Progressive damage analysis of green composite laminates subjected to in-plane crashworthiness

In this paper the initiation and propagation of delamination in thin-walled green composite structures were studied. In particular, laminates of flax and hemp fibers with epoxy resin were investigated from experimental and numerical points of view, using the finite element code LS-DYNA. First, an experimental campaign was conducted using DCB and 4ENF tests to obtain the values of the interlaminar fracture modes, required for the cohesive fracture modeling. In addition, in-plane crashworthiness tests were performed on composite plates to analyze the damage of the specimens, under both quasi-static and dynamic conditions. A trigger mechanism was considered to help delamination to start and to ensure the most progressive crushing possible. The predominant damage mode was splaying, but some ply fragmentation in the middle layers and some buckling phenomena were also observed. In general, more stable progressive crushing was observed under dynamic conditions than under quasi-static ones, even if a reduction in terms of absorbed energy was obtained by moving to the dynamic condition. The numerical predictions showed a good agreement with the experimental reference results, validating the current framework for crashworthiness analysis of green composite structures.