1IntroductionThere are many applicationa reas where the ability to accurately predict the speed of expansion of fragments from explosively disseminated porous shells is important.F or inert materials (e.g. blast mitigants) this speed, in part, determines the size of the resulting cloud. For reactive materials this speed, in part, determinest he ability to ignite the material and determines the trade-off betweenr eactive and inertial fragment effects.As imple analytical modelf or fragments peed from exploding cased munitions, derived by R. W. Gurney[ 1] during WWII, is still very much in use today.B ya ssuming uniform internal gas density and al inear variationo fg as velocity from the center of axis ofc harge out to the casing, the terminal shell or case material velocity V Gurney was approximated to be af unction both of the explosive properties and the ratio M/C,w here M is the case mass and C the charge mass:Here E (commonly known as the Gurney Energy)i sa n energy per unit mass associated with individual explosives and n varies with the geometry of the system, i.e. plane n = 1, cylinder n = 2, or sphere n = 3. Gurney analysis has been used extensively for many years to approximate the speed of fragmenting solid material shells [2,3].K ennedy gives ad etailed description of the Gurney model as does Cooper,w ho also providesarange of usefule ngineering approximationsf or av ariety of explosives. Reaugha nd Souers [4] extended the Gurney approach to the Cylinder Te st taking account of shell thickness effects. Hutchinson [5] has also considered extensions to Gurney theory for blast and fragment applications.For porouss hells and liquids it is known [6] that the shell breaks up very early in the expansion. It is thus naturalt o ask whether solid shell Gurney theory applies.The aim of this work is to investigate the behavior of HE driven porouss hells in spherical and cylindrical geometry and to identify any appropriate factorso ne can use to multiply the solid shell Gurney velocity by to predict the speed of aporousshell.
2B asic Model and ResultsOur approach in this work will be to consider the effect of replacing as olid case surroundinga ne xplosivew ith ap orous material. We use the EDEN hydrocode to study these effects numerically.T he effect of changing explosive type with the Gurney equation has beene xhaustively studied and Refs.[2] and [3] give good summaries of this work. We thus are free to choose any ideal High Explosive as our baseline. We have recently undertaken some experiments using COMP A4 explosive, which we will compare with in this work so choose this for use in our basic numerical model. The detonations peed for the A4 used in calculations was 7026 ms À1 .C ooper [3] has recorded an engineer-Abstract:T here are manya pplication areas, where the ability to accurately predict the speed of expansiono ff ragments from explosively disseminated porous shells is important. For inert materials this speed in part determines the size of the resultingc loud. For reactive materials this speed in part de...