Abstract
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 con- sider successively multicontacts under (i) static normal loading by a spherical indentor and (ii) frictional steady sliding conditions against a cylindrical indentor, for an increas- ing 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, signifi- cant 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 satisfacto- rily 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 compli- ances of the multicontact interface.
Highlights
We have described a Mechanical Systems (MEMS)-based set-up allowing for spatially resolved measurements of both the normal and tangential stress fields at the rigid base of a compliant layer
On the practically relevant situation of elastic rough surfaces bearing micrometer-sized asperities, we considered two classical types of loading in contact mechanics: (i) the static normal indentation by a rigid sphere and (ii) the steady sliding indentation by a rigid cylinder
The measurement technique used here is of very broad interest in contact mechanics because they provide a significantly richer information than the classical measurements of the total normal and shear forces P and Q
Summary
Knowledge of the surface and subsurface stress fields at the contact region between two solids is of considerable interest to numerous domains such as mechanical engineering (e.g. [1,2,3,4,5]), solid friction [6,7,8,9,10,11,12], biomechanics (e.g. [13,14,15,16,17]) or seismology (e.g. [18, 19]). Macroscopic MCI usually obey the empirical Amontons’ friction law which states that irreversible sliding occurs when the ratio of tangential to normal forces reaches a static friction coefficient μmacro without any prior deformation of the interface [7, 20]. The classical approach for calculating contact stress fields for MCIs consists in considering a smooth interface exhibiting an analog rigid-plastic response: μmacro defines the threshold ratio between shear and normal stress components for local slip to occur [21,22,23,24]. Few recent works tried to explicitely take into account the effect of the finite tangential compliance of MCIs on the contact stress [25, 26] We consider two differents situations: (i) static sphere-on-plane MCIs under purely normal load, modeled using finite elements (section 3) and (ii) steady-sliding cylinder-on-plane MCIs, for which we developed an original semi-analytical calculation (section 4)
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