ICAMS / Interdisciplinary Centre for Advanced Materials Simulation


Modeling phase transformations during mechanical loading

Date: 20.06.2011
Place: 3rd Sino German Symposium 2011, Xi'an, China

Alexander Hartmaier
Christoph Begau
Benjamin Schmaling
Anxin Ma

Different mechanisms can contribute to the plastic deformation of materials. In this work we focus our attention on plastic deformation by dislocation slip and phase transformations. These mechanisms are often alternative and competing for different materials under different loading conditions described by stress level, strain rate and temperature. Two illustrative examples for competing mechanisms of dislocation-based plasticity and austenite-martensite transformation-induced plastic deformation will be given:

(i) A continuum model for transformation induced plasticity (TRIP) steels based on the well-known work of Olson and Cohen [1] is modified in the following aspect: a dislocation mechanism based crystal plasticity approach calculates local stress and plastic shear in each slip system of face centered cubic (FCC) austenite. Thus, we estimate the shear band intersections and calculate the resulting martensite nucleation probability. To calculate the macroscopic material properties we make use of a micromechanical approach, by setting up a representative volume element (RVE) in which all phases are represented by their correct volume concentration and morphology. Consequently, the properties of the RVE can be homogenized to yield the macroscopic mechanical properties that result from the given microstructure.

(ii) With an atomistic model for shape memory alloys (SMA) the competition between dislocation-based transformation of the austenite and the austenite-martensite transformation that is the origin of the shape memory effect can be studied without any assumptions on such processes. Different loading scenarios reveal that dislocation-based deformation occurs preferentially for deformation along certain crystallographic axes. However, it is also observed that dislocations can stabilize the martensite due to their eigenstress field.

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