Investigation on the reduction of in-plane compressive strength in thick preconditioned composite panels

This paper investigates the effects of damage characteristics and local curvature change on the residual compressive strength (RCS) of flat 4-mm thick carbon/epoxy panels through the examination of their buckling behavior. The damage was induced by impact, quasi-static loading and embedment of artificial delamination for a variety of damage areas, intensities and different local curvature changes. The embedment technique of artificial delaminations allowed the separation of the damage from the local curvature change. Panels with no or less significant damage in conjunction with no or little local curvature change failed in end crushing because of large membrane reaction, in-plane shear resistance and flexural rigidity. Prebuckling and Poisson's effect dictated their compressive behavior. Panels with significant damage followed the sequential behavior of prebuckling, local buckling, global buckling and ultimate failure in the mid-section region. Their RCSs were dictated by a combination of delamination size, intensity and local curvature change. Propagation of the damage with certain size and intensity associated with reduced flexural rigidity in the damaged area led to the local-to-global buckling transition and the panels failed at the global buckling-to-postbuckling transition at a nodal line. The effect of increasing the panel thickness on the ratio of RCS to a baseline value was not straightforward due to the end crushing failure of the thicker intact panels.