Showing papers in "Journal of Tribology-transactions of The Asme in 1998"

The Role of Interstitial Fluid Pressurization and Surface Porosities on the Boundary Friction of Articular Cartilage

Abstract: Articular cartilage is the remarkable bearing material of diarthrodial joints. Experimental measurements of its friction coefficient under various configurations have demonstrated that it is load-dependent, velocity-dependent, and time-dependent, and it can vary from values as low as 0.002 to as high as 0.3 or greater. Yet, many studies have suggested that these frictional properties are not dependent upon the viscosity of synovial fluid. In this paper, a theoretical formulation of a boundary friction modelfor articular cartilage is described and verified directly against experimental results in the configuration of confined compression stress-relaxation. The mathematical formulation of the friction model can potentially explain many of the experimentally observed frictional responses in relation to the pressurization of the interstitial fluid inside cartilage during joint loading, and the equilibrium friction coefficient which prevails in the absence of such pressurization. In this proposed model, it is also hypothesized that surface porosities play a role in the regulation of the frictional response of cartilage. The good agreement between theoretical predictions and experimental results of this study provide support for the proposed boundary friction formulation.

Film Thickness in Starved EHL Point Contacts

Abstract: This paper presents a numerical study of the effects of inlet supply starvation on film thickness in EHL point contacts. Generally this problem is treated using the position of the inlet meniscus as the governing parameter; however, it is difficult to measure this in real applications. Thus, in this paper an alternative approach is adopted whereby the amount of oil present on the surfaces is used to define the degree of starvation. It is this property which determines both meniscus position and film thickness reduction. The effect of subsequent overrollings on film thickness decay can also be evaluated. In the simplest case a constant lubricant inlet film thickness in the Y direction is assumed and the film thickness distribution is computed as a function of the oil available. This yields an equation predicting the film thickness reduction, with respect to the fully flooded value, from the amount of lubricant initially available on the surface, as a function of the number of overrollings n. However, the constant inlet film thickness does not give a realistic description of starvation for all conditions. Some experimental studies show that the combination of side flow and replenishment action can generate large differences in local oil supply and that the side reservoirs play an important role in this replenishment mechanism. Thus the contact centre can be fully starved whilst the contact sides remain well lubricated. In these cases, a complete analysis with a realistic inlet distribution has been carried out and the numerical results agree well with experimental findings.

A new principle in contact mechanics

Abstract: Two nonrotating elastic half-planes in quasi-static contact without coupling of the normal and tangential surface stresses are analyzed in this paper. It is proved that the tangential traction under constant normal forces and increasing tangential forces is equal to the difference between the actual normal pressure and the pressure for a smaller contact area, multiplied by the coefficient of friction. Every stick area corresponds to a contact area (or a configuration of multiple contact areas) that is smaller than the present contact area. In the same way as the contact area develops with increasing pressure, the stick area recedes with increasing tangential traction. General loading scenarios are solved by superposition of oblique increments under constant angles. As an example, this principle is applied to a rigid surface of the form A k x k , in contact on 0 ≤ x ≤ a and with a corner at x = 0, indenting an elastic half-plane.

Frictional Response of Sliding Interfaces Subjected to Time Varying Normal Pressures

Abstract: In the present investigation a plate-impact pressure shear loading device is employed to study frictional characteristics of sliding interfaces subjected to step changes in normal pressure. The present experimental configuration represents a significant improvement over the conventional tribology experiments by allowing the control of interfacial tractions through the use of pressure-shear loading waves instead of manipulating actuator motion. Moreover, the expermental configuration allows critical frictional parameters such as the applied normal pressure, the interfacial slip resistance, and the interfacial slip velocity to be interpreted by using the framework of one-dimensional plane wave analysis. The experimental results, deduced from the response to step changes imposed on the normal pressure at the frictional interface, reinforce the importance of including frictional memory in the development of the rate-dependent state variable friction models. The scope of the above experiments include technologically important combinations of workpiece materials such as 4340VAR structural steel and a commercially available titanium alloy (Ti-6Al-4V), and tool materials such as tungsten based tool cermets ( WC-Co alloys).

