Recovery Experiments for Adiabatic Shear Localization: A Novel Experimental Technique

A novel experimental technique has been developed that allows the recovery of specimens within which an adiabatic shear band has been grown as the result of a single torsional pulse. The technique uses a new device called the compression-torsion Kolsky bar; this is an adaptation of the classical torsional Kolsky bar in which both compression and torsion are stored in the clamped length. Recovery of the specimen is obtained by causing the transmitted compression pulse to reflect from the free end of the output bar as a tensile pulse which then causes failure of the specimen/output-bar interface. All further pulses then cause no more than rigid motions of the specimen. Thus the specimen is recovered after it has been loaded by a single torsional pulse; microscopic examination of the recovered specimen now allows the rigorous determination of the evolution of microstructure and the identification of deformation mechanisms that are active under the dynamic shear loading. As an example of the utility of this recovery technique, its application to the study of adiabatic shear localization in alpha-titanium is presented. The technique allows a systematic study of the microscopic mechanisms that drive the initiation and growth of adiabatic shear bands by recovering samples within which shear bands have been grown under controlled conditions; further characterization through sectioning, followed by optical, scanning, and transmission electron microscopy is then possible. The technique also allows one to study the influence of the shape and size of geometric defects (for example, notch tip radius and notch depth) on the initiation of adiabatic shearing failures. The effect of normal stresses on the susceptibility of a material to shear localization can also be investigated.