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Quantitative characterization of micro-topography a bibliography of industrial surface metrology

Surface roughness and/or surface imperfections are well known to significantly affect the performance of concentrated contacts. Any deviation from the smooth surface will act as a stress raiser for itself (bump) or of its neighborhood (dent), and will therefore reduce the fatigue life of the component it is part of. These imperfections can also act as initiation sites of other types of contact failure such as scuffing, when contact conditions such as load, speed and film thickness become more and more severe. With the help of increasing computer speeds and more efficient numerical techniques, a theoretical analysis of the failure of concentrated contacts becomes possible. The full answer will involve many aspects of the contact, including the generation of heat, thermal response of the lubricant and solids, non-Newtonian as well as surface chemistry effects. This paper concentrates on the way the lubricant film thickness is affected by waviness and tries to identify the locations and the conditions where the film thickness is minimal. The lubrication ofnonsmooth surfaces is a transient two-dimensional problem, which will be treated without any geometrical simplification. More precisely, this paper focuses on the influence of rolling speed and the slide-to-roll ratio on the film thickness separating a smooth surface and one with transverse waviness.

Numerical Analysis of the Influence of Waviness on the Film Thickness of a Circular EHL Contact

The effect of surface texture on EHL point contact is studied numerically by using the multigrid method. Numerical simulations have been performed for waviness and random roughness with three different orientations, transverse, oblique and longitudinal. Results reveal a strong domination of unidirectional Couette flow in the EHL conjunction. The geometrical variations at inlet of the contact are transported downstream throughout the EHL conjunction. As a consequence, the oblique surface roughness striations are largely distorted, forming nearly longitudinal wary passages. Results show that the oblique roughness induces local three dimensional EHL pressure fluctuations. The maximum pressure is higher than that of the transverse roughness. For sinusoidal waviness, oblique orientation gives the smallest minimum film thickness as compared with those of longitudinal and transverse waviness.

The effects of surface texture on EHL point contacts

The problem of surface waviness in ElastoHydrodynamic Lubrication is commonly considered as a first step towards understanding the lubrication of rough surfaces. Both problems are generally transient. The current paper investigates the deformation of sinusoidal waviness in the contact, more precisely it studies the amplitude reduction of one-sided waviness in a transient EHL line contact. The film thickness amplitude at X = 0 is called A d (deformed amplitude). It is shown that for waviness amplitudes smaller than the film thickness A i H c , the ratio A d / A i is independent of the undeformed amplitude A i . In other words: for small amplitudes the deformed amplitude depends linearly on the initial amplitude A i . Rather surprisingly, the same behaviour is found for A i > H c . The results show that qualitatively waviness with short wavelengths λ/ b A d ≃ A i . Long wavelengths on the contrary, disappear nearly completely: A d ≪ A i thus A d / A i ≃ 0. However, quantitatively the amplitude reduction was found to depend also on the contact operating conditions. With a generalized coordinate ∇, instead of λ/ b , the relative amplitude A d / A i can be described by a single function of ∇ for all operating conditions: A d / A i = F (∇),∀( M, L ). A possible way of expressing ∇ is:∇ = λ/ bM 3/4 / L 1/2 .

Amplitude Reduction of Waviness in Transient EHL Line Contacts

Surface roughness plays an important role in ElastoHydrodynamically Lubricated contacts, a role which is currently only partially understood. Recent work on waviness in EHL line contacts has shown and quantified the elastic deformation of the waviness inside the contact as a function of a single dimensionless parameter. In the present paper this work is extended to the circular contact problem. First it is shown that the amplitude reduction of an isotropic harmonic pattern can also be described as a function of a single dimensionless parameter. Subsequently, the effects of anisotropy are investigated varying from purely transverse to purely longitudinal. It is shown that one can create a single curve for the case varying from isotropic to longitudinal, and another for the case varying from isotropic to transverse. Both curves can be combined in a single formula.

R.D. Gibson

Papers

The effect of surface roughness in elastohydrodynamic lubrication

Surface roughness effects in point contact elastohydrodynamic lubrication