Motohiro Kaneta

Mechanism of Crack Growth in Lubricated Rolling/Sliding Contact

In order to explain the mechanism of rolling-contact fatigue crack growth analytically, fracture mechanics are applied to a semicircular surface crack inclined at an angle to the elastic half-space loaded by Hertzian stresses. It is shown that the surface traction is the controlling factor for lubricant seepage into the crack and for shear mode crack growth rate. It is also clarified that the generation of pits results from tensile mode crack growth mainly due to the oil hydraulic pressure action.

Effects of Surface Roughness on Point Contact EHL

The effects of orientation of surface roughness, entrainment (rolling) velocity, and slide/roll ratio on micro-elastohydrodynamic lubrication (micro-EHL) are investigated under pointcontact conditions using the optical interferometry technique. Long bumps with constant height and wavelength produced artificially on the surface of a highly polished steel ball are used as a model roughness. It is shown that the asperities are elastically deformed and the magnitude depends on the film factor A, defined by the ratio of the central film thickness based on smooth surfaces to the composite surface roughness, as well as the surface kinematic conditions and the orientation of the asperities. It is also found that a thin or thick oil film formed at the inlet of the contact by a moving rough surface travels through the contact region at a speed very close to the average speed of the contacting surfaces. The possible mechanism is discussed.

Optical Interferometric Observations of the Effects of a Bump on Point Contact EHL

The effects of surface kinematic conditions on micro-elastohydrodynamic lubrication (micro-EHL) are investigated under rolling and/or sliding point contact conditions using the optical interferometry technique. A long bump of chromium sputtered on the surface of a highly polished ball is used as a model asperity. It is shown that the film thickness distribution or the elastic deformation of the bump is influenced significantly by the surface kinematic conditions and the orientation of the bump

Analysis of Surface Crack Propagation in Lubricated Rolling Contact

Growth behavior of surface cracks formed on lubricated rolling-sliding contact surfaces is studied by calculating three-dimensional mixed-mode stress intensity factors KI, KII, and KIII. It is shown from the viewpoint of the fatigue crack propagation that the hydraulic pressure effect pointed out by Way may be accepted as a possible mechanism of surface crack growth. Some of the experimental facts on pitting are also confirmed qualitatively.

Abnormal Phenomena Appearing in EHL Contacts

In a previous paper the authors showed that when the surface velocity of a body having lower elastic modulus is faster than that of a body having higher elastic modulus, and when the radius of curvature of the former is larger than that of the latter, a deep conical depression (dimple) is produced in the contact surface. This dimple occurs in place of the flat plateau predicted by the point contact elastohydrodynamic lubrication (EHL) theory. In this paper, the effects of surface kinematic conditions on the formation of such abnormal phenomena, which cannot be predicted by the present EHL theory, are investigated under rolling/sliding conditions using the optical interferometry technique. Transient behavior of the dimple caused by a groove passing through the EHL conjunction is also discussed based on direct observations. It has been found that the dimple occurs when the lubricating oil in the contact area is composed of solidified and unsolidified parts, and the dimple itself corresponds to the solidified part. On the basis of this finding, it has been asserted that the establishment of a new EHL theory is needed.

Formation of Steady Dimples in Point TEHL Contacts

Experimental results of steady dimples measured in elliptical glass-steel contact under pure sliding conditions are presented. It is found that two dimples connected with a shallower furrow are generated, each near an end of the major radius of the contact ellipse. The complete solution of the corresponding thermal elastohydrodynamic lubrication (TEHL) problem is calculated numerically. Good agreement is obtained between the experimental and theoretical results. This agreement can be explained by the temperature-viscosity wedge mechanism, Correctness of this mechanism is demonstrated using additional experiments with ceramic balls in contact with glass and sapphire disks.

Effects of oil hydraulic pressure on surface crack growth in rolling/sliding contact

Abstract Rolling/sliding contact fatigue tests were conducted using a pair of transparent discs containing a hole or a surface crack produced artificially on the disc surface. The crack initiation from the hole or the growth of the surface crack were compared with predictions by numerical analyses based on fracture mechanics. Experiments and analyses showed that Ways hypothesis on pitting should be accepted as a plausible mechanism. The experimental results verified several important theoretical predictions on crack growth under rolling and/or contact conditions.

Observation of wall slip in elastohydrodynamic lubrication

A new experimental technique using optical interferometry has been developed to obtain a direct indication of non-Newtonian response of an oil film under conditions of elastohydrodynamic (EHD) lubrication. A glass disk or a steel ball has been driven by a stepping motor so that crescent-shaped thick oil films with undulation in thickness along the direction of motion have been generated. The experiments have been carried out under pure rolling and pure sliding conditions. It has been found that the oil in an EHD contact behaves like a solid and slips at or near the contact surfaces.

Non-Newtonian Thermal Analyses of Point EHL Contacts Using the Eyring Model

A non-Newtonian numerical solution system for the thermal elastohydrodynamic lubrication (EHL) problems in point contacts has been developed. The Eyring rheology model has been used to describe the non-Newtonian flow of the lubricant. An effective viscosity has been defined for the Eyring fluid. The Newtonian solver can be applied easily to the non-Newtonian problems when the viscosity of the Newtonian fluid is replaced by the effective viscosity. A novel technique for the determination of the effective viscosity is proposed. Numerical solutions for the conventional point contact and normally crossing cylinders contact problems are presented and the effects of the entraining velocity, the load, the slide-roll ratio, and the characteristic shear stress of the Eyring fluid on the lubricating performance are discussed. The results indicate that the non-Newtonian thermal EHL theory predicts more realistic film temperatures and traction coefficients.

Optical Interferometric Observations of the Effects of a Moving Dent on Point Contact EHL

In 1979, Wedeven and Cusano [1] observed very interesting feature concerning EHL film which was influenced by a moving dent. That is, if the dent is on the faster moving surface, the film shape upstream of the dent is influenced by the dent. Ai and Cheng [2] solved numerically this problem using the multigrid method, and pointed out that the dent is extended in the direction of sliding with a rate approximately equal to the sliding velocity, resulting in the pressure increase at the edge of the dent in the direction of sliding. The present study offers more detail experimental results, by duochromatic optical interferometry, concerning the effects of a moving dent on EHL films.