COMPOSITES SCIENCE AND ENGINEERING

Reliability and sensitivity analysis of the edgewise compressive strength of scarf repaired honeycomb sandwich structures

WANG Xuan, WANG Wei, YU Fen, ZOU Runwen, WANG Kuikui

2024, 0(1): 5-12. DOI: 10.19936/j.cnki.2096-8000.20240128.001

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Taking the scarf repaired honeycomb sandwich structure of composite materials as the research object and considering the uncertainty of the adhesive layer material properties, the edgewise compression progressive damage analysis model of the scarf repaired honeycomb sandwich structure was established by ABAQUS-MATLAB-Python simulation, and the corresponding output response of random variables was obtained. Then, the reliability analysis was carried out based on Monte Carlo method, and the global sensitivity analysis method based on variance and failure probability was used to analyze the parameter sensitivity. The results show that the failure probability of the structure has great differences under different numerical intervals of external loads, and the failure probability increases significantly when approaching the ultimate failure load. The elastic modulus in the thickness direction of the adhesive layer and the shear modulus in the two mutually perpendicular directions in the plane have a great influence on the variance of the lateral compressive strength and failure probability of the honeycomb sandwich structure of the digging and repair.

A study of key issues in modeling the microstructure of 3D woven composites

LIU Shuai, WANG Zhen, LU Guosheng, LIU Fang, SHEN Min

2024, 0(1): 13-21. DOI: 10.19936/j.cnki.2096-8000.20240128.002

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Numerical analysis based on micromechanics is an effective method to study the mechanical properties of three-dimensional (3D) braided composites, in which the establishment of micromechanics model is the basis of mechanical analysis. The direction cosine of fiber yarns and the characterization of geometric parameters of microstructure are two key issues in the modeling of microstructure. Focusing on these two key issues, the three-cell model of 3D four-directional braided composites is studied to analyze various spatial directions of fiber yarns in the 45° division and horizontal division of unit cell, so as to obtain the detailed fiber yarn direction cosine. Aiming at the cross sections of three types of fiber yarns, the complex relationship between the braiding process parameters and the geometric parameters of the unit cell is analyzed and deduced. The unit cell structure is quantitatively characterized by using the braiding process parameters as the initial parameters, and the calculation methods of the volume fraction of fiber yarns and yarn filling coefficient are obtained. This paper can provide a theoretical reference for the microstructure modeling of 3D multi-directional braided composites, and has certain practical value in engineering.

In-plane mechanical properties of embedded co-cured perforated fiber reinforced damping composites

SUN Ruijun, LIANG Sen, LUO Hao, LIU Zhaoyang, HU Zijian

2024, 0(1): 22-29. DOI: 10.19936/j.cnki.2096-8000.20240128.003

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An embedded co-curing perforated fiber-reinforced damping composite panel (ECPFDCP) structure was proposed. The structure does not only reduce the stiffness loss and improve the bearing capacity, but also improves the damping performance. The finite element model and the theoretical model of the in-plane equivalent parameters of the perforated fiber reinforced damping film are established, and the effectiveness of the theoretical model and method are verified by numerical simulation. The effects of design parameters on the in-plane mechanical properties of perforated fiber reinforced damping films of ECPFDCP were investigated by verified theoretical models and methods. The results show that increasing the thickness of the damping layer and the aperture of the damping layer and decreasing the distance of the damping layer are beneficial to increase the shear modulus. The model and method presented in this paper have important guiding significance for the theoretical study of dynamic properties of embedded co-cured discontinuous damping composite structures and provide a reference for the design and manufacture of structures.

