Effect of Indentation Depth on Friction Coefficient in Adhesive Contacts: Experiment and Simulation

Abstract

The quasi-static regime of friction between a rigid steel indenter and a soft elastomer with high adhesion is studied experimentally. An analysis of the formally calculated dependencies of a friction coefficient on an external load (normal force) shows that the friction coefficient monotonically decreases with an increase in the load, following a power law relationship. Over the entire range of contact loads, a friction mode is realized in which constant shear stresses are maintained in the tangential contact, which corresponds to the “adhesive” friction mode. In this mode, Amonton’s law is inapplicable, and the friction coefficient loses its original meaning. Some classical works, which show the existence of a transition between “adhesive” and “normal” friction, were analyzed. It is shown that, in fact, there is no such transition. A computer simulation of the indentation process was carried out within the framework of the boundary element method, which confirmed the experimental results.

Controlling the Friction Coefficient and Adhesive Properties of a Contact by Varying the Indenter Geometry

“…In the classical works [48,49], it is stated, that there exists a transition from the "adhesive" friction mode (Equation ( 2)) to the "normal" friction mode (Equation ( 4)) with increasing normal load F N . But, in our previous experimental work [38], we did not find such a transition in a wide range of external loads. On the contrary, it was shown that the experimental results of [48] can be well described with the "adhesive" friction law (Equation ( 2)) in the whole range of normal forces used in [48].…”

“…In macroscopic contacts, the friction force is often roughly proportional to the normal force and, thus, Amontons's law F x = µF N is valid [32]. On the microscale, on the contrary, many studies show the proportionality of the frictional force to the contact area A, i.e., F x = τA [33][34][35][36][37][38][39], where τ is the (approximately constant) tangential stress in the contact area necessary to shear the interface. The widely accepted solution of this controversy is that the contact area in macroscopic contacts is roughly proportional to the normal load [40].…”

“…In our previous work [38], the effect of the indentation depth of spherical indenters on the friction coefficient was studied experimentally. The present work extends this study to the frictional properties of indenters with power law profiles f (r) = c n r n .…”

“…This approach opens opportunities to create new types of surfaces with predefined coefficients of friction. The experimental setup as well as the experimental techniques used in the present study are similar to those described in [38].…”

Transition between Friction Modes in Adhesive Contacts of a Hard Indenter and a Soft Elastomer: An Experiment

“…However, the material CRG N0505 has a lower elasticity modulus, which means it can be deformed even more significantly under tangential shear, leading to more complex dynamic nonlinear effects; contact restructuring in the case of CRG N0505 is more complex than for stiffer CRG N3005 used in the present study. Our recent study [23] provides a comparison of the behavior of these two materials (the difference is particularly noticeable in supplementary videos attached to the article). Primarily, in our experiments, we prefer to use the stiffer material, CRG N3005.…”