Low velocity impact tests of laminate glass-fiber-epoxy matrix composite material plates

This work deals with the characterization of composite material suitable for constructing structural parts devoted to dissipate kinetic energy during impacts. In particular glass-fiber-epoxy matrix laminates are considered, both with unidirectional layers and with woven layers stacking, with three different layers orientations.Experimental tests are performed according to ASTM standards using a free-fall drop dart testing machine. The specimens are plates completely constrained on a circular edge by the clamping fixture. Two energy absorption parameters (namely saturation impact energy and damage degree), two relevant characteristic values of the impact force history (namely the first damage force and the maximum force) and the sensitivity of the material mechanical characteristic to the strain rate effect are considered in order to describe the impact behavior of the material. Diagrams are presented to show the history of relevant kinematical, dynamic and energetic quantities, both to synthesize the dependency of the energy parameters and force threshold values on the impact velocity. The considered materials, under the considered loading conditions, show no sensitivity to the strain rate effect.