High-rate J-testing of toughened polyamide 6/6: Applicability of the load separation criterion and the normalization method

This paper examines the applicability of the load separation criterion and the normalization method in determining JR curve of a toughened polyamide 6/6 at high loading rates (1 m/s). The analysis of procedure problems associated to this high experimental rate is performed. The results obtained using the normalization method are then compared with those measured via multi-specimen testing procedures proposed by ESIS (Technical Committee 4). The results show that, unlike low loading rate tests, the presence of the oscillations in the load vs displacement traces, due to the inertial effects produced during the impact, complicate considerably the elaboration of the data, with particular reference to the identification of the separable blunting region. The comparison of JIc values obtained according to the different procedures examined indicates that the values of JIc = J0.2 (taken at 0.2 mm crack growth) are in good agreement, whereas consistent differences among the values of JIc = J-blunting (taken at the blunting line) are observed.