Showing papers in "Tribology Transactions in 1998"
TL;DR: In this article, the antiwear properties were examined on a Plint rubbing machine by measuring the amount of wear as a function of time and the concentrations of the additives, and it was shown that the dominant species from MoDTC in the anti-wear films resembles that of a MoS2-like film, and in the thermal films, the dominant properties are those of a sulphate and MoO3.
Abstract: In order to obtain a better understanding of the decomposition mechanisms of antiwear and antioxidant engine oil additives such as zinc dialkyldithiophosphate (ZDDP) and molybdenum dithiocarbamate (MoDTC), tribochemical and thermally deposited films were prepared from oil solutions containing varying concentrations of these two additives. The chemistry of these films was studied by using X-ray absorption (XANES) spectroscopy and X-ray photoelectron (XPS). The antiwear properties were examined on a Plint rubbing machine by measuring the amount of wear as a function of time and the concentrations of the additives. The XANES and XPS spectra indicate that the dominant species from MoDTC in the antiwear films resembles that of a MoS2-like film, and in the thermal films, the dominant species are those of a sulphate and MoO3. The spectra also indicate that the phosphorus from ZDDP forms polyphosphate chains of varying lengths. The combined use of organo-Mo compounds and Zn alkyl dithiophosphates showed a synergi...
109 citations
TL;DR: In this paper, a new test rig has been developed for evaluating foil air bearings at high temperatures and speeds, which have been successfully applied to a variety of turbomachinery operating up to 650°C.
Abstract: A new test rig has been developed for evaluating foil air bearings at high temperatures and speeds. These bearings are self-acting hydrodynamic air bearings which have been successfully applied to a variety of turbomachinery operating up to 650°C. This unique test rig is capable of measuring bearing torque during start-up, shutdown and high speed operation. Load capacity and general performance characteristics, such as durability, can be measured at temperatures to 700°C and speeds to 70,000 rpm. This paper describes the new test rig and demonstrates its capabilities through the preliminary characterization of several bearings. The bearing performance data from this facility can be used to develop advanced turbomachinery incorporating high temperature oil-free air bearing technology. Presented as a Society of Tribologists and Lubrication Engineers paper at the World Tribology Congress in London, United Kingdom, September 9–12, 1997
91 citations
TL;DR: In this article, the authors simulated the interaction between the wafer and the polishing pad in a range of commercially common CMP conditions, including hydrodynamic and non-hydrodynamic conditions.
Abstract: One of the fundamental mechanisms of chemical-Mechanical polishing (CMP) is the mechanical interaction between the wafer and polishing pad. This interaction was simulated in experiments. The vertical displacement of the wafer with respect to the polishing pad, the fictional drag of the wafer against the pad, and the pressure of the slurry trapped between the wafer and pad were measured. These experiments were performed over a range of commercially common CMP conditions. In addition, polishing rates were measured for CMP performed under induced hydrodynamic conditions where the wafer was separated from the pad by a film of slurry. It was found that no appreciable polishing occurred under hydrodynamic CMP conditions. Under commercial CMP conditions, it was found that the wafer contacts the polishing pad asperities as evidenced by near-zero wafer displacement and high friction coefficients (˜0.4). It was also found that pad conditioning (intentional roughening) causes a suction force to develop between the w...
62 citations
TL;DR: In this article, an analytical model for strip rolling in the mixed lubrication regime is developed, where the average Reynolds equation for Christensen surfaces with the arbitrary Peklenik surface pattern parameter is combined with an analysis for asperity flattening under conditions of bulk plastic flow to treat lubrication.
Abstract: An analytical model for strip rolling in the mixed lubrication regime is developed. The average Reynolds equation for Christensen surfaces with the arbitrary Peklenik surface pattern parameter is combined with an analysis for asperity flattening under conditions of bulk plastic flow to treat lubrication in the mixed regime. An inlet zone analysis and the influence of pressure on viscosity are included and, by using special numerical techniques, the model can be used over a wide speed range. Presented as a Society of Tribologists and Lubrication Engineers paper at the World Tribology Congress in London, United Kingdom, September 8–12, 1997
58 citations
TL;DR: In this paper, over-based detergents and ZnDTPs form insulating boundary lubrication films and electrical contact resistance (ECR) is used to monitor boundary film changes in a sliding contact.