Effects of different impact angles on the damage characteristic of composite laminates under low-velocity impact

LIN Yi, LIU Ling

2024, 0(1): 30-37. DOI: 10.19936/j.cnki.2096-8000.20240128.004

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Composite structures are usually subjected to low-velocity impact during service, which results in invisible internal damage and decreases the loading ability of structures. In the actual engineering, when the low-velocity impactor interacts with the structure, it may present different impact angles. Consequently, in this paper, focusing on a typical layup of carbon/epoxy laminate, a low-velocity impact numerical model of 90° and different impact angles were established using ABAQUS. The model is used to analyze the effects of different impact angles to the contact force and damage of laminate, and the effects of second contact caused by impactor rotation to damage. In numerical model, the intralaminar damage was simulated using the continuum damage mechanics and 3D Hashin criterion. The interlayer delamination was simulated using cohesive model and bilinear tractor-separation constitutive relation. The comparison between the 90° simulation result and the test result proves the reliability of the numerical model. The simulation results of different impact angles show that, when the impact angle increases from 30° to 90°, the normal contact force always increases, while the tangential contact force first increases and then decreases. With the decrease of the impact angle, the overall deviation of the damage is more obvious, and the damage areas caused by the matrix tension is always larger. The simulation results of the successive contact under different energies show that, with the increase of impact energy, the impact angle range causing the successive contact decreases, and the successive contact causes new damage to the top of laminates.

Correlation between structural frequencies and the residual compressive strength of CFRP laminates with delamination damage

GUO Jingjing, ZHANG Zhifang, LUO Ziwei, LIU Wendi

2024, 0(1): 38-44. DOI: 10.19936/j.cnki.2096-8000.20240128.005

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Fiber reinforced polymer (FRP) laminates are prone to delamination damage during the production and use. To understand the effect of delamination damage on the residual compression strength of FRP laminates, this article has conducted compression tests and modal testing on composite beams with precast mid-plane delamination of different sizes. The effects of different delamination on the natural frequencies and the compressive strength of FRP beams are studied and the correlation between frequencies and compressive strength are investigated. The finite element model of delaminated FRP laminates was established in ABAQUS, and the simulation analysis results were compared with the testing results to validate the simulation model. The finite element method is used to analyze the influence of the delamination size on the frequency and compressive strength. The results show that the natural frequencies of the FRP beams decreases with the increase of the delamination area. Compared with those without initial damage, the FRP beams with delamination were mainly fractured in the interface where the delamination occurs. The delamination has expanded to different extent depending on the initial delamination sizes. With the increase of delamination size, the decrease of compressive strength of composite laminates has increased. When the layups of the FRP specimen changes, with the increase of the delamination sizes, there still exists the correlation between the structural frequencies and the residual compressive strength. Experiments and simulations both show that the natural frequencies are closely correlated to the residual compression strength of the FRP beams with delamination, and an exponential relationship is observed. However, if the layups changes, the exponential relationship will be changed accordingly between the frequencies and the residual compression strength.

Numerical simulation of progressive damage of composite laminates considering shear nonlinearity

HE Lile, LI Shubao, ZHENG Jianxiao, SHAO Xianzhong

2024, 0(1): 45-53. DOI: 10.19936/j.cnki.2096-8000.20240128.006

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Based on the basic principle of continuous damage mechanics, a three-dimensional progressive damage model considering shear nonlinearity is established to analyze and predict the mechanical behavior, failure load and failure mechanism of composite laminates. The high-order exponential function is used to describe the shear nonlinear behavior of composite materials. Considering the combination of progressive and sudden reduction of composite stiffness to characterize the stiffness change of materials in the damage process, a UMAT subroutine is compiled, and ABAQUS software is used to analyze the progressive damage failure of perforated AS4/PEEK composite laminates. The model proposed in this paper has higher accuracy than the traditional model simulation results without considering shear nonlinearity, and the error value is less than 4% compared with the reported experiments. The simulation results show that the larger the aperture, the greater the stress limit around the inner hole before the damage occurs, the greater the stress distribution gradient, and the smaller the bearing capacity of the laminated plate. When the [±45]_2S ply is adopted, the simulated stress is in good agreement with the experimental results, which further verifies the applicability and accuracy of the model.

