EXPERIMENTAL AND ANALYTICAL STUDY OF EARLY TIME MATERIAL PROCESSING, IN A COLLAPSING SHAPED - CHARGE LINER, USING SOFTLY - RECOVERED PARTIALLY - COLLAPSED COPPER LINERS
L. Zernow et Ej. Chapyak, EXPERIMENTAL AND ANALYTICAL STUDY OF EARLY TIME MATERIAL PROCESSING, IN A COLLAPSING SHAPED - CHARGE LINER, USING SOFTLY - RECOVERED PARTIALLY - COLLAPSED COPPER LINERS, International journal of impact engineering, 14(1-4), 1993, pp. 863-875
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.