Characteristics Analysis of Shape Memory Alloy Elastic Coupling System Based on Improved Phase Transformation Equation

An improved phase transformation model based on the Brinson constitutive equation and the phase transformation principle of shape memory alloy（SMA） is proposed in order to accurately describe the actuating characteristics of SMA elastic coupling system,considering the complexity of the model and actual engineering requirements. A discontinuous problem of martensite fraction during the martensitic transformation in the positive phase transformation process of the Brinson phase transformation model is addressed.The twin martensite phase is transformed into a mixture of twin martensite phase and non-twin martensite phase at the end point of the phase transformation, and the volume fractions of each crystal at this point are considered as the crystal volume fractions at the end point of the positive phase transformation of martensite. The positive phase transformation of martensite is treated as a continuous process, and the equation for the positive phase transformation of martensite in the original Brinson phas