COMPOSITES SCIENCE AND ENGINEERING

Effect of molding temperature on defects and mechanical properties of CF/PPEK composites

WANG Meng, LIU Cheng, ZHANG Yu, JIA Hang, QIAO Yue, JIAN Xigao

2024, 0(3): 5-12. DOI: 10.19936/j.cnki.2096-8000.20240328.001

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In this paper, continuous carbon fiber reinforced poly(phthalazinone ether ketone)(CF/PPEK) prepreg and composites were prepared by solution impregnation method and vacuum hot-molding method, respectively. The ultrasonic phased array and three-dimensional X-ray microscope (XRM) nondestructive testing was carried out for composites prepared at different molding temperatures. The CF/PPEK composites were characterized by rotary rheometer, electronic universal testing machine, dynamic mechanics analyzer (DMA), Fourier transform infrared spectrometer (FT-IR), scanning electron microscope (SEM) and metallographic microscope. The influence of molding temperature on the wetting quality of the fiber, the porosity, the bending behavior and interlaminar shear properties of the composite were systematically investigated. Furthermore, the fracture mechanism and the influence of defects on its properties were studied by mechanical property analysis and fracture morphology characterization. The experimental results showed that the bending modulus and interlaminar shear strength of CF/PPEK composites reach up to 125 GPa and 64 MPa, respectively when the molding temperature is 350 ℃. And when the molding temperature is 360 ℃, the CF/PPEK composite has the least defects and the bending strength can reach up to 1 376 MPa. However, at 370 ℃, the composite has obvious defects, and its performance in all aspects has declined sharply.

Acoustic emission study on bending failure mechanisms of GLARE laminates with different stacking structures

ZHANG Mai, ZHENG Yingxiao, HU Kejun, HAN Wenqin, DUAN Liuyang, SHI Qinghe

2024, 0(3): 13-19. DOI: 10.19936/j.cnki.2096-8000.20240328.002

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Glass fiber reinforced aluminum(GLARE) laminates are hybrid composite materials widely used in the aerospace industry. In this study, the three-point bending test method is used to carry out the bending loading, and the Acoustics Emission (AE) technique is used to monitor the real-time damage behavior of the laminates during the bending process, based on the multi-AE parameters and K-means clustering method, the bending performance and failure mechanism of GLARE laminate with different ply structures were investigated. The results show that the location of aluminum alloy layer has a significant effect on the bending properties of GLARE laminates, and the deformation coordination of the outermost aluminum alloy layer and the composite layer can effectively delay the initiation and evolution of the damage. The damage modes and corresponding peak frequencies of GLARE laminate during bending failure include 0~50 kHz for aluminum alloy damage, 80~210 kHz for matrix cracking, 210~320 kHz for fiber peeling and interface delamination, and 320~400 kHz for fiber breakage.

CIVA simulation and experimental study on ultrasonic testing sound field of glass fiber reinforced composites

SHI Hongyuan, REN Wenjian, DANG Jie, ZHOU Peng

2024, 0(3): 20-24. DOI: 10.19936/j.cnki.2096-8000.20240328.003

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For ultrasonic testing of the sound field distribution in the glass fiber reinforced laminate, the change law of the sound field in the material with different thickness wedges was obtained by using CIVA software. At the same time, conducting the simulation test of prefabricated defects with different specifications in the test block, through the analysis of B-scan and A-scan echo waveforms of defects, the echo characteristics and wave height rules of defects with different depths are obtained. Finally, the ultrasonic testing instrument is used to carry out the actual inspection and verification test on the glass fiber laminate made. The test results show that the waveform characteristics and detection results of layered defects with different sizes and buried depths are the same as the simulation test results. When the defect is too close to the surface, the detected size is much larger than the actual defect; when the defect is in the middle of the laminate, the detection results are close to the actual size; when the defect is at the bottom of the laminate, the detection result is smaller than the actual size.

