This study presents a representative volume element (RVE) based modeling approach to analyze the bending response and mesoscale damage evolution of 3D five-directional (3D5D) braided composites. These composites, recognized for their exceptional delamination resistance and impact toughness, are widely utilized in critical aerospace applications. In the proposed approach, the actual bending specimen is idealized as a homogeneous plate composed of periodically arranged RVEs, each subjected to a uniform bending moment. A shell-based periodic boundary condition (PBC) is developed, enabling simulation of the entire specimen using a single RVE with high efficiency and accuracy. A continuum damage model is integrated within the framework to capture the internal damage mechanisms and mesoscale fracture patterns. Experimental validation conducted across various braiding angles demonstrates strong agreement between the simulated and measured curvature-moment response, as well as matching full-strain fields with DIC data. The proposed model effectively captures both macroscopic bending response and the evolution of internal damage, providing valuable insights into the structural performance of braided composites under bending loads.

Accurate evaluation of the high-temperature uniaxial tensile properties of needle-punched carbon fiber reinforced silicon carbide (NP C/SiC) composites fabricated by chemical vapor infiltration (CVI) and polymer infiltration and pyrolysis (PIP) is essential for aerospace applications but remains challenging. In this work, the thermo-mechanical behavior of NP C/SiC composites at room and high temperatures is systematically investigated using experimental characterization and numerical modeling. High-temperature uniaxial tensile tests are performed to characterize the evolution of mechanical response and damage mechanisms with temperature. A high-fidelity meso-scale finite element (FE) model employing beam-brick combined elements (BBE) is developed to simulate the material response and damage mechanisms at room temperature (RT). Model validity is confirmed by comparing the predicted mechanical response curves with experimental data and close agreement is obtained. The findings of this study contribute to the practical utilization of NP C/SiC composites in aerospace applications and provide reference for the design of ceramic matrix composites (CMCs) for ultra-high-temperature environments.

The increasing use of high-energy laser systems has raised concerns about the ablation resistance of aerospace carbon fiber-reinforced polymer (CFRP) structures. Predicting the response of such materials is challenging because laser irradiation triggers a strongly coupled interaction between heat transfer, thermomechanical deformation, and matrix pyrolysis. In this work, a multi-physics finite element (FE) framework is developed to investigate the ablation behavior of laminated CFRP composites subjected to continuous laser exposure. The model incorporates anisotropic heat conduction, thermally induced stresses, and temperature-dependent pyrolysis rate, enabling the evolution of temperature fields, stress distributions, and interlaminar damage to be examined under different laser power densities and fiber orientations. The simulations indicate that laser power density plays a dominant role in controlling the ablation process, whereas the influence of ply orientation is comparatively limited within the considered parameter range. To accelerate parametric evaluation, surrogate models based on Random Forest (RF) and Multi-Layer Perceptron (MLP) algorithms are constructed using datasets generated from Latin hypercube sampling of the simulations. Once trained, these models reproduce the numerical predictions with high accuracy while reducing the computational time. The proposed framework offers an efficient approach for rapid evaluation of laser-induced damage in CFRP structures and assists in the design of laser-resistant composite components.

In composite stiffened structures, discontinuities at truncated stiffener ends often precipitate premature compressive failure. This study investigates this issue through compression tests on stiffened panels featuring hybrid bonded-bolted stiffener terminations, with variations in stiffener thickness and global stiffness. Experimental monitoring, employing strain gauges and digital image correlation (DIC), captures full-field strain, out-of-plane displacement, load-displacement responses, and failure modes. Numerically, simulations conducted in ABAQUS/Explicit incorporate an intralaminar damage model, a cohesive zone model for the skin-stiffener interface, and bolt preload effects. Results for baseline specimens reveal significant skin-induced out-of-plane tension at the stiffener ends, culminating in mixed failure modes including debonding, flange fracture, and buckling-induced skin fracture. The influence of stiffener thickness and global stiffness on the structural response and damage progression is elucidated, with numerical predictions showing excellent agreement with experiments. Furthermore, an extensive parametric study utilizing the finite element (FE) model quantifies the effects of key geometric parameters on buckling and failure performance. Finally, a design equation for predicting the buckling load is developed and validated against experimental and numerical data, demonstrating its reliability and accuracy.

