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**Source: **STP37323S

Creep crack growth behavior in Type 316 stainless steel at 593°C has been examined under displacement control and the results are compared with those under load control. The growth rates were analyzed in terms of linear elastic stress-intensity factor, *K*, reference stress, *σr*, and elastic-plastic energy rate parameters, *J**, to determine which one of the three is best suited for correlating creep crack growth rates in the stainless steel. The results indicate that the correlations in terms of the three parameters do not depend on the method of testing, that is, displacement of load-controlled tests. Furthermore, the data correlate best with J*-integral, with a spread in the data by a factor of 10 in comparison with a factor of 1000 in terms of the other two parameters. Since the dimensions and the range of values for *K* and *J** are significantly different, to facilitate a more meaningful comparison between elastic and elastic-plastic parameters, a linear elastic energy rate parameter *K** is defined which is equivalent to *J** in the linear elastic approximation. The analysis indicates that the crack growth data for the two types of tests correlate better in terms of *K** than in terms of *J** at low *K**-values. At high values of *K**, plasticity effects become pronounced, thus invalidating its applicability. Thus, in spite of the lack of correlation on a *K* basis, linear elastic fracture mechanics concepts may still be valid since the data can be correlated on a *K** basis. But the present work clearly shows that the *J**-integral is better than the stress-intensity factor *K* for creep crack growth in stainless steel.

**Keywords:**

creep crack growth, fracture mechanics, stress-intensity parameter, J*-integral for creep, elastic-plastic fracture mechanics, energy-rate parameter stainless steel

**Author Information:**

Sadananda, K *Metallurgists, Material Science and Technology Division, Naval Research Laboratory, Washington, D.C.,*

Shahinian, P *Metallurgists, Material Science and Technology Division, Naval Research Laboratory, Washington, D.C.,*

**Committee/Subcommittee:** E08.08

**DOI:** 10.1520/STP37323S