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

Abstract

Engineering wear models are generally empirical and lack connections to the physical processes of debris generation at the nanoscale to microscale. Here, we thus analyze wear particle formation for sliding interfaces in dry contact with full and reduced adhesion. Depending on the material and interface properties and the local slopes of the surfaces, we find that colliding surface asperities can either deform plastically, form wear particles, or slip along the contact junction surface without significant damage. We propose a mechanism map as a function of material properties and local geometry, and confirm it using quasi-two-dimensional and three-dimensional molecular dynamics and finite-element simulations on an amorphous, siliconlike model material. The framework developed in the present paper conceptually ties the regimes of weak and strong interfacial adhesion together and can explain that even unlubricated sliding contacts do not necessarily lead to catastrophic wear rates. A salient result of the present paper is an analytical expression of a critical length scale, which incorporates interface properties and roughness parameters. Therefore, our findings provide a theoretical framework and a quantitative map to predict deformation mechanisms at individual contacts. In particular, contact junctions of sizes above the critical length scale contribute to the debris formation.

Role of Adhesion Stress in Controlling Transition between Plastic, Grinding and Breakaway Regimes of Adhesive Wear

“…The fundamental consequence of the relation (1) is that the condition for changing the mode of wear is not determined by the absolute value of specific attractive force σ 0 , but by the ratio of this force to the shear strength of the material. This result differs from the criterion obtained by Aghababaei et al 6 but is consistent with a later study 14 . The physical reason for this discrepancy may be the following: While the Rabinowicz-Aghababaei criterion 4-7 considers the competition of the plasticity in the contact plane and separation in the region of stress concentration, our criterion considers the competition of plasticity and cracking directly in the region of a possible initial crack.…”

“…Using the developed model, we numerically studied the basic modes of asperities deformation and fracture including slipping, grinding/attrition, fragmentation, wear particle formation. The observed modes of interaction of asperities and involved mechanisms of asperity wear well agree with those reported for nanoscale asperities 8,14 . Two dimensionless parameters have been identified as especially important in determining the character of wear.…”

“…The described factors generally facilitate a shear band formation in a contact zone. A similar effect for nanoscale asperities was extensively studied by molecular dynamics simulations 8,14,15 . Thus, the higher the attractive force σ 0 the stronger is the tendency for strain localization and shear bands formation.…”

“…The competition of plasticity and cracking at the same place (but in different planes) is well known both in molecular dynamics simulations and at the macroscale (as Orowan criterion). In a recent work by Brink and Molinari 14 , it was shown by direct three-dimensional quasi-molecular simulations that under some conditions the transition from one to another wear mode becomes "size insensitive".…”

Regimes of adhesive wear in dry contact: Conditions of realization and determining parameters

“…In recent years, great progress has been made thanks to molecular-dynamic modeling in understanding the characteristics of adhesive wear of plastic and brittle materials with nanoscale asperity [8,9]. Despite the importance of atomistic modeling [10,11] for understanding nanoscale wear mechanisms, direct transfer of the obtained results to higher scales is difficult, because on these scales the values of the mechanical characteristics that determine the plasticity and strength of the material significantly depend on the characteristics of the internal structure.…”