An Elliptic Elastic-Plastic Asperity Microcontact Model for Rough Surfaces

Abstract: An elastic-plastic microcontact model, that takes into account the directional nature of surface roughness, is proposed for elliptic contact spots between anisotropic rough surfaces. In addition, the plasticity index was modified to suit more general geometric contact shapes. This contact model, which expands the usefulness of the CEB model, is also utilized to determine the effect of effective radius ratio (γ) on microcontact behavior and to compare the results of this model and other models under different surface topographies. The results show that the elliptic contact model and circular contact model deviate considerably in regard to the separation (h), total real contact area (At ), plastic area (Ap ) and plasticity index (Ψ). The present model can be simplified to become other stochastic models.

Tilting-Pad Journal Bearings With Electronic Radial Oil Injection

Abstract: This paper gives a theoretical treatment of the problem of journal bearings modeling connected to electronic oil injection into the bearing gap. The feasibility of influencing the static behavior of hydrodynamic forces by means of such oil injection is investigated. The lubricant is injected into the bearing gap by two mechanisms of lubrication. the conventional hydrodynamic lubrication and through orifices distributed along the bearing surface (active lubrication in the radial direction). By controlling the pressure of the oil injection, it is possible to get large variations in the active hydrodynamic forces; such effects could be useful for reducing vibrations in rotating machines.

A Mixed-TEHD Model for Journal-Bearing Conformal Contacts—Part I: Model Formulation and Approximation of Heat Transfer Considering Asperity Contact

Abstract: A mixed- TEHD (thermal elastohydrodynamic) model was developed for journal bearings working at large eccentricity ratios in order to facilitate a better understanding of mixed-lubrication phenomena for conformal-contact elements. The model consists of a mixed-lubrication process that considers the roughness effect and asperity contact, a thermal process for temperature analyses, and a thermal-elastic process for deformation calculations. In this model, the interactive journal, lubricant, and bearing were treated as an integrated system. Finite-element, finite-difference, and influence-function methods were utilized in the numerical process. The overall solution was achieved by the iteration method. Analyses of a simulated bearing-lubricant-journal system working under mixed-lubrication conditions were conducted, and the influence of the changes of lubricant flows as a result of the asperity contact on the system heat transfer and temperature distributions was numerically investigated.

Finite element analysis of herringbone groove journal bearings : A parametric study

Abstract: Currently, the herringbone groove journal bearing (HGJB) has important applications in miniature rotating machines such as those found in the computer information storage industry. Grooves scribed on either the rotating or stationary member of the bearing pump the lubricating fluid inward thus generating support stiffness and improving its dynamic stability when operating concentrically. The narrow groove theory (NGT), traditionally adopted to model the concentric operation of these bearings, is limited to bearings with a large number of grooves. A finite element analysis is introduced for prediction of the static and rotordynamic forced response in HGJBs with finite numbers of grooves. Results from this analysis are then compared to available experimental data as well as to estimates from the NGT. A bearing geometry parametric study is then conducted to determine optimum rotordynamic force coefficients. A discussion on the temporal variation of the bearing reaction forces and force coefficients for a rotating journal with a small number of grooves is also presented. These changes can be significant at high operating eccentricities, possibly inducing a parametric excitation in rotating systems employing this type of bearing.

EHD Film Thickness in Non-Steady State Contacts

Abstract: This paper describes a study of EHD film thickness in non-steady state contact conditions. A modification of ultrathin film interferometry is employed which is able to measure both central film thickness and film thickness profiles 50 times a second. Film thickness with two perfluoropolyethers and two mineral base oils are investigated in a number of different types of non-steady state motion, including acceleration/deceleration, stop/start and reciprocation. The results demonstrate a range of transient behaviors of EHD film whose thicknesses deviate from those in steady state conditions.

