Notch tensile measurements and fracture toughness correlations for austenitic stainless steels

Thirty-two alloys were included in a study of conventional notch tensile testing as a method of fracture toughness characterization for austenitic stainless steels at liquid helium temperature, 4 K. For the same austenitic stainless steels, tensile and J-integral fracture toughness (K/sub Ic/(J)) measurements have also been conducted. For these materials the notch tensile strength (sigma/sub NTS) generally increases with yield strength (sigma/sub y/), and the contains/sub NTS//sigma/sub y/ ratios are typically much greater than 1.0. Correlations between sigma/sub NTS/, K/sub Ic/(J), and sigma/sub y/ were assessed. The best data fit was found between the ratio, sigma/NTS/K/sub Ic/(J), and the toughness, K/sub Ic/(J). Unfortunately, from this relation there is not uniqueness of K/sub Ic/ from sigma/sub NTS/. Therefore at this time it is not considered practical to obtain estimates of K/sub Ic/ from notch tensile tests for austenitic steels at 4 K. However, one may compare the J-integral fracture toughness and cylindrical bar notch tensile measurements. There are three regions: (1) linear elastic (sigma/sub NTS/ increases as K/sub Ic/(J) increases); (2) elastic-plastic (sigma/sub NTS/ is essentially independent of K/sub Ic/(J); (3) plastic (sigma/sub NTS/ decreases as K/sub Ic/(J) increases. The elastic-plastic (transition) region is associated with a plastic zone that extends completely through the notched cross-sectional area