Slip and twinning are two important deformation modes governing Shape Memory Alloys (SMAs) plasticity, which results in affecting their pseudoelasticity and shape memory performance. Precisely determining Peierls stress in dislocation slip and critical twin nucleation stress in twinning is essential to facilitate the design of new transforming alloys. This study presents an advanced energetic approach to investigate the attributes of phase transformation, slip and twinning in SMAs utilizing Density Functional Theory based ab initio calculations, and the role of energy barrier is characterized. Through different length scales incorporating atomistic simulations into dislocation-based mechanics, an extended Peierls-Nabarro (P-N) model is developed to establish flow stresses in SMAs and the predicted Peierls stresses are in excellent agreement with experiments. In addition, a twin nucleation model based on P-N formulation is proposed to determine the critical twin nucleation stresses in SMAs, and the validity of the model is confirmed by determining twinning stresses from experiments. Hence, we suggest that the results provide a quantitative methodology to understanding and designing new SMAs.
About the Speaker
Jifeng Wang received his Bachelor degree in Jet propulsion from Beijing University of Aeronautics and Astronautics. He had worked in China Aerospace Science and Industry Corporation and Moscow Aviation Institute for three years. Following this, he obtained a Masters in Mechanical Engineering at Michigan State University before he joined his Ph.D. program at UIUC under the supervision of Prof. Sehitoglu. His Ph.D. research work focuses on the dislocation slip and twinning in shape memory alloys. He successfully passed his Final Defense on November 5, 2013.
Host: Professor Martin Ostoja-Starzewski