On the possible applications of the non-linear acoustic phenomena for the evaluation of the granular materials (original) (raw)
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Nonlinear acoustics in granular assemblies
Granular Matter, 2001
We present a brief review of the problem of acoustic propagation in granular media and discuss recent progress on nonlinear acoustics in granular media. The presentation emphasizes the solitary wave like properties of impulse propagation in granular media at vanishingly small loading conditions and discusses the possible spectroscopic applications of nonlinear impulse acoustics in the detection of buried inclusions.
Acta Acustica united with Acustica, 2008
The problem of the nonlinear reflection of acoustic waves from a mechanically free surface of an unconsolidated granular layer under gravity is solved analytically using the successive approximations method. The theory revealed specific dependencies of the characteristics of the generated acoustic harmonics of longitudinal and shear waves on frequency and the thickness of the granular layer, which are related to a power-law gravity-induced depth stratification of linear and nonlinear mechanical properties of the granular layer. The developed theory could be useful for the analysis of the acoustic experiments directed to the investigation of fundamental mechanical properties of unconsolidated granular media near the jamming transition taking place at zero confining pressure.
Acoustic modes induced by force chains in granular lattice
The influence of force chains on acoustic wave propagation in granular media is investigated by modeling a granular medium as a cubic lattice of particles. In this spatially periodic media, general physical arguments as well as an analytical theory indicate that, in addition to a traditional method of wave control through gap opening in an allowed frequency band, there exists an opportunity to control waves through window opening in a forbidden frequency band. Loading unconsolidated granular crystal periodically in space creates a periodic system of force chains, which modulates periodically the medium rigidity and makes possible to guide high-frequency acoustic waves in the direction initially forbidden for their propagation. The influence of the modulation period and amplitude on the spectrum of the propagating modes is investigated. Even a single force chain creates a channel for wave propagation in the forbidden frequency band.
PROBING GRANULAR MEDIA COMPACTION BY NONLINEAR ACOUSTIC METHODS
Compaction process due to mechanical shak-ing changes the mechanical and structural properties of an unconsolidated granular material. In this study, acoustic waves are used to monitor contact network evolution during the compaction process. Both linear and nonlinear acous-tic methods are applied in order to compare their sensitivity with the strenghtening of the granular medium. While lin-ear parameter (linear sound velocity) behaves linearly with compacity and saturates with the saturation average load-ing of the contacts, nonlinear measurements give an insight in the dynamics of the contact force distribution through the evolution of nonlinear dissipative processes to nonlinear elastic ones.
Towards a Mathematical Model for Elastic Wave Propagation in Granular Materials
Engineering, 2012
A theoretical model for the propagation of acoustic waves in dry granular media is presented within the framework of the nonlinear granular elasticity. An essential ingredient is the dependence of the elastic moduli on compression. For the purpose of illustration, we analyze the case of a time-harmonic plane wave propagation under isotropic compression. We derive explicit relations for the wave speed dependence with the confining pressure. The present approach provides an accurate description of acoustic wave propagation in granular packings and represents a powerful tool to interpret the results of current experiments.
2019
Understanding how forces propagate through granular media is broadly relevant in acoustic and non-acoustic warfare applications. For example, sediment type can impact acoustic propagation during bottom bounce events that undersea assets use for navigation. There is not yet a complete theory of force propagation in granular media due to several nonlinearities, like friction and Hertzian contact interactions. Of particular interest is the crossover region between linear and nonlinear regimes, where the propagating stresses are comparable to the initial confining stress in the system, as well as the shock regime, where stresses greatly exceed confining prestress. Aiming to develop more complete theories of force propagation in these regimes, we perform experimental impact tests and analyze how forces propagate in two-dimensional, frictional granular media. Assemblies of photo elastic disks are subjected to a vertical confining stress and then impacted from the side by a pendulum. Both ...
Probing the shear-band formation in granular media with sound waves
Physical Review E, 2012
We investigate the mechanical responses of dense granular materials, using a direct shear box combined with simultaneous acoustic measurements. Measured shear wave speeds evidence the structural change of the material under shear, from the jammed state to the flowing state. There is a clear acoustic signature when the shear band is formed. Subjected to cyclic shear, both shear stress and wave speed show the strong hysteretic dependence on the shear strain, likely associated with the geometry change in the packing structure. Moreover, the correlation function of configuration-specific multiply scattered waves reveals an intermittent behavior before the failure of material.
Characterization of granular compaction by nonlinear acoustic resonance method
Applied Physics Letters, 2008
A method of nonlinear acoustic resonance is applied to monitor the evolution in the linear and nonlinear elastic and dissipative mechanical properties of a granular packing in the process of its compaction by consecutive mechanical taps. It is demonstrated that the variations in the nonlinear mechanical properties are more pronounced than those in the linear ones, indicating the advantage of nonlinear acoustic methods for the compaction control. The experimental observations revealed for the first time the modification in the statistical distribution of the grain-grain contact interaction forces by the compaction.
Acoustical properties of double porosity granular materials
The Journal of the Acoustical Society of America, 2011
Granular materials have been conventionally used for acoustic treatment due to their sound absorptive and sound insulating properties. An emerging field is the study of the acoustical properties of multiscale porous materials. An example of these is a granular material in which the particles are porous. In this paper, analytical and hybrid analytical-numerical models describing the acoustical properties of these materials are introduced. Image processing techniques have been employed to estimate characteristic dimensions of the materials. The model predictions are compared with measurements on expanded perlite and activated carbon showing satisfactory agreement. It is concluded that a double porosity granular material exhibits greater low-frequency sound absorption at reduced weight compared to a solid-grain granular material with similar mesoscopic characteristics.