Nanotribological Properties of Organic Boundary Lubricants: Langmuir Films Versus Self-Assembled Monolayers

Abstract: Frictional characteristics of several types of boundary lubricants were tested using scanning probe microscopy (SPM). These include Langmuir monolayers of stearic acids (STA), their cadmium salts (STCd), self-assembling monolayers (SAMs) of alkylchlorsilanes, and complexes of STA with rigid naphthoylene benzimidazole (x-NBI) fragments. We observed that a Langmuir monolayer deposited on a silicon surface had a very low friction coefficient against a silicon nitride tip (about 0.01–0.05) but also low mechanical stability. SAMs were found to be much more stable but had the drawback of growth in the friction coefficient at high sliding velocities. Composite NBI/STA monolayers were much more stable and were not damaged by the highest normal load applied. The frictional behavior of different monolayers was analyzed in relation to their structural organization (the type of tethering to the surface and packing density). We introduced a figure of merit (FOM) parameter which allowed comparison of frictional properties of very different lubricant materials to those of the supporting substrate. For Langmuir monolayers the FOM increased strongly with surface packing density whereas for SAMs and x-NBI/STA complexes it possessed a maximum at surface densities in the range 3.5–4.5 molecules per nm2 . Because of the possibility of tailoring the surface packing density of aliphatic tails in the complexes, they are a promising alternative to both LB films and SAMs. For such composite monolayers, the surface packing density can be optimized to give a desired frictional behavior.

Friction Force Microscopy Measurements: Normal and Torsional Spring Constants for V-Shaped Cantilevers

Abstract: A combination of finite element analysis (FEA ) calculations and resonant frequency measurements are applied for determining normal and lateral spring constants of microfabricated ceramic/gold cantilevers for friction force microscopes. The cantilever Si 3 N 4 and Au layers are combined analytically into an equivalent single composite layer. Bending and torsion behavior of the cantilever under typical operating forces are determined through FEA. Effective Young's modulus for the composite Si 3 N 4 -Au beam from 172 to 185 GPa is determined through assimilation of FEA and fundamental resonant frequency measurements. Several current analytical solutions are compared to the full FEA evaluation. A new analytical expression is derived for obtaining the ratio of lateral to normal spring constants and thereby evaluation of absolute values of friction coefficients. Calibration plots are presented for assessment of both vertical and torsion spring constants of bicomponent cantilevers by measuring their resonant frequencies and thickness of gold overlay.

Partial Hydrodynamic Lubrication With Large Fractional Contact Areas

Abstract: An alternative average REeynolds equation for use under conditions of large fractional contact area is proposed. The flow factors for this form of the equation are calculated for a variety of longitudinal surfaces and the results are shown to be relatively insensititve to the initial height distribution and a variety of Peklenik surface pattern parameters are also derived form the work of Patir and Cheng, Lo and Tripp. These are represented by semi-empirical equations over the full range of contact conditions. The implicaitons of the results, with respect to the lubrication of metal forming processes, is discussed.

A 3-D Model for a Multilayered Body Loaded Normally and Tangentially Against a Rigid Body: Application to Specific Coatings

Abstract: Coatings are increasingly used to improve the mechanical and tribological behavior of surfaces. It is necessary to develop models to guide the initial choice of coating/ substrate combinations that can withstand the applied load, A three-dimensional model of an elastic multilayered body, loaded both normally and tangentially against an elliptical rigid body ( partial sliding, rolling/sliding conditions ), is presented here. This model is based on linear elasticity theory, integral transforms, Fast Fourier Transform, and unilateral contact analysis with friction. Normal and tangential contact conditions between the two bodies are first determined and then used to calculate the multilayered body stress field. One application is given here: The influence of the mechanical properties of coating and substrate, as well as coating thickness, is studied on contact conditions, internal stresses, and potential failure mechanisms.

