Mechanical impulse propagation in a packing of 3D spheres confined at constant pressure

TL;DR

This study investigates how mechanical impulses propagate in 3D granular packings under constant pressure, revealing a transition from nonlinear to linear wave behavior influenced by confinement pressure and impulse amplitude.

Contribution

It demonstrates the transition from nonlinear to linear wave propagation in granular media under hydrostatic pressure, controlled by flexible confinement and impact impulse characteristics.

Findings

Wave speed follows Hertz contact law predictions.

Transition from nonlinear to linear propagation with increasing pressure.

Attenuation depends on impulse amplitude in nonlinear regime.

Abstract

Mechanical impulse propagation in granular media depends strongly on the imposed confinement conditions. In this work, the propagation of sound in a granular packing contained by flexible walls that enable confinement under hydrostatic pressure conditions is investigated. This configuration also allows the form of the input impulse to be controlled by means of an instrumented impact pendulum. The main characteristics of mechan- ical wave propagation are analyzed, and it is found that the wave speed as function of the wave amplitude of the propagating pulse obeys the predictions of the Hertz contact law. Upon increasing the confinement pressure, a continuous transition from nonlinear to linear propagation is observed. Our results show that in the low-confinement regime, the attenuation increases with an increasing impulse amplitude for nonlinear pulses, whereas it is a weak function of the confinement pressure for linear waves.