Thermomechanical behavior of an Fe-Based shape memory alloy :Transformation conditions and hystereses

The transformation conditions of an Fe-based polycrystalline shape memory alloy are determined experimentally under the multiaxial stress state. The martensite start condition is represented as an oval conical surface in the axial stress-shear stress-temperature space, meaning the transformation condition is not the von Mises type condition in plasticity and clearly depends on the third invariant of the stress tensor. The austenite start and finish conditions are also determined as the planes in the multiaxial stress-temperature space. The uniaxial stress-strain-temperature hysteretic behavior determined under the uniaxial thermomechanical loads is simulated by introducing the internal state variables which represent the status of the microscopic internal structures.