Characterization of fracture toughness based on yield stress and successful application to construct a lower-bound fracture toughness master curve

Abstract

The fracture toughness KJc of ferritic steels in the ductile-to-brittle transition region is important for analyzing the structural integrity of structures subjected to large temperature variations. In this study, a σYS-based lower-bound (LB) KJc master curve (MC) was developed to overcome the failure of the ASTM E1921 MC to predict KJc above room temperature (RT). The characteristic KJc, was first identified after finding KJc for the load P5, which is the upper limit load for KIc defined in ASTM E399. It can be approximated as KL = 0.6σYS (W)1/2 for various materials and specimen types. Then, the characteristic σYS was selected to be σYSRT/σYS. Assuming that KJc > KLRT at RT, KLRT was assumed to give an LB, which is empirically true for materials tested in accordance with ASTM E1921. Finally, the MC was formulated as KJcLB = KLRT (σYSRT/σYS)5.5, by applying the critical distance scaling method. KJcLB was successfully a LB for 715 unirradiated KJc data points, including eight heats of reactor pressure vessel (RPV) steel and seven heats of non-RPV steel. This MC can be constructed without conducting fracture toughness tests if σYSRT is known, because a temperature-based σYS MC exists.