Modeling and simulations of transformation and twinning induced plasticity in advanced high strength austenitic steels

The current work is focused on the development of a combined micromechanical model of transformation and twinning induced plasticity in austenite based steels. Both mechanisms are combined by incorporating transformation in twinning based crystal plasticity model. Initially, mechanical twinning is incorporated in slip based crystal plasticity model. Afterwards, austenite to martensite transformation is included in the developed slip and twin based model. Kinematics of the mechanisms is developed by defining elastic, plastic, and transformation deformation gradients. Energy balanced principle is used to develop thermodynamic framework where dissipated energy and driving potential equations are formed. A fully implicit integration scheme is developed to solve constitutive equations. Numerical integration algorithm is then implemented in ABAQUS as a user-defined subroutine. Three dimensional finite element model of single and polycrystal austenite are developed. The orientation of each grain is defined through Euler angles. The performance of the model is evaluated through finite element simulations to predict elastic-plastic and transformation behaviors of single and polycrystal austenite. The developed model is in good agreement with the published experimental and simulation results. A prominent difference in stress magnitude is found once twinning mode is incorporated in slip and transformation. This difference has significant magnitude in case of polycrystal austenite. This shows substantial advantage in terms of strength and formability of incorporating mechanical twinning along with slip and transformation.