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

The authors would like to acknowledge Chomarat (Ardeche, France) and Prof. S.W. Tsai (Stanford University, USA) for providing the material, Aldila (Poway, California, USA) for the epoxy system pre-preg and VX Aerospace (Leesburg, Virginia, USA) for manufacturing the panel. The authors also acknowledge the support of the Spanish government through the Ministerio de Economia y Competitividad under the contracts DPI2012-34465 and MAT2012-37552-C03-03. The first author especially acknowledges the support of the Generalitat de Catalunya with the pre-doctoral Grant FI-DGR (2013FI-801062)