Optimization of feature weights of filament winding dropping point trajectory sampling based on improved NSGA-Ⅱ

TIAN Huifang, QIU Zhenxing, WU Yingfeng

2024, 0(1): 54-59. DOI: 10.19936/j.cnki.2096-8000.20240128.007

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To solve the problem that the feature weight cannot be automatically selected in the sampling algorithm of filament winding doffing point trajectory based on the feature function of the spatial feature curve, a bi objective optimization model is established, which takes the feature weight as a variable and the MAE and RMSE of the linear interpolation generated curve and the original curve of the sampling point obtained as the objective function. A bi objective optimization method based on improved NSGA-Ⅱ algorithm is proposed to optimize the feature weight. The example verification shows that the MAE and RMSE of the Pareto solution set obtained by the improved NSGA-Ⅱ algorithm are reduced by 0.002 and 0.105 on average compared with the traditional NSGA-Ⅱ algorithm, the MAE and RMSE of the feature weight selected by the algorithm are reduced by 12.9% and 8.5% respectively when the feature weight is (0.1, 0.3), and the bit feature weight is reduced by 20.6% and 11.4% respectively when the feature weight is (0.9, 0.1), effectively improving the accuracy of the doffing point trajectory sampling.

Experimental study on the influence of carbon fiber on the flexural strength and microstructure of nano metakaolin recycled concrete

YAN Jie, LUO Yan, YU Xutao, WANG Lijun, XIE Jun, SHU Xinqian

2024, 0(1): 60-65. DOI: 10.19936/j.cnki.2096-8000.20240128.008

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To make full use of recycled concrete resources, using carbon fiber to modify the flexural strength of nano metakaolin recycled concrete and preparing recycled concrete with different carbon fiber contents and nano metakaolin contents as variables, combing with the mercury injection method and scanning electron microscope to study recycled concrete’s pore structure and microscopic morphological characteristics. Then analyzing the modification mechanism of carbon fiber on nano metakaolin recycled concrete. Results show that the strengthening effect of carbon fiber on flexural strength is noticeable. The suitable content of carbon fiber varies under different nano metakaolin contents. When the content of nano metakaolin is 7%, 10%, and 12%, the optimum content of carbon fiber is 0.1%, 0.15%, and 0.2%, respectively. When the content of nano metakaolin is 10%, and the content of carbon fiber is 0.15%, the flexural strength reaches the maximum, which is 59.1% higher than that of ordinary recycled concrete. The incorporation of carbon fiber refines the internal pore structure of recycled concrete, decreasing the proportion of harmful and multi-harmful pores and increasing the proportion of less harmful pores. Carbon fiber plays a role in bearing and cracking resistance in recycled concrete. The filling effect of nano metakaolin and the volcanic ash activity enhance the bonding strength of the interfacial transition zone, which makes the carbon fibers more effective and thus promotes the improvement of the strength of the recycled concrete.

Multiscale numerical study of CFRP winding hydrogen storage cylinder based on asymptotic homogenization method

FENG Jun, ZHANG Nan, SONG Meili, CHEN Yang, ZHAO Xiaodong, LIANG Jianguo

2024, 0(1): 66-73. DOI: 10.19936/j.cnki.2096-8000.20240128.009

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In order to simulate the complex structure and stress state of carbon fiber reinforced polymer (CFRP) wound layer in hydrogen storage cylinder, representative volume element (RVE) of composite layer was modeled, and the effective stiffness matrix of RVE was obtained based on the asymptotic homogenization (AH). The correctness of AH and the macroscopic effective parameters of simulated CFRP laminates is verified by tensile test. The parameters of winding layer were determined based on the grid theory, and the hoop winding layers adjacent to the lining were modeled microscopically, while the rest is seen as an RVE. Accordingly, the response of cylinder can be accurately predicted. The response of type Ⅳ cylinder with three CFRP winding modes under 70 MPa nominal pressure was studied by multiscale modeling. The results show that compared with the mesoscopic model, the maximum error of the fiber direction stress of the composite layer is 8.7%, and the maximum error of the Von-Mises stress of the lining is 2%, and the less the number of alternate winding, the smaller the error of the homogenized model is. The lay-up winding with separated hoop and helical layers may improve the burst pressure by 15% approximately.

