Showing papers in "Journal of Tribology-transactions of The Asme in 2009"
TL;DR: In this article, some of the most widely used RCF models are reviewed and discussed, and their limitations are addressed, and the modeling approaches recently proposed by the authors to develop life models and better understanding of the RCF.
Abstract: Ball and rolling element bearings are perhaps the most widely used components in industrial machinery. They are used to support load and allow relative motion inherent in the mechanism to take place. Subsurface originated spalling has been recognized as one of the main modes of failure for rolling contact fatigue (RCF) of bearings. In the past few decades a significant number of investigators have attempted to determine the physical mechanisms involved in rolling contact fatigue of bearings and proposed models to predict their fatigue lives. In this paper, some of the most widely used RCF models are reviewed and discussed, and their limitations are addressed. The paper also presents the modeling approaches recently proposed by the authors to develop life models and better understanding of the RCF.
438 citations
TL;DR: In this paper, the authors used a mass-conservative algorithm to predict the behavior of cavitation in flat surfaces enhanced with dimples, and the multigrid method was used to accelerate the convergence speed.
Abstract: The Floberg―Jakobsson―Olsson cavitation theory is implemented using a mass-conservative algorithm to accurately predict the behavior of cavitation in flat surfaces enhanced with dimples. The multigrid method is used to accelerate the convergence speed. Comparison is made on different cavitation theories. The results reveal that the load-carrying capacity of dimple-enhanced surfaces is limited under the simulated conditions.
179 citations
TL;DR: A numerical algorithm for fully dynamical lubrication problems based on the Elrod-Adams formulation of the Reynolds equation with mass-conserving boundary conditions is described in this article, where a simple but effective relaxation scheme is used to update the solution maintaining the complementarity conditions on the variables that represent the pressure and fluid fraction.
Abstract: A numerical algorithm for fully dynamical lubrication problems based on the Elrod― Adams formulation of the Reynolds equation with mass-conserving boundary conditions is described. A simple but effective relaxation scheme is used to update the solution maintaining the complementarity conditions on the variables that represent the pressure and fluid fraction. The equations of motion are discretized in time using Newmark's scheme, and the dynamical variables are updated within the same relaxation process just mentioned. The good behavior of the proposed algorithm is illustrated in two examples: an oscillatory squeeze flow (for which the exact solution is available) and a dynamically loaded journal bearing. This article is accompanied by the ready-to-compile source code with the implementation of the proposed algorithm.
164 citations
TL;DR: In this paper, a physics-based fluid mechanics model is proposed to predict spin power losses of gear pairs due to oil churning and windage, and the model is applied to a unity ratio spur gear pair to quantify the individual contributions of each power loss component to the total spin power loss.
Abstract: A physics-based fluid mechanics model is proposed to predict spin power losses of gear pairs due to oil churning and windage. While the model is intended to simulate oil churning losses in dip-lubricated conditions, certain components of it apply to air windage losses as well. The total spin power loss is defined as the sum of (i) power losses associated with the interactions of individual gears with the fluid, and (ii) power losses due to pumping of the oil at the gear mesh. The power losses in the first group are modeled through individual formulations for drag forces induced by the fluid on a rotating gear body along its periphery and faces, as well as for eddies formed in the cavities between adjacent teeth. Gear mesh pumping losses will be predicted analytically as the power loss due to squeezing of the lubricant, as a consequence of volume contraction of the mesh space between mating gears as they rotate. The model is applied to a unity-ratio spur gear pair to quantify the individual contributions of each power loss component to the total spin power loss. The influence of operating conditions, gear geometry parameters, and lubricant properties on spin power loss are also quantified at the end. A companion paper (Seetharaman et al., 2009, "Oil Churning Power Losses of a Gear Pair: Experiments and Model Validation," ASME J. Tribol., 131, p. 022202) provides comparisons to experiments for validation of the proposed model.
117 citations
TL;DR: Hu et al. as discussed by the authors proposed a 3D deterministic line contact model based on the 3D L-EHL model for rough surface line-contact mixed-elastohydrodynamic lubrication problems.
