Effects of Out of Plane Stress on Progressive Kinking in Internal Zero Plies

Compressive strength and failure are a common benchmark to qualify the performance of a composite material for many applications. Standard test procedures typically involve compressive test of unidirectional or quasi-isotropic composites from where the properties are back calculated for a single composite ply to obtain the compressive strength of a ply and the laminate. In many applications, the composite material is under multi-axial stress states. In this paper, the influence of through-the-thickness stress on the compressive behavior is studied, with specific intent of replicating loading conditions seen in a bolted joint. Plane strain model of a laminated composite with explicit modeling of fiber and matrix is used in a layered stack-up with different boundary conditions to study the changes in compressive strength as well as residual (post-peak) strength.