Abstract: Overbased detergents and ZnDTPs form insulating boundary lubrication films. Electrical contact resistance (ECR) is therefore a convenient method of monitoring boundary film changes in a sliding contact. Separately, ZnDTPs and overbased detergents rapidly form insulating films. In combination, however, films may form slowly and, furthermore, may be less stable than films formed by the individual additives. Examples of film formation by ZnDTP-detergent combinations are described. ECR provides no information on boundary film chemistry. X-ray photoelectron spectroscopy (XPS) has been used to help identify some of the films. Inferences as to the chemistry of film formation can be drawn in some cases. Presented as a Society of Tribologists and Lubrication Engineers paper at the World Tribology Congress in London, United Kingdom, September 8–12, 1997
57 citations
TL;DR: In this article, a 6.1-mm (0.24-inch) diameter cylindrical pin is mounted on a carousel with a pitch diameter of 46 mm (1.813 inch).
Abstract: High temperature erosion and impact texts were developed for evaluation of thermal barrier coating (TBC) systems that are being generated for the High-Speed Civil Transport supersonic aircraft under NASA's Enabling Propulsion Materials program. The TBC-coated test specimen is a 6.1-mm (0.24-inch) diameter cylindrical pin. Twelve pins are mounted on a carousel with a pitch diameter of 46 mm (1.813 inch). This carousel is rotated at 500 rpm, 50 mm (two inches) from the combustor exhaust of a burner rig, while the TBC temperature is controlled at 1232°C (2250°F) using a pyrometer. The particulate is injected radially into the combustor in two horizontally opposed positions. Two separate types of particulate are used in the tests: 50-micron and 560-micron crushed alumina. The effects of the 50-micron erosion and 560-micron impact tests are quite different, but in each case excellent similarity is seen between damage to test specimens and that of commercial engine service hardware. The temperature of the impin...
53 citations
TL;DR: In this article, the scuffing behavior of four materials sliding against carburiud steel was experimentally studied under dry sliding conditions, and it was concluded that scuffings are due to a subsurface material failure.
Abstract: The scuffing behavior of four materials sliding against 1018 carburiud steel is experimentally studied under dry sliding conditions. These materials are commercially pure aluminum (1100), die-cast hypereutectic aluminum-silicon alloy (390-T6), extruded Bi-containing eutectic aluminum-silicon alloy (DHT-3), and 1018 steel. The major emphasis is on the 390-T6 aluminum alloy. The environment for the tests is either air or tetrafluoroethane (R134a). The effects of load, sliding velocity, mechanical strength, environmental temperature, specimen size, time, loading history, and type of environment are evaluated. The mechanisms leading to scuffing are studied by examination of surfaces, subsurfaces and wear debris of specimens in the process of scuffing. Quantitative measurements of subsurface plastic deformation are also obtained. Based on the experimental observations it is concluded that scuffing is due to a subsurface material failure. This process involves initiation of cracks due to subsurface plastic defo...
37 citations
TL;DR: In this paper, a more accurate performance prediction system was proposed for bearing designs with associated savings in engine performance, weight, and cost as well as improved reliability in aircraft gas turbines.
Abstract: The internal thrust loads in aircraft gas turbines are carried by angular-contact ball bearings, one on each of the compressor-turbine-driven shafts. There are typically two or three concentric shafts, rotating at individual speeds to generate the required aerodynamic loading with a resultant thrust load on each of the ball bearings. The designs of these bearings are based primarily on the required life or fatigue endurance. Estimation of this parameter is currently accomplished using empirically developed, factor-based calculation methods, e.g., material life and lubrication life factors. Experience has demonstrated in many instances that bearing fatigue lives predicted by this method are less than those achieved in practice. A more accurate performance prediction system would allow improved optimization of bearing designs with associated savings in engine performance, weight, and cost as well as improved reliability. As thrust-to-weight ratio increases with new engine designs, the need for more compact ...
34 citations
TL;DR: In this paper, a subboundary lubrication (SBL) model for calculating the static friction coefficient of contacting real surfaces in the presence of very thin liquid films is compared with published static friction measurements performed on different magnetic storage hard disks.
