Direct Mandrel prestraining method for shape memory couplers: Insight into mechanics of prestraining and implications on SME

Shape memory coupling technologies offer an alternative to welded, machined and bonded joints. They provide advantages such as self-locking assembly, reduced stress concentration, rapid installation, suitability for confined spaces, and in some cases cost efficiency. However, several factors influence joint performance, including the prestraining method, heat treatment, prestraining levels, activation temperature, and wall thickness, all of which affect the gripping capacity of Fe-SMA tubes. Notably, the prestraining method significantly affects the nature and distribution of stress-induced phase transformations and residual stresses, making it crucial to understand its mechanics and implications. This study provides a comprehensive characterization of the direct Mandrel prestraining method for Fe-based shape memory couplers, an essential step in their development. Specifically, the research aims to explore the mechanics of the Mandrel prestraining method through an extensive simulation-supported experimental campaign. Using validated finite element (FE) models, a quantitative assessment of deformations and residual stresses is achieved. Furthermore, the method is used for a parametric study to elucidate the relationship between the shape memory effect (SME) and various geometric and implementation factors, including heat treatment, prestraining level, wall thickness, and activation temperature.