A Mixed-TEHD Model for Journal-Bearing Conformal Contact—Part II: Contact, Film Thickness, and Performance Analyses

Abstract: Investigation of the mixed lubrication of journal-bearing conformal contacts is very important for failure prevention and design improvement. This paper studies the asperity contact in heavily loaded journal bearings with Lee and Ren's asperity contact theory in a newly developed mixed-TEHD (Thermal Elasto-Hydro-Dynamic) model and analyzes the performance of simulated journal bearings under high eccentricity ratios. The effects of operating conditions, bearing structures, and thermal conditions on the contact severity were numerically investigated. The results indicate that the asperity contact pressure and the performance of journal bearings in the mixed lubrication are strongly affected by the geometric design and the thermal-elastic deformations. The heat transfer of the bearing-lubricant-journal system was also shown to play a role.

Tool Surface Topographies for Controlling Friction and Wear in Metal-Forming Processes

Abstract: A conceptual framework is introduced for the design of tool surface topographies in bulk metal forming processes. The objective of the design is to control friction to desired levels while minimizing wear of the workpiece and tool surfaces and adhesive metal transfer between the workpiece and tool. Central to the design framework are the tool/workpiece interface properties of lubricant retention and interface permeability. Lubricant retention refers to the capacity of an interface to retain lubricant rather than freely channel it to the exterior of the tool/workpiece conjunction. Permeability refers to the capacity to distribute lubricant to all areas within the conjunction. These properties lead to the concept of two-scale surface topography consisting of a fine scale background of interconnected channels on which is superimposed an array of coarser-scale cavities. Control of friction and wear is achieved by designing the tool surface topographies at these two scales to address the unique tribological conditions of specific bulk metal forming processes. The coarser scale is designed to ensure adequate supply of lubricant within the conjunction. The finer scale is designed to ensure adequate delivery of lubricant to all parts of the conjunction where nascent workpiece surface is being formed. The design concepts are illustrated with results from laboratory experiments using the rolling process as an example, and comparing the performance of various roll surface topographies under similar processing conditions. A two-scale surface topography consisting of hemispherical cavities distributed across a background surface of finer scale, interconnected channels was shown to reduce friction compared to a single-scale ground finish, but not as much as a single-scale coarse topography consisting of densely-packed cavities produced by an electrical discharge treatment. On the other hand, the smoother cross-sections of the cavities, especially when elongated in the direction of greatest relative motion, produced significantly less wear than either of the single-scale tool surface treatments. It is concluded that two-scale engineering of tool surface topographies based upon the concepts of lubricant retention and interface permeability can provide a broad basis for achieving desired levels of interface friction while minimizing workpiece surface wear and adhesive material transfer in many metal-forming processes.

Temperature Rise Simulation of Three-Dimensional Rough Surfaces in Mixed Lubricated Contact

Abstract: A numerical simulation of the temperature rise for a three-dimensional rough surface sliding against a smooth surface in mixed lubricated contact has been developed. The effects of lubricant film friction and solid asperity friction are considered in the simulation. The moving grid method, which greatly reduces the required computer memory size and computing time, is used to solve the coefficient matrix of temperature equations. The time-dependent surface temperature rise at very small subregions is obtained. Different friction coefficients for lubricant shearing, surface film shearing and dry solid asperity contact are used to simulate the change of frictional heat in mixed lubricated contact. A critical temperature criterion is used to determine whether the friction coefficient is controlled by lubricant film, surface film, or dry solid asperity contact. Solutions for different contact conditions are presented for verification of the present simulation.

A Physically Based Model for Endurance Limit of Bearing Steels

Abstract: Available models are not suitable for calculating the load rating of bearings when an infinite life is required. This paper presents a new model that has been developed from a detailed analysis of the damage mechanism responsible for failure of bearings operating under EHD pure rolling conditions. It is based on the comparison between the local shear stress concentration built up around inhomogeneities present in steels and the microyield stress of the martensitic matrix. The predictions of this model are in good agreement with some literature data concerning the fatigue limit of bearing steels. Finally, the influence of material parameters and operating conditions on the endurance limit of bearings is investigated.

