On the impact essential work of fracture of ductile polymers

The essential work of fracture method (EWF) to evaluate the fracture toughn ess of ductile materials in plane stress with prevalent gross yielding cond itions was originally developed by the Cotterell-Mai research group in Sydn ey University more than ten years ago. Since then, the EWF method has been proven independently by many researchers to be a valid tool for a range of ductile metals, polymers, paper sheets and fibrous composites. The current interest in the technical community of the plastics industry is to extend t he EWF methodology to high-rate impact testing of polymers and their blends and to determine the impact specific essential work of fracture. Since the literatures related to the applicability of this methodology under dynamic loading conditions appear controversial, our purpose in this work is to cl arify under what conditions the impact EWF method is applicable. The EWF me thodology was applied to the energy impact data obtained on two PP copolyme rs and one ABS polymer at different specimen thickness and geometry. The re sults showed that the EWF method can be applied to high-rate testing provid ed the ligament is fully yielded and the plastic zone is scaled with the sq uare of the ligament length, When these conditions are fully satisfied, the impact specific EWF is a material constant independent of specimen geometr y for a given sheet thickness in plane stress; and it is also invariant wit h specimen thickness when plane strain conditions are met.