Effects of Cyclic Loading on the Deformation and Elastic-Plastic Fracture Behavior of a Cast Stainless Steel

Abstract

The objective of this program was to develop the appropriate material properties to characterize the cyclic tensile deformation, cyclic elastic-plastic crack growth, and the ductile tearing resistance of a pipe elbow made from a cast stainless steel equivalent to ASME SA-351CF8M. This material was used for large-scale tests in the high level vibration test program, which applied intense cyclic loadings to reactor piping system components and revealed that fatigue crack growth could be a serious problem in these components. The tests conducted included monotonic and cyclic tension tests, monotonic J-R curve tests, and cyclic elastic and elastic-plastic fatigue crack growth rate tests. The cyclic elastic-plastic fracture behavior of the stainless steel was of primary concern and was evaluated using a cyclic J-integral approach. It was found that the cast stainless steel was very resistant to ductile crack extension. J-resistance curves essentially followed a blunting behavior to very high J levels. High cycle fatigue crack growth rate data obtained on this stainless steel was typical of that reported in standard textbooks. Low cycle fatigue crack growth rate data obtained on this material using the cyclic J-integral approach was consistent with the high cycle fatigue crack growth rate and with a standard textbook correlation equation typical for this type of material. Evaluation of crack closure effects was essential to determine accurately the crack driving force for cyclic elastic-plastic crack growth in this material.