Torsional modeling and experimental characterization of a shape memory alloy rod, using Brinson's asymmetric model

In this work, torsional modeling and experimental characterization of a Shape Memory Alloy (SMA) rod is investigated. Experimental tests of previous studies proved that different direction of loading is effective on torque-angle response of a rod. Accordingly, using improved Brinson’s model and converting it to a torsional model and referring a twist deformation in the clockwise direction to a positive twist and a twist deformation in the counter clockwise direction to a negative twist, the asymmetry effect on the rod is investigated. Assuming a linear strain through the cross section and then finding stresses, using the asymmetric Brinson model, and integrating the stresses through the cross section the torque-angle response of the rod is presented, by using a numerical procedure. The parameters for Brinson model, including phase transformation temperatures, are derived from experimental tests and there is more than 95% agreement between the present model and experimental test. Regarding the results, a verification for the derived parameters is presented and a parametric study on SMA rod is considered. The average error of asymmetric and symmetric models with respect to the experimental tests are 5% and 15% respectively. Moreover, hysteresis inner loops are studied and asymmetric model is compared to the experimental tests. The results show good agreement of the asymmetric model when compared to experimental tests.