Infrared imaging of hot spot upon impact of a crystal

During this experiment the reaction of a crystalline solid to the plastic deformation brought about by the stimulus of a shock or impact was studied. It is often assumed that upon impact, the energy from the impact is distributed homogeneously throughout the crystal. This is often not the case. Instead, the energy distribution is localized to specific areas of the crystal. The phenomenon of the heterogeneous distribution manifested as shear bands throughout the impacted solid is the subject of this study. More specifically, the role of the shear banding process in the hot spot formation in an impacted crystal was explored in the course of this experiment. In order to explore the behavior of the crystal upon impact, the crystalline samples were subjected to low velocity impacts provided by a drop weight impact machine. The shear bands were imaged with the use of arrays of fast responding infrared detectors. The detectors monitored the amount of energy given off as infrared photons by the impacted crystalline solid. Previous studies have observed the shear bands after their formation. The main emphasis of this study was the real time observance of the shear band formation during the impact. The signal was recorded over the duration of the impact, heating of the solid and relaxation of the crystal. These processes occurred over a 40 to 100 microsecond timescale. The detectors recorded shear banding occurring on a nanosecond timescale. The data obtained from these experiments rendered insight on the size, occurrence of localization, and initial mechanisms of formation of the hot spots and shear banding for low velocity impacts. These parameters made it possible to resolve an image of the formation of hot spots from shear banding within a crystal during low velocity impacts.