Dynamic response and failure mechanism of double triangular truss core sandwich structure under low velocity impact

YANG Sixin, CAO Zhongliang, GU Fuwei

2024, 0(3): 25-34. DOI: 10.19936/j.cnki.2096-8000.20240328.004

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A nonlinear finite element simulation method was used to study the impact resistance of the double triangular truss core sandwich structure. A hemispherical impactor with a diameter of 16 mm was used to impact the nodes and substrate positions of the sandwich panel with different impact energies to study the failure mechanism and dynamic response of the truss core sandwich panel, as well as the influence law of each variable on the impact resistance of the sandwich panel. The results show that the main failure form of the double triangular truss core sandwich structure is the tensile rupture of the substrate of the panel, while the failure form of the core is influenced by its own structure and force mode, presenting mainly in the form of brittle collapse fracture and plastic deformation. The load-time curves show that the punch energy and impact location have a significant influence on the damage failure behavior of the sandwich panel. Under the same impact energy, the damage degree and load peak of sandwich panel at nodal impact are better than that of basal impact, and the impact resistance is more excellent; the energy absorption effect of nodal impact under high impact energy is better than that of basal impact, but the load change trend is increasingly similar.

Influence of Kagome lattice structure parameters on its compression characteristics and lightweight design

ZHANG Bin, ZHAO Jing, WANG Shijie

2024, 0(3): 35-42. DOI: 10.19936/j.cnki.2096-8000.20240328.005

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In order to study the compressive properties of the three-rod support (Kagome) structure and carry out lightweight design, the Kagome multilayer dot matrix structure with 12 different relative cell densities was modeled by changing the structural parameters of the cell elements, and the quasi-static compressive mechanical properties were analyzed using compression experiments and simulations. It is concluded that at a certain cell height, the increase of the inclination angle and cross-sectional diameter of the support rod will improve the anti-compression performance of the Kagome multilayer lattice structure, and the influence of the inclination angle on the overall maximum equivalent flat compressive strength of the structure is greater than that of the rod diameter. The relative density of Kagome increased from 16.6% to 60.7%, the overall equivalent flat compressive modulus increased by 5.54 times, and the maximum equivalent flat compressive strength increased by 4.52 times, and the simulated and experimental results were consistent. In addition, the lightweight design of the Kagome reinforced point structure showed that the overall weight reduced by 16.3%. The compression simulation results showed the lightweight design slightly improved the overall equivalent flat compressive modulus, maximum equivalent flat compressive strength, relative specific strength, specific stiffness and other parameters of the point structure before the compression collapse failure.

Computational study on failure behavior of L-shaped laminates considering both intra-laminar matrix cracking and inter-laminar delamination

WANG Yuxuan, CAO Dongfeng, HU Haixiao, Li Shuxin

2024, 0(3): 43-53. DOI: 10.19936/j.cnki.2096-8000.20240328.006

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L-shaped laminates are the most common and critical composite components in commercial aircraft, and the study of their failure mechanism is very important for the safety of aircraft structures. The crack propagation in matrix and the delamination failure between plies are the two most important failure mechanisms of L-shaped composite laminates. These two failure mechanisms may occur simultaneously and have coupling effects. In this paper, two sets of numerical analysis models are presented to describe the failure process of L-shaped composite laminates. In Model Ⅰ, zero-thickness cohesive elements are inserted between plies in the curved region of L-shaped laminates to simulate delamination and radial-pattern zero-thickness cohesive elements are inserted in the 90° layer to simulate matrix cracks. In Model Ⅱ, the XFEM method was used to simulate the initiation and propagation of matrix cracks and the cohesive behavior method was used to simulate the delamination. In comparison with the experimental results, the feasibility of the proposed methods is validated. Furthermore, the capability as well as the advantages and disadvantages of the two models in terms of failure modes and critical load predictions are evaluated. The results show that both models can describe the propagation of matrix crack and delamination as well as possible coupling effects. The failure modes predicted by numerical analysis agree well with the experimental results, and the predicted initial failure loads and maximum failure loads are also in good agreement with the experimental results.

Prediction and experimental verification of mechanical properties of 3D four-directional carbon/carbon composites

GENG Jian, DONG Jiuzhi, MEI Baolong, JIANG Xiuming

2024, 0(3): 54-60. DOI: 10.19936/j.cnki.2096-8000.20240328.007

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Aiming at the prediction of mechanical properties of 3D four-directional carbon/carbon composites, a microstructure model was established based on the multi-scale analysis method of parameter transfer, and the prediction of basic mechanical properties was realized by combining micromechanics. Firstly, the yarn representative volume element (RVE) model was constructed by using the random disturbance algorithm at the microscopic scale, and the effective performance parameters of the fiber bundle were predicted. At the same time, the 3D four-directional carbon/carbon composite meso-RVE model was constructed by observational test method. Finally, the elastic performance parameters of composites were accurately predicted by homogenization theory, and the influence of yarn filling factor on the elastic performance parameters of 3D four-directional carbon/carbon composites was discussed. The results show that the error between the tensile simulation prediction results and the experimental results of the multi-scale finite element model established in this paper is about 5.5%; the sensitivity of elastic properties of composites to yarn filling factor is different.

