Thermomechanical behaviors of Ni–Ti shape memory alloy ribbons and their numerical modeling

The thermomechanical behaviors of Ni–Ti shape memory alloy (SMA) ribbons, associated with stress and temperature-induced transformations, are experimentally and numerically investigated. A 2-D incremental formulation of an SMA model is proposed and implemented in an ABAQUS finite element program through a user-defined material (UMAT) subroutine for the purpose of predicting the thermomechanical characteristics of SMA films. The evolution of stress–strain curves and phase transformation temperatures is examined with various annealing temperatures. The rhombohedral phase (R-phase) transformation appears in the specimen of an Ni–Ti SMA ribbon. The uncommon behaviors of permanent elongation and partial pseudoelastic behavior are observed. The 2-D SMA model with a new transformation function shows a good prediction for the hysteresis of the strain–stress curve and the recovery stress. For application of the developed numerical model of 2-D SMAs, the feasibility of the gripper actuator with the SMA ribbon is numerically demonstrated.