Impact-induced damage and damage propagation under flexural load in TiNi and Kevlar-stitched carbon/epoxy laminates

This paper presents a study of the effect of stitched reinforcements on impact-induced damage and damage propagation under flexural load. TiNi and Kevlar threads were used as the superelastic element and the reference thread, respectively. Unstitched carbon/epoxy laminates were also produced. Embedded damage (matrix cracks, fiber rupture and delamination) was induced by low velocity impact testing. The performance of the unstitched and stitched specimens was assessed in terms of the energy per unit volume of damage created during impact testing, and the energy to failure of the impacted specimens during their three-point bending testing. A finite element model was used for simulating the propagation of damage, and particularly delamination, in stitched and unstitched structures during the bending test, and, depending on the mechanical properties of the stitching threads, different propagation schemes were predicted with this model.