This paper presents a shell-based multiscale model for predicting the mechanical properties of through-thickness woven composites (TTWC) under in-plane and out-of-plane loadings, with capturing coupled damage evolution at the meso- and macroscale. A reduced shell scheme is employed for the macroscale, while full-thickness RVEs of TTWC are established at the mesoscale to account for inhomogeneous response along the thickness direction. The macro- and mesoscale simulation are coupled and executed simultaneously within a nonlinear concurrent framework. This approach enables the nonlinear macro-shell behavior, characterized by generalized strain and stress resultants, to be directly derived from the realistic mesoscale damage response. By incorporating scanned mesoscale geometries and damage constitutive relations, the shell-based multiscale model is applied to investigate damage and failure mechanisms in notched tensile and simply-supported bending plate samples, respectively. The predicted results are analyzed and compared with existing experimental data and direct numerical simulations (DNS), validating the efficacy and accuracy of the proposed model.

This paper presents experimental and numerical studies on the compression after impact (CAI) behavior of composite tapered laminates. It introduces newly designed impact platforms and compression fixtures specifically tailored for the specimens. Drop-weight impacts are applied to the center of the specimens, and the resulting damage is briefly described. Compression tests are then conducted on both non-impacted and impacted specimens, with strain gauges used to monitor the strain distribution. Internal damage is detected using CT scanning and ultrasonic C-scan techniques. The numerical simulations are performed using ABAQUS/Explicit finite element analysis (FEA), incorporating an intra-laminar progressive damage model and an inter-laminar cohesive model, while additionally modeling resin pockets as elastomers. The simulation and experimental results indicate that before compression failure, impact damage in the thin section minimally affects the out-of-plane displacement, which is predominantly influenced by structural asymmetry. Stress concentration is observed at the junction between the thin and tapered sections in the compression test, while in the CAI test, stress concentration appears in the impact zone. The impact induces a notable shift in failure location and damage modes, resulting in decreased compressive strength, although the impact on stiffness remains minimal.

A hierarchical coupled multiscale method is developed to capture the onset and propagation of damage within the three-dimensional four-directional (3D4D) braided composites subjected to bending loading. Using a directly two-scale coupled scheme, the macroscopic nonlinear behavior at the structural dangerous region could be iteratively solved, combined with the progressive damage response of the realistic mesoscale architecture. The continuum damage model is merely defined at the mesoscale and considers failure in each of constituents with the well-established Hashin failure criteria and the Bazant crack band damage model. To accelerate finite element computation in two scales, a parallel numerical implementation is presented alongside the commercial software ABAQUS/Standard. Besides the good agreement between the experimental and the predicted values, the results also show a significant effect of the braiding angle on the bending performance of 3D4D braided composites. With the increase of braiding angle, the bending stiffness and strength of 3D4D braided composites decreases, but the fracture toughness increases. This phenomenon was numerically investigated by identifying the different fundamental failure mechanism and damage development process at both the scales.

Three-dimensional orthogonal woven composites (3DOWCs) offer significant advantages in engineering applications due to their designability for spatial structures and ability to minimize delamination damage. As primary load-bearing structures, 3DOWCs are always in preloading conditions prior to potential low-velocity impact (LVI) events. This paper presents a macro-meso coupled finite element (FE) model for investigating the response of preloaded 3DOWCs subjected to LVI. The accuracy of the proposed numerical model is validated by a comparison with available experimental data in terms of impact performance and damage state. Furthermore, the influence of preload and impactor shape on the LVI performance of 3DOWCs is examined, and detailed analysis is provided regarding the associated damage mechanisms. This study offers a transferable numerical approach that can be applied to studying the coupling problems of LVI and preload in other textile composite structures.

Pore defects are inevitable in the manufacturing process and significantly affect the mechanical properties of composite materials. In this work, a novel algorithm capable of concurrently generating both ellipsoidal and gourd-shaped pores in composite materials is proposed and the interference detection procedure is optimized for efficient interference detection between the generated geometrical bodies. Besides, the algorithm is integrated with RVE-based finite element (FE) simulation to explore the effects of various pore types, volumes, aspect ratios, and porosity on the elastic properties of unidirectional C/C composites. The present work provides a valuable reference for generating general pore defects and investigating their resulting effects on mechanical properties of related composite structures.

