Damage occurrence at edges of non-crimp-fabric thin-ply laminates under off-axis uniaxial loading

Thin-ply based laminates are a promising development in composite materials and are expected in the near future to outperform conventional laminates in mechanical performance. A rational design with thin plies requires understanding the effect of ply thickness on each damage mechanism. This paper presents an experimental investigation into damage occurrence in a quasi-isotropic laminate made from thin-ply, bi-axial, Non-Crimp-Fabric (NCF), under different off-axis uniaxial loadings. The NCF layers are positioned through the laminate thickness creating two regions, namely THICK and THIN (with and without ply clustering). Then, the onset and progress of three damage mechanisms (transverse matrix cracking, matrix crack induced delamination and free-edge delamination) for both regions are analyzed by monitoring the specimen's free-edge. The results show that the critical region where damage occurs is that with ply clustering (THICK), whereas delamination originating from matrix cracks or free edge effects are delayed or even suppressed in the THIN region