Stress-induced ductile-to-brittle transition of metallic materials: Atomistic simulations and a unified criterion

Existing ductile-to-brittle transition (DBT) criteria often fail to account for the combined effects of stress states and intrinsic material parameters, which are two crucial factors governing failure behaviors and mechanical properties of metallic materials. In this study, we propose a new DBT criterion that integrates both stresses and intrinsic material strength, effectively capturing the competition between distortion and dilatation during material failure. The DBT criterion is formulated in terms of the von Mises-to-hydrostatic stress ratio and the shear-to-hydrostatic strength ratio, which, respectively, represent the external and internal factors governing failure modes. To validate the proposed DBT criterion, molecular dynamics simulations are conducted on five representative metals, including face-centered cubic, body-centered cubic, and hexagonal close-packed metals, as well as a metallic glass and a high-entropy alloy, across a wide temperature range. The simulation results exhibit good agreement with the criterion's predictions, demonstrating its effectiveness and broad applicability. The proposed DBT criterion provides a quantitative framework for predicting the transition from ductile failure to brittle fracture, and its potential integration into finite element analysis could enhance the design of more reliable engineering materials and components under various loading conditions.