Properties of phosphorus-containing POSS flame retardant vinyl ester resin

GAO Kun, ZHANG Zhaoheng, XING Yajuan, ZUO Xiaobiao, Wang Boyao, ZHAO Zehua

2024, 0(3): 61-64. DOI: 10.19936/j.cnki.2096-8000.20240328.008

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Adding phosphorus-containing POSS (DMPOSS) with the dosage of 5wt%, 10wt% and 15wt% to vinyl ester resin, the effects of phosphorus-containing POSS addition on the thermodynamic properties, flame resistance, and microstructure of vinyl resins were studied by differential scanning calorimetry (DSC), thermo-gravimetric analysis (TG), limiting oxygen index (LOI), cone calorimeter and scanning electron microscopy (SEM). The DSC results show that the addition of DMPOSS can significantly increase the glass transition temperature, the LOI results show that the oxygen index of vinyl ester resin increase with the increase of DMPOSS content. The cone calorimeter results show that the addition of DMPOSS can effectively reduce the heat release of vinyl ester resin. When adding 15wt% DMPOSS, the peak heat release rate of vinyl ester resin decreased by 44.9%, while the total heat release decreased by 30.4%.

Extracting orientation index of short fiber reinforced composites by computer vision methods

ZHENG Zijun, QIAO Ying, SHAO Jiaru

2024, 0(3): 65-72. DOI: 10.19936/j.cnki.2096-8000.20240328.009

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The orientation of fibers has a significant impact on the macroscopic properties of short fiber reinforced composite materials. The fiber orientation index is extracted from scanning electron microscope (SEM) images by machine vision methods. To build the training/testing data sets, a fiber orientation distribution is derived based on the orthogonal elliptic closed approximation, and then many simulated SEM images are generated by using the acceptance-rejection and random sequential adsorption algorithms. Based on these simulated images, a BP neural network based on gray-level co-occurrence matrix (GLCM-BP) was proposed to predict the fiber orientation index, and the results were compared with commonly used methods, including morphological segmentation, structure tensor relationship, and convolutional neural network (CNN) algorithms. The results showed that the GLCM-BP model could effectively predict the fiber orientation with a fitting correlation of 0.99 and a mean square error of approximately 0.01, meeting engineering requirements. In comparison, the structure tensor formula systematically underestimates the orientation in planar distributions; morphological and GLCM-BP methods perform better for low fiber volume fractions; GLCM-BP and CNN methods perform better for high fiber volume fractions. The proposed GLCM-BP method also shows capability to resist image noise.

Service performance study of three-dimensional large spaced woven spacer fabric flexible composites

XU Xiaoting, HAO Enquan, SHAO Huiqi, SHAO Guangwei, BI Siyi, CHEN Nanliang, JIANG Jinhua

2024, 0(3): 73-78. DOI: 10.19936/j.cnki.2096-8000.20240328.010

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In order to investigate the factors influencing the service performance of flexible composites with three-dimensional large-spaced woven spacer fabrics for land-based inflatable antennas, three main aspects were investigated: the splicing strength caused by cutting and splicing, the material strength in acid and alkaline working environments, and the folding resistance after folding, unfolding and refolding. The results show that the splicing width of 30 mm, the adhesive polyurethane A584, and PVC laminated fabric warp to obtain the best splicing strength, which can reach the fracture strength of the reflective surface material. In the acid and alkali resistance test, both polyurethane A584 and TPU hot melt adhesive film did not come off, which showed good corrosion resistance, indicating that the materials of the reflective surface can adapt to various working environments of the antenna. The inflatable reflective surface material shows good folding performance, and its folding performance has a certain correlation with the number of folding times and splicing width, but not with the splicing glue. The width of the splicing material increases, the smaller the effect of the number of folding times on its role, and the folding return performance is better.

