Modelling of the Asperity Contact Area on Actual 3D Surfaces 2005-01-1864

The Greenwood model has been extensively used for calculation of the asperity pressures under mixed lubrication conditions, but usually assuming that the surfaces are gaussian. In this work, the Greenwood parameters are calculated from actual, non-gaussian, engine surfaces measured by White Light Interferometer. Results from 2D profiles and 3D measurements are compared. An improved way to calculate the Greenwood parameters and to apply them for estimation of the contact area and pressure is described. To illustrate the methodology, some examples of topography characterization and modeling for engine liners are presented. The influence of the asperity summit height average on the predicted contact area calculation is discussed.

To explore and validate the proposed method, several WLI measurements from different engine HDD liners were analyzed using a proprietary code. For each surface, the bearing contact area against a flat plane was calculated for different surface separations, e.g. 0.5 to 3.0 micrometer. The values were then compared with those predicted by the Greenwood model using the calculated asperity summit distribution. With the corrections proposed the correlation was very good. The contact area, and the resultant asperity pressure, were significantly higher than the values usually predicted by commercial codes.