Static Friction of Contacting Real Surfaces in the Presence of Sub-Boundary Lubrication

Abstract: A model for calculating the static friction coefficient of contacting real (rough) surfaces in the presence of very thin liquid films (sub-boundary lubrication) is developed. The liquid has a very high affinity for the surfaces and its thickness is of the order of the surface roughness average. An extension of the Greenwood and Williamson (GW) asperity model and an improved Derjaguin, Muller and Toporov (DMT) adhesion model are utilized for calculating the contact and adhesion forces, respectively. The effects of the liquid film thickness and the surface topography on the static friction coefficient are investigated. A critical film thickness is found above which the friction coefficient increases sharply. The critical thickness depends on the surface roughness and the external normal load. This phenomenon is more profound for very smooth surfaces and small normal loads, in agreement with published experimental work on magnetic hard disk interfaces.

Waviness Amplitude Reduction in EHL Line Contacts Under Rolling-Sliding

Abstract: Due to technological pressures the lubricant film thickness in EHD contacts has decreased over the years and will continue to do so for the foreseeable future. On the other hand, financial constraints cause the surface roughness in these contacts to decrease very slowly, or might even cause an increase. As a result, the ratio of film thickness to composite roughness will continue to decrease. The question that remains to be answered is to what extent this decrease will affect the contact performance. A third development makes this question even more acute, the request of increased reliability. As a consequence, the problem of the detailed understanding of the elastohydrodynamic lubrication with rough surfaces is as urgent as ever. Recent work has shown that the features inside the contact deform, and that the level of deformation is a function of the wavelength of the feature and the contact operating conditions, including slip. This last aspect of the problem, which has not been addressed previously, forms the central topic of the current paper. Instead of studying the deformation of a real roughness profile, the deformation of its sinusoidal Fourier components is investigated.

Three-Dimensional Elastic-Plastic Fractal Analysis of Surface Adhesion in Microelectromechanical Systems

Abstract: High adhesion is often encountered at contact interfaces of miniaturized devices, known as microelectromechanical systems, due to the development of capillary, electrostatic, and van der Waals attractive forces. In addition, deformation of contacting asperities on opposing surfaces produces a repulsive interfacial force. Permanent surface adhesion (referred to as stiction) occurs when the total interfacial force is attractive and exceeds the micromachine restoring force. In the present study, a three-dimensional fractal topography description is incorporated into an elastic-plastic contact mechanics analysis of asperity deformation. Simulation results revealing the contribution of capillary, electrostatic, van der Waals, and asperity deformation forces to the total interfacial force are presented for silicon/silicon and aluminum/aluminum material systems and different mean surface separation distances. Results demonstrate a pronounced effect of surface roughness on the micromachine critical stiffness required to overcome interfacial adhesion.

Theoretical analysis of heat partition and temperatures in grinding

Abstract: A theoretical analysis is presented of heat partition and surface temperatures for the grinding of hardened steel with both aluminum oxide and CBN wheels. The numerical predictions of the model are shown to agree with experimental results available in the literature. It is found that heat partition varies over a wide range depending on grinding conditions. Also, heat partition is strong function of position inside the grinding zone. The presence of the fluid inside the grinding zone can reduce the heat flux into the workpiece and the workpiece temperature significantly. For typical grinding of steel with CBN wheels, or creep feed grinding of steel with aluminum oxide or CBN wheels, it is possible to keep the fluid active and therefore to reduce thermal damage. However, the analysis suggests that the fluid may not be effective inside the grinding zone, in the conventional grinding of steel with aluminum oxide, due to boiling.

Elastohydrodynamic Film Forming With Shear Thinning Liquids

Abstract: Recent advances in high pressure rheometry have elucidated the shear response of liquid lubricants at the high shear stress characteristic of the traction generating region of lubricated concentrated contacts. These new measurement techniques are used to characterize the shear response of shear thinning liquids at low (<10 MPa) shear stress. A recently developed numerical scheme for calculating film thickness is extended to accommodate sliding. Film thickness predictions are compared with measurements using shear thinning liquids including a polymer/mineral oil blend, a highly elastic liquid, and synthetic base oils. Useful insights are provided concerning the effects of pressure-viscosity behavior for Newtonian liquids, sliding, and starvation for non-Newtonian liquids and the relevant shear stress for film forming.

