Time-Resolved Impact Response and Damage of Fiber-Reinforced Composite Laminates

Abstract

An experimental technique for time-resolved characterization of the mechanical response and induced damage of fiber-reinforced composite laminates during 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 contact force, displacement and energy absorption of the specimen during impact are measured. The materials analyzed are IM7/K3B, a graphite-fiber polyimide-matrix composite, and S2 glass/5250-4, a glass-fiber bismaleimide-matrix composite. Experiments conducted characterize the responses of the materials over a range of impact energy. The initial peak force sustained by the specimen 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 same amount of energy dissipated through damage, the glass fiber composite retains a higher percentage of its tensile strength than the graphite-fiber composite. Postmortem X-ray radiography and ultrasonic tests are used to assess the extent and effects of damage. The mean square amplitude of the transverse vibratory response of an impacted specimen decreases with increasing impact-induced damage quantified in terms of dissipated energy. A similar correlation is observed between the through-thickness wave speed of an impacted specimen and the dissipated energy.