Abstract: Results from a subboundary lubrication (SBL) model for calculating the static friction coefficient of contacting real surfaces in the presence of very thin liquid films are compared with published static friction measurements performed on different magnetic storage hard disks. Four levels of surface roughness represented by the standard deviation of surface heights σ and by the GW plasticity index ty are studied, ranging from σ = 43.1 nm (ψ= 1.15) for the roughest surfaces to σ = 2.95 nm (ψ = 0.39) for the smoothest surfaces. In all four cases, good correlation is obtained between the model and the experimental results, suggesting that the subboundary lubrication model is a reliable model which accounts for the main parameters that influence stiction in thin-film disks. A critical film thickness of the lubricant, above which the static friction coefficient increases sharply (stiction), is predicted by the model in agreement with the experiments. A physical examination of the stiction phenomenon, in relati...
32 citations
TL;DR: In this paper, it is demonstrated that the interfacial temperature in the extreme pressure regime varies linearly with the applied load in a pin and v-block testing apparatus and that temperatures in excess of 1000 K can be attained.
Abstract: Chlorinated hydrocarbons are commonly added to a base lubricating fluid when it is used for extreme-pressure (EP) lubrication of ferrous metals. It is demonstrated here that the interfacial temperature in the EP regime varies linearly with the applied load in a pin and v-block testing apparatus and that temperatures in excess of ˜ 1000 K can be attained. Thermally decomposing chlorinated hydrocarbon vapors on iron heated to these temperatures (1) shows that a film consisting of an iron chloride which incorporates small carbon particles (˜50A) is formed. In this paper, tribological measurements at extreme pressures and the corresponding analyses of the rubbing surfaces and wear particles also indicate that this film, formed from the chlorinated lubricant reacting with these surfaces, is the critical antiseizure material at less severe EP loads and interfacial temperatures less than ˜1000 K.
31 citations
TL;DR: The self-propelled rotary tool (SPRT) incorporating round-shaped carbide cutting inserts exhibits superior wear resistance when machining titanium IMI 318 alloy under finishing conditions involving a low depth of cut of 0.25 mm.
Abstract: The self-propelled rotary tool (SPRT) incorporating round-shaped cemented carbide cutting inserts exhibits superior wear resistance when machining titanium IMI 318 alloy under finishing conditions involving a low depth of cut of 0.25 mm. The rotary cutting action extends tool life by more than 60 times compared with the rhomboid and round inserts used in single-point turning. Excessive chipping was the dominant failure mode when machining IMI 318 with the SPRT due to thermal and mechanical shocks as well as vibration during machining. When machining nickel-based Inconel 718 alloy with the SPRT tipped with CVD-coated carbide inserts, improvement in tool life was not significant as a result of severe attrition and abrasion wear mechanisms. Component forces recorded with the SPRT were lower than those obtained during conventional single-point turning. An increase in feed rate only had a marginal adverse effect on the surface finish due to increased burnishing action between the tool and the workpiece during ...
TL;DR: In this article, a single-cylinder, air-cooled, spark-ignition (gasoline) engine was measured at the topping reversal point of a singlecylinder engine during break-in, and the instantaneous factional torque of the engine was determined and correlated with the wear rate and surface roughness.
Abstract: Cylinder liner wear and surface roughness were measured at the topping reversal point of a single-cylinder, air-cooled, spark-ignition (gasoline) engine during break-in. In addition, the instantaneous factional torque of the engine was determined and correlated with the wear rate and surface roughness during this period. The engine friction, liner surface roughness and wear had their highest values at the beginning of the break-in period. The wear rate dropped sharply during the first hour, after which it maintained a steady lower rate. The surface roughness and friction took longer than the wear rate to stabilize. Friction was found to change in three modes. The first mode took one hour and was characterized by a sharp drop in wear rate and a small drop in friction. The second mode was a transition to the third mode, and took about 2.5 hours. The third mode lasted about 20 hours and was characterized by a drop in both surface roughness and friction. The wear rate did not change much during this mode. Aft...
TL;DR: In this article, pressure shear plate impact experiments are conducted to study the kinetics of friction on a submicrosecond time scale, where the interfacial conditions are varied from sticking to slipping by varying the angle of impact and/or the surface roughness.