Abstract: This paper reports the development of a novel three-dimensional (3D) deterministic model (3D L-EHL) for rough surface line-contact mixed-elastohydrodynamic lubrication (EHL) problems. This model is highly demanded because line contacts are found between many mechanical components, such as various gears, roller and needle bearings, cams and followers, and work rolls and backup rolls in metal-forming equipment. The macro aspects of a line-contact problem can be simplified into a two-dimensional (2D) model; however, the topography of contacting rough surfaces, microasperity contacts, and lubricant flows around asperities are often three-dimensional. The present model is based on Hu and Zhu 's unified 3D mixed-EHL model (Hu and Zhu, 2000, "Full Numerical Solution to the Mixed Lubrication in Point Contacts, " ASME J. Tribal., 122(1), pp. 1-9) originally developed for point contacts and the mixed fast Fourier transform (FFT)-based approach for deformation calculation formulated by Chen et al. (2008, "Fast Fourier Transform Based Numerical Methods for Elasto-Plastic Contacts With Normally Flat Surface," ASME J. Appl. Mech., 75(1), 011022-1-11). It is numerically verified through comparisons with results from the line-contact Hertzian theory and the conventional 2D line-contact smooth-surface EHL formulas. Numerical examples involving 3D sinusoidal and digitized machined surfaces are also analyzed. Sample cases indicate that transverse roughness may yield greater film thickness than longitudinal roughness. This observation is qualitatively in agreement with the trend predicted by Patir and Cheng's stochastic model (1978, "Effect of Surface Roughness on the Central Film Thickness in EHL Contacts, " Proceedings of the Fifth Leeds-Lyon Symposium on Tribology, London, pp. 15-21). However, the roughness orientation effect does not appear to be quantitatively as great as that shown in the work of Patir and Cheng for the same range of λ ratio.
106 citations
TL;DR: In this paper, the authors present the results of an experimental study on load-independent (spin) power losses of spur gear pairs operating under dip-lubricated conditions and demonstrate that the model is capable of predicting the measured spin power loss values as well as the measured parameter sensitivities reasonably well.
Abstract: This paper presents the results of an experimental study on load-independent (spin) power losses of spur gear pairs operating under dip-lubricated conditions. The experiments were performed over a wide range of operating speed, temperature, oil levels, and key gear design parameters to quantify their influence on spin power losses. The measurements indicate that the static oil level, rotational speed, and face width of gears have a significant impact on spin power losses compared with other parameters such as oil temperature, gear module, and the direction of gear rotation. A physics-based gear pair spin power loss formulation that was proposed in a companion paper (Seetharaman and Kahraman, 2009, "Load-Independent Spin Power Losses of a Spur Gear Pair: Model Formulation, " ASME J. Tribol., 131, p. 022201) was used to simulate these experiments. Direct comparisons between the model predictions and measurements are provided at the end to demonstrate that the model is capable of predicting the measured spin power loss values as well as the measured parameter sensitivities reasonably well.
101 citations
TL;DR: In this article, a von Mises stress-based pitting life prediction approach based on the 3-D line contact mixed elastohydrodynamic lubrication (EHL) model was developed for analyzing various gears, roller/needle bearings, cams and followers and other line contact components.
Abstract: Surface pitting due to contact fatigue is a major failure mode of many mechanical components, such as various gears and rolling element bearings. Pitting life prediction, therefore, is vital to design and performance/reliability improvements. Conventional prediction methods, commonly found in industrial standards, are based on the Hertzian contact theory under assumptions that surfaces are ideally smooth with no lubrication. The present study aims to develop a von Mises stress-based pitting life prediction approach based on the 3-D line contact mixed elastohydrodynamic lubrication (EHL) model recently developed for analyzing various gears, roller/needle bearings, cams and followers and other line-contact components. Pitting life evaluation employs the fatigue life model developed by Ioannides-Harris and Zaretsky et al, using the von Mises stress field obtained. Sample cases are analyzed for model validation, and the life prediction results are compared with available transmission gear test data.
94 citations
TL;DR: In this paper, the influence of airborne particles in the atmosphere on human health has been studied, and sliding contacts are a significant source of airborne particle in urban environment, and they have been investigated.
Abstract: Recently, much attention has been paid to the influence of airborne particles in the atmosphere on human health. Sliding contacts are a significant source of airborne particles in urban environment ...
69 citations
TL;DR: In this paper, a Voronoi finite element method (VFEM) was developed to simulate the microstructure of bearing materials, and the VFEM was then used to investigate the effects of micro-structure randomness on rolling contact fatigue.
