Nonlinear effects for coda-type elastic waves in stressed granular media

Abstract

Experimental results and their interpretations are presented on the nonlinear acoustic effects of multiple scattered elastic waves in unconsolidated granular media. Short wave packets with a central frequency higher than the so-called cut-off frequency of the medium are emitted at one side of the statically stressed slab of glass beads and received at the other side after multiple scattering and nonlinear interactions. Typical signals are strongly distorted compared to their initially radiated shape both due to nonlinearity and scattering. It is shown that acoustic waves with a deformation amplitude much lower than the mean static deformation of the contacts in the medium can modify the elastic properties of the medium, especially for the weak contact skeleton part. This addresses the problem of reproducibility of granular structures during and after acoustic excitation, which is necessary to understand in the non destructive testing of the elastic properties of granular media by acoustic methods. Coda signal analysis is shown to be a powerful time-resolved tool to monitor slight modifications in the elastic response of an unconsolidated granular structure.

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

“…1 and 2(d)]. The structure changes may be evaluated by these configuration-specific acoustic speckles, via the resemblance parameter (0)] 1/2 that was used previously [13]. Here C i,i+1 (τ ) with the time lag τ is the cross-correlation function between two successive speckle signals S i (t) and S i+1 (t) recorded every 30 s, before and after the high-amplitude sound transient at low frequency (f = 50 kHz).…”

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 compressibility of dense granular shear flows

“…It provides a unique tool to probe the mechanical response of such materials, to detect heterogeneities, aging or avalanche precursors. In the static case, grain elasticity is the only restoring force; elastic waves present most of the known behaviors of mechanical waves: velocity dispersion, non-linearity associated to contact geometry, scattering associated to disorder, anisotropy, aging, mode coupling, wave-guiding in the presence of macroscopic heterogeneities, fragility, etc [3][4][5][6][7][8]. Recent studies [9][10][11] have focused on the failure of the mean field description of elasticity when approaching the jamming transition separating the solid-like from the liquid-like regime.…”