Effect of Slider Burnish on Disk Damage During Dynamic Load/Unload

Abstract: Two of the most difficult issues to resolve in current design of head/disk interface in magnetic recording devices are stiction and durability problems. One method of overcoming these problems is by implementing a technology known as load/unload, where the system is designed so that the slider never touches the disk surface. One potential problem with this type of system is slider/disk contact induced disk defects. The objective of this paper is to show that the likelihood of disk scratches caused by head/disk contacts during the load/unload process can be significantly decreased by rounding the edges of the air-bearing surface. Using the resistance method, we observe that head/disk contacts burnish the corners of the slider and thereby decrease exponentially with load/unload cycles. A well burnished slider rarely causes any disk damage thus resulting in an interface with significantly higher reliability. A simple Hertzian contact stress analysis indicates that the contact stress at the head/disk interface can be greatly decreased by increasing the radius of curvature of the air-bearing surface edges.

Experimental and Theoretical Investigation on Rolling Contact Fatigue of 52100 and M50 Steels Under EHL or Micro-EHL Conditions

Abstract: The purpose of this investigation is to clarify the role of roughness on rolling contact fatigue Tests have been carried out on a two-disk machine, for two rolling bearing steels (52100 and M50), two surface roughnesses corresponding to EHL and micro-EHL conditions (two different surface finishing), three normal loadings (15, 25 and 35 GPa), and under pure rolling or rolling plus sliding conditions No surface damage has been observed up to 50 10 6 cycles for tests with smooth specimens Tests with rough specimens have produced a typical surface damage, called here surface distress, made of a large population of asperity-scale micro-cracks and micro-spalls The paper describes the surface distress observed, such as micro-cracks and micro-spalls Surface damages obtained are different for tests under pure rolling conditions and tests under rolling plus sliding conditions Therefore, the role of the friction direction is underlined A link is made between our experimental observations and calculations that have been carried out using a transient EHL model The influence of an indent in a line contact, simulating a micro-spall, is studied Surface pressure and associated sub-surface stress field are analyzed versus the sliding direction

Ultra-Thin Overcoats for the Head/Disk Interface Tribology

Abstract: Areal density in magnetic storage is increasing at a blistering pace of 60% annually. Recently IBM announced its mobile product with the industry highest areal density of 2.64 Gb/In{sup 2}. The areal density demonstrations have shown up to 5 Gb/In{sup 2} possible. Reaching higher areal density targets dictate that magnetic spacing between heads and disks be reduced. For the example of a 10 Gb/In{sup 2} areal density goal, the magnetic spacing should be {approx}25 nm. In budgeting this magnetic spacing, it is required that disk and slider air bearing surface overcoats thickness be reduced to 5 nm range. Present choice of carbon overcoat in the magnetic storage hard disk drive industry is sputter deposited, hydrogenated carbon (CH{sub x}) with thickness in the range of 12-15 nm on heads and disks. Novel overcoats such as nitrogenated carbon (CN{sub x}) and cathodic arc carbon films are being developed for future applications. Cathodic arc deposition forms ultra-thin amorphous hard carbon films of high sp{sup 3} content, high hardness, and low coefficient of friction. These properties make it of great interest for head/disk interface application, in particular for contact recording. In many cases, the tribological properties of the head disk interface could be improved by factors up to ten applying cathodic arc overcoats to the slider or disk surface. This paper reviews the results of cathodic arc ultra-thin (2-10 nm) carbon overcoats for head/disk interface tribological applications.