Abstract: Microlevel material failure has been recognized as one of the main modes of failure for rolling contact fatigue (RCF) of bearing. Therefore, microlevel features of materials will be of significant importance to RCF investigation. At the microlevel, materials consist of randomly shaped and sized grains, which cannot be properly analyzed using the classical and commercially available finite element method. Hence, in this investigation, a Voronoi finite element method (VFEM) was developed to simulate the microstructure of bearing materials. The VFEM was then used to investigate the effects of microstructure randomness on rolling contact fatigue. Here two different types of randomness are considered: (i) randomness in the microstructure due to random shapes and sizes of the material grains, and (ii) the randomness in the material properties considering a normally (Gaussian) distributed elastic modulus. In this investigation, in order to determine the fatigue life, the model proposed by Raje et al. ("A Numerical Model for Life Scatter in Rolling Element Bearings," ASME J. Tribol., 130, pp. 011011-1-01101}-10), which is based on the Lundberg-Palmgren theory ("Dynamic Capacity of Rolling Bearings," Acta Polytech. Scand., Mech. Eng. Ser., 1(3), pp. 7-53), is used. This model relates fatigue life to a critical stress quantity and its corresponding depth, but instead of explicitly assuming a Weibull distribution of fatigue lives, the life distribution is obtained as an outcome of numerical simulations. We consider the maximum range of orthogonal shear stress and the maximum shear stress as the critical stress quantities. Forty domains are considered to study the effects of microstructure on the fatigue life of bearings. It is observed that the Weibull slope calculated for the obtained fatigue lives is in good agreement with previous experimental studies and analytical results. Introduction of inhomogeneous elastic modulus and initial flaws within the material domain increases the average critical stresses and decreases the Weibull slope.
67 citations
TL;DR: A model for deep-groove and angular-contact ball bearings was developed to investigate the influence of a flexible cage on bearing dynamics, and a significant reduction in ball-cage pocket forces occurs as a result of modeling the cage as a flexible body.
Abstract: A model for deep-groove and angular-contact ball bearings was developed to investigate the influence of a flexible cage on bearing dynamics. The cage model introduces flexibility by representing the cage as an ensemble of discrete elements that allow deformation of the fibers connecting the elements. A finite element model of the cage was developed to establish the relationships between the nominal cage properties and those used in the flexible discrete element model. In this investigation, the raceways and balls have six degrees of freedom. The discrete elements comprising the cage each have three degrees of freedom in a cage reference frame. The cage reference frame has five degrees of freedom, enabling three-dimensional motion of the cage ensemble. Newton's laws are used to determine the accelerations of the bearing components, and a fourth-order Runge-Kutta algorithm with constant step size is used to integrate their equations of motion. Comparing results from the dynamic bearing model with flexible and rigid cages reveals the effects of cage flexibility on bearing performance. The cage experiences nearly the same motion and angular velocity in the loading conditions investigated regardless of the cage type. However, a significant reduction in ball-cage pocket forces occurs as a result of modeling the cage as a flexible body. Inclusion of cage flexibility in the model also reduces the time required for the bearing to reach steady-state operation.
66 citations
TL;DR: In this paper, the authors presented a theoretical study and experimental method to recognize the dynamic performance (stiffness and damping coefficients) of an externally pressurized deep/ shallow pockets hybrid conical bearing compensated by flat capillary restrictors.
Abstract: This paper presents a theoretical study and experimental method to recognize the dynamic performance (stiffness and damping coefficients) of an externally pressurized deep/ shallow pockets hybrid conical bearing compensated by flat capillary restrictors. The equations governing the flow of fluid film in the conical bearing together with the pressure boundary condition and the restrictor flow equation are solved by using the finite element method. A delicate test rig is constructed and bearings having a big end diameter of 97 mm, a length of 90 mm, and a radial clearance of 0.02-0.025 mm are analyzed. It is assumed that the fluid film force of the hydrostaticlhydrodynamic conical bearing is characterized by a set of linear stiffness and damping coefficients. The experiment used the impulse excitation method to recognize these coefficients and established their characteristics under different operating conditions. Numerical results are compared with the experimental results. The stability parameters of hybrid conical, hydrodynamic, and hydrostatic bearings are compared. The results show that the hybrid conical bearing has the advantages of high load carrying capability and high stability under small eccentricity.
