On the Impact Essential Work of Fracture of Ductile Polymers

FASCE, LAURA ALEJANDRA; BERNAL, CELINA RAQUEL; FRONTINI, PATRICIA MARÍA; MAI, YIU-WING

POLYMER ENGINEERING AND SCIENCE

Society of Plastics Engineers

Año: 2001 vol. 41 p. 1 - 17

0032-3888

The Essential Work of Fracture method to evaluate the fracture toughness of ductile materials in plane stress with prevalent gross yielding condictions was originally developed by Cotterell-Mai research group in Sydney University more than ten years ago. Since then the EWF method has been proved 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 plastic 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 method under dynamic loading conditions appear controversial our purpose in this work is to clarify under what conditions the impact EWF methos is applicable. The EWF 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 mehod 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 lenght. When these conditions are fully satisfied, the impact EWF specific is a material constant independent of specimen geometry for a given sheet thickness in plane stress ; and it is also invariant when  plane strain condition are met.