A TRANSFERABILITY MODEL FOR BRITTLE-FRACTURE INCLUDING CONSTRAINT ANDDUCTILE TEARING EFFECTS - A PROBABILISTIC APPROACH

This study describes a computational framework to quantify the influen ce of constraint loss and ductile tearing on the cleavage fracture pro cess, as reflected by the pronounced effects on macroscopic toughness (J(c), delta(c)). Our approach adopts the Weibull stress sigma(w) as a suitable near-tip parameter to describe the coupling of remote loadin g with a micromechanics model incorporating the statistics of microcra cks (weakest link philosophy). Unstable crack propagation (cleavage) o ccurs at a critical value of sigma(w) which may be attained prior to, or following, some amount of stable, ductile crack extension. A centra l feature of our framework focuses on the realistic numerical modeling of ductile crack growth using the computational cell methodology to d efine the evolution of near-tip stress fields during crack extension. Under increased remote loading (J), development of the Weibull stress reflects the potentially strong variations of near-tip stress fields d ue to the interacting effects of constraint loss and ductile crack ext ension. Computational results are discussed for well-contained plastic ity, where the near-tip fields for a stationary and a growing crack ar e generated with a modified boundary layer (MBL) formulation (in the f orm of different levels of applied T-stress). These analyses demonstra te clearly the dependence of sigma(w) on crack-tip stress triaxiality and crack growth. The paper concludes with an application of the micro mechanics model to predict the measured geometry and ductile tearing e ffects on the cleavage fracture toughness J(c) of an HSLA steel. Here, we employ the concept of the Dodds-Anderson scaling model, but replac e their original local criterion based on the equivalence of near-tip stressed volumes by attainment of a critical value of the Weibull stre ss. For this application, the proposed approach successfully predicts the combined effects of loss of constraint and crack growth on measure d J(c)-values.