Modeling of brittle to ductile transition in bcc metals: Strain rate and temperature dependence in alpha-Iron and Tantalum monocrystals

Brittle to ductile transition is an important mechanical property that is observed in metals, especially in those which have Body Centered Cubic structure. We present a framework that describes this transition by linking the dislocation dynamics with the resulting mechanical behavior and constitutive equations. Two different models based on dislocation theory are developed and applied are applied to Alpha-Iron and Tantalum monocrystals, One is a stress ratio model that is dependent on dislocation nucleation and the other is an Activation energy ratio model based on dislocation mobility. Both the models predict the Brittle to ductile transformation temperature and its dependence on various strain rates and temperatures. These models are compared and are accordingly found to be suitable for different strain rate and temperature conditions in terms of accuracy. The study highlights the possible significance as well as the applications of these ratios in dislocation and plasticity study of the respective materials. The conformity obtained between input and output in the models is predicted to be useful for experimentalists attempting to extract microscopic data from deformation tests on BCC single crystals.