Simon David Schmidt

• This thesis is concerned with the modeling of the solid-solid phase transformation, such as the martensitic transformation. The allotropes austenite and martensite are important for industry applications. As a result of its ductility, austenite is desired in the bulk, as opposed to martensite, which desired in the near surface region. The phase field method is used to model the phase transformation by minimizing the free energy. It consists of a mechanical part, due to elastic strain and a chemical part, due to the martensitic transformation. The latter is temperature dependent. Therefore, a temperature dependent separation potential is presented here. To accommodate multiple orientation variants, a multivariant phase field model is employed. Using the Khachaturyan approach, the effective material parameters can be used to describe a constitutive model. This however, renders the nodal residual vector and elemental tangent matrix directly dependent on the phase, making a generalization complicated. An easier approach is the use of the Voigt/Taylor homogenization, in which the energy and their derivatives are interpolated creating an interface for material law of the individual phases.