TL;DR: In this paper, a model for elastic-plastic spherical contact of rough surfaces under combined normal and tangential loadings, with full stick contact condition, is presented, which allows evaluation of the effect of surface roughness on the real contact area, static friction and junction growth under small normal loads.
Abstract: A model for elastic-plastic spherical contact of rough surfaces under combined normal and tangential loadings, with full stick contact condition, is presented. The model allows evaluation of the effect of surface roughness on the real contact area, static friction and junction growth under small normal loads. It is shown that as the normal load approaches a certain threshold value, which depends on the plasticity index, the results of the present rough surface model approach these of previous corresponding models for smooth sphere and a rigid flat. At normal load values below the threshold load, the correlation of the present results and published experimental results is much better in comparison with the results of the smooth surface models.
TL;DR: In this paper, Wu et al. applied load sharing between asperities and fluid film in conjunction with lubricated sliding wear formulation to predict the steady state adhesive wear in gears, and verified the prediction of the model by comparing simulation results with published experimental data pertinent to steady state wear rate.
Abstract: The concept of load sharing between asperities and fluid film is applied in conjunction with lubricated sliding wear formulation proposed by Wu and Cheng (1991, “A Sliding Wear Model for Partial-EHL Contacts,” ASME J Tribol, 113, pp 134–141; 1993, “Sliding Wear Calculation in Spur Gears,” ASME J Tribol, 115, pp 493–500) to predict the steady state adhesive wear in gears Thermal effects are included using a simplified thermoelastohydrodynamic analysis The prediction of the model is verified by comparing simulation results with published experimental data pertinent to steady state wear rate The main advantages of this method are the accuracy and the remarkable computational efficiency The results of parametric simulation study are presented to investigate the effect of speed and surface roughness on a portion of load carried by asperities and wear rate
TL;DR: In this paper, the authors extended the numerical contact model of dissimilar materials developed by the authors to evaluate the maximum tangential force (in terms of the static friction coefficient) that can be sustained by a rough surface contact.
Abstract: The relative motion between two surfaces under a normal load is impeded by friction. Interfacial junctions are formed between surfaces of asperities, and sliding inception occurs when shear tractions in the entire contact area reach the shear strength of the weaker material and junctions are about to be separated. Such a process is known as a static friction mechanism. The numerical contact model of dissimilar materials developed by the authors is extended to evaluate the maximum tangential force (in terms of the static friction coefficient) that can be sustained by a rough surface contact. This model is based on the Boussinesq-Cerruti integral equations, which relate surface tractions to displacements. The materials are assumed to respond elastic perfectly plastically for simplicity, and the localized hardness and shear strength are set as the upper limits of contact pressure and shear traction, respectively. Comparisons of the numerical analysis results with published experimental data provide a validation of this model. Static friction coefficients are predicted for various material pairs in contact first, and then the behaviors of static friction involving rough surfaces are extensively investigated.
TL;DR: In this article, the structural stiffness of a gas bearing with bump-strip compliant layers is estimated for increasing shaft temperatures, and the results show that the stiffness decreases with increasing amplitude of the applied load and shaft temperature and increases with increasing excitation frequency.
Abstract: Oil-free turbomachinery relies on gas bearing supports for reduced power losses and enhanced rotordynamic stability. Gas foil bearings (GFBs) with bump-strip compliant layers can sustain large loads, both static and dynamic, and provide damping to reduce shaft vibrations. The ultimate load capacity of GFBs depends on the material properties and configuration of the underlying bump-strip structures. In high temperature applications, thermal effects, which change the operating clearances and material properties, can considerably affect the performance of the GFB structure. This paper presents experiments conducted to estimate the structural stiffness of a test GFB for increasing shaft temperatures. A 38.17 mm inner diameter GFB is mounted on a nonrotating hollow shaft affixed to a rigid structure. A cartridge heater inserted into the shaft provides a controllable heat source and thermocouples record the temperatures on the shaft and GFB housing. For increasing shaft temperatures (up to 188°C), increasing static loads (0–133 N) are applied to the bearing and its deflection recorded. In the test configuration, thermal expansion of the GFB housing, larger than that of the shaft, nets a significant increase in radial clearance, which produces a significant reduction in the bearing’s structural stiffness. A simple physical model, which assembles the individual bump stiffnesses, predicts well the measured GFB structural stiffness. Single frequency periodic loads (40–200 Hz) are exerted on the test bearing to identify its dynamic structural stiffness and equivalent viscous damping or a dry-friction coefficient. The GFB dynamic stiffness increases by as much as 50% with dynamic load amplitudes increasing from 13 N to 31 N. The stiffness nearly doubles from low to high frequencies, and most importantly, it decreases by a third as the shaft temperature rises to 188°C. In general, the GFB dynamic stiffness is lower than its static magnitude at low excitation frequencies, while it becomes larger with increasing excitation frequency due apparently to a bump slip-stick phenomenon. The GFB viscous damping is inversely proportional to the amplitude of the dynamic load, excitation frequency, and shaft temperature. The GFB dry-friction coefficient decreases with increasing amplitude of the applied load and shaft temperature, and increases with increasing excitation frequency.
