Morphology of damages to thick witness-plates produced by fragments of high-velocity projectiles made of different materials | Mekhanika | kompozitsionnykh | materialov i konstruktsii
> Volume 25 > №1 / 2019 / Pages: 37-56

Morphology of damages to thick witness-plates produced by fragments of high-velocity projectiles made of different materials

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The experimental study of the fragmentation of projectiles at high-velocity impact perforation of thin bumpers is not rich with technologies for in-situ observation. One of the reliable methods for the retrieving of data characterizing the fragment clouds produced by the impact is the analysis of the damage of witness plates situated in the path of the moving fragments at some distance from a bumper. In this work we performed a comparative analysis of the morphological features of the damages on the witness-plates produced by the fragments of projectiles made of different materials: polyethylene, aluminum alloy and caprolon embrittled by embedding of glass microspheres. The experiments were performed in the range of impact velocities from 2900 m/s to 7000 m/s. The tested bumpers were of three types: continuous bumpers (aluminum plates), steel meshes, and sets of steel strings (string bumpers). The analysis showed that at similar experimental conditions in tests with string bumpers the polyethylene projectile could reveal lower degree of fragmentation than embrittled caprolon material. The sufficient part of initial kinetic energy remains in the rear part of the polyethylene projectile without transition into other projectile parts or transformation into the energy of fracture. The projectile of caprolon keeps the tendency to generate jets from the frontal part similar to the case of non-brittle polyethylene. These jets produce linear chains of craters on the witness-plate surface. The fragmentation of a polyethylene projectile on a continuous bumper provides a formation of a fragment cloud containing chunky fragments and threadlike fragments as well. The threadlike fragments can combine into closed structure. This type of fragment clouds was observed in experiments with continuous bumpers and soda-lime glass projectiles. It is remarkable that the distribution of thread like craters formed by the fragments of the polyethylene projectile is similar to the distribution of the ensemble of small craters produced by the fragments of aluminum projectiles. There exists significant morphological similarity between a pair of experiments: in the first one the projectile was made of polyethylene and the bumper was a steel mesh, in the second there were an aluminum projectile and a mesh bumper made of tungsten wires. It seems that the parameter that controls the similarity in these experiments is the ratio of the projectile density to the bumper density.