The Residual Tensile Strength of Stitched and Unstitched Carbon/Epoxy Laminates Impacted under Tensile Load

This paper presents preliminary results of a study into the effect of stitching on the residual strength of tensile loaded panels subject to impact and their propensity to catastrophic failure when impacted. The 2 mm thick orthotropic panels were produced from ten layers ([(0,90){2},0]{s}) of Uniweave T300 carbon fabric stitched with aramid yarn and impregnated with GY260 epoxy resin using the resin transfer moulding process. The specimens were impacted with a 9 g projectile at impact velocities ranging to 70 m/sec while subject to tensile loads ranging to 72% of the specimen ultimate tensile strength. No significant difference was found between stitched and unstitched panels in their impact resistance or tolerance, indicating that Mode I fracture was not a dominant contribution to the failure modes. Boundaries of impact velocity and preload have been established above which catastrophic failure occurred on impact and a mechanism has been postulated for such failure. Results are presented for damage area and residual strength.