Studies On Constitutive Model For Shape Memory Alloy In Large Strain Deformation

Shape memory alloy(SMA) is a new functional materials and has excellent shape memory effect, pseudoelasticity and other characteristics. SMA has been attracted interest by widespread concern of scholars domestic and overseas. In the application and development of SMA process, the constitutive relations of SMA materials are the key to portray the complex mechanical properties of the shape memory alloys. During the SMA material's transformation process, the deformation can reach up to 6%-8%or even 10%. So it needs to consider the impact of large deformation to explain the physical phenomena. Therefore, based on the large deformation theory, we do the research of the constitutive relations of SMA materials is carried out. The main work and achievements are as follows:1,This thesis introduces two basic theories, continuum mechanics and thermodynamics, which can be used for constitutive relations of SMA materials; analyzes two usual ways of establishing macroscopic phenomenological model. Summarizes the difference of the existing macroscopic phenomenological model's features of the SMA materials, including the selection and decomposition of the martensite volume fraction and the different selection of the phase transformation surfaces. Focuses on introducing several common phenomenological models based on the deformation gradient and the Green-Cauchy tensor, and how to use the return-mapping algorithms based on the Euler algorithms to control the stress in the transformation process in the transformation surfaces.2,During the phase transformation process of the shape memory alloy with the changing martensite volume fraction, the effective composite modulus of SMA is an important factor influencing the mechanical properties. Based on micromechanics, this paper finds an approximate solution of the effective composite modulus of SMA. This method's form is simple and the computation is convenience, what's more the numerical results are accord with the experimental data. Compared with the conventional linear interpolation method, this method has a better practical value and engineering application.3,Based on thermodynamics and phase transformation driving force, we explain a SMA constitutive model and apply the model on the large deformation analysis and small deformation analysis of SMA materials. Simulations under different loading conditions of uniaxial tension and shear illustrate the characteristics of the model in large strain deformation and small strain deformation. The results indicate that the difference between the two methods is small under uniaxial tension while the large deformation method is more closely to the actual results under shear deformation. This thesis lays a foundation for the further studies of the constitutive model of SMA, especially in the multiaxial non-proportional loading aspects.