The J-integral technique applied to toughened nylons under impact loading

Abstract

The J-integral technique has been used to characterize the toughness of two rubber-toughened nylons under impact loading conditions, at impact speeds from 1–3 ms−1, using single-edge-notched three-point bend specimens. A falling weight impact tester was used to generate different amounts of crack growth, allowing the resistance curve (J-R curve) to be constructed using the multi-specimen technique. The technique is experimentally straightforward and permits the toughness characterization of tough materials with relatively small specimens. For a rubber-toughened nylon 66, the resistance curve is very similar to that obtained at quasi-static loading rates, indicating a low dependence of toughness on rate. However, for a rubber-toughened amorphous nylon, a higher resistance curve was obtained under impact conditions than at low loading rates. This result probably indicates a limitation in the test method, rather than a genuine material response.