MODELING THE TRANSIENT FLOW BEHAVIOR OF DYNAMIC STRAIN AGING MATERIALS

Stress and strain rate transients which accompany small perturbations from steady state deformation in the regime of dynamic strain ageing are modelled. The constitutive relation employed includes the local solute concentration at arrested mobile dislocations as a time dependent state variable. Using linear perturbation theory it is shown that four types of transient behaviour are possible: monotonic decay, oscillatory decay, oscillatory growth and monotonic growth of the perturbation. A transient behaviour map is developed which shows the transient behaviour as a function of the strain rate sensitivity of flow stress and the machine stiffness. The results of the analysis are compared with recent experimental measurements of transient yield behaviour associated with dynamic strain ageing.