On the applicability of the load separation criterion in determining the fracture resistance (JIc) of ductile polymers at low and high loading rates

In this work, the applicability of a procedure based on the load separation criterion in determining the fracture resistance (JIc) of a rubber modified polyamide 66 (PA66) was analyzed and discussed. In particular, the effects of the testing conditions, with particular reference to geometry and loading rate, on the applicability of the method were investigated. The tests were performed both at low (from 0.5 to 50mm/min) and moderately high (0.6m/s) loading rates, on single edge notched in bending specimens with different initial crack length to width ratios (a0/W), which ranged between 0.3 and 0.7. Among the various findings it is worthwhile to point out that this analysis revealed that the plastic displacement at the end of the blunting process (at fracture initiation) resulted geometry independent. A clear dependence of such a parameter on the loading rate was observed. Further, it was shown that load separation is maintained beyond the blunting phase, as observed in the experiments carried out at low rate.