共查询到20条相似文献,搜索用时 62 毫秒
1.
We present extensive computational results for the effective temperature,
defined by the fluctuation-dissipation relation between the mean square
displacement and the average displacement of grains, under the action of
a weak, external perturbation, of a sheared, bi-disperse granular packing
of compressible spheres. We study the dependence of this parameter on the
shear rate and volume fractions, the type of particle and the observable
in the fluctuation-dissipation relation. We find the same temperature
for different tracer particles in the system. The temperature becomes
independent on the shear rate for slow enough shear suggesting that it is
the effective temperature of the jammed packing. However, we also show
that the agreement of the effective temperature for different observables
is only approximate, for very long times, suggesting that this defintion
may not capture the full thermodynamics of the system. On the other hand,
we find good agreement between the dynamical effective temperature and a
compactivity calculated assuming that all jammed states are equiprobable.
Therefore, this definition of temperature may capture an instance
of the ergodic hypothesis for granular materials as proposed by theoretical
formalisms for jamming. Finally, our simulations indicate
that the average shear
stress and apparent shear viscosity follow the usual relation with the shear
rate for complex fluids. Our results show that the application of
shear induces jamming in packings whose particles interact
by tangential forces. 相似文献
2.
Mechanical spectroscopy measurements were performed on decagonal quasicrystalline Al–Cu–Fe–Cr coatings of three different thicknesses deposited on a mild steel substrate. The mechanical loss spectra indicate that the internal friction is mostly caused by the quasicrystalline coating and that the contributions of both the steel substrate and the interface are small. The shear modulus measured in torsion increases with temperature, while the Young’s modulus measured in flexion behaves normally. This shear modulus anomaly is interpreted as being due to solid friction between cracked segments of the quasicrystalline coating. This phenomenon also explains the broad athermal maximum found to occur in isochronal internal friction measurements. A quantitative model successfully reproducing the observed behaviour has been developed. Finally, the reversible high-temperature exponential background was interpreted as being due to the onset of the brittle-to-ductile transition in the quasicrystalline coating. The measured activation enthalpy is similar to the value that was deduced from compression tests performed at high temperatures on icosahedral Al–Cu–Fe bulk material. 相似文献
3.
Taberlet N Richard P Jenkins JT Delannay R 《The European physical journal. E, Soft matter》2007,22(1):17-24
This paper presents numerical findings on rapid 2D and 3D granular flows on a bumpy base. In the supported regime studied
here, a strongly sheared, dilute and agitated layer spontaneously appears at the base of the flow and supports a compact packing
of grains moving as a
whole. In this regime, the flow behaves like a sliding block on the bumpy base. In particular, for flows on a horizontal base,
the average velocity decreases linearly in time and the average kinetic energy decreases linearly with the travelled distance,
those features being characteristic of solid-like friction. This allows us to define and measure an effective friction coefficient,
which is independent of the mass and velocity of the flow. This coefficient only loosely depends on the value of the micromechanical
friction coefficient whereas the infuence of the bumpiness of the base is strong. We give evidence that this dilute and agitated
layer does not result in significantly less friction. Finally, we show that a steady regime of supported flows can exist on
inclines whose angle is carefully chosen. 相似文献
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5.
The aim of this work is to determine the viscoelastic behaviour of the interface in a coaxial composite material made of a tough shield and a ductile core. The elastic modulus and the amplitude-independent internal friction are measured using a longitudinal oscillating resonant system at 50 kHz. The contribution of the interface is modelled as a shear stress that modifies the elastic behaviour of the constituents. The value of this shear stress is determined for different interfaces (epoxy resin-brass, epoxy resin-Pyrex and paraffin-Pyrex). The model is autovalidated by the excellent agreement between the calculated and experimental values of the internal friction (damping) of the composites. 相似文献
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7.
J. Nissen S. Gritsch G. Wiegand J.O. Rädler 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,10(2):335-344
We report on the wetting behavior of phospholipid membranes on solid surfaces immersed in aqueous solution. Using fluorescence
microscopy, the spreading velocity of fluid bilayers advancing from a lipid source is investigated. The kinetic spreading
coefficient was measured as a function of temperature for pure DMPC membranes and as a function of charge density and cholesterol
content for binary membranes. A theoretical model for the membrane flow is presented, which takes into account the liquid
crystalline bilayer architecture of the lipid membrane. The spreading power results from the membrane-solid VdW interaction
and is dissipated in hydrodynamic shear flow as well as by inter-monolayer friction within the bilayer. The frictional drag
causes a dynamic tension gradient in the spreading membrane, which is manifested by a single exponential decay of the fluorescence
intensity profile along the spreading direction. Obstacles are shown to act as pinning centers deforming the advancing line
interface. However, no depinning was observed, since the centers are circumflown without abrupt relaxation.
