Is there a thickness effect on compressive strength of unnotched composite laminates?

The effect of laminate thickness was investigated on the compressive behavior of unidirectional and crossply composites. A recently developed compression test method for thick composites was used to test specimens from 16 to 200-plies thick. In all cases the stress-strain behavior to failure is nonlinear and failure strength is matrix dominated. Longitudinal compressive failure is triggered by matrix failure accompanied by fiber microbuckling and the compressive strength is greatly degraded by initial fiber misalignment. The longitudinal compressive strength shows a mild trend of decreasing values with increasing thickness. It can be explained that, even if such a trend is significant, increasing size would have a diminishing effect on compressive strength for initial fiber misalignments greater than 1.5 to 2°. © 1999, Kluwer Academic Publishers.