Abstract: Pressure-shear plate impact experiments are conducted to study the kinetics of friction on a submicrosecond time scale. The configuration offers the simplicity of allowing the interpretation of the experimental results by using the framework of one-dimensional plane wave analysis. To address the problem of high-speed machining, one of the impacting plates is chosen to correspond to a wear-resistant grade of tungsten-carbide tool material and the other to a commercial-grade titanium alloy (Ti-6Al-4V). The interfacial conditions are varied from sticking to slipping by varying the angle of impact and/or the surface roughness. Also, within a single experiment, transitions from conditions of fully sticking to intermittent, to full sliding are introduced by subjecting the interface to step changes in normal pressure. The experimentally obtained time-resolved frictional response of the interface is used to examine the role of the interfacial normal pressure, slip velocity, slip distance, and surface roughness in...
TL;DR: In this article, the concept of Type I antiseizure behavior for chlorinated hydrocarbons in extreme-pressure (EP) lubrication of ferrous metals was introduced; interfacial temperature measurements and surface analyses revealed that a solid lubricating layer consisting of iron chloride (FeCl2) and carbon prevents seizure and acts as a solid lathering at less than 1000 K.
Abstract: In Part I (1), the concept of “Type I” antiseizure behavior for chlorinated hydrocarbons in extreme-pressure (EP) lubrication of ferrous metals was introduced; interfacial temperature measurements and surface analyses revealed that a solid lubricating layer consisting of ferrous chloride (FeCl2) and carbon prevents seizure and acts as a solid lubricant at less than ˜1000 K. In this paper, careful measurement of the film growth and removal rates successfully rationalizes this tribological behavior. Thermodynamic calculations also show that iron carbides are favored at higher decomposition temperatures. Analysis of films formed from the thermal decomposition of carbon tetrachloride (CCl4) and chloroform (CHCl3) at ˜1000 K using Mossbauer spectroscopy demonstrates that iron carbide is indeed formed in this case; tribological measurements also confirm this material as critical antiseizure material at high loads in “Type II” tribological behavior for chlorinated hydrocarbons with ferrous metals.
TL;DR: In this paper, a theoretical study using FEM is performed of multirecess capillary compensated hydrostatic/hybrid journal bearings which find use in number of engineering applications in this study, bearings having four different recess shapes were observed for their static and dynamic performance parameters which include minimum film thickness, flow rate, rot dynamic coefficients and threshold speed.
Abstract: A theoretical study using FEM is performed of multirecess capillary compensated hydrostatic/hybrid journal bearings which find use in number of engineering applications In this study, bearings having four different recess shapes were observed for their static and dynamic performance parameters which include minimum film thickness, flow rate, rotordynamic coefficients and threshold speed The bearings with four different recess geometries included in the present study were a square recess bearing, a circular recess bearing a triangular recess bearing and an elliptical recess bearing Comparisons of performance characteristics were made to determine which recess shape gives the best performance The results presented in this paper are expected to help machine tool designers make better use of the recess shapes Presented at the 52nd Annual Meeting In Kansas City, Missouri May 10–22, 1997
TL;DR: In this paper, a mixed elastohydrodynamic lubrication model for finite-long journal bearings has been developed to account for the effects of surface waviness, roughness and bearing housing deformation.
Abstract: Modern high performance engines require bearings to operate under high temperature and heavy bad with complicated hading cycles. These severe conditions result in mainshaft and connecting rod bearings operating in an ever thin film lubrication regime. The effects of surface waviness, roughness and bearing housing deformation can no longer be neglected. To account for such effects a mixed elastohydrodynamic lubrication model for finite-long journal bearings has been developed. This model couples an average Reynolds equation for a particular longitudinal surface texture with an asperity-to-asperity contact model. The governing equations of the model were discretized by the finite element method. The resulting nonlinear equations were subsequently solved by a modified Newton-Raphson algorithm. Simulations have been performed for various waviness and roughness with both rigid and flexible bearing housings.
TL;DR: In this article, the dynamic squeeze film pressures become less reproducible for consecutive cycles of journal orbital motion and the overall peak-to-peak film pressures decrease as the mixture void fraction (air/oil volume ratio) increases.
