actuators to the surface of composite structures to make deformable structures has many advantages, but there are also problems in ensuring the quality of the bonding and designing the allowable reversible strain. In this paper, we firstly treat the surface of SMA sheets with suitable infrared laser parameters, then SMA sheet actuators are obtained by introducing pre-strain, followed by adhering them to the upper surface of the composite plate beams to produce deformable composite beams. The deformation performance of composite beams with different pre-strain is investigated experimentally. It is shown that a suitable laser surface treatment can make the composite beam obtain a greater deformation capability without the failure of the adhesive layer. However, with the increment of pre-strain, the adhesive layer of the composite beam will still undergo large area cohesive damage during the actuation process.
    Design and performance research of carbon fiber reinforced epoxy resin prepreg tow for dry filament winding
    YANG Ze-hao, TAO Lei, QI Liang-liang, LI Zhao-yang, LI Xin-he, DAI Jun, LIU Yong, ZHANG Hui
    2022, 0(3):  87-95.  DOI: 10.19936/j.cnki.2096-8000.20220328.013
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    Dry filament winding can effectively improve the quality stability of composite products, which is one of the research focuses of composite material preparation. In this paper, we develop an epoxy resin system that is suitable for prepreg tow. Then, prepreg tow which can be stored at room temperature is prepared by hot melt method. Through the study of epoxy resin's process performance, mechanical properties, glass transition temperature and non-isothermal rheological curve, the formula was determined. In the meanwhile, storage performance at room temperature of the prepreg tow made of this resin system was systematically studied. The research results show that the optimal epoxy resin system has excellent processing performance and mechanical properties at the same time. Its tensile strength is 109 MPa and its flexural strength is 69 MPa, fracture toughness and impact strength are 1.36 MPa·m1/2 and 42.8 kJ/m2, respectively. In addition, the storage stability of the prepreg tow made of the epoxy resin system is excellent. After 60 days of storage at room temperature, process performance and mechanical properties of the prepreg tow's epoxy resin is maintained at a relatively stable level.
    Study on fabrication technique of new thermal protection structure based on resin matrix composite
    LIANG Heng-liang, CHEN Jing, LIU Yu, ZHANG Shou-chun
    2022, 0(3):  96-103.  DOI: 10.19936/j.cnki.2096-8000.20220328.014
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    The thermal protection structure was fabricated by co-curing graphite film and BMP350 polyimide composite. The graphite film was fabricated at a temperature of 3 000 ℃, making polar functional groups hardly exist on film surface, which prevents the bonding of the film to the composite. This work improves the surface treatment technique of the graphite file and interface controlling technique. As a result, typical composite plate specimens with thermal protection structure could be made. Nondestructive testing (NDT), test of bonded strength between the film and composite and thermal shock testing were conducted. This structure could pass NDT test, airflow erosion test and thermal shock testing of 400 ℃, 547 h and 800 ℃, 30 min. The pull off failure occurs inside the film. These testing results show the thermal protection structure possesses the potential of engineering application.
    Fatigue properties of basalt fiber composites and temperature effects on the properties
    ZHAO Gu-xian, CAO Sheng-hu, ZHANG Jian
    2022, 0(3):  104-109.  DOI: 10.19936/j.cnki.2096-8000.20220328.015
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    In order to study the tensile fatigue properties of basalt fiber (BF) reinforced epoxy unidirectional composites at different ambient temperatures, a series of experimental tests and life prediction were carried out. Firstly, the maximum failure stress σm at room temperature was obtained by static tensile test. Then, the tension-tension fatigue tests with stress levels of 75%σm, 70%σm, 65%σm and 60%σm were carried out at three ambient temperatures (room temperature, 50 ℃, and 70 ℃), respectively, and the corresponding fatigue life cycles and obtained relevant fatigue stiffness data were achieved at different stress levels. Finally, the fatigue life at different ambient temperatures were estimated according to the exponential S-N curve. The results show that the fatigue life of basalt fiber composite increased with the decrease of stress level under the same temperature. The fatigue life decreased significantly with the increase of temperature under the same stress level, and the fiber-drawing of fatigue fracture increased dramatically with the increase of temperature. In the initial stage of tension-tension fatigue, the higher the temperature, the more obvious the stiffness degradation and the greater the degradation rate. The comparison analysis show that the fatigue properties of basalt fiber composites is better than that of glass fiber composites at room temperature.
