Dynamic J-R Curve Testing of a High Strength Steel Using the Key Curve and Multispecimen Techniques

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Abstract
J-integral R-curve tests were performed on three-point bend specimens of a 3-Ni steel at three loading rates: quasi-static, intermediate (25 mm/s), and drop tower (2.54 m/s). The key curve and multispecimen procedures were employed for the higher rate tests; this investigation is focused primarily on details of the test method development. The multispecimen and key curve techniques were found to yield upper shelf J-R curves which were in substantial agreement at the elevated loading rates. Numerical smoothing techniques required to apply a key curve method appear to separate the oscillatory high frequency component from the load-displacement record. For the 3-Ni steel tested for this investigation both JIc and T were found to be elevated with increasing loading rate.