Material characterization of SMA actuators under nonproportional thermomechanical loading

The application of SMA actuators in smart structures usually involves thermally induced phase transformation with a variable applied stress in SMA actuators, resulting in thermomechanical nonproportional loading of SMAs in stress-temperature space. To investigate the constitutive response of SMAs under thermomechanical nonproportional loading, experiments for thermally induced phase transformation of binary NiTi SMA wires loaded by an elastic linear spring are performed in the Active Materials Laboratory at Texas A&M University. A constitutive model developed by Ba and Lagoudas (1998a, b, c) and Lagoudas and Bo (1998) is used as the basis for the theoretical prediction of the response of SMA line actuators loaded by springs with different elastic constants. Model predictions are compared with experimental results.