    Effect of melting bonding depth and lap mode on mechanical properties of plain glass fiber/MC nylon composites
    GUO Wei-jian, TAO You-rui, DONG Li-jun, WU An-ru
    2022, 0(3):  110-114.  DOI: 10.19936/j.cnki.2096-8000.20220328.016
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    Plain glass fiber/MC nylon composite material has the advantages of high specific strength, corrosion resistance and recyclability. It is one of the materials worthy of attention in the field of automobile in the future. In this paper, the effects of lap mode and fusion depth on joint strength of plain glass fiber/MC nylon composites were studied by experimental method under melting bonding process. The experimental results show that, under the same process parameters, the double lap butt joint has the best mechanical properties, and the tensile shear strength of the lap joint increases first and then decreases with the increase of melting depth. When the melting depth of the lap joint is 2 mm, the shear strength reaches the maximum of 19.24 MPa. Micro-CT technique was used to scan the single lap specimens with different melting depths. The results show that the matrix of lap interface gradually decreases with the increase of melting depth. With the increase of melting depth, the failure modes were plastic deformation and cracking of nylon matrix, cracking of nylon matrix and debonding of glass fiber and nylon matrix, debonding of glass fiber and nylon matrix.
    Structure design and application study of engineering of lightweight composite pole
    KE Rui, ZHU Xiao-dong, MEI Duan, HE Chang-lin, WU Xiong, WU Feng, SHEN Fan
    2022, 0(3):  115-120.  DOI: 10.19936/j.cnki.2096-8000.20220328.017
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    In order to develop a kind of lightweight, stable structure performance and durability of composite electric pole, this paper, based on the pilot project of mountainous environment in coastal area, starts with the load calculation of transmission electric pole under various working conditions, establishes the finite element analysis model, and carries on the structural design of composite electric pole. A 12 m long composite electric pole with two sections was prepared by small Angle cone-winding process using modified polyurethane as matrix material and glass fiber as reinforcement material. Mechanical true load performance evaluation and series of material aging test of the full-size electric pole were carried out. The results show that the composite pole with the insertion coefficient of 2.0 based on simulation meets the practical application requirements in terms of strength and deflection, and has excellent weather resistance. The segmented structure of the pole is smaller in size and lighter, which will greatly improve the convenience of construction and transportation and provide a new idea for the construction of distribution network lines.
    REVIEW
    Research status of impact test and simulation of honeycomb sandwich structures
    LI Zong-quan, ZHANG Sheng-lan, YANG Wen
    2022, 0(3):  121-128.  DOI: 10.19936/j.cnki.2096-8000.20220328.018
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    Honeycomb sandwich structures have been widely used in aeronautics, automotive and marine industry because of their excellent crashworthiness performance, fatigue resistance and energy absorption ability. The honeycomb sandwich structure is susceptible to various speed impacts during service, and these impacts would cause the performance of the honeycomb sandwich structure to decrease or even be damaged. Therefore, it is very important to test and simulate the honeycomb sandwich structure to study the impact resistance and impact process of the honeycomb sandwich structure. This article summarizes the impact test and numerical simulations of honeycomb sandwich structures at home and abroad. In the experimental study, the low-velocity impact and high-velocity impact test scheme are summarized, including Charpy impact test, drop impact test and gas gun test. At the same time, in the simulation research, the modeling of honeycomb sandwich structure, the damage and failure of composite materials, the impact process and the influence of structural parameters on the impact performance are summarized. Finally, a preliminary prospect on the future development direction of the honeycomb sandwich structure impact experiment and simulation is given.