Characterizing crack using configurational forces and assessment of constraint in SS316LN (0.07)

Abstract

Austenitic stainless steel is the preferred material for permanent components of sodium-cooled fast breeder reactors due to its high-temperature tensile and creep strength, compatibility with liquid sodium, ease of fabrication, and weldability. Type SS316LN containing 0.02–0.03 wt.% carbon and 0.06–0.08 wt.% nitrogen is designated as SS316LN. The metallic materials exhibit time-dependent deformation in high-temperature applications of fast breeder reactors (FBR), such as primary and secondary piping, heat exchangers, and the main vessel. To ensure the structural integrity of these components, it is important to understand the crack behavior and the resistance offered by the materials used in these components. In creep conditions, conventionally, C* and Ct parameter are used for characterizing the crack tip. However, the true crack driving force or its rate cannot be described by any of the conventional parameters. The theoretical validity of conventional crack tip-characterizing parameters like Ct and J is also restricted, making it hard to anticipate underlying cracks driving forces. To investigate the creep crack growth behavior of this material, an experimental and numerical analysis of SS316LN is performed with different constraint conditions. This study explores the influence of in-plane constraint on the creep crack behavior of a SS316LN with 0.07% nitrogen under stationary and growing cracks through experimental and numerical approaches. To examine constraint Q parameter is calculated to characterize the in-plane constraint, while the C∗ parameter is used to analyze creep deformation and fracture behavior. Comprehensive experimental tests and finite element simulations provide insights into the interaction between in-plane constraints and crack-tip stress fields. The results enhance the understanding of constraint effects in stationary crack scenarios, contributing to the development of improved methodologies for high-temperature failure assessments and life prediction of structural components made of SS316LN.