Simulation analysis of interface peel strength of CFRP laminate single lap adhesive joint

ZHANG Yanan, CHEN Dong, SHI Jianwei, TIE Ying, LI Cheng

2024, 0(1): 74-82. DOI: 10.19936/j.cnki.2096-8000.20240128.010

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Focusing on adhesively bonded carbon fiber reinforced polymer (CFRP) single-lap structure, location and intensity of peeling stress on the plate/adhesive interface are mainly studied by finite element method (FEM) on the basis of intensity of singular stress field (ISSF). Simulation results are verified by comparing with experiments. Higher accuracy FEM results that close to real situation are obtained by applying mesh-independent finite element stress ratio method. The difference of simulation procedure and FEM results of CFRP and homogeneous material are compared. The influence of different bonding parameters on the plate/adhesive interface stress distribution of CFRP single-lap structure under tensile load are mainly studied. Applying these conclusions and characteristics in engineering practice can help optimize peeling stress, improve adhesive bonding technology and enhance the strength of single lap joint. The results show that when the CFRP plate/adhesive interface with different layer parameters is loaded, the location of maximum peeling stress should be constrained by three dimensions. The constraint results for two dimensions is the same as that of homogeneous materials, the extreme value is located at the edge of the plate/adhesive interface, which is perpendicular to the tensile direction. Failure initiation in actual structures is also common here. The third dimension that locates the dangerous point is affected by the multilayer anisotropy of the laminate and bonding parameters. The dangerous point with the maximum peeling stress on the edge is neither at the midpoint of the edge nor at the corner of the interface, the specific position is affected by material parameters and bonding structure.

Research on automatic detection of composite inclusion defects based on Mask R-CNN

LI Leilei, WANG Mingquan, ZHAO Fubao, ZHU Huanyu, FENG Xiaoyu, XIE Shaopeng

2024, 0(1): 83-88. DOI: 10.19936/j.cnki.2096-8000.20240128.011

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In order to improve the detection efficiency of composite inclusion defects, an automatic inclusion defect detection system based on deep learning network is proposed in this paper. In the process of image preprocessing, a two-stage unsharping mask algorithm is used to highlight the features of inclusion defects, and a composite image database of inclusion defects is constructed. The Mask R-CNN network model is used, and the optimal weight parameters are obtained through network model training. Finally, the defect detection software system is designed and realized. The experimental results show that the network accuracy of Mask R-CNN algorithm is 94.6%, the recall rate is 92.4%, and the AP value is 87.3%. The system is convenient and fast in application, and will effectively improve the efficiency and accuracy of defect detection for front-line personnel.

Ballistic impact characteristics and damage analysis of aramid plain woven composite plates

MOU Haolei, LI Yi, SONG Dongfang, XIE Jiang, FENG Zhenyu

2024, 0(1): 89-97. DOI: 10.19936/j.cnki.2096-8000.20240128.012

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To study 1000D629T/EPMOLD110 aramid woven composite plates’ impact resistance behavior and damage characteristics, plates with different thicknesses are processed using vacuum assisted resin infusion molding (VARI) and resin transfer molding (RTM). Ballistic impact tests were carried out with air gun device. Based on basic mechanical test data, a verified representative volume element (RVE) model is established, and material constitutive parameters of macro model are determined with fitting and calibration; a macro finite element model for ballistic impact is established to further analyze ballistic limit and damage morphology with CT scanning results. It was shown that aramid plain woven composite plates’ballistic impact damage modes are mainly fiber fracture, fiber prolapse, out of plane shear and inter-layer separation; the ballistic limit increase with plate thickness, and compared with VARI process, RTM process can improve ballistic limit by 5%; the damage behaviors of simulation agree well with experimental results and the error for ballistic limit is within 1%.