TL;DR: In this paper, the interfacial contact pressure and shear traction distributions for a sphere pressed onto an elastically similar half-space whose surface is populated by a uniform array of spherical asperities, when the normal load is constant and an oscillatory shear, less than that needed to cause sliding, is imposed.
Abstract: The interfacial contact pressure and shear traction distributions are found for a sphere pressed onto an elastically similar half-space whose surface is populated by a uniform array of spherical asperities, when the normal load is constant and an oscillatory shear, less than that needed to cause sliding, is imposed. Details of the load history suffered by asperities in an outer sliding annulus and an inner disk, where they experience partial slip, are found, together with the effects of the roughness on the overall tangential compliance and the frictional energy losses. It is shown that for the example combination of parameters chosen, under light shear loads, the rough contact absorbs less energy than a smooth one subject to the same loading history, but that for larger shearing forces the reverse is true.
TL;DR: In this article, the structure-property relationships of a wear resistant cobalt-based alloy (Stellite 6) produced from two different processing routes of powder consolidated hot isostatic pressing (HIPing) and casting were analyzed.
Abstract: Manufacturing process routes of materials can be adapted to manipulate their microstructure and hence their tribological performance. As industrial demands push the applications of tribological materials to harsher environments of higher stress, starved lubrication, and improved life performance, manufacturing processes can be tailored to optimize their use in particular engineering applications. The aim of this paper was therefore to comprehend the structure-property relationships of a wear resistant cobaltbased alloy (Stellite 6) produced from two different processing routes of powder consolidated hot isostatic pressing (HIPing) and casting. This alloy had a nominal wt % composition of Co–28Cr–4.5W–1C, which is commonly used in wear related applications in harsh tribological environments. However, the coarse carbide structure of the cast alloy results in higher brittleness and lower toughness. Hence this research was conducted to comprehend if carbide refinement, caused by changing the processing route to HIPing, could improve the tribomechanical performance of this alloy. Microstructural and tribomechanical evaluations, which involved hardness, impact toughness, abrasive wear, sliding wear, and contact fatigue performance tests, indicated that despite the similar abrasive and sliding wear resistance of both alloys, the HIPed alloy exhibited an improved contact fatigue and impact toughness performance in comparison to the cast counterpart. This difference in behavior is discussed in terms of the structure-property relationships. Results of this research indicated that the HIPing process could provide additional impact and fatigue resistance to this alloy without compromising the hardness and the abrasive/sliding wear resistance, which makes the HIPed alloy suitable for relatively higher stress applications. Results are also compared with a previously reported investigation of the Stellite 20 alloy, which had a much higher carbide content in comparison to the Stellite 6 alloy, caused by the variation in the content of alloying elements. These results indicated that the fatigue resistance did not follow the expected trend of the improvement in impact toughness. In terms of the design process, the combination of hardness, toughness, and carbide content show a complex interdependency, where a 40% reduction in the average hardness and 60% reduction in carbide content had a more dominating effect on the contact fatigue resistance when compared with an order of magnitude improvement in the impact toughness of the HIPed Stellite 6 alloy. DOI: 10.1115/1.2991122
TL;DR: In this article, the Doolittle free-volume equation was used to investigate the traction behavior in heavily loaded thermo-elastohydro-dynamic lubrication (EHL) line contacts.
