Effects of inter-ply mismatch angle on interlaminar properties and their influence in numerical simulations

In this study, the interlaminar shear strength and mode II fracture toughness of carbon-epoxy laminates with respect to different inter-ply mismatch angles are determined and shown to generally decrease as inter-ply mismatch angle increases. Despite this dependency, most numerical simulations of multi-directional laminates involving delamination adopt interlaminar properties measured from unidirectional laminates only. Using the derived angle-dependent shear strength and fracture toughness, computational simulations of short-beam shear and out-of-plane loading of multi-directional laminate plates were performed and compared with physical experiments. It is shown that delamination tends to form intensively at interfaces with larger mismatch angles where delamination resistance is lower. This characteristic is captured by assigning interlaminar properties corresponding to the inter-ply mismatch angles in the numerical simulation. The practice of applying interlaminar properties obtained from tests on unidirectional samples may lead to erroneous predictions of varying severity for the simulation of multi-directional laminates.