Repeated Impact Failure of Coiitiiiuous Fiber Reinforced Thermoplastic and Thermoset Composites

(Rc\i\cJ Augusl.?I. IYN) ARSTRACI': An elTort was made to study the chmage niechanisna in both thernio-plastic and thennoset composites in response to repeated low-velocity impacts. An instru-mented fallingdart impact tester was used that provided the load-deflection and energy-deflection curves plus other numerical data on material properties. Bolh poly(pheny1ene sulfide) (PPS) and epoxy composites prepared from different preform styles and stacking sequences \\ere tested. For any composite with given dimensions a threshold incident im-pact energy (E.) could be identified a b v e which delaniination \\auld occur at the first iin-pact. As a consequence, both the stiffness and the strength of this composite Here reduced and these properties could bc measued using the same impact tester as a function of im-pact cycles. If instead a subcritical incident energy (&. < E,) \\as imposd on the niate-rial, no appreciable property loss wuld be observed until a critical number of impact cycles (N<) \\as reached. In this subcritical s tag, matrix cracking preceded delamination as impacts were repeated. Both the number and size of delamination cracks were then found to increase as the number of repeated impacts \\as increased. An elastic strain en