Intragranular fracture and frictional effects on wave propagation through granular media

Parametric studies were conducted to investigate how fracture and friction mechanisms in granular materials contribute to the decay of waves propagated by high speed impact. Numerical simulations of a plate impact driver with a sinusoidal cross-sectioned face were driven into a contained granular particle field at two different velocities in order to propagate a sinusoidal stress wave into the particles. The 2D, elastic, plain-strain simulations were conducted using Peridigm, a massively-parallel simulation code developed by Sandia National Laboratories for conducting simulations involving fracture. The rate of decay of the stress wave was measured by calculating the change in amplitude of a sinusoidal curve fit to the wavefront. The displacement of the wavefront was measured by recording the distance traveled by those same particles on the wavefront. The amplitude and displacement curves were plotted against time and compared for many variations of fracture and friction. The results suggest that fracture plays a larger role than friction in the amplitude decay and travel of a perturbed stress wave, and that the effect of both parameters is amplified by increased impact velocity.