Line Contact Condition Research Articles

Effect of Shot Peening Treatment on Rolling Contact Fatigue Properties of Austempered Ductile Iron

Austempered ductile iron (ADI) has lower density and higher damping capacity compared to steel. To evaluate the applicability of ADI to electric car driving gears, rolling contact fatigue (RCF) tests were carried out using two rollers of shot peened ADI for lower rotating velocity roller mated with case hardened alloy steel for higher rotating velocity roller in gear oil lubricant. In case of line contact condition, RCF lives of ADI tend to increase by shot peening in the higher stress region, while slightly decrease in the lower stress region. On the other hand, in point contact condition, RCF life is not affected by finishing of the surface. These results suggest that surface compressive residual stresses and hardening introduced by shot peening counterbalance the harmful effects due to surface roughening. Presented at the 57th Annual Meeting in Houston, Texas May 19–23, 2002

GSD-18 EFFECT OF SURFACE MODIFIED LAYER ON ROLLING FATIGUE STRENGTH(GEAR STRENGTH AND DURABILITY)

Surface modified rollers and ball bearings were fatigue-tested under pure rolling contact conditions. Electroless Ni-P alloy plating and sulfurizing treatments were employed. Failure mode of all rollers and bearings was spalling/flaking due to subsurface cracking. Fatigue lives of both rollers and bearings were improved by surface modifications. The influence of elastic modulus of a plated layer on contact pressure and subsurface stresses was examined under line contact and point contact conditions. The contact pressure and subsurface stresses were reduced by the soft surface modified layer, especially at the edge of the contact width under the line contact condition. The conformity due to wear of the plated layer led to the reduction of the contact pressure and the subsurface stresses. The reason why the rolling fatigue strengths of surface modified rollers and bearings were higher than those of the non-coated ones would be due to the smaller contact pressure and the smaller subsurface stresses by the smaller elasticity as well as the conformity of the plated layer.

On the effects of the temperature profile approximation in thermal Newtonian solutions of elastohydrodynamic lubrication line contacts

The assumptions of a quadratic temperature profile and mean viscosity across the film, which are frequently used in the analysis of thermal elastohydrodynamic lubrication (EHL), are examined and discussed. Two different approaches for solving the thermal EHL problem are compared for line contact conditions, namely (a) a one-dimensional model based upon both the assumption of a quadratic temperature profile and the adoption of the mean physical properties across the film and (b) a two-dimensional model which includes changes in temperature and physical properties of a lubricant across the film and which takes into account the conditions of reverse flow and heat convection across the film occurring at the inlet region. A multi-grid algorithm is implemented to solve these two conditions. The temperature profile and the general solutions in the conjunction obtained in both approaches are compared. For the one-dimensional model, results reveal that temperature peaks just prior to the inlet of the conjunction. This feature is not apparent in the two-dimensional model and results in lower values in film thickness and larger frictional coefficients than in the two-dimensional model. In the high-pressure region, both equations yield almost the same mean temperature.

A general analytical solution to the problem of microelastohydrodynamic lubrication of low elastic modulus compliant bearing surfaces under line contact conditions

A general governing equation for the pressure perturbation associated with the microelastohydrodynamic lubrication action generated by asperities superimposed upon compliant bearing surfaces of low elastic modulus has been derived in this study. It has been shown that the equation derived not only governs the lubrication of the asperities superimposed upon a macroelastohydrodyn-amic contact but also the asperity lubrication of a hydrodynamic lubrication conjunction such as a parallel face seal. Analytical solutions to the governing equation have been obtained under various conditions. The main characteristics associated with the microelastohydrodynamic lubrication mechanism predicted from the present analysis have been found to be in good agreement with the full numerical solutions presented by Dowson and Jin (1, 2) for the lubrication of normal human ankle joints. Furthermore, it is pointed out that the simple analytical method developed in this study can be applied not only to a layered surface on a rigid backing, as in the natural synovial joint, but also to the more general situation of semi-infinite solids with low elastic modulus.

Semi-Analytical Modeling of Crack Initiation Dominant Contact Fatigue Life for Roller Bearings

The fatigue test of a needle roller bearing suggests that the dominant failure mechanism is subsurface crack initiation and propagation. Therefore, a new semi-analytical contact fatigue model is derived from a micromechanics based crack initiation model. The analysis indicates that in the life calculation the selection of the critical stress, such as the maximum orthogonal shear stress, maximum shear stress, octahedral shear stress, or von Mises equivalent stress, becomes arbitrary under the nonfrictional Hertzian line contact condition. The fatigue life of roller bearings under the pure rolling condition can be predicted by simply knowing the Hertzian contact pressure and the contact width, which avoids complicated calculation of the subsurface stresses. The film thickness, roughness, and the material hardness effects on contact fatigue are also included in the new model. The comparisons with different models and the experimental data indicate that the new model makes similar life predictions as the Ioannides-Harris model, but the new model is much simpler to use. The Lundberg-Palmgren model does not fit with the experiment data.

Computation of fatigue strength in case-hardened cylindrical components using the local fatigue strength concept: [Berechnung der Dauerschwingfestigkeit Einsatzgeharteter Zylindrischer Korper mit dem Konzept der Lokalen Dauerfestigkeit]. Kuttner, T. and Zieger, H. Harterei-Technische Mitteilungen (Nov.–Dec. 1992) 47 (6), 367–375 (in German)

Rolling contact fatigue (RCF) regularly causes mechanical components to fail under cyclic loads. Popular surface treatment processes such as case hardening (carburization), nitriding and tempered martensitic reduce the effect of RCF damage. This paper presents multi-stage S-N curve for steels with different surface treatments, under point and line contact conditions using RCF tribometers for the experiments and finite element (FEM) simulation to simulate localised stresses in the contacts. Additionally, S-N tests with 0, 5 and 11% slide to roll ratio (SRR) are presented. This work demonstrates the importance of testing key points at RCF S-N curves to optimize the hardened layers.