A Possible Mechanism for Rail Dark Spot Defects

Abstract: Rail dark spot defect, also termed squat failure or shelling, which is a kind of rolling contact fatigue failure and occurs frequently on running surfaces of railway rails carrying high speed traffic, is one of the most dangerous rail failures. The dark spot crack is characterized by a principal crack propagating in the direction of traffic and a second crack growing in the direction opposite to traffic. By using a newly developed two-disk machine, the authors have succeeded in reproducing very similar dark spot cracks to those which appear in actual rails. It is found that the dark spot defects are caused by frequent repetitions of dry and wet runnings, and that the traction force plays an important role for the occurrence of the cracks. The principal crack may occur from a tiny pit formed a posteriori on the contacting surface and after that, the second crack is formed by cracks branched from the extended principal crack. It has also been proved experimentally that water is capable of entering the tip of the crack. Furthermore, a possible mechanism for the dark spot cracking has been proposed on the basis of the fracture mechanics approach.

Magnetic Field Assisted Finishing of Ceramics—Part I: Thermal Model

Abstract: A thermal model for magnetic field assisted polishing of ceramic balls/rollers is presented. The heat source at the area of contact between the balls and the abrasives where material removal takes place is approximated to a disk. The disk heat source is considered as a combination of a se ries of concentric circular ring heat sources with different radii. Each ring in turn is considered as a combination of a se ries of infinitely small arc segments and each arc segment as a point heat source. Jaeger's classical moving heat source theory (Jaeger, 1942; Carslaw and Jaeger, 1959) is used in the development of the model, starting from an instantaneous point heat source, to obtain the general solution (transient and steady-state) of the moving circular ring heat source problem and finally the moving disc heat source problem. Due to the formation of fine scratches during polishing (on the order of a few micrometers long), the conditions are found to be largely transient in nature. Calculation of the minimum flash temperatures and minimum flash times during polishing enables the determination if adequate temperatures can be generated for chemo-mechanical polishing or not. This model is applied in Part II for magnetic float polishing (MFP) of ceramic balls and in Part III for magnetic abrasive finishing (MAP) of ceramic rollers.

Dent Initiated Spall Formation in EHL Rolling/Sliding Contact

Abstract: Dents in elasto-hydrodynamic lubricated (EHL) contacts will initiate spalls and shorten the fatigue life significantly. Experimental results are provided from a ball-on-rod rolling contact fatigue tester with the rod predented with a single large dent. The results indicate that the spall usually initiated at the trailing edge of the dent on the driving surface. These cracks and spalls can also be created in the absence of lubricant. Based on the accumulated plastic strain and damage mechanics concept, a line contact spall initiation model was developed to investigate the dent effects on spall initiation and propagation. The near surface volume of the contact solid was divided into many small metal cells and for each cell the damage law was applied to determine whether the cell is undergoing damage or not. If the cell on the surface is damaged, then it is removed from the surface and a spall will be formed. If the damaged cell occurs below the surface, then a subsurface void is generated, this void could grow to the surface depending on the running conditions. The spall will further modify the surface geometry and initiate a new spall, hence, the spall will propagate. The results indicate that the location of spall initiation depends on the EHL and dent condition. Spalls can initiate at either the leading or trailing edge of the dent depending on the surface traction.

Analysis of Mechanical Seal Behavior During Transient Operation

Abstract: A mathematical model that predicts the transient behavior of gas or liquid lubricated hydrostatic mechanical seals has been developed The analysis includes an evaluation of the fluid, contact, and deformation mechanics of a mechanical seal subject to constant or varying rotational speed and sealed pressure Squeeze film effects are included For gas seals, slip at the walls is also taken into account Results include predictions of film thickness distributions, contact forces, leakage rates, pressure distributions, heat generation rates, thermal deformation, and mechanical deformation

Analysis of Load Distributions Within Solid and Hollow Roller Bearings

Abstract: The virtual contact loading method is further developed in this paper to study the multi-body contact phenomena within solid and hollow roller bearings. The distributive virtual contact loads are used to simulate the contact constraint forces on each contact surface. The deepest penetration criterion is proposed to select and determine the contact nodes in an orderly way, so as to ensure the local iteration process converged and to increase the computational efficiency. The load distributions within the solid and hollow roller bearings have been studied in more detail and some reasonable results are obtained.