Computer simulation of Portevin-LeChatelier effect based on strain softening model

A new phenomenological theory for the Portevin-LeChatelier effect is proposed. The theory is based on an unknown internal stress Y_ir which decreases with strain (work softening) and increases with time (age hardening). Y_ir is introduced to satisfy the negative rate sensitivity (n.r.s.) of flow stress and it is supposed to be due to very fine clusters which are cut by dislocation and restored by solute atom diffusion. Almost all constants used in the theory can be determined by tensile test. The results of simulation can explain the effect of temperature, strain and strain rate on the onset strain of P-L effect. Especially, the model can explain the no-occurrence of P-L effect under the n.r.s. condition in aged Al-Cu alloy, and the quantity of transition strain in tensile test in which the crosshead speed is abruptly changed.