REVERSE-BALLISTIC IMPACT STUDY OF SHEAR PLUG FORMATION AND DISPLACEMENT IN TI6AL4V ALLOY

Gas-gun reverse-ballistic experiments have been performed in which Ti6Al4V alloy disks were impacted onto smaller diameter, hardened steel rods to push out shear plugs from the disk material. The range of disk velocities was 219-456 m/s. For each experiment, the disk, plug, and rod were soft recovered after impact. Below 290 m/s, the plugs were pushed only partway through the disks, but localized shear bands outlining the plug shapes were easily recognized in metallographic sections. Optical and scanning electron microscopies were used to determine shear zone widths and to describe microstructural details associated with the primary shear zones. There is evidence for appreciable adiabatic heating and consequent thermal softening and melting of material in the main shear zone. A simple model is used to relate the observed plug displacements to the impact velocities and to provide estimates of several features: the shear zone strength, the threshold energy for shear plug displacement, and the threshold energy for shear plug separation. Clear evidence is presented of molten material having been produced as part of the plug separation process.