In this study, the issue of random fiber strength resulting from initial fiber defects and matrix pore defects in the strength response of C/C composite materials is addressed. A method for generating random numbers following the Weibull distribution is proposed and an improved random sequence adsorption (RSA) algorithm is employed to describe pore defects in the matrix, ultimately leading to the development of a representative volume element (RVE) model for C/C composite materials. The influence of fiber strength distribution and pore defects on the mechanical properties of unidirectional C/C (UD-C/C) composite materials is analyzed. This study offers a new approach to investigate the mechanical behavior of C/C composite materials, taking into account both fiber initial defects and pore defects.

This paper presents a hierarchical coupled multiscale model for evaluating the progressive damage behavior of notched 3D woven composites subjected to the tensile loading. In the present work, the constitute behavior of structural dangerous area is iteratively solved, in conjunction with the finite element analysis (FEA) realized on realistic mesoscale architecture. This two-scale method is capable of simulating the propagation process of macro-meso coupled damage nearby the hole-edge using mesoscale continuum damage model without applying any macroscopic phenomenological failure criterion. Besides the good agreement between the experimental and the predicted stress–strain responses, the experimental phenomenon of the damage initiation location and branching pattern nearby the hole-edge are successfully tracked. The effect of apertures on the notched strength and failure mechanisms is numerically investigated. The present work provides routine support for the numerical study of structural damage behavior of composite materials with complex macro and meso geometries.

3D braided composites have been increasingly applied in the aerospace, automotive, and other high-tech industries as primary load-bearing structures due to their excellent integrated performance. Evaluation on the failure behavior of 3D braided composites subjected to off-axial loading still remains a challenging topic. We present in this paper a meso-scale finite element (FE) model containing void defects for investigating the off-axial tensile behavior of 3D braided composites. The FE model is verified and the effects of porosity are discussed in on-axial tensile conditions, and then it is executed to predict the mechanical response in general off-axial tensile cases. The strength properties of 3D braided composites, and more importantly the progressive damage behavior under typical off-axial loadings, are analyzed in detail. It is found that the off-axial tensile strength and corresponding failure mode of 3D braided composites are mainly affected by the braiding angle of specimen. The proposed FE modeling provides an appropriate reference for the numerical study of void defects and off-axis load problems in other textile composites.

建立了TC4钛合金材料的疲劳裂纹萌生寿命的预测模型,并通过试验验证了此模型在预测TC4钛合金材料疲劳裂纹萌生寿命时的可行性.基于裂纹萌生的细观位错模型,采用Tanaka-Mura的开裂寿命公式,考虑了表面粗糙度,提出了分析TC4钛合金材料疲劳裂纹萌生的有限元模型,并通过实验验证仿真模型的有效性.结果 表明:模型裂纹萌生形式在不同载荷水平下存在差异,高应力水平状态下,模型除了主裂纹的萌生扩展还伴有大量独立微裂纹,裂纹密度大,而在低应力水平状态下,模型存在少量独立微裂纹,裂纹密度小.

Sandwich structure T-joints are increasingly broadly applied in aviation and aerospace industries due to the need for lightweight design. This paper deals with the lightweight optimization of a typical adhesively bonded Nomex honeycomb-core sandwich T-joint in side bending load, considering the strength constraints. The optimization problem, with discrete and continuous design variables, is a compound optimization problem involving size optimization for the whole structure and stacking sequence optimization for multiple variable-thickness composite laminates. A self-adjusted parametric modeling with user-defined suppression process is proposed. An integrated combination of progressive damage model methodology, self-adjusted parametric modeling with user-defined suppression process and multi-island genetic algorithm is applied for the optimization problem. The optimization result showed 30.75% weight reduction compared to the original T-joint configuration. On the basis of history data, we investigate the correlations between design variables and concerned constraint variables.

This paper deals with the optimization of multi-laminate structures by Multi-Island Genetic Algorithm (MIGA) coupled with CAE solver. The optimization problem is a compound problem which relates to size optimization for object structure and stacking sequence optimization for variable-thickness composite laminates. Taking a typical adhesive bonded sandwich T-joint under a reference pull-off load as an instance object and establishing strength conditions on the basis of progressive damage analysis, optimum design is carried out with the total weight of joint as the target function. Progressive damage model (PDM) methodology and cohesive zone model (CZM) methodology are employed to develop an exact finite element model of the object structure. Classified failure criteria are chosen to investigate the capability of the joint in bearing the applied load. The optimization procedure on the typical adhesive bonded sandwich T-joint showed 34.24% weight reduction compared to the initial laminated structure. On the basis of history data, the study further brings out the influence of design variables on some main constraint variables.

