Numerical Evaluation of Ultimate Strengths of Composites Considering Both In-Plane Damage and Delamination

Traditional laminate strength analysis only considers face failure under in-plane loads. In fact, owing to the mismatch of the mechanical properties of the adjacent layers, a three-dimensional interlaminar singular stress fields develop in a small boundary region in the vicinity of the free edges of the laminate under mechanical load, which may lead to interlaminar delamination failure. Neglecting this interlaminar failure mode, the failure strength of laminate will be overestimated. In this paper, face failure and interlaminar failure are both considered. So for a lamina, three major failure modes are considered: matrix failure, fiber breakage and delamination. Finite element method is used to obtain the stresses in a laminate under mechanical loads. Stress-based criterions are adopted to predict the failure mode of laminas. When a lamina is failed, the lamina stiffness is reduced according to the corresponding failure mode, and the stresses of the laminate are re-analyzed. This procedure is repeatedly performed until the whole laminate fails and thus the ultimate strength is determined. The predicted ultimate strengths are in good agreement with experiment results in the open literature.

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