In this work, a modified split Hopkinson pressure bar (SHPB) is used to impact one-dimensional granular chain of spheres. These homogeneous chains used here comprise of brass, aluminum, or stainless steel spherical beads, ranging from a single sphere to a chain of fourteen, and are of interest because of their unique wave propagation characteristics, as seen in earlier efforts. Loading magnitudes spanning from 9 kN to 40 kN – considerably higher than most previous works on these systems which have been conducted in the elastic regime – cause the granular chains to deform plastically. These conditions allow for solitary waves, which propagate in the one-dimensional array of elastic spheres, to be studied in the plastic regime. The propagating pulse assumes a distinctive shape after travelling through five beads, and can consequently be realized as a plastic solitary wave. The wave speed of this pulse was seen to depend on maximum force, as in the elastic as, although it was measured to be less than the elastic wave speed. In addition, the plastic velocity varied with the 1/9th power instead of the 1/6th power for the elastic speed. For the case of brass, the plastic wave propagates at 50% to 80% the speed of the elastic wave, depending on whether the incident or transmitted force is compared. It was found that there is also decreasing plasticity along the chain length except at the end beads in contact with the SHPB, which rebounds into the bar and are hit again. This research is the first to investigate in detail the development and evolution of a plastic solitary wave and will form the basis of future work in this area.
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Experimental study of the development of plastic solitary waves in one-dimensional granular media
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