A parallel multiscale numerical framework based on the FE 2 method is established to perform the non-linear failure analysis of three-dimension (3D) composite materials with complicated architectures. Parallelization of the nested solution process is presented, as well as the strategy used to implement the FE 2 method alongside the finite element package ABAQUS. The emphasis is put on the detailed numerical implementation in both scales, using a set of python scripts and UMAT subroutines to allow the service of commercial finite element packages ABAQUS instead of the in-house code. The novel framework can be scalable to the distributed clusters and carries out the progressive damage analysis of 3D braided composite materials under uniaxial tensile loading and three-point bending loading, respectively. As a validation, the results obtained have been compared with experimental data from the literature. The parallel performances of numerical examples in runtime and acceleration effect are addressed to demonstrate the capabilities of the proposed framework.

The variational asymptotic homogenization (VAM) theory is extended to access freely to commercial finite element (FE) software to deal with periodic plate structures. In this work, the finite element format for periodic plate structures based on the variational asymptotic homogenization is developed, ensuring the commercial finite element software can be utilized to obtain the effective plate stiffness. A standard numerical framework and an integration algorithm are proposed for unifying the dimensional reduction analysis and the homogenization analysis in a formalized manner. As for model validation, the periodic plates composed of unit cells with three-dimension (3D) heterogeneous geometry are simulated by various elements and modeling techniques using the commercial FE software rather than programming in-house code. Compared to the results provided in the existing literature, the proposed approach shows excellent performance in terms of computational efficiency and time without compromising the VAM accuracy. It is preferable to enhance the application of the variational asymptotic homogenization theory for the more sophisticated heterogeneous plate structures.

A finite element model was established based on Hashin failure criteria and the progressive damage theory to predict the damage of integrated composite T-joint structures with fixed support subjected to low-velocity impact. The cohesive zone model was employed to simulate the delamination behaviors of adhesive in the finite element model. The fiber damage and matrix damage of each ply can be provided by the finite element model in details. The damage behaviors of composite T-joint structure subjected to different impact energies were compared using the finite element model. The numerical results showed that the impact caused an elliptical projected area with its major axis along the surface fiber direction. Besides, the in-plane damage dimension is proportional to the impact energy. It is obviously noted that the damage of the first ply is the most serious owing to the delamination between soleplate and fillet caused by the stretching of the L-ribs. A low-velocity impact experiment of composite T-joint was also conducted and the damage dimension was determined by the ultrasonic C-scan. Results showed that the shape and size of our experimental damage agreed well with the simulation results. Our finite element model can be used to effectively analyze the damage behaviors of the integrated composite T-joint subjected to low-velocity impact.

The purpose of this paper is to investigate the influence of fixed L-ribs on the damage behavior of integrated composite T-joints subject to low velocity impact. Experimental test is performed on a vertical drop-weight testing device with two different impact energies. Detailed inspection by visual and ultrasonic C-scan reveals that different impact energies result in different damage types and shapes. Experimental results show that without fixed L-ribs the impact caused an elliptical damage around the impact point at the impact energy of 4.45J/mm and a trumpet delamination at the impact energy of 8.90J/mm. In comparison, the impact only caused serious damage around the impact point without delamination at the impact energy of 8.90J/mm with fixed L-ribs. This experimental study has demonstrated that fixing the L-ribs is an effective way to prevent the delamination of the integrated composite T-joint subject to low velocity impact.

对复合材料双钉单剪螺栓连接结构进行挤压强度试验,并基于Hashin准则建立了三维有限元渐进损伤模型.通过编写和调用VUMAT子程序,建立复合材料双钉单剪和多钉单剪有限元模型.分析了结构破坏的发生和演化,同时探讨了复合材料板的厚度、金属与复合材料板之间的摩擦、宽径比及孔距对双钉单剪的连接刚度和挤压强度的影响、厚度和孔距对双排四钉单剪连接刚度和挤压强度的影响.仿真结果与实验结果进行了比对,验证了模型的正确性.