KINK-BAND FAILURE ANALYSIS OF THICK COMPOSITES IN COMPRESSION

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 ex perimentally showed a decrease in strength with increasing thickness. The analysis was performed to determine if the reduction in strength w as 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 formatio n of kink-band failures in the presence of fibers misaligned with the principal axis of compression loading. The fiber misalignment was dete rmined by a finite element analysis that accounted for the displacemen t of the laminate outer plies where the laminate exited the compressio n test fixture. The correlation between the experimental results and t he theoretical analysis showed the compression strength of the AS4/350 1-6 and S2/3501-6 laminates to be independent of thickness and directl y proportional to the through-thickness fixture restraint on through-t hickness Poisson expansion. This theoretical and experimental comparis on also demonstrated a strong correlation between fiber misalignment, its resulting shear stress state and the kink-band compression failure mechanism.