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Modeling and simulation in tribology across scales: An overview

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Contact Mechanics In Tribology

Mechanics of axisymmetric adhesive contact of rough surfaces involving power-law graded materials

This paper is devoted to an analytical, numerical, and experimental analysis of adhesive contacts subjected to tangential motion. In particular, it addresses the phenomenon of instable, jerky movement of the boundary of the adhesive contact zone and its dependence on the surface roughness. We argue that the “adhesion instabilities” with instable movements of the contact boundary cause energy dissipation similarly to the elastic instabilities mechanism. This leads to different effective works of adhesion when the contact area expands and contracts. This effect is interpreted in terms of “friction” to the movement of the contact boundary. We consider two main contributions to friction: (a) boundary line contribution and (b) area contribution. In normal and rolling contacts, the only contribution is due to the boundary friction, while in sliding both contributions may be present. The boundary contribution prevails in very small, smooth, and hard contacts (as e.g., diamond-like-carbon (DLC) coatings), while the area contribution is prevailing in large soft contacts. Simulations suggest that the friction due to adhesion instabilities is governed by “Johnson parameter”. Experiments suggest that for soft bodies like rubber, the stresses in the contact area can be characterized by a constant critical value. Experiments were carried out using a setup allowing for observing the contact area with a camera placed under a soft transparent rubber layer. Soft contacts show a great variety of instabilities when sliding with low velocity — depending on the indentation depth and the shape of the contacting bodies. These instabilities can be classified as “microscopic” caused by the roughness or chemical inhomogeneity of the surfaces and “macroscopic” which appear also in smooth contacts. The latter may be related to interface waves which are observed in large contacts or at small indentation depths. Numerical simulations were performed using the Boundary Element Method (BEM).

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Adhesion and friction in hard and soft contacts: theory and experiment

In this study, models are proposed to analyze the combined effect of surface microgeometry and adhesion on the load–distance dependence and energy dissipation in an approach–separation cycle, as well as on the formation and rupture of adhesive bridges during friction. The models are based on the Maugis–Dugdale approximation in normal and frictional (sliding and rolling) contacts of elastic bodies with regular surface relief. For the normal adhesive contact of surfaces with regular relief, an analytical solution, which takes into account the mutual effect of asperities, is presented. The contribution of adhesive hysteresis into the sliding and rolling friction forces is calculated for various values of nominal pressure, parameters of microgeometry, and adhesion.

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Combined effect of surface microgeometry and adhesion in normal and sliding contacts of elastic bodies

Solutions of two three-dimensional contact problems for a linearly viscoelastic foundation in sliding contact with a separate indenter and a periodic wavy surface taking into account adhesion are p...

Adhesion effect in sliding of a periodic surface and an individual indenter upon a viscoelastic base

A model of the adhesive component of the sliding friction force

A model for calculating the sliding friction force between a surface with regular relief and a viscoelastic foundation in dry conditions is suggested. The Winkler type viscoelastic foundation with both normal and tangential compliances is considered. The local Coulomb friction law is assumed between the surfaces. The total friction is calculated including the contribution of both local adhesive friction and hysteretic losses in the viscoelastic material when elements of the surface relief cyclically deform the material during sliding. The contact problem is solved by the strip method in which the area of interaction is divided into strips parallel to the direction of sliding, and a 2D contact problem is solved in each strip in the closed form. Two types of periodic profile of the moving surface are considered—a profile with trapezoidal asperities and a doubly periodic sinusoidal profile. The model is applied to analyze the influence of the parameters of surface relief on the coefficient of sliding friction for various values of external load and sliding velocity.

Effect of surface relief on sliding friction of viscoelastic bodies

A model is proposed to describe the steady-state regime of wear for a fibrous composite material in contact with a rigid counter body. The composite material is modeled by an elastic half-space with embedded elastic fibers arranged parallel to each other and distributed uniformly. The fibers hardness is assumed to be different from that of the matrix, whereas their elastic moduli are equal. Analytic relations are obtained, and analysis is performed for the characteristics of wear (worn surface shape, effective wear rate, contact pressure distribution) depending on the composite structure parameters such as fiber size and density, relative hardness of the matrix and fibers. In particular, it is shown that the effective wear rate as a function of the fiber density increases if the fibers are harder than the matrix and decreases in the opposite case. The results obtained can be used to control the wear resistance of fibrous composites by choosing appropriate microstructure parameters.

Yulia Makhovskaya

Papers

Combined effect of surface microgeometry and adhesion in normal and sliding contacts of elastic bodies

Adhesion effect in sliding of a periodic surface and an individual indenter upon a viscoelastic base

A model of the adhesive component of the sliding friction force

Effect of surface relief on sliding friction of viscoelastic bodies

Modeling of Fiber Composite Wear