On The Stress-Strain Hysteresis Of The SMAs At Different Temperatures

In this paper, a mathematic model of the stress-strain hysteresis of the SMAs was set up for engineering calculation. The model could describe the characteristics of the reorientation among martensitic variants and the stress-induced martensitic transformation microscopically. Moreover, it can also describe the behaviors of the hysteresis and inner-hysteresis of the stress-strain macroscopically. An internal variable梙ysteresis element distribution function was introduced into the model to show the inner situation of materials and be defined as a normal distribution. Six parameters were introduced to reflect the distribution styles of hystersis element. This paper researched on the numerical method for model computation and parameters identification. The numerical solution was studied to reveal the law of the variation for the phase fractions in material when the SMAs were loaded and unloaded at random. An equation was obtained to identify the material parameters. So, a software package has been developed for the purpose of the parameter identifications, numerical simulations and forecasting computations of strain -stress hysteresis and inner-hysteresis curves for the SMAs at different temperatures. Using the developed software package, the material parameters of the strain-stress curves at different temperatures and heat treatments have been figured out for NiTi and CuZnAl. Furthermore, the physical meanings of these parameters were investigated and came to the following conclusions: Namely, cfv and Zvcharacterized the average flow stress and the dispersion of the flow stress in quasiplastic hysteresis. ah and , reflected the average height and its dispersion of pseudoelastic hysteresis. CTW and Zw characterized the average width and its dispersion of the pseudoelastic hysteresis. The effect of temperature on the parameters was also discussed: when T (designates temperature) was lower than Mf, avof NiTi decrease with T increasing, and an reverse result was achieved for CuZnAl, but Zv basically remained unchanged. When T was higher than Af, ah and