Received 6 November 1998 相似文献
8.
The shear response of molecularly thin liquid films on solid substrates when subjected to an applied air stress has been measured. The response corresponds to viscous friction while the same films sheared between two solid surfaces display static friction. These results show that molecularly thin liquid films partially confined by a single solid surface do not solidify as when confined between two solid surfaces. We are also able to observe several novel properties for liquid films on single solid surfaces not previously observed or expected. 相似文献
9.
In horizontally shaken granular material different types of pattern formation have been reported. We want to deal with the
convection instability which has been observed in experiments and which recently has been investigated numerically. Using
two dimensional molecular dynamics we show that the convection pattern depends crucially on the inelastic properties of the
material. The concept of restitution coefficient provides arguments for the change of the behaviour with varying inelasticity.
Received 3 March 1999 相似文献
10.
Local friction at a sliding interface between an elastomer and a rigid spherical probe 总被引:1,自引:0,他引:1
This paper reports on spatially resolved measurements of the shear stress distribution at a frictional interface between a
flat rubber substrate and a glass lens. Silicone rubber specimens marked close to their surface by a colored pattern have
been prepared in order to measure the surface displacement field induced by the steady-state friction of the spherical probe.
The deconvolution of this displacement field then provides the actual shear stress distribution at the contact interface.
When a smooth glass lens is used, a nearly constant shear stress is achieved within the contact. On the other hand, a bell-shaped
shear stress distribution is obtained with rough lenses. These first results suggest that simple notions of real contact area
and constant interface shear stress cannot account for the observed changes in local friction when roughness is varied. 相似文献
11.
R. Böhme 《Applied Surface Science》2006,252(13):4392-4396
In situ reflectivity measurements of the solid/liquid interface with a pump-probe setup were performed during laser-induced backside wet etching (LIBWE) of fused silica with KrF excimer laser using toluene as absorbing liquid. The intensity, the temporal shape, and the duration of the reflected light measured in dependence on the laser fluence are discussed referring to the surface modification and the bubble formation.The vaporisation of the superheated liquid at the solid interface causes a considerable increase of the reflectivity and gives information about the bubble lifetime. The alterations of the reflectivity after bubbles collapse can be explained with the changed optical properties due to surface modifications of the solid surface. Comparative studies of the reflectivity at different times and the etch rate behaviour in dependence on the laser fluence show that the in situ measured surface modification begins just at the etch threshold fluence and correlates further with etch rate behaviour and the etched surface appearance. The already observed surface modification at LIBWE due to a carbon deposition and structural changes of the near surface region are approved by the changes of the interface reflectivity and emphasizes the importance of the modified surface region in the laser-induced backside wet etching process. 相似文献
12.
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14.
Pascal Moucheront François BertrandGeorg Koval Laurent Tocquer Stéphane RodtsJean-Noël Roux Alain CorfdirFrançois Chevoir 《Magnetic resonance imaging》2010
The rheology of granular materials near an interface is investigated through proton magnetic resonance imaging. A new cylinder shear apparatus has been inserted in the magnetic resonance imaging device, which allows the control of the radial confining pressure exerted by the outer wall on the grains and the measurement of the torque on the inner shearing cylinder. A multi-layer velocimetry sequence has been developed for the simultaneous measurement of velocity profiles in different sample zones, while the measurement of the solid fraction profile is based on static imaging of the sample. This study describes the influence of the roughness of the shearing interface and of the transverse confining walls on the granular interface rheology. 相似文献
15.
J.A. Åström H.J. Herrmann J. Timonen 《The European physical journal. E, Soft matter》2001,4(3):273-279
A numerical model for packing of fragmenting blocks in a shear band is introduced, and its dynamics is compared with that
of a tectonic fault. The shear band undergoes a slow aging process in which the blocks are being grinded by the shear motion
and the compression. The dynamics of the model have the same statistical characteristics as the seismic activity in faults.
