Showing papers in "Journal of Tribology-transactions of The Asme in 2013"

The Effect of Nanoparticles on the Real Area of Contact, Friction, and Wear

Abstract: Although nanoparticle additives have been the topic of multiple studies recently, very little work has attempted to explicitly model the third body contact of nanoparticles. This work presents and uses a novel methodology to model nanoparticles in contact between rough surfaces. The model uses two submodels to handle different scales of contact, namely the nano-sized particles and micrometer-sized roughness features. Silicon nanoparticles suspended in conventional lubricant are modeled in contact between steel rough surfaces. The effect of the particles on contact force and real area of contact has been modeled. The model makes predictions of the coefficient of friction and wear using fundamental models. The results suggest that particles would reduce the real area of contact and, therefore, decrease the friction force. Also, particles could induce abrasive wear by scratching the surfaces. The implications of the model are also discussed, and the arguments and results have been linked to available experimental data. This work finds that particle size and distribution are playing a key role in tribology characteristics of the nanolubricants. [DOI: 10.1115/1.4024297]

Complete Analytical Expression of the Stiffness Matrix of Angular Contact Ball Bearings

Abstract: Angular contact ball bearings are predominantly used for guiding high speed rotors such as machining spindles. For an accurate modelling, dynamic effects have to be considered, most notably in the bearings model. The paper is based on a dynamic model of angular contact ball bearings. Different kinematic hypotheses are discussed. A new method is proposed for the computation of the stiffness matrix: a complete analytical expression including dynamic effects is presented in order to ensure accuracy at high shaft speed. It is demonstrated that the new method leads to the exact solution, contrary to the previous ones. Besides, the computational cost is similar. The new method is then used to investigate the consequence of the kinematic hypotheses on bearing stiffness values. Last, the relevance of this work is illustrated through the computation of the dynamic behavior of a high speed milling spindle. The impact of this new computation method on the accuracy of a finite element spindle model is quantified.

Analysis of Micro-Elastohydrodynamic Lubrication and Prediction of Surface Fatigue Damage in Micropitting Tests on Helical Gears

Abstract: The paper describes results obtained from the micro-elastohydrodynamic lubrication (micro-EHL) modeling of the gear tooth contacts used in micropitting tests together with a contact fatigue and damage accumulation analysis of the surfaces involved. Tooth surface profiles were acquired from pairs of helical test gears and micro-EHL simulations were performed corresponding to surfaces that actually came into contact during the meshing cycle. Plane strain fatigue and damage accumulation analysis shows that the predicted damage is concentrated close to the tooth surfaces and this supports the view that micropitting arises from fatigue at the asperity contact level. A comparison of the micropitting performance of gears finish-ground by two alternative processes (generation-grinding and form-grinding) suggests that 3D “waviness” may be an important factor in explaining their different micropitting behavior.

An Efficient Numerical Method With a Parallel Computational Strategy for Solving Arbitrarily Shaped Inclusions in Elastoplastic Contact Problems

Abstract: The plastic zone developed during elastoplastic contact may be effectively modeled as an inclusion in an isotropic half space. This paper proposes a simple but efficient computational method to analyze the stresses caused by near surface inclusions of arbitrary shape. The solution starts by solving a corresponding full space inclusion problem and proceeds to annul the stresses acting normal and tangential to the surface, where the numerical computations are processed by taking advantage of the fast Fourier transform techniques with a parallel computing strategy. The extreme case of a cuboidal inclusion with one facet on the surface of the half space is chosen to validate the method. When the surface truncation domain is extended sufficiently and the grids are dense enough, the results based on the new approach are in good agreement with the exact solutions. When solving a typical elastoplastic contact problem, the present analysis is roughly two times faster than the image inclusion approach and six times faster than the direct method. In addition, the present work demonstrates that a significant enhancement in the computational efficiency can be achieved through the introduction of parallel computation.

