Deformation due to contact between a rough surface and a smooth ball

Theoretical and experimental results are presented to evaluate the deformation behavior of the contact between a real rough flat surface and a smooth ball. There are three deformation responses: plastic deformation of the asperities only, plastic deformation of the bulk only and combined plastic deformation of both the asperities and the bulk. The effects of the surface roughness and the Hertzian contact parameters on the effective contact pressure are presented. The experimental results confirmed the theoretical prediction very well. For a given Hertzian contact situation the surface roughness plays an important role in controlling the deformation behavior of the contacting surfaces. A criterion is presented to predict the deformation behavior of contacting engineering surfaces

Existence of a tribo-modified surface layer of BR/S-SBR elastomers reinforced with silica or carbon black

The existence of a modified surface layer on top of a rubber disk, in contact with a rigid counter-surface, is still a point of discussion. In this study, we show that a modified surface layer with different mechanical properties exists. Modification of the reinforced elastomers is discussed and the subsequent effect of existence of such a layer on the friction is emphasized. The elasticity modulus both inside and outside the wear track is determined by atomic force microscope nano-indentations and compared with the macroscale mechanical properties measured using dynamical mechanical analysis. The elastic modulus inside the wear track is lower than the bulk. Intensifying the tribological conditions by means of increasing normal pressure and sliding velocity will result in a greater loss of mechanical propertie

Application of deterministic contact model to analyze the contact of rough surface against a flat layered surface

In this paper, a rough surface is modeled as an array of asperities represented by spheres with different radii and heights to be able to calculate the deformation (elastic, elastic-plastic, and plastic) at each asperity in contact. The total contact area and the total load carried are calculated by summarizing respectively the contact area and the load carried by each individual asperity (deterministic model). This model will diminish the assumption of an average asperity radius and enable one to calculate the contact of non-Gaussian surface more precisely. Further, in this paper, the deterministic model is used to analyze the contact behavior of a rough surface against a flat layered surface by modeling the flat layered surface as a solid that has effective mechanical properties as a function of indentation depth

Running-In of Systems Protected by Additive-Rich Oils

Recent research on mild wearing systems running under boundary lubrication conditions focus more and more on the role of the nano-crystalline layer present at the surface of the components in contact. This layer has a typical thickness of a few tenths of nano-meters up to a few microns depending on the operational conditions. The role of this layer with respect to wear is, however, still unclear as well as its mechanical behavior. In this study, a first step is made in incorporating this type of layer into a wear model. Using an elasto-plastic semi-analytical-method the effect of different material behaviors reported through out current literature for the nano-crystalline layer on wear is studied. From the results it can be concluded that the effect of this mechanically altered layer has an important influence on the wear of the system, especially during the initial phase of running

Mild wear prediction of boundary lubricated contacts

In this paper, a wear model is introduced for the mild wear present in boundary-lubricated systems protected by additive-rich lubricants. The model is based on the hypothesis that the mild wear is mainly originating from the removal of the sacrificial layer formed by a chemical reaction between the base material and the additive packages present in the lubricant. By removing a part of this layer, the chemical balance of the system is disturbed and the system will try to restore the balance for which it uses base material. In this study, mechanical properties reported throughout literature are included into the wear model based on observed phenomena for this type of systems. The model is validated by model experiments and the results are in very good agreement, suggesting that the model is able to simulate wear having a predictive nature rather than on empirical-based relationships as Archard’s linear wear model. Also a proposal is made to include the transition from mild to severe wear into the model creating a complete wear map

Friction regimes in the lubricants solid-state regime

Friction measurements were performed in the lubricant's solid-state regime to study the transition from full-film lubrication, in which the separation is maintained by a solidified lubricant, to mixed lubrication. Special attention is paid to the influence of temperature (inlet viscosity) and roughness on this transition.\ud \ud The friction measurements showed that in the lubricants solid-state region three lubrication modes can be distinguished: A) full-film lubrication; separation is maintained by a solid film (S-EHL), B) mixed lubrication (ML); the load is carried by the interacting asperities as well as the lubricant (acting like a solid or as a liquid) and C) boundary lubrication (BL). Further, the dependency of the transition S-EHL to ML on temperature (inlet viscosity) depends on the lubricant used. The transition S-EHL to ML depends slightly more on roughness as found for L-EHL to ML transition. Finally, the film thickness formulas developed for EHL contacts in which the lubricant behaves as a liquid become doubtful when operating in the lubricant solid-state regime. This on the basis of the calculated film thickness over roughness ratios for the transition S-EHL to ML

Friction Reduction in Lubricated-MEMS with Complex Slip Surface Pattern

AbstractMany types of micro-electro-mechanical-system (MEMS) based products are currently employed in a variety of applications. However, high friction in these systems is a problem which limits the development of MEMS devices in which sliding contacts are involved. The aim of this research is to evaluate the effect of boundary slip on the hydrodynamic friction in a low load lubricated MEMS, in particular when boundary slip takes places in the certain region of the lubricated sliding contact, i.e. complex slip surface pattern. The effectiveness of the boundary slip in reducing friction is highlighted. The results indicate that the deterministic complex slip pattern has a beneficial effect on decreasing friction