Experimental study of deformation properties of a bulk layer from plumbum balls under dynamic and quasistatic loading

Bulk layers of metal balls are a promising damping element that protects structures from impulsive actions. To assess their damping properties, the knowledge of the deformation and strength characteristics for static and dynamic compression is required. Three stages can be distinguished in the deformation of bulk porous media: re-stacking to close packing without appreciable deformation of the particles (elimination of free porosity); deformation to almost complete layout (absence of pores); deformation as a continuous material without pores. To obtain the dynamic characteristics of the layer, we used the Kolsky method with the Hopkinson bar system. The results of investigations at various deformation rates determined by the initial speed of the striker's departure are presented. Due to the small resistance of the porous sample to the deformation at the stages of repackaging and the initial stage of the deformation of the balls, most of the compression pulse formed when the striker projectile the loading bar is returned to the first measuring bar. This leads to a repeated cyclic loading of the sample with an increasingly decreasing load amplitude. In addition to the active loading curves, the technique allows obtaining unloading curves in the course of one experiment. It is demonstrated that a developed plastic flow and fragmentation of the balls are observed as a result of deformation of the samples with increasing load. Static compression of the bulk was carried out on a Zwick test machine. The tests carried out in a wide range of loads showed great differences between the static and dynamic deformation curves characteristic of highly porous media. The obtained results can be used for predictive mathematical modeling of elements of structures containing bulk layers.