Evolution of the strain energy release rate during ductile or brittle failure in woven-ply reinforced thermoplastic laminates under high temperature conditions

Depending on laminates' stacking sequence, the contribution of matrix behavior to the strain energy release rate is evaluated during failure in brittle and ductile composite laminates subjected to high temperature conditions (T > T-g) when matrix toughness is enhanced. The purpose of this work is therefore to investigate the strain energy released along with crack growth in 5-harness satin weave carbon fabric reinforced polyphenylene sulfide (PPS) structures with a Single Edge Notch. The crack growth appears to be self-similar in quasi-isotropic (QI) laminates, and nonself-similar in angle-ply (AP) laminates. Based on fracture mechanics concepts, semianalytical representations of the translaminar failure are combined with an Acoustic Emission (AE) technique to correlate the cumulative AE energy to the strain energy release rate. The experimental results reveal that the fracture toughness increases with increasing precrack length in QI laminates, whereas the effect of increase in precrack length exhibits reduced fracture toughness in AP laminates. The energy released during a non-self-similar crack growth is all the more significant than the stress concentration factor is reduced. A small defect (e.g., precrack) means a larger portion of the mechanical energy brought to the specimen to be dissipated during failure by means of large plastic deformations. With respect to QI laminates, the contribution of PPS matrix toughness to the fracture energy released is more significant in highly ductile AP laminates, resulting in higher fracture toughness. POLYM. COMPOS., 40:121-131, 2019. (c) 2017 Society of Plastics Engineers