Abstract: Squeeze film dampers (SFDs) provide damping to rotating machinery, thus reducing excessive vibration amplitudes, supressing instabilities, and isolating structural components. Large amplitude SFD journal motions while traversing critical speeds enhance the ingestion of air and lead to operation with a bubbly mixture of lubricant and air. This phenomena lacks firm analytical understanding and controlled tests presented here show its effect on SFD performance. The experiments report measurements of the dynamic pressure field in an SFD apparatus operating with a controlled bubbly mixture of oil and air. The journal describes circular-centered orbits at a fixed whirl frequency and the damper is fully submerged in an oil bath. The dynamic squeeze film pressures become less reproducible for consecutive cycles of journal orbital motion and the overall peak-to-peak film pressures decrease as the mixture void fraction (air/oil volume ratio) increases. An unstable zone of null squeeze pressure generation in the dyn...
TL;DR: In this paper, the authors investigated the mechanism by which the normal load dependency arises using a simple boundary lubrication model, and the configuration and distribution pattern of small asperities on the contact surface and the property of the lubricant were considered.
Abstract: It has often been reported that the normal load dependency of the coefficient of friction under boundary lubrication is observed and that Amontons' low of friction is not realized. The mechanism by which such a property arises in friction has not been clarified sufficiently. Thus, the authors investigate the mechanism by which the normal load dependency arises using a simple boundary lubrication model. In this model, the configuration and distribution pattern of small asperities on the contact surface and the property of the lubricant are considered. Some friction characteristics under boundary lubrication are discussed.
TL;DR: In this article, the authors have noted that corrosive wear was mainly determined by electrochemical dissolution, where the wear volume was equivalent to the corrosion volume calculated according to the graph.
Abstract: In previous works, authors have noted that corrosive wear was mainly determined by electrochemical dissolution, where the wear volume was equivalent to the corrosion volume calculated according to ...
TL;DR: In this paper, an axisymmetric numerical model was developed to predict fluid and solid temperature distributions for an arbitrary mechanical face seal geometry and operating conditions based on a computational fluid dynamic (CFD) code.
Abstract: Based on a computational fluid dynamic (CFD) code, an axisymmetric numerical model was developed to predict fluid and solid temperature distributions for an arbitrary mechanical face seal geometry and operating conditions. The effects of varying coolant source location and rates were investigated. Also, various seal chamber configurations were examined. For dead-ended seals, the CFD model shows how heat is transferred away from the seal by turbulent diffusion. Predictions of the local heat transfer coefficients using the present procedure were made and compared to available heat transfer coefficient correlations in the literature. The predictions are also compared to seal fluid and seat temperature measurements. Presented at the 53rd Annual Meeting in Detroit, Michigan May 17–21, 1998
TL;DR: In this article, a surface force apparatus was used to determine film thickness and film properties of adsorbed neutral and basic diisobutyl zinc dithiophosphates (ZnDTPs) on cobalt surfaces.
Abstract: A surface force apparatus (SFA) has been used to determine film thickness and film properties of adsorbed neutral and basic diisobutyl zinc dithiophosphates (ZnDTPs) on cobalt surfaces. Sliding experiments were also carried out and film characteristics determined after sliding. Dodecane was used as the solvent. Experiments with dodecane only show dodecane molecules form an immobile monolayer on cobalt surfaces. When subjected to sliding, this monolayer is displaced, and attractive forces between the cobalt surfaces are observed. Neither the films formed initially upon adsorption of the ZnDTPs nor those films after sliding are displaced by the tangential motion. After 80 nm of sliding, the coefficient of friction was 1.2 in dodecane and 0.4 in the ZnDTP solutions. Elastic compressive and shear moduli for the physisorbed ZnDTP films were ˜0.1 GPa and 0.01-1 GPa, respectively. The distance of first repulsion between the approaching surfaces corresponds roughly to two monolayers of ZnDTP on each surface. Unde...
TL;DR: In this article, a systematic study of the elastohydrodynamic (EHD) film-forming properties of polymer solutions is described, in which a range of well-characterized, low dispersivity polymers is employed to investigate the influence of polymer type, molecular weight and concentration in base oil on EHD film thickness.
