Thermocouple temperature measurements in shock-compressed solids

Abstract

The emf produced by 5-μm-thick foil thermocouples when subjected to shock loading was studied over a stress range from 0.5 to 10 GPa. Thermocouples of either copper and constantan or chromel and alumel were embedded in the host materials, polymethyl methacrylate (PMMA), Epon 828 epoxy, single-crystal Al2O3, or vitreous SiO2. The observed emf history rises to a plateau in a period that varied from less than 100 ns for Al2O3 to about 500 ns for PMMA. Temperatures inferred from the constant-voltage portion of the records using standard thermocouple tables (corrected for pressure) compare favorably with calculated temperatures for PMMA and epoxy below 2.0 and 4.5 GPa, respectively. Above these threshold stresses, the observed temperatures increase rapidly with compression, which may indicate an exothermic reaction. Inferred temperatures for the two types of thermocouples are in good agreement. The shape of the response history, and agreement with predicted temperatures for PMMA and epoxy, indicate that the thermocouple and host material come to thermal equilibrium during the transient portion of the response. In the elastic materials Al2O3 and SiO2, the observed temperatures are better correlated with temperatures predicted for shock compression of the thermocouple materials than those predicted for the host materials, indicating that thermal equilibration is not achieved in the available test time.