59 research outputs found
Effect of fingerprints orientation on skin vibrations during tactile exploration of textured surfaces
In humans, the tactile perception of fine textures is mediated by skin
vibrations when scanning the surface with the fingertip. These vibrations are
encoded by specific mechanoreceptors, Pacinian corpuscules (PCs), located about
2 mm below the skin surface. In a recent article, we performed experiments
using a biomimetic sensor which suggest that fingerprints (epidermal ridges)
may play an important role in shaping the subcutaneous stress vibrations in a
way which facilitates their processing by the PC channel. Here we further test
this hypothesis by directly recording the modulations of the
fingerpad/substrate friction force induced by scanning an actual fingertip
across a textured surface. When the fingerprints are oriented perpendicular to
the scanning direction, the spectrum of these modulations shows a pronounced
maximum around the frequency v/lambda, where v is the scanning velocity and
lambda the fingerprints period. This simple biomechanical result confirms the
relevance of our previous finding for human touch.Comment: Addendum to: Scheibert J, Leurent S, Prevost A, Debr\'egeas G. The
role of fingerprints in the coding of tactile information probed with a
biomimetic sensor. Science 2009; 323:1503?6 3 pages, 1 figur
Adhesive contact of model randomly rough rubber surfaces
We study experimentally and theoretically the equilibrium adhesive contact
between a smooth glass lens and a rough rubber surface textured with spherical
microasperities with controlled height and spatial distributions. Measurements
of the real contact area versus load are performed under compression by
imaging the light transmitted at the microcontacts. is found to be
non-linear and to strongly depend on the standard deviation of the asperity
height distribution. Experimental results are discussed in the light of a
discrete version of Fuller and Tabor's (FT) original model (\textit{Proceedings
of the Royal Society A} \textbf{345} (1975) 327), which allows to take into
account the elastic coupling arising from both microasperities interactions and
curvature of the glass lens. Our experimental data on microcontact size
distributions are well captured by our discrete extended model. We show that
the elastic coupling arising from the lens curvature has a significant
contribution to the relationship. Our discrete model also clearly shows
that the adhesion-induced effect on remains significant even for
vanishingly small pull-off forces. Last, at the local asperity length scale,
our measurements show that the pressure dependence of the microcontacts density
can be simply described by the original FT model
Probing the micromechanics of a multi-contact interface at the onset of frictional sliding
Digital Image Correlation is used to study the micromechanics of a
multi-contact interface formed between a rough elastomer and a smooth glass
surface. The in-plane elastomer deformation is monitored during the incipient
sliding regime, i.e. the transition between static and sliding contact. As the
shear load is increased, an annular slip region, in coexistence with a central
stick region, is found to progressively invade the contact. From the
interfacial displacement field, the tangential stress field can be further
computed using a numerical inversion procedure. These local mechanical
measurements are found to be correctly captured by Cattaneo and Mindlin (CM)'s
model. However, close comparison reveals significant discrepancies in both the
displacements and stress fields that reflect the oversimplifying hypothesis
underlying CM's scenario. In particular, our optical measurements allow us to
exhibit an elasto-plastic like friction constitutive equation that differs from
the rigid-plastic behavior assumed in CM's model. This local constitutive law,
which involves a roughness-related length scale, is consistent with the model
of Bureau \textit{et al.} [Proc. R. Soc. London A \textbf{459}, 2787 (2003)]
derived for homogeneously loaded macroscopic multi-contact interfaces, thus
extending its validity to mesoscopic scales.measurements allow for the first
quantitative test of Cattaneo and Mindlin (CM) classical model of the incipient
sliding of a smooth interface. Small deviations are observed and interpreted as
a result of the finite compliance of the rough interface, a behavior which
contrasts with Amontons' law of friction assumed to be valid locally in CM's
model. We illustrate how these measurements actually provide a method for
probing the rheology of the rough interface, which we find to be of the
elasto-plastic type.Comment: 11 page
Mécanique du contact rugueux et perception tactile
5 pages, 2 figuresNational audienceDans un contact entre solides rugueux, l'interface constitue la partie la plus déformable. Son comportement mécanique détermine les contraintes s'établissant dans les deux solides, ainsi que la dynamique de frottement. Deux nouvelles méthodes expérimentales, fondées respectivement sur une observation optique directe et sur l'utilisation d'un microcapteur de force MEMS, permettent de sonder la mécanique locale de ces interfaces. Le dispositif MEMS, qui est un analogue très rudimentaire de l'extrémité du doigt humain, nous a permis de proposer un rôle possible des empreintes digitales dans la transduction de l'information tactile
Forcing and Velocity Correlations in a Vibrated Granular Monolayer
The role of forcing on the dynamics of a vertically shaken granular monolayer
is investigated. Using a flat plate, surprising negative velocity correlations
are measured. A mechanism for this anti-correlation is proposed with support
from both experimental results and molecular dynamics simulations. Using a
rough plate, velocity correlations are positive, and the velocity distribution
evolves from a gaussian at very low densities to a broader distribution at high
densities. These results are interpreted as a balance between stochastic
forcing, interparticle collisions, and friction with the plate.Comment: 4 pages, 5 figure
A comparative performance evaluation framework for power based wind turbine fault detection methods
International audienc
Non-equilibrium two-phase coexistence in a confined granular layer
We report the observation of the homogenous nucleation of crystals in a dense
layer of steel spheres confined between two horizontal plates vibrated
vertically. Above a critical vibration amplitude, two-layer crystals with
square symmetry were found to coexist in steady state with a surrounding
granular liquid. By analogy to equilibrium hard sphere systems, the phase
behavior can be explained through entropy maximization. However, dramatic
non-equilibrium effects are present, including a significant difference in the
granular temperatures of the two phases.Comment: 4 pages, 3 figures, RevTex4 forma
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