Abstract: It is well-known that the elastohydrodynamic (EHD) film thicknesses formed by solutions of medium to high molecular weight polymers in lubricating oils are less than those predicted from EHD theory based on the low shear rate viscosities of the polymer solutions. This is usually ascribed to shear thinning of polymer solutions in the high shear stress conditions in the inlet of the EHD contact. This paper describes a systematic study of the EHD film-forming properties of polymer solutions in which a range of well-characterized, low dispersivity polymers is employed to investigate the influence of polymer type, molecular weight and concentration in base oil on EHD film thickness. It is shown that the disparity between measured film thickness and that predicted from EHD theory using low shear rate viscosity increases progressively as both polymer concentration and polymer molecular weight are raised. Analysis of the results suggests, however, that conventional EHD film thickness equations can be employed to ...
TL;DR: In this paper, the influence of the time dependence of grease behavior was studied using rheometer experiments and a parameter for the description of the structural degradation, the limiting energy density, was quantified and compared for different temperatures.
Abstract: The influence of the time dependence of grease behavior was studied. In using rheometer experiments an interpretation of the obtained flow curves is given. A parameter for the description of the structural degradation, the limiting energy density, is quantified and compared for different temperatures. Also, the deformation properties of some greases were investigated from the viewpoint of time dependence. Finally, for the state of maximum degradation, the friction coefficient is estimated.
TL;DR: A theoretical relationship for basic dynamic load rating based on a three-parameter life equation for a linear motion ball guide (LMBG) system is derived, including the effect of crowning on guide block, by calculating accumulated stress cycles on rail and guide blocks, rolling body had and equivalent average ball load as mentioned in this paper.
Abstract: A theoretical relationship for basic dynamic load rating based on a three-parameter life equation for a linear motion ball guide (LMBG) system is derived, including the effect of crowning on guide block, by calculating accumulated stress cycles on rail and guide blocks, rolling body had and equivalent average ball load The values for basic dynamic load rating are then calculated for different strokes, load eccentricities and conformity factors A life test is carried out for both the LMBG system and component The test data are analyzed by three-parameter Weibull distribution and the effect of crowning is clarified Presented as a Society of Tribologists and Lubrication Engineers paper at the World Tribology Congress in London, United Kingdom, September 8–12, 1997
TL;DR: In this article, the effects of the face loading surface roughness, material properties and operating conditions on the static sealing performance of mechanical gas seals are investigated, and the combined problems of contacting rough surfaces and pressure-induced flow in their interface are formulated and solved.
Abstract: The combined problems of contacting rough surfaces and pressure-induced flow in their interface are formulated and solved. The analysis is valid for thin gas films, where rarefaction effects are significant. The effects of the face loading surface roughness, material properties and operating conditions on the static sealing performance of mechanical gas seals are investigated. It is found that, as the surface roughness and the Knudsen number increase, the leakage also increases. For very low leakages, corresponding to high face loading the effect of the Knudsen number on the leakage is still significant but the effect of the surface roughness diminishes. A semi-empirical model that relates the leakage with the face loading and the other relevant parameters is developed. This model favorably compares with available experimental data and provides a simple tool for evaluating static sealing performance of mechanical gas seals. Presented at the 53rd Annual Meeting in Detroit, Michigan May 17–21, 1998
TL;DR: In this article, a thrust-on-washer adapter was used to stimulate flat-onflat contacts under lubricated and dry sliding conditions, where graphite particles were mixed with 6061 aluminum alloy powders to create a self-lubricating composite material by means of cold pressing and sintering.
Abstract: A thrust-on-washer adapter was used to stimulate flat-on-flat-type contacts under lubricated and dry sliding conditions. The upper specimens were made of a cast aluminum alloy, A356.0 Al, and the lower specimens were prepared by powder metallurgy. Fine graphite particles were mixed with 6061 aluminum alloy powders, by means of cold pressing and sintering to create a self-lubricating composite material by means of cold pressing and sintering. The tribological performance of the composite materials was evaluated under both dry and oil-lubricated conditions. The optimum graphite content was determined by frictional performance, Stribeck curves, the product of nominal pressure and sliding speed (PV), graphite content, and wear mechanisms. The results showed that, regardless of contact pressure, the seizure, which often occurs in aluminum, can be avoided by adding graphite. Seizure can be delayed in low-speed dry sliding contacts with high graphite content. However, either too much or no graphite in aluminum a...
