Experimental and computational study of the impact deformation of titanium Taylor cylinder specimens

Abstract Gas-gun reverse-ballistic Taylor cylinder impact deformation experiments have been performed with specimens of 99.7% titanium. The flat-ended, 6.35 mm diameter, 25.4 mm long solid cylindrical specimens were impacted by sabot-mounted 34.0 mm diameter, 19.0 mm thick disks of maraging 350 steel. Experiments were performed at 225 and 294 m/s; a soft recovery system prevented post-impact damage to the specimens. Plastic deformation extended over approximately 57 and 64% of the deformed specimen length, respectively, with little lateral spreading. The specimen shapes were digitized via a toolmaker's microscope connected to a computer. Metallographic examination of longitudinal sections through the specimens revealed extensive deformation twinning, with twinned grains appearing throughout the deformed regions. Distributions of twins as a function of distance from the impact end were determined for each specimen. The importance of twinning in the computational modelling of deformation in body centered cubic (BCC) iron was shown by Zerilli and Armstrong. It is also very important for hexagonal close packed (HCP) titanium which exhibits a BCC type of behavior. Deformation twinning can cause a reduction in the effective size of the twinned grains; an associated increase in the yield stress could explain the relatively small amount of lateral spreading observed for the titanium Taylor specimens. Computational simulations of the impact experiments performed without provision for twinning show significant differences between the simulations and the experimental shapes. When twinning effects are included, good fits to the experimental shapes are obtained.