ELECTRICAL RESPONSE OF A BIMETALLIC JUNCTION TO SHOCK COMPRESSION

The electrical response of a copper-Constantan junction to shock compression has been studied over a pressure range 14.5-36.0 GPa. Four possible sources of anomalous response were found: electrical noise due to circuit closure at impact, shock demagnetization of a ferromagnetic material, high local temperature at the junction interface due to shock compression of a surface damage layer, and two-dimensional flow in the pressurized region due to pressure relief from the edges. Using a diffusion-welded junction in uniaxial strain the emf measured is within 20% of the predicted emf based on normal thermocouple response to shock-compression temperatures. In a geometry in which a guard ring was used to prevent lateral flow behind the shock front, the observed voltage-time profile was a step with constant plateau. In a similar configuration where radial pressure relief was allowed behind the shock front, the initial step (which compares directly in amplitude to the above results) is followed by a marked positive ramping. This ramping was directly correlated with the two-dimensional flow due to radial pressure relief. The results indicate that any fundamental anomaly which exists for one-dimensional strain is less than 10-20% of the observed signals in the pressure range studied.