A modified local approach including plastic strain effects to predict cleavage fracture toughness from subsize precracked Charpy specimens

This work addresses a probabilistic, micromechanics-based methodology incorporating plastic strain effects on cleavage fracture and its dependence on the microcrack distribution. The present model extends current developments of a local approach to fracture (LAF) adopting a plastic-strain based form of the Weibull stress ((sigma) over tilde (w)) to assess changes in cleavage fracture toughness for a reactor pressure vessel (RPV) steel due to constraint loss effects in subsize precracked Charpy (PCVN) specimens. Cleavage fracture toughness data obtained by Rathbun et al. (2006) for an A533 Gr B reactor pressure vessel steel are employed to demonstrate the capability of the modified LAF in predicting the strong influence of specimen geometry on fracture toughness. By combining detailed non-linear, 3-D finite element analyses for the side-grooved C(T) and PCVN specimens with varying geometries, the plastic-strain based form of the Weibull stress is shown to effectively remove the dependence of J(c)-values on specimen geometry thereby generating more accurate assessments of cleavage fracture behavior in larger crack configurations from small specimens.