Time-resolved impact response and damage of fiber-reinforced composite laminates

An experimental technique for time-resolved characterization of the mechani cal response and induced damage of fiber-reinforced composite laminates dur ing low-velocity, transverse impact is presented. The configuration uses a three-point bend fixture in a split Hopkinson pressure bar (SHPB) apparatus for controlled loading and real-time diagnosis. The full histories of cont act force, displacement and energy absorption of the specimen during impact are measured. The materials analyzed are IM7/K3B, a graphite-fiber polyimi de-matrix composite, and S2 glass/5250-4, a glass-fiber bismaleimide-matrix composite. Experiments conducted characterize the responses of the materia ls over a range of impact energy. The initial peak force sustained by the s pecimen is found to be constant over the range of impact energy studied. A monotonic relation is observed between the amount of energy absorbed by the specimens and the post-impact tensile strength of the materials. For the s ame amount of energy dissipated through damage, the glass fiber composite r etains a higher percentage of its tensile strength than the graphite-fiber composite. Postmortem X-ray radiography and ultrasonic tests are used to as sess the extent and effects of damage. The mean square amplitude of the tra nsverse vibratory response of an impacted specimen decreases with increasin g impact-induced damage quantified in terms of dissipated energy. A similar correlation is observed between the through-thickness wave speed of an imp acted specimen and the dissipated energy.