Abstract: This paper investigates the traction behavior in heavily loaded thermo-elastohydro-dynamic lubrication (EHL) line contacts using the Doolittle free-volume equation, which closely represents the experimental viscosity-pressure-temperature relationship and has recently gained attention in the field of EHL, along with Tail's equation of state for compressibility. The well-established Carreau viscosity model has been used to describe the simple shear-thinning encountered in EHL. The simulation results have been used to develop an approximate equation for traction coefficient as a function of operating conditions and material properties. This equation successfully captures the decreasing trend with increasing slide to roll ratio caused by the thermal effect. The traction-slip characteristics are expected to be influenced by the limiting shear stress and pressure dependence of lubricant thermal conductivity, which need to be incorporated in the future.
TL;DR: In this article, the final configuration of a cylindrical Hertzian contact subject to oscillatory shear and undergoing wear is studied, and it is shown that the extent of the finial contact corresponds to that of the initial adhered region and the pressure distribution, and state of stress at the new contact edge are all derived.
Abstract: The final configuration of a cylindrical Hertzian contact, subject to oscillatory shear and undergoing wear, is studied. It is assumed that wear has proceeded for a long time, so that the final, modified contact is wholly adhered. It is shown that the extent of the finial contact corresponds to that of the initial adhered region and the pressure distribution, and state of stress at the new contact edge are all derived, so that the environment in which cracks nucleate is well described.
TL;DR: In this article, an integration-based multilevel contact model is proposed to estimate the accurate contact area and contact pressure under a given load. But the model is not suitable for the real contact area.
Abstract: Elastic-plastic contact of a smooth sphere and a half-space with a real machined surface is simulated using an integration-based multilevel contact model. The total surface deflection is composed of bulk and asperity deformations. They are calculated at the global and the asperity level, respectively, which are connected through the asperity-supporting load. With this new model, the accurate contact area and contact pressure under a given load are quickly predicted using a relatively coarse grid system. The calculated load-area curve shows good agreement with the experimental data. Finally, the effects of the surface topography, including roughness and the asperity radius, upon the real contact area are analyzed.
TL;DR: In this article, the effect of engine operating conditions on the distribution of power loss at component level was investigated using a single-cylinder Ricardo Hydra gasoline engine with a single cylinder.
Abstract: With new legislation coming into place for the reduction in tail-pipe emissions, the OEMs are in constant pressure to meet these demands and have invested heavily in the development of new technologies. OEMs have asked lubricant and additive companies to contribute in meeting these new challenges by developing new products to improve fuel economy and reduce emissions. Modern low viscosity lubricants with new chemistries have been developed to improve fuel consumption. However, more work is needed to formulate compatible lubricants for new materials and engine technologies. In the field of internal combustion engines, researchers and scientists are working constantly on new technologies such as downsized engines, homogeneous charge compression ignition, the use of biofuel, new engine component materials, etc., to improve vehicle performance and emissions. Mathematical models are widely used in the automotive and lubricants industry to understand and study the effect of different lubricants and engine component materials on engine performance. Engine tests are carried out to evaluate lubricants under realistic conditions but they are expensive and time consuming. Therefore, bench tests are used to screen potential lubricant formulations so that only the most promising formulations go forward for engine testing. This reduces the expense dramatically. Engine tests do give a better picture of the lubricants performance but it does lack detailed tribological understanding as crankcase oil has to lubricant all parts of the engines, which do operate under different tribological conditions. Oil in an engine experiences all modes of lubrication regimes from boundary to hydrodynamic. The three main tribological components responsible for the frictional losses in an engine are the piston assembly, valve train, and bearings. There are two main types of frictional losses associated with these parts: shear loss and metal to metal friction. Thick oil in an engine will reduce the boundary friction but will increase shear losses whereas thin oil will reduce shear friction but will increase boundary friction and wear. This paper describes how engine operating conditions affect the distribution of power loss at component level. This study was carried out under realistic fired conditions using a single cylinder Ricardo Hydra gasoline engine. Piston assembly friction was measured using indicated mean effective pressure method and the valve train friction was measured using specially designed camshaft pulleys. Total engine friction was measured using pressure-volume diagram and brake torque measurements, whereas engine bearing friction was measured indirectly by subtracting the components from total engine friction. The tests were carried out under fired conditions and have shown changes in the distribution of component frictional losses at various engine speeds, lubricant temperatures, and type of lubricants. It was revealed that under certain engine operating conditions the difference in total engine friction loss was found to be small but major changes in the contribution at component level were observed.
TL;DR: Cavitation erosion pits and their effects on erosion progression were investigated in detail for SUS 304 stainless steel, α + β brass (60/40), and pure aluminum (Al-99.999) by means of vibratory erosion as discussed by the authors.
