Carbon Fiber Reinforced Polymer (CFRP) composites have become indispensable in the aerospace industry due to their superior mechanical properties. Delamination, often initiated by impact events, manufacturing defects or fatigue loading, reduces the stiffness and structural integrity of the structure. In actual structures delamination can propagate through multiple plies, causing both interlaminar and intralaminar fractures. Conventional finite element approaches, such as virtual crack closure technique (VCCT) and cohesive zone modelling (CZM), are inadequate for modelling both interlaminar and intralaminar failures. The purpose of this paper is to explain how to overcome these limitations by integrating the Extended Finite Element Method (XFEM) with cohesive zone surface‐based modelling. A comprehensive numerical model capable of accurately predicting both interlaminar and intralaminar crack propagation in multiangular CFRP composites under Mode‐1 loading is presented. Details of numerical modelling of various delamination interfaces and its comparison with experimental data are presented.
Shell-based cohesive elements tend to overestimate the compression ahead of the crack tip because of approximations in the penalty stiffness. In this study, the higher-order structural cohesive element previously developed by the authors is enhanced with a resin-rich layer-dependent penalty stiffness to improve both computational efficiency and predictive accuracy. The proposed formulation distinguishes between the normal and shear penalty stiffnesses. It extends the resin-rich layer-based penalty stiffness from the layer-wise to the equivalent single-layer framework. This extension is achieved using the through-thickness distributions of the out-of-plane normal and transverse shear stresses derived from beam theory. The proposed method is verified and validated against benchmark problems for Mode I, Mode II, mixed-mode, and reinforced DCB configurations. Compared with the conventional formulation, it exhibits significantly improved mesh convergence and provides more accurate predictions of the compression distribution ahead of the crack tip and the delamination propagation.
Xiaopeng Ai, C. Kassapoglou, Boyang Chen· 0 citations
Addressing the apparent contradiction between the macroscale pseudo‐ductile response of ceramic matrix composites (CMCs) and the intrinsic brittleness of their constituents, this study proposes a new trilinear cohesive zone model (CZM) to provide new insights into the mesoscale damage evolution mechanisms. Developed within the classical cohesive zone framework, the model introduces a stable propagation stage, enabling precise characterization of the triphase crack behavior within the interphase: initiation, stable growth, and instability. Numerical validations using standard fracture specimens—a double cantilever beam (DCB) and an end‐notched flexure (ENF)—demonstrate the model's superior performance in predicting both brittle and ductile interfacial failures. Specifically, under Mode II ductile interfacial conditions, its predictions for peak load and damage evolution significantly outperform those of the conventional bilinear model. In simulations of microscopic representative volume elements (RVEs) and mesoscopic multi‐directional laminate models, the model successfully captures the competitive evolution sequence of interface debonding, multiple matrix cracking, and fiber fracture. It explicitly reveals the core role of the “weak interphase” design, which guides crack deflection and promotes fiber bridging, thereby facilitating load redistribution and progressive energy dissipation. From a micromechanics perspective, this study clarifies that the macroscopic pseudo‐ductile behavior of CMCs essentially originates from the active regulation of crack paths by interfacial properties. This mechanism effectively unlocks the toughening potential of brittle constituents, providing a valuable theoretical reference and simulation tool for the damage‐tolerant design of advanced CMCs.
