L. Maragoni

Influence of manufacturing induced defects on damage initiation and propagation in carbon/epoxy NCF laminates

Abstract In the present work, two sets of NCF carbon/epoxy laminates have been produced via liquid infusion molding, with the aim to investigate the influence of some process parameters on damage initiation and propagation in composite laminates. In the first set the resin was degassed before infusion and the bleeding time was large. In the second set the resin was not degassed and the bleeding time was kept very short. Microscopy analyses revealed an evident void content in the second set of panels, whereas no voids were detectable in the first one. Incremental static tests on cross-ply specimens and DCB tests on [(90/0)3]S and [(+45/u2009−u200945)3]S laminates obtained with the two processes were carried out, with the aim to characterise the influence of voids on damage initiation and propagation. Tensile tests revealed that the multiple cracking process in cross-ply laminates was detrimentally affected by the presence of defects. Conversely, DCB tests showed a negligible influence of the presence of defects on the mode I fracture toughness, its propagation value being even higher in the specimens with voids. Damage mechanisms were carefully analyzed to deeply understand the role of voids mainly in the crack initiation process. Finite element analyses carried out considering the actual geometry of voids showed that their local shape, and the related stress/strain concentration, are fundamental parameters to properly describe this phenomenon.