An Investigation on Starvation Onset of Rough Surface Line Contacts

Utilizing a computational approach, this study quantifies the onset of lubrication starvation for line contacts of rough surfaces operating under typical ranges of automotive gearing applications. The response parameter is selected as the critical film thickness supply, at which starvation initiates. The potential influential parameters (predictors) considered include normal force density, rolling velocity, sliding, lubricant viscosity, and surface roughness amplitude. A non-Newtonian thermal mixed lubrication model is employed to determine the critical lubricant supply under various operating and surface roughness conditions. General linear regression is implemented to reach an easy-to-use equation (R-squared value higher than 97%), facilitating the quantification of starvation dependence on the predictors that are statistically significant.

Roughness-Induced Adhesive Hysteresis in Self-Affine Fractal Surfaces

It is known that in the presence of surface roughness, adhesion can lead to distinct paths of loading and unloading for the area–load and penetration–load relationships, thus causing hysteretic loss. Here, we investigate the effects that the surface roughness parameters have on such adhesive hysteresis loss. We focus on the frictionless normal contact between soft elastic bodies and, for this reason, we model adhesion according to Johnson, Kendall, and Roberts (JKR) theory. Hysteretic energy loss is found to increase linearly with the true area of contact, while the detachment force is negligibly influenced by the maximum applied load reached at the end of the loading phase. Moreover, for the micrometric roughness amplitude hrms considered in the present work, adhesion hysteresis is found to be affected by the shorter wavelengths of roughness. Specifically, hysteresis losses decrease with increasing fractal dimension and cut-off frequency of the roughness spectrum. However, we stress that a different behavior could occur in other ranges of roughness amplitude.

Cylinder-Flat Contact Mechanics with Surface Roughness

We study the nominal (ensemble averaged) contact pressure p(x) acting on a cylinder squeezed in contact with an elastic half space with random surface roughness. The contact pressure is Hertzian-like for $$\alpha < 0.01$$ α < 0.01 and Gaussian-like for $$\alpha > 10$$ α > 10 , where the dimensionless parameter $$\alpha = h_{\rm rms}/\delta $$ α = h rms / δ is the ratio between the root-mean-square roughness amplitude and the penetration for the smooth surfaces case (Hertz contact).

Extraction of series resistance and mobility degradation parameter in MOSFETs using iterative method

Series resistance and mobility attenuation parameter are parasitic phenomena that limit the scaling of advanced MOSFETs. In this work, an iterative method is proposed to extract the series resistance and mobility degradation parameter in short channel MOSFETs. It also allows us to extract the surface roughness amplitude. The principle of this method is based on the exponential model of effective mobility and the least squares methods. From these, two analytical equations are obtained to determine the series resistance and the low field mobility as function of the mobility degradation. The mobility attenuation parameter is extracted using an iterative procedure to minimize the root means squared error (RMSE) value. The results obtained by this technique for a single short channel device have shown the good agreement with measurements data at strong inversion.

Extraction of Series Resistance and Mobility Degradation in MOSFETs Using Iterative Method

Series resistance and mobility attenuation parameter are parasitic phenomena that limit the scaling of advanced MOSFETs. In this work, an iterative method is proposed to extract the series resistance and mobility degradation parameter in short channel MOSFETs. It also allows us to extract the surface roughness amplitude. The principle of this method is based on the exponential model of effective mobility and the least squares methods. From these, two analytical equations are obtained to determine the series resistance and the low field mobility as function of the mobility degradation. The mobility attenuation parameter is extracted using an iterative procedure to minimize the root means squared error (RMSE) value. The results obtained by this technique for a single short channel device have shown the good agreement with measurements data at strong inversion.

Calculation of Gear Meshing Stiffness Considering Lubrication

Gear meshing stiffness is the key parameter to study the gear dynamic performance. However, the study on the calculation of gear meshing stiffness considering lubrication, especially mixed lubrication, is still insufficient. Based on the three-dimensional linear contact mixed elastohydrodynamic lubrication model and the contact stiffness calculation method of rough surface, a method for calculating the gear meshing stiffness under mixed lubrication is proposed in this paper. According to the proposed calculation method, the effects of speed, external load, and roughness amplitude on gear meshing stiffness are further explored. The method can take into account the real rough surface topography and lubrication in the meshing process, so it may be more advantageous than the conventional method to some extent.

A note on the effect of surface topography on adhesion of hard elastic rough bodies with low surface energy

Adhesion between bodies is strongly influenced by surface roughness. In this note, we try to clarify how the statistical properties of the contacting surfaces affect the adhesion under the assumption of long-range adhesive interactions.Specifically, we show that the adhesive interactions are influenced only by the roughness amplitude hrms, while the rms surface gradient h0rmsonly affects the non-adhesive contact force. This is a remarkable result if one takes into account the intrinsic difficulty in defining $h_{\mathrm{rms}}^{^{\prime }}.$Results are also corroborated by a comparison with self-consistent numerical calculations.

Effects on lubrication characteristics of water-lubricated rubber bearings with journal tilting and surface roughness

To study the effect of surface roughness on the lubrication characteristics of water-lubricated rubber bearings (WLRBs) when the stern shaft is tilted, the surface roughness of the bearings was measured by a surface roughness measuring instrument. Considering the tilting stern shaft and surface roughness, a mathematical model was constructed and water film thickness equation was deduced. By adopting the finite difference method, the film thickness and pressure distribution of WLRBs with tilt angle and roughness were analysed. The effects of tilt angle on film thickness and pressure under different surface roughness amplitudes and wavelengths were studied, and the results were then compared with those of smooth surface bearings without tilt angle. Finally, the minimum film thickness and maximum film pressure were analysed. The results showed that when the tilt of rotor and surface roughness of bearing were considered simultaneously, the film thickness exhibited a jagged distribution in the circumferential direction and decreased gradually in the axial direction. The film pressure had slightly irregular fluctuations and a sharp pressure peak. The tilt angle and roughness reduced the minimum film thickness, and the film thickness difference increased. The film pressure increased rapidly and local pressure exhibited slight, sudden changes. The surface roughness amplitude and wavelength had a considerable influence on the water film thickness, and the roughness amplitude had a clear effect on the film pressure. As the roughness amplitude increased, the minimum film thickness gradually declined and film pressure peak fluctuation grew. As the roughness wavelength increased, the film thickness fluctuated irregularly within a certain range of magnitude, and the minimum film thickness was almost constant.