Xiao-Fei Hu, Zhen-Guo Lei, Yu Wang et al.· Journal of The American Cera...· 0 citations
Transverse fiber bridging is an extrinsic toughening mechanism in cross-ply composite laminates, but its numerical representation remains challenging because it involves coupled transverse cracking and interlaminar delamination. This study develops a cohesive-zone-based finite element model to investigate the apparent bridging response during Mode I delamination in cross-ply double cantilever beam (DCB) specimens with prescribed transverse cracks. Delamination growth is simulated using cohesive elements, while transverse cracks are explicitly introduced in the
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sublaminate. Experimental data reported in the literature are used to relate in-plane strain, transverse crack density, and propagation fracture toughness, from which representative transverse crack spacings are derived. The model is validated against reported DCB responses for cross-ply laminates with and without pre-induced transverse cracking. Parametric studies are then performed to evaluate the effects of interfacial heterogeneity configuration, interface strength contrast, transverse crack spacing, specimen width, and
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ply thickness. Within the proposed equivalent cohesive-interface representation, the results show that the apparent bridging response is governed mainly by the local interfacial heterogeneity configuration and transverse crack spacing, while global specimen dimensions have a secondary influence. The proposed model provides a mechanistic framework for interpreting bridging-enhanced Mode I delamination resistance and may help guide the design of interface architectures in damage-tolerant composite laminates.
R. Wirawan, Mhd Sukri, M. Firdaus et al.· Proceedings of the Instituti...· 0 citations
This paper presents a study on multi‐scale modelling of progressive damage model in laminated composites using shell finite elements, with considerations for the effects of manufacturing defects. The approach utilises second‐order homogenisation with 5‐parameter shell formulation to capture the effects of complex sub‐structural geometry and damage mechanisms in a smeared, equivalent single layer manner. During analysis, the shell constitutive tensors are continually updated and derived from high‐fidelity unit cell simulations. The key benefits are two‐fold. First, manufacturing defects can be directly introduced to targeted regions by assigning unit cells containing said defects. Second, the effects of progressive damage, including delamination, are accounted for in a smeared fashion without requiring complex mesh‐stacking nor discontinuous kinematic enhancements. A series of numerical benchmarks are presented to demonstrate the model's ability to accurately predict damage/defect induced stiffness degradation, failure loads and damage morphology in laminated composites under loading conditions, including bending, shear, buckling and static indentation. Overall, the findings in this paper presents a proof‐of‐concept for a multi‐scale framework that enables defect assessment and damage modelling in shell‐based simulations of composite structures, and lays the groundwork for future computational acceleration via surrogate modelling.
A. Hii, S. Hallett, Bassam El Said· International Journal for Nu...· 0 citations
This study investigates the manufacturing process, progressive damage behavior, and multiobjective structural optimization of 3D angle‐interlock woven composites (3DAWCs) fabricated via the resin transfer molding process. The 3DAWCs consist of T700‐12K carbon fiber preforms and an epoxy matrix system (LT‐5028A/B). A representative volume element model is constructed from metallographic measurements. An enhanced Linde‐based progressive damage model incorporating shear coupling was implemented through the user‐defined material subroutine to capture the damage evolution of complex woven architectures. The numerical model is validated against uniaxial tensile tests in both warp and weft directions. And this model is employed to investigate the effects of the viscosity regularization coefficient and porosity on the mechanical response. Furthermore, an orthogonal experimental design combined with Pareto effect analysis and response surface methodology is employed to evaluate the effects of yarn spacing, width, and height on the warp‐ and weft‐direction peak stress and Young's modulus. The results indicate that weft height is the dominant parameter affecting the tensile strength, whereas warp width has a significant influence on stiffness. The optimized configurations achieve a balance between strength and stiffness in different loading directions, demonstrating the potential of mesostructural design for improving the mechanical performance of 3DAWCs.
Delamination is a critical damage mode in laminated composites, involving hidden layer separation that can compromise structural performance. This study presents an efficient finite element approach for free and forced vibration analyses of delaminated composite plates using a rectangular element. The effects of delamination size, location, plate’s geometry, length-to-thickness ratio, stacking sequence, and boundary conditions on the vibration response are systematically investigated. In addition, the dynamic response is analyzed with and without a dynamic contact formulation to assess interaction effects between delaminated layers. The results demonstrate how these parameters influence vibrational behavior, providing valuable insights into structural health monitoring and damage assessment in composite structures. The proposed method offers a robust tool for predicting dynamic characteristics in delaminated laminates, aiding in the design and maintenance of reliable composite systems.