Abstract: Cavitation erosion pits and their effects on erosion progression were investigated in detail for SUS 304 stainless steel, α + β brass (60/40), and pure aluminum (Al-99.999 and Al-99.92) by means of vibratory erosion. Two kinds of erosion pits were found on the specimen surfaces, one by microjet impact and the other by shockwave blow. Systematic observations of the feature of microjet-pits with the testing time showed that the sizes and shapes of microjet-pits did not change at all and such pits scarcely played an important role in developing the erosion. Moreover, the feature morphology of eroded surfaces, and dislodged particles and their large sizes revealed that microjet-pits had a limited effect on erosion and that the predominant failure was a fatigue process.
TL;DR: In this article, a particle-augmented mixed lubrication (PAML) model was proposed to predict material removal rate from a measured surface topography during chemical mechanical polishing.
Abstract: Chemical mechanical polishing (CMP) is a manufacturing process that is commonly used to planarize integrated circuits and other small-scale devices during fabrication. Although a number of models have been formulated, which focus on specific aspects of the CMP process, these models typically do not integrate all of the predominant mechanical aspects of CMP into a single framework. Additionally, the use of empirical fitting parameters decreases the generality of existing predictive CMP models. Therefore, the focus of this study is to develop an integrated computational modeling approach that incorporates the key physics behind CMP without using empirical fitting parameters. CMP consists of the interplay of four key tribological phenomena—fluid mechanics, particle dynamics, contact mechanics, and resulting wear. When these physical phenomena are all actively engaged in a sliding contact, the authors call this particle-augmented mixed lubrication (PAML). By considering all of the PAML phenomena in modeling particle-induced wear (or material removal), this model was able to predict wear-in silico from a measured surface topography during CMP. The predicted material removal rate (MRR) was compared with experimental measurements of copper CMP. A series of parametric studies were also conducted in order to predict the effects of varying slurry properties such as solid fraction and abrasive particle size. The results from the model are promising and suggest that a tribological framework is in place for developing a generalized first-principle PAML modeling approach for predicting CMP.
TL;DR: In this paper, the authors evaluate a cavitation model based on the complete Rayleigh-Plesset (RP) equation for use in squeeze film damper calculations, and the results underline the influence of the effects contained in the RP equation on the pressure field.
Abstract: This work is intended to evaluate a cavitation model based on the complete Rayleigh–Plesset (RP) equation for use in squeeze film damper calculations. The RP equation governs the variation in the radius of the cavitation bubbles at rest, surrounded by an infinite incompressible fluid and subjected to an external pressure. This equation is obtained from the momentum equation and it takes into account the ensemble of the phenomena related to the dynamics of the bubbles (surface tension, damping, and inertia). All the terms in the RP equation will be taken into account in the present work plus a dilatation viscosity introduced by Someya in 2003. Numerical results will be compared with experimental data obtained by Adiletta and Pietra in 2006. The results underline the influence of the effects contained in the RP equation on the pressure field.
TL;DR: In this paper, a three-dimensional thermo-elasto-plastic contact model of counterformal bodies is presented, which takes into account transient heat flux, temperature-dependent strain hardening behavior, and a realistic heat partition between surfaces.
Abstract: Sliding electrical contacts are found in many electromechanical devices, such as relays, switches, and resistance spot welding. Temperature rise due to sliding friction and electrical current may be the major source of sliding electrical contact deterioration. This paper reports the development of a three-dimensional thermo-elasto-plastic contact model of counterformal bodies, which takes into account transient heat flux, temperature-dependent strain hardening behavior, and a realistic heat partition between surfaces. Transient contact simulations induce a significant increase in computational burden. The discrete convolution and fast Fourier transform and the conjugate gradient method are utilized to improve the computation efficiency. The present model is used to study the case of a half-space sliding over a stationary sphere, and both are made of 7075 aluminum alloy; the contact resistance is considered mainly due to the surface oxide film. The simulation results indicate that the transient contact model is able to capture the history of plastic deformation accumulation and the material melting inception.
TL;DR: In this article, a porous elastic sheet damper with a magnetic fluid is proposed to compensate for the defect of a small size precision equipment, and an analytical estimation of this sheet dammer is presented to investigate variation of damping characteristics with intensity and direction of a magnetic field and to give effects of porosity of porous sheets on damping properties.
