Elastic weakening of a dense granular pack by acoustic fluidization: Slipping, compaction, and aging

Abstract

Sound velocity measurements in dense glass bead packs reveal significant softening effect at large amplitudes, due to the frictional nonlinearity at the grain contacts. Beyond a certain amplitude, the sound-matter interaction becomes irreversible, leaving the medium in a weakened and slightly compacted state. A slow recovery of the initial elastic modulus is observed after acoustic perturbation, revealing the plastic creep growth of microcontacts. The cross-correlation function of configuration-specific acoustic speckles highlights the relationship between the macroscopic elastic weakening and the local change of the contact networks, induced by strong sound vibration, in the absence of appreciable grain motion.

Effect of boundary vibration on the frictional behavior of a dense sheared granular layer

“…Furthermore, we showed that an amplitude threshold exists for triggering of frictional weakening events and this threshold is larger for higher confining stresses. This is also in agreement with the recent experimental observation by Jia et al where they found that the acoustic fluidization threshold increases by increasing the confining pressure of the granular medium [11].…”

“…The intrinsic stick-slip dynamics of a granular layer can be perturbed by external factors including boundary vibrations. Laboratory scale observations as well as Discrete Element Method (DEM) simulations show and confirm that mechanical and acoustic vibrations with adequate amplitudes can change the mechanical and frictional properties of a confined and sheared granular layer, and consequently its macro-scale response [6,7,8,9,10,11,12]. Many aspects of this vibration-induced changes including its grain-scale mechanisms, its dependence on the loading state of the granular layer and on the vibration amplitude are unexplored.…”

Nonlinear ultrasound: Potential of the cross-correlation method for osseointegration monitoring

“…The method showed convincing results for the study of linear and nonlinear scattering regimes in granular media. 8,9 As shown in Fig. 1(c), three parameters are extracted from the CCM: (i) the intercorrelation amplitude for a 0-shift, (ii) the time-shift value s max corresponding to the maximum intercorrelation, and (iii) the value of this maximum.…”

Dynamic induced softening in frictional granular materials investigated by discrete-element-method simulation

“…This behaviour arises from rearrangements of the contact network, resulting in a reduction in the average contact number but without significant rearrangement of particle positions [28]. However, the effect of friction on the elastic softening [9,30] is absent in these frictionless systems.…”

“…A granular solid shows strong nonlinear elasticity and sound propagation provides a footprint of this feature [2][3][4][5]. The nonlinear dynamic response found in granular media such as resonance frequency softening, slow dynamics and harmonic generation [6][7][8][9] is very similar to those discovered in rocks [10][11][12][13][14].…”