Parametric Study of Exploding Foil Burst Phenomenon for Thin Flyer Impact Initiation of Explosives

Abstract

In an Exploding Foil Initiator (EFI), thin polyimide flyer is accelerated at a velocity of 3-4 km/s by exploding metal foil, which bursts when high electrical energy is applied in short duration. The working of an EFI at low energy depends on many factors such as circuit parameters, characteristics of foil, flyer, barrel and types of explosive. Keeping the material, voltage, capacitance, length and width of foil constant, and varying foil thickness, parametric study of exploding foil is presented. When a large amount of electrical energy is deposited at very fast rate to fine bridge foil, it passes through the melting, boiling and vaporization phases up to the plasma state, giving off thermal energy and shock waves. In this work, the electrical Gurney Energy is calculated for estimation of flyer velocity using burst current density that defines action- integral characteristics of burst phenomenon. A MATLAB code is developed for studying variations in parameters and their interrelationships. The program computes foil burst parameters based on input values and thus helps in determination of exploding foil behavior. It is observed that keeping voltage 2 kV and charging capacitor capacity at 1 μF, as the thickness of exploding metal foil increases from 3 to 6 μm, the flyer velocity slightly increases, and remains constant up to 9 μm, thereafter, decreases marginally up to 13 micron, after which there is sharp decrease and no burst occurs at thickness greater than 20 micron. Also, for a given dimension of metal foil, the flyer velocity is highest for Gold material as compare to Copper and Aluminum. Experimental trials were carried out to establish parameters for successful working of EFI at low energy using an etched copper bridge foil. Experimental results are in good agreement with the results of the theoretical modeling using MATLAB, which will enable design of relatively low energy slapper detonator or explosive initiator for various applications.