Lock-in thermography for investigation of impact damage in hybrid polypropylene/glass composites LT to hybrid thermoplastic composites

The damage tolerance of multi-layer structures is strongly related to the stacking sequence and the properties of constituent plies. This contribution deals with interlaminar graded interface strength (IGIS) laminated structures, prepared by properly alternating layers of a woven glass fabric with peculiar sequences of compatibilized and not compatibilized polypropylene film layers, symmetrically arranged with respect to the middle plane. The low-velocity impact behaviour of all the laminated structures is investigated at two impact energies (namely 6 and 25 J). Sound and impacted specimens are nondestructively evaluated with lockin thermography (LT). The obtained results show that the impact damaging mode is strongly dependent on the stacking sequence in the IGIS laminate and especially on the type of matrix at the impacted surface.