Abstract
Machine downsizing, increased loading and better sealing performance have progressively led to thinner lubricant films and an increased chance of direct surface interaction. Consequently, mixed and boundary regimes of lubrication are prevalent with ubiquitous asperity interactions, leading to increased parasitic losses and poor energy inefficiency. Surface topography has become an important consideration as it influences the prevailing regime of lubrication. As a result a plethora of machining processes and surface finishing techniques have emerged. The stochastic nature of the resulting topography determines the separation at which asperity interactions are initiated and ultimately affect the conjunctional load carrying capacity and operational efficiency. The paper presents a procedure for modelling of asperity interactions of real rough surfaces, from measured data, which do not conform to the usually assumed Gaussian distributions. The model is validated experimentally using a bench top reciprocating sliding test rig. The method demonstrates accurate determination of the onset of mixed regime of lubrication. In this manner, realistic predictions are made for load carrying and frictional performance in real applications where commonly used Gaussian distributions can lead to anomalous predictions.
Highlights
A sufficiently thick low shear strength film of lubricant is usually desired to form in all contact conjunctions to carry the applied load and guard against the direct interaction of asperities on the opposing surfaces, reducing frictional losses
It can be seen from the convolution of the peak height distributions (Fig. 5a) that there are significantly more asperities above the centre-line than would be predicted by a Gaussian distribution with a mean of 0
This is in part due to the increased proportion of asperities in the higher regions of the surface for the case of surface specific data
Summary
A sufficiently thick low shear strength film of lubricant is usually desired to form in all contact conjunctions to carry the applied load and guard against the direct interaction of asperities on the opposing surfaces, reducing frictional losses. Many contacts suffer from a Meccanica lack of a coherent lubricant film where a proportion of applied load is carried by the ubiquitous asperities on the counterface surfaces These interactions increase the generated friction, for example in the cases of piston-cylinder system at dead centre reversals [5,6,7,8] and cam-follower contact in the inlet reversal positions [9]. Consideration of typical rough surfaces suggests that a peak height distribution would have a mean value above the mid-line of the surface as the majority of the peaks would reside in the upper reaches of the surface It is, advantageous to develop an asperity model which allows more representative peak height distributions to be utilised, for lubricated contacts which were not discussed by Greenwood and Tripp [10]. The original Greenwood and Tripp model [10] has been widely used in many applications [18,19,20,21]
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