An experimental investigation of the mechanical properties and failure mode of 3D stitched composites

Abstract

Mechanical behavior and failure modes of three-dimensional (3D) stitched composites were experimentally investigated. In addition, a comparative analysis between these materials and equivalent laminates (2D) was accomplished. The 3D composite plates were manufactured using sheets of glass fiber manually sewn with aramid tows and molded with epoxy resin by vacuum-assisted resin transfer molding. Three-points bending, Charpy impact, double cantilever beam (DCB), and short-beam shear (SBS) mechanical tests were carried out on both types of materials. The DCB test results revealed that the action of reinforcement tows inhibited the propagation of the delamination cracks, which led to an increase in the fracture toughness of the 3D composites. However, the damage caused by the stitching process, such as fiber breakage and misalignment as well as crimping, and resin-rich regions, was responsible for reducing the flexural and shear properties of these materials. In addition, it was revealed that the stitching did not influence the impact toughness, although it prevented delamination from quick propagation, avoiding a catastrophic failure, which enhanced the damage tolerance of these materials, mainly for aeronautical applications.