Analyzing the effectiveness of the Gurney method for small scale fragmentation propulsion using Exploding Bridgewire detonators

Abstract

Explosives are common in military, mining, and construction applications where the explosive properties are understood, but mechanics of how the explosive's energy fragments and throws materials are less known. Considering the type of confining material around an explosive, creates variability in fragmentation behavior due to the individual material characteristics. The most common method for assessing fragmentation behavior is the Gurney method, which eliminates any consideration of fragmenting material properties. The Gurney method assumes that, on a large scale, the inconsistencies in material are irrelevant and only the mass of the confiner need be considered. However, it is known in many fields that energy is consumed in the breaking of a material. In this paper, the detonation and resultant fragmentation propulsion of Exploding Bridgewire (EBW) detonators with the same explosive material, but different casing characteristics, is observed. The Gurney method was used to predict fragmentation velocities of the casing following detonation, which were compared to the behavior observed through high-speed video of the actual event. The EBWs were selected to provide variability in casing material, casing thickness, charge length, and charge diameter. It was found that when the amount of explosive is small, the material properties of the casing play a significant role, with 70 % of the total explosive mass lost in fragmenting PMMA EBWs and 30 � 3 % lost in Aluminum EBWs. There is significant energy loss to breaking the casing material that cannot be ignored on the small scale and could impact large explosives with high casing to explosive ratios.