Dynamic yielding and fracture of grade 4 titanium in plate impact experiments

Abstract

The dynamic yielding and fracture (spalling) of commercially pure (grade 4) titanium are investigated using symmetric plate impact experiments for a peak stress range of 5.6 GPa–12.5 GPa. Velocity interferometry system for any reflector rear free surface velocity profiles display both a Hugoniot elastic limit (HEL) and a velocity pullback, which are indicative of dynamic compressive yielding and tensile fracture (spalling), respectively. The HEL decreases with peak stress from 2.2 GPa for 5.6 GPa peak stress to 2.0 GPa for 12.5 GPa peak stress. The decrease in the HEL corresponded to an increase in twinning observed in recovered samples. The spall strength increases with peak stress from 3.3 GPa to 3.8 GPa over the measured peak stress range and shows a good power law fit with the decompression strain rate. The differences in the dynamic yield and fracture behavior indicate that void nucleation is the dominant mechanism affecting the spall strength of grade 4 titanium.