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 aMEMS-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.