Investigation on the Evolution of Electrothermal Instability in Electrically Exploding Aluminum Wires

Experimental and computational studies on the evolution of electrothermal instability in electrically exploding aluminum wires with material strength taken into consideration are reported. Experiments on the electrically exploding 20-mm-long, 25-μm-diameter aluminum wires are conducted in vacuum. A synchronisation strategy based on a silicon detector, which reduces the time-delay jitter of the optical diagnostics, is proposed to trigger the circuit. The stratified structure with alternating light and dark stripes is observed in shadowgram. These stripes, which are perpendicular to the direction of current flow, are formed early in the electrical explosion process. This instability gradually evolves over time in diagnostic images, providing initial conditions for the evolution of magneto-Rayleigh-Taylor instability. The Johnson-Cook model is employed in computational model to describe the failure process of material strength before the melting point. The resistive inclusions distort the surrounding current density and generate thermal disturbances in exploding products. The reduction of material strength by several resistive inclusions provides the foundation for the evolution of stratification instability during the electrical explosion. The distributions of density and temperature derived by magnetohydrodynamics simulations are in accordance to the structures of electrothermal instability observed in shadowgram. The results indicate that temperature-dependent resistivity and resistive inclusions are important factors causing electrothermal instability.