Experimental and Numerical Study of Wave Propagation in Granular Media

One dimensional stress waves travelling in granular chains exhibit interesting characteristics such as filtering, tunability and wave mitigation because on the formation of solitary waves, and solitary wave trains, within them. An idealized one dimensional granular medium, consisting of a linear array of contacting spherical brass beads, was loaded dynamically in a modified split Hopkinson pressure bar, with loading pulses that span a variety of rates and profiles using pulse shaping techniques. Different chain lengths were studied to determine how solitary waves form in a varying length granular medium, as well as the speed of wave propagation. It is found that the wave speed propagates faster for longer chains of brass beads. The high loading rates of the Hopkinson bar also allowed us to investigate plastic dissipation effects in the granular chain when composed of different types of metals. To further our understanding of wave propagation in ductile ordered granular media, the experimental results are compared with companion numerical simulations based on a particle contact law that accounts for plastic dissipation. Knowing the behavior of a stress wave propagating through such materials can lead to arrangements that can produce desired stress wave mitigation characteristics as the waves travel through the granular chain.