Effect of out-of-plane wrinkles in curved multi-directional carbon/epoxy laminates

Defects such as out-of-plane wrinkles are known to strongly affect in-plane strength but there has been very little research on their effect on out-of-plane properties. Experimental and numerical studies of multi-directional curved-beam laminates were thus carried out to understand the effects of out-of-plane wrinkles on through thickness tensile strength. The initially selected layup saw free-edge delamination interacting with transverse cracking, which is undesirable. After suppressing the free-edge delamination by dispersing the plies near the specimen surfaces, through-thickness tensile failure was observed near the mid-plane. The effects of out-of-plane wrinkles could be studied with this appropriate layup, showing a 16% reduction in strength. A High-fidelity Finite Element Method (Hi-FEM) has been used to distinguish between the different failure modes and to understand the effects of wrinkles. Good agreement was achieved between the numerical and experimental results in terms of through-thickness tensile strengths and delamination locations.