Kink-Band Failure Analysis of Thick Composites in Compression

Abstract

This article describes an analysis of 6.4-25.4 mm (0.25-1.0 in.) thick composite laminates subjected to uniaxial compressive loading that experimentally showed a decrease in strength with increasing thickness. The analysis was performed to determine if the reduction in strength was an intrinsic thickness material effect or if it could be attributed to through-thickness restraint on the specimen caused by the test fix ture. The analysis was based on closed form solutions for the formation of kink-band fail ures in the presence of fibers misaligned with the principal axis of compression loading. The fiber misalignment was determined by a finite element analysis that accounted for the displacement of the laminate outer plies where the laminate exited the compression test fixture. The correlation between the experimental results and the theoretical analysis showed the compression strength of the AS4/3501-6 and S2/3501-6 laminates to be inde pendent of thickness and directly proportional to the through-thickness fixture restraint on through-thickness Poisson expansion. This theoretical and experimental comparison also demonstrated a strong correlation between fiber misalignment, its resulting shear stress state and the kink-band compression failure mechanism.