Low-velocity impact behavior of glass fabric composite laminates at low temperature

In the last decades, fiber reinforced polymer composites (FRPCs) have gained an increased attraction, with respect to traditional materials, for a wide range of applications mainly for their superior strength, lightness and ability to tailor their performances by an opportune choice of matrix, reinforcements and eventual coupling agent as well as of their structural design. However, for these materials, impact issues as damage mechanisms and extent assume a relevant role especially under low velocity impact loading due to foreign objects. In composite laminates, above a certain impact energy threshold, accidental events could cause various damages as matrix cracks, delaminations, fiber fracture, fiber-matrix debonding and fiber pull-out, with effect often not visible at the naked eye but which irreversibly affect the reliability of FRPCs based items. Although, a huge amount of data is already available about impact behavior of polymer composite materials and related mechanisms of damage [1,2], previous studies, performed under realistic environmental conditions, have often provided contradictory results. Therefore, taking into account that, during their service life, composite laminates may be subjected not only to significant dynamic loads but also to thermal excursions, with the awareness that these topics still need more investigations, authors focused on the influence of temperature on the low-velocity impact behavior of thermoplastic laminates prepared by the traditional film-stacking approach. In more details, glass fabric reinforced thermoplastic composite laminates based on commercial low-density polyethylene (LDPE) and thermoplastic polyurethane (TPU) resins were compared with thermosetting vinyl ester based ones in terms of low-velocity impact behavior. All systems were characterized in extreme low temperature conditions. The results about different matrixes were compared and the damage behavior was explored by photographic inspections and morphological analysis. Preliminary results, recorded as load-displacement and absorbed energy-time curves, showed interesting perspectives for thermoplastic systems mainly because of their lower glass transition temperatures with respect to thermosetting matrices and, thus, such to ensure, low stiffness and high damping ability of FRCPs based items.