Emergence of self-affine surfaces during adhesive wear

Abstract

Friction and wear depend critically on surface roughness and its evolution with time. An accurate control of roughness is essential to the performance and durability of virtually all engineering applications. At geological scales, roughness along tectonic faults is intimately linked to stick-slip behaviour as experienced during earthquakes. While numerous experiments on natural, fractured, and frictional sliding surfaces have shown that roughness has self-affine fractal properties, much less is known about the mechanisms controlling the origins and the evolution of roughness. Here, by performing long-timescale molecular dynamics simulations and tracking the roughness evolution in time, we reveal that the emergence of self-affine surfaces is governed by the interplay between the ductile and brittle mechanisms of adhesive wear in three-body contact, and is independent of the initial state.

Hydraulic Transport Through Calcite Bearing Faults With Customized Roughness: Effects of Normal and Shear Loading

“…Indeed, by preconditioning the reservoir (reducing the effective stress on it; Fryer et al, 2018Fryer et al, , 2020, the predictions of transmissivity should become more accurate. We can speculate that the use of more complex models that include shear stress and wear processes can strongly improve the prediction of transmissivity with shear displacement (Aghababaei et al, 2016;Frérot et al, 2019;Milanese et al, 2019;Molinari et al, 2018;Shvarts & Yastrebov, 2018a, 2018bShvarts, 2019;Yastrebov et al, 2017). The results obtained for a single rough-fault could then be input into discrete fracture models (DFMs) to evaluate the hydraulic transport in fracture networks (McClure & Horne, 2013).…”

“…It is noticeable that the contact model does not include a shear stress component analysis nor a wear analysis. From our knowledge, integrating an elasto‐plastic shear component and wear components to the analysis is not a straightforward task and is out of the scope of this study (Aghababaei et al, 2016; Frérot et al, 2019; Milanese et al, 2019; Molinari et al, 2018). In section 6.1, we use the developed numerical procedure to simplify the shear loading problem and study the influence of reversible shear loading and irreversible shear displacement on fracture transmissivity.…”

“…We interpret these differences at low and high confining pressure as due to strong changes in surface roughness (due to plastic deformation and wear) with ongoing slip. Indeed, the model presented here is extremely simplified because it does neither consider the evolution of an applied shear stress on the fracture's macroscopic wavelengths nor the production of wear particles (Aghababaei et al, 2016; Milanese et al, 2019; Molinari et al, 2018). The plasticity (Frérot et al, 2019) and wear (Archard, 1959; Molinari et al, 2018; Tesei et al, 2017; Yamashita et al, 2015) processes should be enhanced by higher applied normal and shear stresses, thus generating larger changes in surface topography in our experiments at high confining pressures.…”

Adhesive wear mechanisms in the presence of weak interfaces: Insights from an amorphous model system

“…First, large angles between the interface and the sliding direction lead to an increased probability of wear particle formation, meaning that a high root-mean-square roughness of the surface leads to more asperity interlock and more wear. Consequently, though, the roughness should reduce during running-in (by wearing off high and thin asperities), while the real contact area and the size of the individual contact spots increases and the wear rate decreases [17,67]. Without the slope-dependent slip mechanism, this effect cannot be explained, since increased contact spot sizes should lead to the formation of more and larger wear particles.…”

“…1(a) left], by formulating a critical length scale in terms of a competition between plastic deformation of an asperity under load and its breaking off [16]. In addition to predicting a minimum size of wear particles, it also provides a way to understand surface roughness evolution [17]: Purely plastic deformation of asperities has been found to mostly flatten the surfaces or lead to welding [18][19][20][21][22][23][24], while the breaking off of wear particles seems to be the ingredient to reroughen worked surfaces [17], although surface kinks due to dislocation plasticity have also been suggested as sources of roughness [25]. The critical length scale is most generally defined as…”