The characteristic magnitude distribution of earthquakes appears to result from frictional slips at small and medium magnitudes,
and from fragmentation of blocks at the largest magnitudes. Aftershocks to large-magnitude earthquakes are local recombinations
of the fragments before they reach a new quasi-static equilibrium. The aftershocks satisfy Omori's law. Local precursor activity
at a few times the normal background level appears at a short time before a major earthquake. Seismic gaps appear as a natural
consequence of the aging process of a fault. Explanation of the heat flux and principal stress direction anomalies at the
faults both involve the value of fracture stress of the blocks in the gouge. The final form of a tectonic fault is predicted
to involve a gouge dominated by fine-grained and rather rounded blocks so that it cannot withstand large shear stresses.
Received 26 July 2000 相似文献
16.
Automated ring shear testers have gained widespread acceptance in the chemical industry. In this paper, comparative measurements with different shear testers are described and possible factors influencing the measurement of flowability, are discussed. The measurement results presented show a dependency on the bulk solid investigated. No significant influence of the shear tester was measured for easy flowing bulk solids. An influence of the shear tester is observed for poor flowing, compressible bulk solids. Experiments have shown that test procedure and shear cell design (tester geometry) affect the measurements considerably. 相似文献
17.
Pournin L Ramaioli M Folly P Liebling TM 《The European physical journal. E, Soft matter》2007,23(2):229-235
We study the jamming of bead assemblies placed in a
cylindrical container whose bottom is pierced with a circular
hole. Their jamming behavior is quantified here by the median
jamming diameter, that is the diameter of the hole for which the
jamming probability is 0.5. Median jamming diameters of
monodisperse assemblies are obtained numerically using the
Distinct Element Method and experimentally with steel beads. We
obtain good agreement between numerical and experimental results.
The influence of friction is then investigated. In particular, the
formation of concentric bead rings is observed for low frictions.
We identify this phenomenon as a boundary effect and study its
influence on jamming. Relying on measures obtained from
simulation runs, the median jamming diameter of bidisperse bead
assemblies is finally found to depend only on the volume-average
diameter of their constituting beads. We formulate this as a
tentative law and validate it using bidisperse assemblies of
steel beads. 相似文献
18.
A. Shakib-Manesh P. Raiskinmäki A. Koponen M. Kataja J. Timonen 《Journal of statistical physics》2002,107(1-2):67-84
The mechanisms of momentum transfer and shear stress of liquid-particle suspensions in two-dimensional Couette flow are studied using direct numerical simulation by lattice-Boltzmann techniques. The results obtained display complex flow phenomena that arise from the two-phase nature of the fluid including a nonlinear velocity profile, layering of particles, and apparent slip near the solid walls. The general rheological behaviour of the suspension is dilatant. A detailed study of the various momentum transfer mechanisms that contribute to the total shear stress indicates that the observed shear thickening is related to enhanced relative solid phase stress for increasing shear rates. 相似文献
19.
Núñez A Darias R Pinto R Paredes V R Medina E 《The European physical journal. E, Soft matter》2002,9(4):327-334
We study a model of concentrated suspensions under shear in two dimensions. Interactions between suspended particles are dominated
by direct-contact viscoelastic forces and the particles are neutrally bouyant. The bimodal suspensions consist of a variable
proportion between large and small droplets, with a fixed global suspended fraction. Going beyond the assumptions of the classical
theory of Farris (R.J. Farris, Trans. Soc. Rheol. 12, 281 (1968)), we discuss a shear viscosity minimum, as a function of the small-to-large-particle ratio, in shear geometries
imposed by external body forces and boundaries. Within a linear-response scheme, we find the dependence of the viscosity minimum
on the imposed shear and the microscopic drop friction parameters. We also discuss the viscosity minimum under dynamically
imposed shear applied by boundaries. We find a reduction of macroscopic viscosity with the increase of the microscopic friction
parameters that is understood using a simple two-drop model. Our simulation results are qualitatively consistent with recent
experiments in concentrated bimodal emulsions with a highly viscous or rigid suspended component.
Received 28 June 2002
RID="a"
ID="a"e-mail: ernesto@pion.ivic.ve 相似文献
20.
We investigate the boundary lubrication in weakly adhered molecularly thin films deposited between a sphere and a plane, below the sliding threshold. The shear contact stiffness and interfacial dissipation at the micrometer scale are determined with a high-frequency quartz oscillator. Two distinct behaviors are found as a function of the shear oscillation: a linear viscoelastic response at low amplitude and a nonlinear frictional microslip at high amplitude. A friction model is proposed to analyze the data, which allows evaluating the shear strength, the friction coefficient, and the interfacial viscosity at different solid interfaces under low load. 相似文献