TL;DR: In this paper, the effects of crack free friction on Mode II stress intensity factors, KII, for a vertical surface crack in a two-dimensional finite element model of TiN/steel subject to rolling line contact were investigated.
Abstract: This work focuses on the effects of crack free friction on Mode II stress intensity factors, KII, for a vertical surface crack in a two-dimensional finite element model of TiN/steel subject to rolling line contact. Second-order extrapolation of KI and KII from nodal stresses ahead of the crack tip is found to be a more consistent technique than linear extrapolation. Results indicate that maximum KJJ values, which occur when the load is adjacent to the crack, may be significantly reduced in the presence of crack face friction. The reduction is more significant for thick coatings than for thin. Crack extension and increased layer thickness result in increased KII values. The effect of crack face friction on compressive KI values appears negligible. Comparative results are presented for MoS2/steel and diamond-like carbon/Ti systems. Presented at the 51st Annual Meeting in Cincinnati, Ohio May 19–23, 1996
TL;DR: In this paper, the anti-wear performance of organic phosphates, such as tricresylphosphate (TCP), TBP, and diphenylhydrogen-phosphates (DPHP), dissolved in several polyol esters is studied.
Abstract: The antiwear performance of organic phosphates, such as tricresylphosphate (TCP), tributylphosphate (TBP) and diphenylhydrogen-phosphate (DPHP), dissolved in several polyol esters is studied. Several trimethylolpropane esters (TMP) and pentaerythritol esters (PE) having different carbon chains were used as base oils. A four-ball tribometer was used to determine the antiwear performance of oils, using commercially available bearing steel balls as test specimens. Although the wear of steel was drastically reduced with low-concentration solutions of these phosphates, the wear increased with increasing concentration in the higher-concentration region. All of the phosphates showed characteristics of an optimum concentration for minimizing wear. This behavior can be attributed to the effective adsorption/reaction of phosphates in the low concentration region and the reaction forming excess inorganic phosphates on the surface that causes corrosive-like wear in the high-concentration region. Different polyol este...
TL;DR: In this article, two influence functions for calculating the steady-stale temperature and the consequent thermal deformation for finite mechanical structures, as well as a method for thermal analyses of complicated tribological systems were presented.
Abstract: Calculations for temperature and thermal deformation in finite tribological systems usually require finite-element (FEM) procedures. Because these calculations may be intermediate steps in iterations for film thicknesses and pressure distributions, combining FEM procedures into the iteration process may be considerably costly or even impractical. This paper reports the development of two influence functions for calculating the steady-stale temperature and the consequent thermal deformation for finite mechanical structures, as well as a method that utilizes these influence functions for thermal analyses of complicated tribological systems. A sample calculation on the thermalelasto hydrodynamic lubrication (TEHD) of a journal bearing was conducted; the results showed that this method is convenient to use and can considerably save programming effort and computation time. Presented at the 52nd Annual Meeting in Kansas City, Missouri May 18–22, 1997
TL;DR: In this article, the experimental results for scuffing of aluminum/steel and steel/steel contacts tested in air and refrigerant environments were derived based on several models describing surface mechanical and thermal interactions.
Abstract: Scuffing of contacts sliding under dry conditions is theoretically investigated. The study is based on the experimental results for scuffing of aluminum/steel and steel/steel contacts tested in air and refrigerant environments. The major focus of the present study is on the material failure leading to the removal of protective surface films and subsequent cold welding. This failure is controlled by the local stresses, temperatures and strains which are estimated with the aid of several models describing surface mechanical and thermal interactions. The existing hypotheses for scuffing are evaluated on the basis of the experimental observations and these theoretical estimates. A new hypothesis for scuffing and its corresponding criterion are proposed. The proposed hypothesis states that scuffing is due to a subsurface failure caused by the initiation and propagation of cracks, removal of portions of the load-bearing surface, generation of large areas of bare metal and, finally, cold welding. It is demonstra...