Determination of ductile damage behaviors of high strain rate compression deformation for Ti-6Al-4V alloy using experimental-numerical combined approach

Ductile damage behavior of Ti-6Al-4V alloy was characterized by the evolution of flow curves and deformed specimens in compression tests at high strain rates and various temperatures. Cracks along the shear bands of deformed specimens were observed at lower temperatures (20 degrees C and 100 degrees C) and high strain rates (2500-10,000 s(-1)). The failure initial strains (FIS) during crack generation were calculated according to the measured flow stresses at the transition from stable plastic to damage evolution stage. Special emphasis is placed on the influence of strain rate and temperature on the ductile failure initiation. The failure initiation parameters of Johnson-Cook (JC) damage model were obtained by genetic algorithm (GA) optimization using a combined experimental-numerical approach. That is, the ductile damage parameters were optimized according to the measured FIS and the simulated stress triaxiality, equivalent strains, stresses and temperatures, using compression simulation without damage model. At lower temperatures (T < 300 degrees C), the failure parameters were used to simulate the flow stresses and deformation of specimen by the JC plastic and damage models. To further validate the failure parameters, at higher temperatures (T >= 300 degrees C), a coupling modified JC (JCM) plastic and energy density based damage model was proposed to characterize the flow curves at damage evolution stage by compression simulation using a subroutine program. The predicted flow stresses and the deformed specimens were consistent with the experimental results.