FEM simulation of a modified DCB test for 3-D orthogonal interlocked fabric composites

A mechanical model for the delamination extension of 3-D orthogonal interlocked fabric composites has been developed by using a 2-D finite-element method to simulate experimental results from modified DCB tests. The fracture phenomena around z-fiber bundles, such as debonding from the in-plane layer, slack absorption and fiber bridging, are introduced in the analysis. The experimental results could be simulated to a reasonable degree by the present model. The slack length and z-fiber slip introduced into the model were determined by the parametric study, and their results indicate that the difference in slack length has a serious effect only in the early stage of crack extension, and that the friction becomes dominant after this phase as a result of the increased number of bridging fibers. It is proved numerically that the coupled mechanism of z-fiber slip, absorption of slack and the fiber breakage provide the increase of the interlaminar fracture toughness of 3-D composites.