Experimental evidence of shock mitigation in a Hertzian tapered chain

TL;DR

This experimental study demonstrates that Hertzian tapered chains of elastic spheres can effectively mitigate shocks by transferring energy to a tail, with the front pulse adopting a self-similar shape and acting as a shock absorber.

Contribution

The paper provides experimental evidence and analysis of shock mitigation in Hertzian tapered chains, confirming numerical predictions and highlighting their potential as shock absorbing devices.

Findings

Impulse propagation maintains shape in monodisperse chains.

Tapered chains transfer energy to a tail, reducing front amplitude.

Chains act as shock absorbers by thermalizing impulses.

Abstract

We present an experimental study of the mechanical impulse propagation through a horizontal alignment of elastic spheres of progressively decreasing diameter $\phi_n$, namely a tapered chain. Experimentally, the diameters of spheres which interact via the Hertz potential are selected to keep as close as possible to an exponential decrease, $\phi_{n+1}=(1-q)\phi_n$, where the experimental tapering factor is either $q_1\simeq5.60$~% or $q_2\simeq8.27$~%. In agreement with recent numerical results, an impulse initiated in a monodisperse chain (a chain of identical beads) propagates without shape changes, and progressively transfer its energy and momentum to a propagating tail when it further travels in a tapered chain. As a result, the front pulse of this wave decreases in amplitude and accelerates. Both effects are satisfactorily described by the hard spheres approximation, and basically, the shock mitigation is due to partial transmissions, from one bead to the next, of momentum and energy of the front pulse. In addition when small dissipation is included, a better agreement with experiments is found. A close analysis of the loading part of the experimental pulses demonstrates that the front wave adopts itself a self similar solution as it propagates in the tapered chain. Finally, our results corroborate the capability of these chains to thermalize propagating impulses and thereby act as shock absorbing devices.