Damage tolerance of impacted curved panels

Abstract

The final aim of this study is to evaluate the influence of impact damage on the residual strength of carbon/epoxy vessels stressed by internal pressure. An intermediate stage determined the residual behaviour of pre-impacted curved panels loaded in tension. Curved panels were impacted, reproducing the damage types observed in impacted vessels filled with propellant. Delamination damage was assessed by ultrasonics and optical microscopy used to observe intra-laminar mechanisms. Tension after impact (TAI) tests quantified the residual behaviour. An experimental design was used as an alternative to the complex analytical modelling of dynamic damage mechanisms. With this original technique, empirical relationships were established, linking impact parameters to residual properties. The force to failure was found to vary in a bi-linear manner with impact energy. Below a specific level of impact energy corresponding to failure in 4/7 of the plies, there is no significant reduction in the residual strength. The composite Young’s modulus decreased linearly with impact energy.