Mechanisms for Explosively-Formed Fuse Performance Degradation

The Explosively-Formed Fuse (EFF) is a high-power opening switch that uses an explosive charge to interrupt current flow in an aluminum conductor [1]. As such we expected the foil's resistance to increase with increasing current density by Joule heating. Yet an analysis of a large number of experiments clearly showed the opposite was true; there was a strong negative correlation between the peak resistance and current density. In the paper we analyze various possible causes including thermal softening of the metal, magnetic loading of the explosive and electric breakdown or conduction in the product gases at the higher applied fields. Our analysis suggests that magnetic loading is responsible for the degradation.