Ductile-to-Brittle Transition of Steel Due to Dynamic Loading

Abstract

The transition from ductile to brittle for metals is usually encountered during fast machining operations, in low-temperature environments, and in all situations involving very high strain rates. Traditionally, classical material models used in the dynamic structural analysis focus on the plastic-stress-versus-strain rate. As a result, those models cannot incorporate sudden changes in failure strains and strengths triggered by material behavior transition. The ability to predict realistically the dynamic behavior of structures based on physical constitutive equations depends on having a comprehensive understanding of such drastic changes in material behavior. This transition is described by the DAMP-PLAST model, incorporating constitutive equations and governed by the shear band speed parameter at a finite time. After the development of the equation set, the material model is tested in regard to its ability to produce three distinguished material responses: elastic-plastic, elastic–plastic with strain-rate sensitivity, and brittle with increased dynamic failure strength. The study identifies metal dynamic brittleness linked to a critical loading rate influencing the plastic flow process. Based on this relation, the identification of the critical loading rate using split Hopkinson bar apparatus, and material constitutive equation is proposed.

Keywords

• strain rate
• plasticity
• upper-yield stress
• DAMP-PLAST model
• shear band velocity
• split Hopkinson bar