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

摘要

The fracture toughness K-Jc 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 sigma(YS)-based lower-bound (LB) K-Jc master curve (MC) was developed to overcome the failure of the ASTM E1921 MC to predict K-Jc above room temperature (RT). The characteristic K-Jc, was first identified after finding K-Jc for the load P-5, which is the upper limit load for K-Ic defined in ASTM E399. It can be approximated as K-L = 0.6s(YS) (W)(1/2) for various materials and specimen types. Then, the characteristic sigma(YS) was selected to be sigma(YSRT)/sigma(YS). Assuming that K-Jc > K-LRT at RT, K-LRT was assumed to give an LB, which is empirically true for materials tested in accordance with ASTM E1921. Finally, the MC was formulated as K-JcLB = K-LRT (sigma(YSRT)/sigma(YS))(5.5), by applying the critical distance scaling method. K-JcLB was successfully a LB for 715 unirradiated K-Jc 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 sigma(YSRT) is known, because a temperature-based sigma(YS) MC exists.