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

Abstract

A discrete-element based model of elastic-plastic materials with non-ideal plasticity and with an account of both cohesive and adhesive interactions inside the material is developed and verified. Based on this model, a detailed study of factors controlling the modes of adhesive wear is performed. Depending on the material and loading parameters, we observed three main modes of wear: slipping, plastic grinding, cleavage, and breakaway. We find that occurrence of a particular mode is determined by the combination of two dimensionless material parameters: (1) the ratio of the adhesive stress to the pure shear strength of the material, and (2) sensitivity parameter of material shear strength to local pressure. the case study map of asperity wear modes in the space of these parameters has been constructed. Results of this study further develop the findings of the widely discussed studies by the groups of J.-f. Molinari and L. pastewka.Adhesive wear is a complex, multiscale and still poorly understood phenomenon 1-3 . This kind of wear occurs in contact pairs where materials of interacting bodies are characterized by equal or similar values of hardness with the possible transfer of material from one surface to the opposite one. Since the publication of Rabinowicz from 1958 4 , it is known that adhesive wear is controlled by the relation of material parameters including elastic modulus, hardness and specific surface energy 4,5 . In a series of recent works by Aghababaei, Molinari et al., it was shown that adhesive wear may develop in two ways: 1) formation and evolution (growth or fragmentation) of wear particles or 2) plastic deformation of micro contacts accompanied by smoothing of asperities 6,7 . These studies together with works by other research groups 8-11 created a solid basis for a theoretical understanding of wear modes and opened possibilities for a new interpretation of classical concepts. In particular, the adhesive wear mode criterion by Rabinowicz was critically revised and details were disclosed of how the wear process occurs in both regimes of debris formation and plastic smoothing.The above mentioned fundamental results revealing the features of asperity fracture and wear were obtained using pseudo molecular dynamics (MD) simulation at the mesoscale, so the question remained whether these conclusions are universal and applicable to real materials. A particular problem of meso MD models consists in the difficulty of separating the plastic and adhesive properties of material as in meso molecular dynamics both of them are determined by the same interaction potential. On the mesoscopic scale, it may be necessary, firstly, to decouple strength from adhesion parameters of the material and, secondly to take into account more complex material properties such as yield stress and strain hardening, both strongly dependent on features of internal structure at lower scales (grain structure, grain boundaries, inclusions of other phases, etc.). This substantiates the need for a detailed theoretical analysis of wear r...

Particle-Based Approach for Simulation of Nonlinear Material Behavior in Contact Zones

“…We have built the qualitative map of asperity wear regimes in terms of dimensionless material parameters σ 0 /σ j and a [46]. Figure 3 shows a rough schematic representation of this classification of wear regimes, which agrees with the results of atomistic studies by other researchers, supplements and generalizes them to higher scales of surface roughness.…”

“…For larger asperities L/d > 10 4 , the results of the analysis of the wear regimes are scale invariant under the condition of scale invariance of the mechanical characteristics of the material. The coefficient α is close to 1 for highly ductile materials and about 0.5-0.6 for brittle materials α = σ * 0 /σ j [46].…”

“…The main result of the study is that we revealed and substantiated two dimensionless material parameters that control the regime of asperity wear [46].…”

“…However, in many real systems, the adhesion of surfaces is an important factor determining the laws of friction and wear [45]. To adequately model the adhesive contact of surfaces, we assume attractive normal force acting between elements even after they are debonded [46,47]. This force varies with separation of the surfaces of interacting elements according to prescribed model of adhesion (Dugdale's, Van-der-Vaals or other interaction potential).…”

A Discrete Element Formalism for Modelling Wear Particle Formation in Contact Between Sliding Metals

“…This formulation makes it possible to implement models of the mechanical behavior of materials with complex rheological properties (including elastic-plastic) [35], as well as to take into account surface adhesion. Using these models, the basic modes of deformation and fracture of initial mesoscopic asperities were systematically analyzed for the first time and the influence of surface adhesion and macroscopic material properties was generalized [36,37].…”