Effect of pre-strain and work hardening rate on void growth and coalescence in AA5052

The effect of work hardening on void growth and coalescence was studied by pulling samples of aluminum alloy 5052 in tension to various amounts of pre-strains. To mimic voids forming during fracture, artificial micron-size voids were created in the pre-strained samples with an ultrafast laser. Void growth and coalescence was then followed in-situ under an optical microscope until failure. The effect of pre-strain on void growth rate and coalescence strains was extracted from the experiments. Comparison was made with the McClintock model for void growth which is only able to predict void growth in the samples without pre-strains. A finite element model without any adjustable parameters was able to capture the effect of pre-strain on both void growth and fracture provided that the proper material properties were used. We finally propose a simple model based on the local state of hardening between voids which is able to capture the change in failure strains due to pre-strain as well as void growth and coalescence.