Emissivity change in pressure-shear plate impact experiment

Concurrent temperature measurement in a Pressure-Shear Plate Impact (PSPI) experiment has been developed by collecting the infrared radiation emitted from the sample/rear-plate interface. In order to convert the measured emittance to sample temperature accurately, the current emissivity of the sample/rear-plate interface is required. The initial emissivity is calibrated statically by comparing the collected emittance from the sample surface with that of a surface with known emissivity. In a PSPI experiment the effective emissivity may change due to inelastic deformation under pressure-shear loading. At thermodynamic equilibrium, the dynamic change of emissivity could be indicated through the change of reflectivity. Pilot experiments are conducted to gain a qualitative understanding of if and how the emissivity changes during a PSPI experiment. A Co$_{\mathrm{2}}$ laser is used to reflect an incident beam off the sample/rear-plate interface. The intensity of this reflected beam is monitored by a fast HgCdTe detector through a pair of 90$^{\mathrm{o}}$ off-axis parabolic reflectors. This measured change of intensity during a PSPI experiment provides an indication of the required change of emissivity.