Non-monotonic dependence of the friction coefficient on heterogeneous stiffness

Giacco, Ferdinando; Ciamarra, Massimo Pica; Saggese, L.; Arcangelis, L. de; Lippiello, Eugenio

doi:10.1038/srep06772

Cited by 5 publications

(6 citation statements)

References 23 publications

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“…The mesh adopted in previous studies of the 2-D spring-block model, e.g. [15], [19], does not include diagonal springs, but we add them to take into account the Poisson effect (our mesh in similar to that used in [9]).…”

Section: Modelmentioning

confidence: 99%

“…The extension to two dimensions is the straightforward improvement to better describe a experimental results and to correctly reproduce phenomena in two dimensions. This has already been done for some systems, like the Frenkel-Kontorova model [12] [13] and the spring-block model applied to geology [14]- [19], but much work remains to be done for friction of complex and structured surfaces.…”

Section: Introductionmentioning

confidence: 99%

“…[15] [18], it is introduced by means of an effective velocity-dependent force [48] [49], in friction studies, e.g. [11] [32], by springs that attach and detach during motion, in [9] [19] by means of the classical Amontons-Coulomb (AC) friction force. These various approaches give rise to slightly different quantitative results, but if they are implemented under reasonable assumptions, they do not significantly affect the overall predictions of the model, which is thought to provide a qualitative understanding of the basic mechanisms of friction.…”

Section: Introductionmentioning

confidence: 99%

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A 2-D model for friction of complex anisotropic surfaces

Costagliola

Bosia

Pugno

2018

Journal of the Mechanics and Physics of Solids

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The friction force observed at macroscale is the result of interactions at various lower length scales that are difficult to model in a combined manner. For this reason, simplified approaches are required, depending on the specific aspect to be investigated. In particular, the dimensionality of the system is often reduced, especially in models designed to provide a qualitative description of frictional properties of elastic materials, e.g. the spring-block model. In this paper, we implement for the first time a two dimensional extension of the spring-block model, applying it to structured surfaces and investigating by means of numerical simulations the frictional behaviour of a surface in the presence of features like cavities, pillars or complex anisotropic structures. We show how friction can be effectively tuned by appropriate design of such surface features.

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Section: Modelmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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A 2-D model for friction of complex anisotropic surfaces

Costagliola

Bosia

Pugno

2018

Journal of the Mechanics and Physics of Solids

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“…Results are obtained under the assumption that the region outside the core is a rigid body, so that the fault of width W can be modelled as two parallel rigid plates of area L x L y confined by a normal stress P 0 and subject to a shear stress σ (figure 1). See [41,42] for results considering elastic confining boundaries. The fault gouge, that in real faults consists of rocks produced in past wearing events, is modelled as a collection of frictional granular particles over a width W. Particles are mono-dispersed spheres of mass m and diameter d. This choice does not lead to crystallization because of the rough confining plates, however poly-dispersed particles would represent a more realistic modellization of real gouges, numerically more demanding.…”

Section: (A) Numerical Modelmentioning

confidence: 99%

Induced and endogenous acoustic oscillations in granular faults

Arcangelis

Lippiello

Ciamarra

et al. 2018

Phil. Trans. R. Soc. A.

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The frictional properties of disordered systems are affected by external perturbations. These perturbations usually weaken the system by reducing the macroscopic friction coefficient. This friction reduction is of particular interest in the case of disordered systems composed of granular particles confined between two plates, as this is a simple model of seismic fault. Indeed, in the geophysical context frictional weakening could explain the unexpected weakness of some faults, as well as earthquake remote triggering. In this manuscript we review recent results concerning the response of confined granular systems to external perturbations, considering the different mechanisms by which the perturbation could weaken a system, the relevance of the frictional reduction to earthquakes, as well as discussing the intriguing scenario whereby the weakening is not monotonic in the perturbation frequency, so that a re-entrant transition is observed, as the system first enters a fluidized state and then returns to a frictional state.

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“…While the bottom plate is kept fixed, the top one is subject to a constant pressure p and attached to a spring of elastic constant k m which is pulled at constant velocity V along the x-direction. We employ a contact force model that captures the major fea- tures of granular interactions, known as spring-dashpot model which also takes into account the presence of static friction [24][25][26]. The normal interaction between two contacting spheres is characterized by a spring constant k n = 2•10 3 k m and a damping coefficient γ n = 50 k m /m.…”

Section: The Modelmentioning

confidence: 99%

Synchronized oscillations and acoustic fluidization in confined granular materials

et al. 2018

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According to the acoustic fluidization hypothesis, elastic waves at a characteristic frequency form inside seismic faults even in absence of an external perturbation. These waves are able to generate a normal stress which contrasts the confining pressure and promotes failure. Here we study the mechanisms responsible for this wave activation via numerical simulations of a granular fault model. We observe the particles belonging to the percolating backbone, which sustains the stress, to perform synchronized oscillations over elliptic-like trajectories in the fault plane. These oscillations occur at the characteristic frequency of acoustic fluidization. As the applied shear stress increases, these oscillations become perpendicular to the fault plane just before the system fail, opposing to the confining pressure, consistently with the acoustic fluidization scenario. The same change of orientation can be induced by external perturbations at the acoustic fluidization frequency.PACS numbers: 45.70.Vn, 63.50.Lm, 91.30.Px Confined granular materials under shear display the typical stick-slip dynamics observed in real fault systems. In the last years this dynamics has been deeply investigated in several experimental settings as well as by means of molecular dynamics simulations [1][2][3][4][5][6][7][8][9][10][11][12][13][14]. These studies mostly focus on two central questions: i) Why the stress responsible for seismic failure is usually orders of magnitude smaller than the value expected on the basis of rock fracture mechanics? ii) Why seismic faults are very susceptible to even small amplitude transient seismic waves? Indeed, the resistance to shear stress of seismic faults is typically much larger than the one obtained in experiments measuring the friction coefficient of sliding rocks [15]. Furthermore, remote triggering of earthquakes [16][17][18][19][20] at distances of thousand kilometers from the main shock epicenter indicates a high susceptibility of seismic faults to the passage of seismic waves. The hypothesis of Acoustic Fluidization (AF), formulated by Melosh [21,22], provides an answer to both questions. According to AF, the elastic waves produced by seismic fracture, at a characteristic frequency ω AF , diffuse and scatter inside the fault and then generate a normal stress which can contrast the confining pressure. In this way seismic failure is promoted. To investigate this scenario, experimental studies [1,2,6,7] have demonstrated that acoustic perturbations modify granular rheology and lead to auto-acoustic compaction [7]. Recently the AF scenario has been explored in 3D molecular dynamics simulations [23] which have shown that weak external perturbations, at the frequency ω AF , even if increasing the confining pressure or reducing the applied shear, induce slip instabilities. Interestingly simulations have also shown that oscillations at the frequency ω AF are activated immediately before each slip, even in the absence of an external perturbation. Nevertheless the mechanisms responsible for this ac...

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Non-monotonic dependence of the friction coefficient on heterogeneous stiffness

Cited by 5 publications

References 23 publications

A 2-D model for friction of complex anisotropic surfaces

A 2-D model for friction of complex anisotropic surfaces

Induced and endogenous acoustic oscillations in granular faults

Synchronized oscillations and acoustic fluidization in confined granular materials

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