The Fracture Behavior of Carbon/Epoxy Laminates Containing Internal Cut Fibers

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Abstract
Fiber breakage in a composite laminate can be caused by impact loads. A study was conducted to investigate the effect of internal fiber breakage on the tensile strength of carbon/epoxy laminates. The specimens contained internal fiber cuts, which were considered “buried cracks” in this study. Four layups, [0, ± 45,90,02], [90, ± 45,0]s, [0, ± 68,0, ± 68]s, and [0]l2, were studied. The results showed a significant strength reduction due to the internal fiber cut. Delamination occurred under load adjacent to the internal crack prior to the final fracture, as shown by ultrasonic C-scan inspection and micro-sectioning inspection. The dimensions of the delamination zones were affected by laminate layups and the length of internal cracks. Prediction of the residual strength was attempted using a principal load carrying ply failure criterion in conjunction with a 3-dimensional anisotropic finite element analysis. Laminate failure prediction was based on the behavior of individual plies. The predicted residual strength was in general agreement with measured residual strength over all the laminates and conditions investigated, indicating the applicability of the criterion.