Experimentally Validated Constitutive Model for NiTi-based Shape Memory Alloys Featuring Intermediate R-phase Transformation: A Case Study of Ni 48 Ti 49 Fe 3

An important group of NiTi-based alloys employed in applications exhibits an intermediate R-phase transformation, which substantially modifies the material’s thermomechanical response. Finite element analysis of products from such alloys requires a constitutive model covering the two-stage transformation sequence in its full thermodynamic nature. We propose an enhanced constitutive model for NiTi-based alloys, which incorporates R-phase as a distinctive phase with loading-dependent transformation strain. We validate the model on a newly acquired extensive experimental dataset on the thermomechanical response of Ni₄₈ Ti₄₉ Fe₃ shape memory alloy and illustrate the capabilities of its implementation into finite element software on a computational structural analysis of a tightening ring.