On the impact essential work of fracture of ductile polymers

Abstract

Abstract The essential work of fracture methd (EWF) to evaluate the fracture toughness of ductile materials in plane stress with prevalent gross yielding conditions was originally developed by the Cotterell‐Mai research group in Sydney University more than ten years ago. Since then, the EWF method has been proven independently by many researches to be a valid tool for a range ofductile metals, polymers, paper sheets and fiorous composites. The current interest in the technical community of the plastics industry is to extend the 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 mehodology under dynamic loading conditions appear controversial, our purpose in this work is to clarify under what conditions the impact EWF method is applicabe. The EWF methodology was applied to the energy impact data obtained on two PP copolymers and one ABS polymer at different specimen thickness and geometry. The results showed that the EWF method can be applied to high‐rate testing provided the ligament is fully yielded and the plastic zone is scaled with the square of the ligament length. When these conditions are fully satisfied, the impact specific EWF is a material constant independent of specimen geometry for a given sheet thickness in plane stress; and it is also invariant with specimen thickness when plane strain conditions are met.