Forming defects and optimization methods of 3D printing for continuous aramid fiber reinforced PLA composites

MENG Yuncong, ZHOU Guangming, CAI Deng'an, ZHANG Nan

2024, 0(1): 98-104. DOI: 10.19936/j.cnki.2096-8000.20240128.013

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Continuous fiber 3D printing technology combines the advantages of high mechanical properties of composite materials and flexible manufacturing of 3D printing, which has great development potential. However, there are some forming defects in the parts produced by the existing process, which affect the large-scale application of this technology. By using self-developed 3D printing equipment, aramid fiber reinforced PLA test parts were manufactured. The molding quality of the test parts was studied and the conditions for slip defects were proposed. The defects of fiber bundle slip, peeling, fracture and interlayer pores were systematically studied. Four process optimization methods such as the printing speed, path angle, cooling system and nozzle shape were proposed and relevant experiments were designed for verification. The results show that optimizing velocity, path angle and cooling system can reduce the slip distance of fiber bundle by 45%, 81% and 50%, respectively, and optimizing nozzle shape can reduce the fracture rate by 90%. The research provides ideas and solution for the design and manufacture of composite materials based on 3D printing.

Research on downsampling voxel technique in failure prediction of angle interlocking composites

LI Xiaohuan, GUO Jushang, ZHU Liping, ZHU Mengdie, YANG Cheng

2024, 0(1): 105-110. DOI: 10.19936/j.cnki.2096-8000.20240128.014

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In order to solve problems of large amount of calculation and low efficiency in failure prediction of angle interlock composites, 4³ voxels in the original model are packed into one representative volume element by adopting the down-sampling voxel technique commonly used in image processing methods, thus greatly reducing the calculation amount and time. The full-voxel model is compared in terms of elastic property, damage state of composites and CPU time. Numerical results show that the model using down-sampling voxel technique is not only identical to the full-voxel model in stiffness prediction, but mimic the full-voxel model in damage state. At the same time, the CPU time is reduced by almost 85% in the model computation with tens of millions voxels, thus it is suitable for high-precision and high-speed prediction of engineering angle interlock composites.

Advances in the applications of polyether-ether-ketone composites preparation technology in the medical field

GAO Liang, BAI Yu, GAO Junpeng, LING Changyue, ZHANG Baoyan, QI Nan

2024, 0(1): 111-118. DOI: 10.19936/j.cnki.2096-8000.20240128.015

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With the progress of science and technology, and the improvement of public health awareness, implantable medical devices are becoming more and more widely used in clinical practice. Polyether ether ketone (PEEK) composites are widely used in the medical field because of its low image interference, light weight, high strength, modulus closer to human tissues, excellent performance under dynamic load, corrosion resistance and wear resistance. This paper introduces three kinds of PEEK composites manufacturing technology, injection molding, 3D printing and hot pressing, with focus on their basic principles, domestic and overseas research, as well as application progress. Comparisons are also provided regarding the technology’s adaptability, advantages and disadvantages. At the same time, problems and challenges in the medical application of PEEK composites are put forward. We hope the related research progress can promote the development of medical materials and the update of implant devices, so as to enhance patient well-being and improve life quality.

General situation and development of tooling materials and structural forms for advanced composites manufacture

MA Quansheng, WANG Wenyi

2024, 0(1): 119-128. DOI: 10.19936/j.cnki.2096-8000.20240128.016

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The manufacture of composite components is generally carried out in the tooling which directly affects the size and surface accuracy of composite components. The composites are formed while the resin is cured. The tooling material is the key factor affecting the quality and surface accuracy of composite components. With the significant growth of the application of advanced composite components in aerospace and other fields, a variety of advanced composite tooling materials and structural forms have emerged to meet the requirements for the improved performance and accuracy of composite products, which providing a wealth of processing methods for high-precision manufacturing of composites. In this paper, the development of tooling materials used for composite manufacture from traditional materials to invar steel, lightweight composites and new materials is summarized. According to different manufacture processes and structural types of composite components, the structural forms of tooling are investigated, and the development direction of composite tooling including new materials research and new structural forms is discussed.

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