We experimentally study nonlinear force propagation into granular material during impact from an intruder, and we explain our observations in terms of the nonlinear grain-scale force relation. Using high-speed video and photoelastic particles, we determine the speed and spatial structure of the force response just after impact. We show that these quantities depend on a dimensionless parameter, M′=tcv0/d, where v0 is the intruder speed at impact, d is the particle diameter, and tc is the collision time for a pair of grains impacting at relative speed v0. The experiments access a large range of M′ by using particles of three different materials. When M′蠐1, force propagation is chainlike with a speed, vf, satisfying vf∞d/tc. For larger M′, the force response becomes spatially dense and the force propagation speed departs from vf∞d/tc, corresponding to collective stiffening of a strongly compressed packing of grains.
All Science Journal Classification (ASJC) codes
- General Physics and Astronomy