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Influence of In-situ Constraining Effect on Transverse Ply Crack Formation in Unidirectional Composite Laminates.



A micromechanical finite element model was developed to predict the initial events of failure in the constrained 90° ply of a [0/90/0] unidirectional cross-ply laminate under in-plane tensile loading. Common manufacturing induced defects, including non-uniform fiber spatial distribution and voids, were considered in the explicit representation of the full thickness multi-fiber 90° ply, while the constraining 0° plies were treated as effectively homogeneous orthotropic materials. The inelastic behavior of the polymeric matrix in the 90° ply was modeled via a pressure-dependent yield criterion, while the carbon fibers were assumed to deform linear elastically. Two metrics for representing failure were considered in the assessment, including distortional and dilatational energy densities that are respectively responsible for local yielding and cavitation in the fiberconstrained matrix. The influence of in-situ effect was studied by comparing the local stress state of the constrained and unconstrained transverse ply. It was observed that the local response of the polymer depends on the fiber spatial distribution. Furthermore, it was found that the in-situ ply constraining effect appears subsequent to the formation of local cracks and not prior. Dissimilar constraining effects were observed in different regions, e.g., resin-rich zone versus fiber-cluster zone, suggesting that inconsistent stress distributions will directly influence the evolution of cracks in the 90° ply.


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