EXPERIMENTAL AND ANALYTICAL STUDY OF EARLY TIME MATERIAL PROCESSING, IN A COLLAPSING SHAPED - CHARGE LINER, USING SOFTLY - RECOVERED PARTIALLY - COLLAPSED COPPER LINERS

It is not yet clear what detailed deformation mechanisms enable copper shaped charge jets to exhibit the extraordinarily high ductility, whi ch characterizes their dynamic behavior. The study described in this.p aper seeks to find some of these answers, by stopping the liner collap se process at various intermediate stages, and examining the grain str uctures in the partially collapsed liners. Well characterized OFE copp er shaped-charge liners, assembled into a cylindrical polycarbonate ca se, of constant length and volume, were partially collapsed, with redu ced-weight cylindrical explosive charges. A series of increasing explo sive charge weights were used to obtain progressively greater partial deformations on individual copper liners. The shock waves from the var ying length explosive charges were coupled to the copper liners throug h intermediate water fill, which was in direct contact with the rear o f the liners. The series of partially collapsed copper liners was capt ured by ''soft recovery'' in low density polystyrene. Flash radiograph y prior to liner recovery, confirmed that the unexpected shapes of the recovered partially collapsed liners, actually existed prior to their entering the recovery medium and were not the result of the recovery process itself. This was an early concern when the unusual shapes of t he recovered liners were first seen. These shapes were also independen tly confirmed by a series of computations at Los Alamos National Labor atory, using MESA 2D. A comparison of the photomicrographs of undeform ed virgin copper liners and the series of partially collapsed liners, shows regions on the inner apex near the liner axis where plastic flow has occurred, with very substantial modifications (refinement and elo ngation) in grain structure even for the small deformations which bare ly change the overall liner shape. Time dependent strain and strain ra te computations, using LaGrangean tracer markers, indicate very large strain rates, between 3x10(7)/sec. and 4.7x10(7)/sec. in those regions with plastic flow where grain refinement and elongation are seen, eve n with very small overall deformation. It is believed likely that this early time material processing and grain refinement, arising from the localized plastic deformation of the liner, plays a key role in prepa ring the liner material structure, so that it can exhibit the high dyn amic ductility, characteristic of copper shaped-charge jets.