Abstract: In progress of anti-shock characteristics of small size precision equipment, a miniaturized damper is required to have better damping characteristics. However, damping efficiency becomes less as damper size decreases, and so for compensation of its defect, a porous elastic sheet damper with a magnetic fluid is proposed. An analytical estimation of this sheet damper is presented to investigate variation of damping characteristics with intensity and direction of a magnetic field and to give effects of porosity of porous sheets on damping characteristics.
TL;DR: In this article, the authors derived closed-form equations governing the shoulder-shoulder contact of asperities based on a generalization by Chang, Etsion, and Bogy.
Abstract: Approximate closed-form equations governing the shoulder-shoulder contact of asperities are derived based on a generalization by Chang, Etsion, and Bogy. The work entails the consideration of asperity shoulder-shoulder contact in which the volume conservation is assumed in the plastic flow regime. Shoulder-shoulder asperity contact gives rise to a slanted contact force comprising tangential and normal components. Each force component comprises elastic and plastic terms, which upon statistical summation yields the force component for the elastic and plastic forces for the contact of two rough surfaces. Half-plane tangential force due to elastic-plastic contact is derived through the statistical summation of tangential force component along an arbitrary tangential direction. Two sets of equations are found. In the first set of equations the functional forms are simpler and provide approximation of contact force to within 9%. The second set is enhanced equations derived from the first set of approximate equations that achieve an accuracy of within 0.2%.
TL;DR: In this article, the authors used a piezoelectric thin film transducer to excite and receive ultrasonic signals and measured the oil-film thickness in a rolling element bearing.
Abstract: This paper describes the measurement of lubricant-film thickness in a rolling element bearing using a piezoelectric thin film transducer to excite and receive ultrasonic signals. High frequency (200 MHz) ultrasound is generated using a piezoelectric aluminum nitride film deposited in the form of a very thin layer onto the outer bearing raceway. This creates a transducer and electrode combination of total thickness of less than 10 μm. In this way the bearing is instrumented with minimal disruption to the housing geometry and the oil-film can be measured noninvasively. The high frequency transducer generates a fine columnar beam of ultrasound that has dimensions less than the typical lubricated contact ellipse. The reflection coefficient from the lubricant-layer is then measured from within the lubricated contact and the oil-film thickness extracted via a quasistatic spring model. The results are described on a deep groove 6016 ball bearing supporting an 80 mm shaft under normal operating conditions. Good agreement is shown over a range of loads and speeds with lubricant-film thickness extracted from elastohydrodynamic lubrication theory.
TL;DR: In this article, a thermohydrodynamic (THD) analysis of multiwound foil bearing is presented, in which the Reynolds' equation is solved with gas viscosity as a function of temperature that is obtained from the energy equation.
Abstract: The applications of foil air bearings have been extended for use in a wide range of turbomachineries with high speed and high temperature. Lubricant temperature becomes an important factor in the performance of foil air bearings, especially at high rotational speeds and high loads or at high ambient temperature. This study presents a thermohydrodynamic (THD) analysis of multiwound foil bearing, in which the Reynolds' equation is solved with gas viscosity as a function of temperature that is obtained from the energy equation. Lobatto point quadrature is utilized to accelerate the iteration process with a sparse mesh across film thickness. A finite element model of the foil is used to describe the foil elasticity. An iterative procedure is performed between the Reynolds equation, the foil elastic deflection equation, and the energy equation until convergence is achieved. A three-dimensional temperature prediction of air film is presented, and a comparison of THD to isothermal results is made to emphasize the importance of thermal effects. Finally, published experimental data are used to validate this numerical solution.
TL;DR: In this paper, the performance characteristics of a constant flow valve compensated multirecess hydrostatic journal bearing operating with micropolar lubricant were analyzed for a wide range of non-dimensional load, lubricant flow, and micropolarity parameters.
Abstract: This paper presents a theoretical study of the performance characteristics of a constant flow valve compensated multirecess hydrostatic journal bearings operating with micropolar lubricant. The finite element method and iterative procedure have been used to solve the modified Reynolds equation governing the micropolar lubricant flow in the bearing. The performance characteristics are presented for a wide range of nondimensional load, lubricant flow, and micropolar parameters. It has been observed that the micropolar parameters significantly influence the performance characteristics of the bearing.