Microstructurally induced fracture nucleation and propagation in martensitic steels

• Published in: Journal of the mechanics and physics of solids 2013-04, Vol.61 (4), p.1091-1105
• Main Authors: Shanthraj, P., Zikry, M.A.
• Format: Article
• Language: English
• Subjects: Boundaries; Crack propagation; Crystal plasticity; Dislocation-density; Dislocations; Failure; Grain boundary; Martensitic stainless steels; Microstructure; Morphology; Nucleation
• ISSN: 0022-5096
• DOI: 10.1016/j.jmps.2012.11.006

A dislocation-density grain boundary (GB) interaction scheme that is representative of dislocation-density transmission and blockage within GBs is developed and incorporated into a dislocation-density based multiple-slip crystalline plasticity framework for a detailed analysis of fracture nucleation and growth in martensitic steels. This formulation accounts for variant morphologies and orientation relationships (ORs) that are uniquely inherent to lath martensitic microstructures. Specialized finite-element (FE) methodologies using overlapping elements to represent evolving failure surfaces and microstructurally-based failure criteria for cleavage are then used to investigate the effects of martensitic variant distributions and ORs on the dominant dislocation-density mechanisms for the localization of plastic strains, and the initiation and propagation of fracture surfaces in martensitic microstructures subjected to quasi-static and dynamic strain-rates. The results indicate that the local dislocation-density behavior at the variant boundaries and the interiors influence dominant failure initiation and growth. A dislocation-density GB interaction, which is based on dislocation-density accumulation and transmission at variant boundaries, is developed and used to predict stress build-up or relaxation, and together with the orientation of the cleavage planes in relation to the lath morphology, intergranular and transgranular fracture modes can be determined. ► New formulation for behavior of martensitic steels at quasi-static and dynamic strain-rates. ► New failure criterion based on resolving stresses on cleavage planes. ► Variation of variant orientations and distributions to control failure. ► New formulation to track dislocation-density accumulation and transmission at variant interfaces.