Influence of notching and molding conditions on determination of EWF parameters in polyamide 6

The evaluation of the fracture toughness of polymers is highly relevant, particularly because of the ongoing development of new polymeric blends, most of which are aimed at increasing the impact resistance of engineering plastics. The toughness evaluation method, known as essential work of fracture (EWF), is a relatively simple method, useful for application on both brittle and ductile materials. This study investigated the effect of thickness, processing and testing conditions on the fracture behavior of polyamide 6. To this end, test specimens of the DDENT (double deeply notched tensile) geometry were tensile-tested under low (uniaxial tension) and high (tensile-impact) strain rates. The results, which are presented in terms of the variation of total fracture energy according to the ligament length, revealed that injection molded specimens without a pre-cracked notch offered the best choice. The geometrical criterion established by the ESIS protocol (test of the European Structural Integrity Society) for application of the EWF was also reviewed. (C) 2003 Elsevier Ltd. All rights reserved.