Low-speed impact damage-initiation characteristics of selected laminated composite plates

The results of an experimental and analytical study of damage initiation in laminated composite plates subjected to low-speed impact are presented. Here, 8-, 16-, 24-, 32-, and 48-ply-thick quasi-isotropic and orthotropic graphite-epoxy and graphite-bismaleimide laminated plates have been impacted with dropped weights and the corresponding plate responses have been predicted analytically. Impact damage-initiation thresholds and damage-initiation mechanisms corresponding to a range of impact-energy levels are identified. Impact-damage initiation for the thicker plates occurs at both the impact site and the plate surface opposite to the impact site. Impact-damage initiation for the thinner plates is predominately due to tensile fracture on the plate surface opposite to the impact site. Three-dimensional stress states that correspond to the impact conditions that initiate damage are determined analytically to help identify damage-initiation mechanisms and to predict failure-initiation modes.