Modeling temperature-driven ductile-to-brittle transition fracture in ferritic steels

Abstract

The most catastrophic brittle failure in ferritic steels is observed as their tendency of losing almost all of their toughness when the temperature drops below their ductile-to-brittle transition (DBT) temperature. There have been put large efforts in experimental and theoretical studies to clarify the controlling mechanism of this transition; however, it still remains unclear how to model accurately the coupled ductile=brittle fracture behavior of ferritic steels in the region of ductileto/brittle transition. Therefore, in this study, an important attempt is made to model coupled ductile/brittle fracture by means of blended micro-void and micro-cracks. To this end, a thermomechanical finite strain-coupled plasticity and continuum damage mechanics models which incorporate the blended effects of microheterogeneities in the form of micro-cracks and micro-voids are proposed. In order to determine the proposed model material constant, a set of finite element model, where the proposed unified framework, which characterizes ductile-to-brittle fracture behavior of ferritic steels, is implemented as a VUMAT, is performed by modeling the benchmark experiment given in the experimental research published by Turba et al., then, using these models as a departure point, the fracture response of the small punch fracture testing is investigated numerically at 22°C and -196°C and at which the fracture is characterized as ductile and brittle, respectively.