Studies on the Traction Coefficient in Partial Elastohydrodynamic Lubrication.

A simplified method for numerical calculation of the traction in partial elastohydrodynamic lubrication (EHL) was proposed. There was a clear difference between the calculated results of the rheology model and the experimental results in partial EHL, the rheology model is an effective method for numerical calculation of the traction in full EHL. In this paper, a successful method for numerical calculation of the traction in partial EHL was proposed. The points of this method are very simple, and express the partial EHL traction coefficient by two factors of asperity interactions and full EHL actions. We used this method for numerical calculation and obtained satisfactory results, and could explain the effect which the surface roughness and difference between line and point contact condition exerted.

Hybrid Transducer Type Ultrasonic Linear Motor Using Flexural Vibrator

Reduction of the size and weight of a hybrid transducer type ultrasonic motor without increase of the resonance frequency was accomplished by using a flexural vibrator in place of a driving vibrator. The contact parts of the transducer were fabricated so that they achieved a line contact condition to a guide rail. The maximum speed and maximum output force were 47 cm/s and 140 gf.

Effects of Lubricant Rheology and Kinematic Conditions on Micro-Elastohydrodynamic Lubrication

The effects of lubricant rheology and surface kinematic conditions on micro-elastohydrodynamic (EHD) lubrication are analyzed under isothermal line-contact conditions. Micro-EHD lubrication is modeled by introducing a surface irregularity in the form of an asperity or a furrow into the contact zone. Under simple sliding conditions, the pressure generated in the vicinity of the irregularity and the resulting surface deformation depend strongly on the lubricant rheology. The surface kinematic conditions have profound effects on micro-EHD lubrication. In general, a stationary surface irregularity produces a relatively strong downstream effect when it is in the inlet region of the contact, and a moving surface irregularity produces a relatively strong upstream effect after it enters the Hertzian central region. The simulated results agree qualitatively with previous experimental measurements and observations.

Speed effects on the dry and lubricated wear of polymers

The influence of speed on the friction and wear of polyphenylene oxide (PPO), polyetheretherketone (PEEK) and polytetrafluoroethylene (PTFE) has been determined in two sliding configurations under both dry and lubricated conditions. With a line-contact geometry, the effects of debris aggregation on wear play a more important role than with a distributed contact. In lubricated conditions, using polydimethyl siloxane fluids, contributions to load support in both sliding configurations appear to persist down to very low speeds of sliding (about 10 −3 m s −1) and no clear regime of “boundary lubrication” can be identified. With PPO in line-contact conditions there is a “dwell period” in which lubrication persists following the removal of excess fluid from the contact, and this is shown to result from the formation of an aggregated layer of plasticized wear debris on the polymer surface. There is no such dwell period, however, for PPO sliding in distributed-contact conditions or for PEEK and PTFE in either contact configuration.

Etched-pocket, dry-bearing materials

Novel, dry-bearing materials have been fabricated by photo-etching an array of very small, blind holes in metal surfaces and filling them with solid lubricant formulations. Friction and wear were assessed against a tool-steel counterface in reciprocating line-contact conditions. Preliminary experiments demonstrated feasibility with a range of substrates (bronze, steel, cobalt alloy) and lubricants (PTFE + Pb, MoS 2 + polyimide). Detailed studies were made with different copper alloys to examine the effects of substrate hardness and the distribution, size, spacing and depth of the etched pockets. BeCu containing PTFE + Pb exhibits wear lives over a range of stresses (Hertzian) to 375 MPa which are appreciably longer than those of a porous bronze composite containing the same lubricant. Wear rates of etched Be-Cu are also much lower than those of a typical, woven PTFE fibre-type of dry-bearing composite. Wear life is not, in general, limited by the depth of the etched pockets and several failure mechanisms have been identified.

The Influence of Polydimethyl Siloxane on the Friction and Wear of Polyphenylene Oxide Under Boundary Lubrication Conditions

Experiments are described in which polyphenylene oxide (PPO) specimens were first slid against EN31 steel in the presence of polydimethyl siloxane (silicone fluid) and then slid without any external injection of silicone fluid until the friction reached the value characteristic of dry conditions. Nominal Hertzian line-contact conditions were maintained throughout each experiment (despite the wear of the PPO) by slowly rotating the PPO pin about its cylindrical axis while its flat end-face was itself sliding against the cylindrical surface of the EN31 steel cylinder, thereby maximizing the possibility of true boundary lubrication. These experiments showed that the modified surface layer produced during sliding in silicone fluid is the result of adsorption of the fluid into the polymer and that absorption is primarily a consequence of the wear process itself. Electron probe microanalysis and Rutherford back-scattering of α-particles were used to examine the worn polymer surfaces to show that some migration ...

The mechanical wear of metals

The design of fundamental experiments for examining the wear phenomena encountered in the conditions of speed and loading of industrial machines is discussed. Apparatus is described in which nominal point or nominal line contact can be maintained indefinitely, and some of the phenomena observed when a lubricant is used are discussed. With carefully run-in specimens, the hydrodynamic condition of lubrication is maintained up to very heavy loads; a method of measuring the thickness of the oil film in line contact conditions is outlined and some results given. In unlubricated conditions the phenomena of wear can be studied using simpler equipment. The main phenomena, the laws and the mechanisms of wear in unlubricated conditions are discussed, and the present state of development of theories of wear is outlined. In conclusion, some suggestions are made about the directions in which fundamental studies of wear need to be pursued.