Structural optimization design of all-carbon fiber composite solar UAV wing

SU Tong, HU Guoxin, LIU Zhen

2024, 0(3): 79-83. DOI: 10.19936/j.cnki.2096-8000.20240328.011

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Aiming at the performance requirements of solar UAV with high aspect ratio, the optimization design of the carbon fiber composite solar UAV wing was carried out in this paper. When NACA4412 was selected as the reference airfoil, the airfoil was optimized based on NSGA-Ⅱ optimization algorithm with xfoil software as the aerodynamic calculation software. On this basis, the three-dimensional modeling of the wing was carried out, the aerodynamic characteristics are analyzed using CFD software, and the fluid-structure coupling analysis of the wing was carried out using the ANSYS Workbench statics module. The results show that the lift coefficient increases by 4.20%, the drag coefficient decreases by 8.74% and the lift-drag ratio increases by 14.18% after the airfoil is optimized. Under the aerodynamic load, the pressure increases gradually from the wing root to the wing tip, and the maximum pressure at the wing tip is 242 Pa relative to the external atmospheric pressure. Under the action of external load, the maximum stress is displayed near the wing root, which is 61.397 MPa, and the maximum value of wing deformation is 40.262 mm, which meets the rigidity requirement that the allowable deformation of solar UAV is within 5%, that is the wing tip deformation shall not be greater than 5% of the half-span length. The research results can provide a theoretical reference for the design and development of carbon fiber composite solar UAV.

Analysis of curing deformation of Z-shaped fiber-reinforced composite laminates

WU Qiang, ZHAO Kai, LIU Pengfei, ZHANG Taotao, ZHU Deyong

2024, 0(3): 84-90. DOI: 10.19936/j.cnki.2096-8000.20240328.012

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The thermochemical and thermal phenomena generated during the curing process of composite laminates are the main reasons for the residual stress and deformation of parts, and Z-shaped composite laminates have great potential in the overall structure of aero-engines, so it is necessary to optimize the curing molding of the Z-shaped laminate. This paper establishes a theoretical model related to curing degree, uses the secondary development function of ABAQUS software to carry out finite element simulation analysis, conducts orthogonal test design, and analyzes the influence of design parameters such as transfer radius, number of layers and stacking sequence on the curing deformation of Z-shaped laminates. The analysis results show that the resin modulus, curing degree and molding process temperature have great correlations, and only the number of layers can significantly affect the deformation, while the transition radius and stacking sequence have little influence. And when the transfer radius is 12 mm, the number of plies is 4, and the stacking sequence is [30], the deformation of the Z-shaped laminate can be locally optimal.

Study on the analysis method and influence factors of the repair of composite laminate by adhesive bonding

SONG Guibin, HUANG Guangqi, YANG Shengchun

2024, 0(3): 91-96. DOI: 10.19936/j.cnki.2096-8000.20240328.013

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The strength characteristics analysis and evaluation method of composite laminates after repair and repair by bonding were studied, and a numerical analysis method was proposed to simulate the gradual failure process and strength prediction of composite repair and repair structures. The tensile tests of non-destructive specimens and wedge repair specimens were designed and completed to verify the validity and accuracy of the calculation model. Finally, using the proposed numerical analysis model, the influence analysis of composite material repair parameters is carried out. It is found that 5° is the optimal repair angle, and the thickness of the adhesive layer is 0.1 mm. When the 0° and ±45° layers in the patch layer account for 50% respectively, the repair laminate has the highest bearing capacity.

High energy storage performance composite films prepared by coprecipitation-hot pressing technique

WANG Yao, SHAO Dandan, LEI Bingyu

2024, 0(3): 97-102. DOI: 10.19936/j.cnki.2096-8000.20240328.014

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High energy storage performance capacitors have received widespread attention in the fields of onboard inverter, photovoltaic power generation, and aircraft carrier ejection systems due to their ultrafast charging-discharging speed and ultrahigh power density. Enhancing the energy storage density (U_e) can accelerate the integration and promote the rapid development of power electronics devices. Here, P(VDF-CTFE) is used as the matrix and linear homopolymer PMMA is used as the filler to limit the crystallization and ferroelectric phase transition, and coprecipitation-hot pressing is used instead of the solution casting method to achieve the homogeneity of the structure. It shows PMMA can be uniformly distributed in P(VDF-CTFE) and limit the ferroelectric relaxation loss, the phase field simulation analysis shows that the uniformly distributed PMMA can optimize the electric field distribution, and the U_e of 10.1 J/cm³ with the charge-discharge efficiency (η) of 74% are obtained under the electric field of 372 MV/m at 20vol% filling, which provides scientific and technological support for the practicalization of high energy storage composite dielectric films.

