9 research outputs found
Role of friction-induced torque in stick-slip motion
We present a minimal quasistatic 1D model describing the kinematics of the
transition from static friction to stick-slip motion of a linear elastic block
on a rigid plane. We show how the kinematics of both the precursors to
frictional sliding and the periodic stick-slip motion are controlled by the
amount of friction-induced torque at the interface. Our model provides a
general framework to understand and relate a series of recent experimental
observations, in particular the nucleation location of micro-slip instabilities
and the build up of an asymmetric field of real contact area.Comment: 6 pages, 5 figure
Experimental evidence of non-Amontons behaviour at a multicontact interface
We report on normal stress field measurements at the multicontact interface
between a rough elastomeric film and a smooth glass sphere under normal load,
using an original MEMS-based stress sensing device. These measurements are
compared to Finite Elements Method calculations with boundary conditions
obeying locally Amontons' rigid-plastic-like friction law with a uniform
friction coefficient. In dry contact conditions, significant deviations are
observed which decrease with increasing load. In lubricated conditions, the
measured profile recovers almost perfectly the predicted profile. These results
are interpreted as a consequence of the finite compliance of the multicontact
interface, a mechanism which is not taken into account in Amontons' law
Stress field at a sliding frictional contact:Experiments and calculations
A MEMS-based sensing device is used to measure the normal and tangential
stress fields at the base of a rough elastomer film in contact with a smooth
glass cylinder in steady sliding. This geometry allows for a direct comparison
between the stress profiles measured along the sliding direction and the
predictions of an original \textit{exact} bidimensional model of friction. The
latter assumes Amontons' friction law, which implies that in steady sliding the
interfacial tangential stress is equal to the normal stress times a
pressure-independent dynamic friction coefficient , but makes no further
assumption on the normal stress field. Discrepancy between the measured and
calculated profiles is less than 14% over the range of loads explored.
Comparison with a test model, based on the classical assumption that the normal
stress field is unchanged upon tangential loading, shows that the exact model
better reproduces the experimental profiles at high loads. However, significant
deviations remain that are not accounted for by either calculations. In that
regard, the relevance of two other assumptions made in the calculations, namely
(i) the smoothness of the interface and (ii) the pressure-independence of
is briefly discussed.Comment: 22 pages, 10 figure
MEMS-based contact stress field measurements at a rough elastomeric layer: local test of Amontons’ friction law in static and steady sliding regimes
We present the results of recent friction experiments in which a MEMS-based sensing device is used to measure both the normal and tangential stress fields at the base of a rough elastomer film in frictional contact with smooth, rigid, glass indentors. We consider successively multicontacts under (i) static normal loading by a spherical indentor and (ii) frictional steady sliding conditions against a cylindrical indentor, for an increasing normal load. In both cases, the measured fields are compared to elastic calculations assuming (i) a smooth interface and (ii) Amontons’ friction law. In the static case, significant deviations are observed which decrease with increasing load and which vanish when a lubricant is used. In the steady sliding case, Amontons’ law reproduces rather satisfactorily the experiments provided that the normal/tangential coupling at the contact interface is taken into account. We discuss the origin of the difference between the Amontons fields and the measured ones, in particular the effect of the finite normal and tangential compliances of the multicontact interface