Impact damage resistance of buckled carbon/epoxy panels

Results are presented for impact tests conducted on postbuckled, thin, orthotropic carbon/epoxy laminates manufactured by the RTM process from preforms of uniweave fabric, some of which were stitched with Kevlar sewing thread. They were impacted by a 13 mm diameter 8.9 g steel projectile at velocities ranging to 90 m/s on their convex and concave faces. For impact velocities above a critical value, either penetration occurred or the specimens failed catastrophically. Their corresponding critical velocity boundaries were established. Their projected impact damage area increased with increased impact velocity, however, it was independent of preload. Their postimpact properties remained largely unchanged. Stitching reduced significantly the projected damage area, however none of their other impact damage resistance and tolerance characteristics were effected, including their critical velocities for penetration and catastrophic damage. Impacting on the concave face, compared to impacting on the convex face, reduced the projected damage area and the penetration critical velocity boundary. No catastrophic damage was observed for these specimens.