Study on high temperature resistance of composite materials in wind blades under desert environment

ZHANG Zhongxiang, LIU Baofeng, FANG Chenxin, CHEN Wenguang, GU Yuhui, LI Junxiang

2024, 0(3): 103-107. DOI: 10.19936/j.cnki.2096-8000.20240328.015

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In the process of serving wind blades in desert, they will encounter extreme high temperature weather, and the inner cavity of the blades cannot dissipate heat, resulting in temperatures far higher than the environment temperature. With the increasing installation of wind generation units in desert area in the future, it is very important to study the high temperature resistance performance of wind blade composite materials in desert. In this paper, the mechanical properties of composite materials used in wind blade skin, spar cap and shell are studied at 60 ℃, which will provide reference for the selection and design of wind blade materials under desert environment. The test results show that the tensile and compressive properties of laminates for skin are degraded to a high degree after being treated at 60 ℃ for 3 h, and the reduction rates of tensile strength and compressive strength are 23.9% and 41%, respectively, but the V-shear strength of laminates is relatively low, which is 1.5%. The V-shaped shear strength of the tensioned plate for the spar cap decreased by 16.3%, while the tensile strength and compressive strength of the pultrusion plate decreased by 3.3% and 6.3%, respectively. The shear strength of PVC60 foam and Balsa sandwich composite for shell decreased by 31% and 4.2%, respectively.

Layer optimization of composite material for wing girder of solar UAV

DENG Zhong, ZHI Yafei, CHENG Jialin, YANG Wen

2024, 0(3): 108-112. DOI: 10.19936/j.cnki.2096-8000.20240328.016

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Solar UAV adopts super aspect ratio wing, which has low cruise speed, low wing load and can not fly with excessive structural weight. Therefore, it has strict requirements on the weight of aircraft structure. The wing girder of the wing accounts for most of the weight of the wing structure, so it is necessary to optimize the layer of the composite wig girder to reduce the weight of the wing girder and optimize the structural force transmission effect. First, the finite element model of the half wing of the solar UAV is established, and then the shape, the thickness and the order of the wing girder composite is optimized. After optimization, the weight of the wing girder decreases by 18.68%, the maximum stress decreases by 21.16%, and the tip deformation decreases by 5.9%.

Research progress of dry fiber automatic placement liquid forming composites

PENG Gongqiu, BAI Yu, ZHONG Xiangyu, ZHANG Lianwang, BAO Jianwen, CAO Zhenghua

2024, 0(3): 113-120. DOI: 10.19936/j.cnki.2096-8000.20240328.017

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Dry fiber automatic placement liquid forming composite technology is a combination of automatic placement technology and liquid forming technology, which can realize the high toughness, automation and low cost of advanced composite materials at the same time. Meanwhile, it is one of the key development directions of expanded application of composite materials. In this review, the origin of dry fiber automatic placement liquid forming composite technology was briefly introduced. The composition, performance and preparation methods of mature dry fiber automatic placement materials were discussed. Then, the verification and application of dry fiber automatic placement liquid forming composite components were summarized. Finally, the current situation of domestic dry fiber automatic placement liquid forming composite technology was briefly introduced. The development and application of domestic dry fiber automatic placement liquid forming composite technology were proposed.

Research progress of new sandwich structures

ZHAO Zehua, ZHANG Zhaoheng, XING Yajuan, WANG Boyao, LIN Jialun, YANG Yi, GAO Kun

2024, 0(3): 121-128. DOI: 10.19936/j.cnki.2096-8000.20240328.018

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With the increasingly urgent demand for heavy launch vehicle in the future, under the condition of a certain total load, the weight of the carrying cargo must be reduced, which puts forward higher requirements for the existing materials and structures. Increasing the payload ratio of materials without sacrificing strength and functionality is a major challenge. At present, the most common and efficient method is through the design and fabrication of a variety of new sandwich structures, meeting the requirements of lightweight, high strength and functional. The paper summarizes the research progress of sandwich structures in China and abroad in recent years, introduces in detail the structural foundation and characteristics, mechanical properties and diverse functions of several sandwich structures, and puts forward some suggestions for the research and development of sandwich structures in our country.

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