Multiscale Modeling of Cleavage Fracture and Applications to Structural Integrity Assessments Using Subsize Fracture Specimens

Abstract

Single-parameter and two-parameter fracture mechanics methodologies have some well-recognized limitations which motivate development of probabilistic approaches to brittle fracture. Such approaches can be extended in straightforward manner to analyze the mechanical integrity of structural components subjected to more complex loading conditions. In particular, probabilistic procedures incorporating local failure criteria (micromechanics model for brittle fracture) coupled do the finite element method describe the conditions for global structural failure in terms of a (local) probabilistic fracture parameter; these methodologies are most often termed local approaches. To describe brittle fracture driven by transgranular cleavage, a number of models explicitly adopt the "weakest link" theory to derive statistical functions incorporating the local (opening) stresses well at the crack-tip region. Here, the "Weibull stress", Sig_w, then emerges as an effective crack-tip driving force controlling fracture. This research focuses on the extension and, more importantly, new developments of structural integrity assessment procedures based upon a micromechanics (local) model. A central objective is to develop a more robust procedure for mechanical integrity and fracture analysis of structural materials, including nuclear structural components and reactor pressure vessels, using a modified Weibull stress, Sig*_w, proposed recently by Ruggieri and Dodds (2015) as the effective crack driving force. This research will have particular emphasis on the correlation and prediction of toughness values measured using small-sized precracked Charpy (PCVN) bend specimens to accurately assess the structural integrity of critical structural components. (AU)