The effect of stitching on the low-velocity impact response of delaminated composite beams

A numerical simulation is performed to predict the effects of stitching on the low-velocity impact response of stitched delaminated beams. The load/displacement relations during the impact are assumed to be the same as in the corresponding static problem. Hence a solution to the problem of a stitched delaminated beam under a static contact force is developed. The effects of stitches are modeled as a constant shear traction in the stitch bridging zone to account for the shear resistance offered by the unbroken stitches. From the static simulation the load/displacement and displacement/crack-extension relations are obtained. From the area under the load/deflection diagram the apparent fracture toughness due to the stitching is also estimated. The impact simulations provide information on the load at which the crack propagation initiates, the maximum contact force, and the extent of crack propagation at the end of the impact event. The results indicate that stitching does not increase the load at which delamination begins to propagate, but greatly reduces the extent of delamination growth at the end of the impact event.