SINGLE AND MULTI-SPECIMEN R-CURVE METHODS FOR JIC DETERMINATION OF TOUGHENED NYLONS

For characterization of the fracture resistance of materials used in the upper shelf toughness regime, J-R curves are widely considered the most promising candidates. However, there still remain problems concerning both the generation and measurement of J-R curves as material characterizing parameters and their application in ductile fracture analyses for failure prediction in polymeric materials. This paper reports the results of investigations conducted on two rubber-toughened nylons at room temperature. Two different methods of J-R curve determination are covered, namely multi-specimen and single specimen test methods. The resulting J-R curves have also been evaluated to obtain values of the initiation toughness, J(IC), following the extrapolation and interpolation schemes prescribed by ASTM E813-81 and ASTM E813-87 test procedures, respectively. The results show that the multiple specimen unloading method and the single specimen partial unloading compliance method can be used to generate comparable crack growth resistance J-R curves of the toughened nylons. The value of J(IC) for the crystalline rubber-toughened nylon was approximately twice the value obtained for the amorphous rubber-toughened nylon. The former material also exhibited a greater resistance to ductile crack growth.