Thermodynamics description of dynamic plasticity in metals

Abstract

In metals, the plastic flow is initiated when externally-supplied energy exceeds limits imposed by energy barriers, where the word “exceeds” is of interest. The extra energy, called here activation energy, is responsible for the nucleation of dislocations and is shown to guide the plastic process toward the state of thermodynamic equilibrium. The macroscopic plastic flow comprises of a large number of discrete dislocation events. The events cause local disturbances in stresses and strains, are associated with micro-inertia forces, and their lifespan is short. It turns out that the micro-kinetic energy affects the plastic flow at all strain rates. However, in the extremes of dynamics, the magnified perturbations corrupt the flow patterns making the flow process increasingly chaotic. In here, the ideas are first discussed on the ground of dislocation-based considerations, and then, the concept of dynamic plasticity is formulated in the framework of the Helmholtz free energy and its dual potential, where the two energies complement each other.

Keywords

• Dynamic plasticity
• Generalized drag mechanism
• Strain rate bursts
• Plasticity-generated heat