Charpy impact toughness of conventional and advanced composite laminates for aircraft construction

Abstract

A weight-based analysis was made of the translaminar Charpy impact toughness performance of conventional and advanced composite materials for aircraft fabrication. The materials were carbon-epoxy (C-Ep) and hybrid fiber-metal TiGr (Titanium-Graphite) laminates. 5 mm-thick three-point bend specimens were tested over a temperature range of -70 to 180 ºC to reproduce typical in-service conditions of supersonic jetliners. The energies required for the processes of damage initiation (Ei), damage propagation (Ep), and whole fracture (Et = Ei + Ep), were evaluated at two loading rates, namely, 2.25 and 5.52 m/s in an instrumented Charpy impact testing machine. C-Ep laminates with unidirectional fiber tapes arranged in cross-ply architecture consistently showed the best performance in terms of damage initiation toughness, whereas the hybrid fiber-metal laminate TiGr excelled in terms of propagation toughness. On the other hand, the overall performance of bi-directional fabric C-Ep laminates was very disappointing. The impact behavior of composite laminates was substantiated by a qualitative analysis of topographic aspects of fracture surfaces.