Crushing characteristics of 3-D braided composite square tubes

Although textile composites have been studied for some time, the crushing failure modes and energy absorption data have been limited. In this study, static crushing tests were conducted on 3-D carbon/epoxy and Kevlar/epoxy braided composite square tubes to investigate the failure modes and energy absorption capability of those materials. During crushing test the carbon/epoxy braided composite square tubes splayed first, then bent until final failure. In contrast, the Kevlar/epoxy braided composite square tubes exhibited a stable progressive folding failure. The failure modes of the crush tests of carbon/epoxy braided composite tubes included compressive shear failure, bending, local buckling of the axials, shear and tensile failure of the braiders, matrix crush, interface debonding and open mode crack propagation. The specific energy absorption capability of carbon braided composite tube is higher than Kevlar braided composite tube, but Kevlar tube has good post-crush structural integrity. In the 3-D braided composite tubes, the axial yarns are the main supplier for energy absorption whereas the braider yarns determine the crushing failure mode.