The Effect of Triangle-Shaped Surface Textures on the Performance of the Lubricated Point-Contacts

Abstract: It has been recognized that purposefully designed surface texturing can contribute to the improvement of tribological performance of elements and friction reduction. However, its optimal parameters may depend on the operating conditions. This paper investigated the effect of a triangle-shaped dimples array on the tribological performance of the lubricated point-contacts under different lubrication regimes, based on the rotational sliding experiment of a patterned steel disk against smooth steel balls. The dimples arrays were produced by laser process and characterized by the 3D profilometer. A series of tests were conducted with different dimple parameters including depth, coverage ratio, size, and direction. Stribecklike curves were obtained to depict the transition of lubrication regimes, and the electrical contact resistance was utilized to qualitatively characterize the lubrication status. The test results showed that the dimples arrays with different sizes, depths and coverage ratios had a distinct effect on the friction behaviors. Compared with the nontextured surfaces, when the dimple depth decreased from 30μm to zero with fixed coverage ratio and size, the friction coefficient firstly decreased, and then increased. The friction coefficient finally approached that of the nontextured surface, during which the lowest value appeared at the dimple depth of approximately 10∼15μm. The coverage ratio of texture showed the similar effect on the friction coefficient. Usually, the coverage ratio of approximately 10% resulted in the lowest friction coefficient. The dimple size and direction also had obvious effects on the friction coefficient. Thus, it can be concluded that there exists a set of optimal values for the dimple depth, coverage ratio, size, and direction to realize the friction reduction.

The Effect of Determining Topography Parameters on Analyzing Elastic Contact Between Isotropic Rough Surfaces

Abstract: Elastic contact between two computer-generated isotropic rough surfaces is studied. First the surface topography parameters, including the asperity density, mean summit radius, and standard deviation of asperity heights of the equivalent rough surface, are determined using an 8-nearest neighbor summit identification scheme. Second, many cross-sections of the equivalent rough surface are traced and their individual topography parameters are determined from their corresponding spectral moments. The topography parameters are also obtained from the average spectral moments of all cross-sections. The asperity density is found to be the main difference between the summit identification scheme and the spectral moments method. The contact parameters, such as the number of contacting asperities, real area of contact, and contact load for any given separation between the equivalent rough surface and a rigid flat, are calculated by summing the contributions of all the contacting asperities using the summit identification model. These contact parameters are also obtained with the Greenwood-Williamson (GW) model using the topography parameters from each individual cross-section and from the average spectral moments of all crosssections. Three different surfaces characterized by a different autocorrelation length, and three different sampling intervals were used to study how the method to determine topography parameters affects the resulting contact parameters.

Novel Model for Partial-Slip Contact Involving a Material With Inhomogeneity

Abstract: Contacts involving partial slip are commonly found at the interfaces formed by mechanical components. However, most theoretical investigations of partial slip are limited to homogeneous materials. This work proposes a novel and fast method for partial-slip contact involving a material with an inhomogeneity based on the equivalent inclusion method, where the inhomogeneity is replaced by an inclusion with properly chosen eigenstrains. The stress and displacement fields due to eigenstrains are formulated based on the half-space inclusion solutions recently derived by the authors and solved with a three-dimensional fast Fourier transform algorithm. The effectiveness and accuracy of the proposed method is demonstrated by comparing its solutions with those from the finite element method. The partial slip contact between an elastic ball and an elastic half space containing a cuboidal inhomogeneity is further investigated. A number of in-depth parametric studies are performed for the cuboidal inhomogeneity with different sizes and at different locations. The results reveal that the contact behavior of the inhomogeneous material is more strongly influenced by the inhomogeneity when it is closer to the contact center and when its size is larger.

Compressible Fluid Model for Hydrodynamic Lubrication Cavitation

Abstract: In this paper, it is shown how vaporous cavitation in lubricant films can be modeled in a physically justified manner through the constitutive (compressibility) relation of the fluid. The method treats the flow as a homogeneous mixture employing a “void fraction” variable to quantify the intensity of cavitation. It has been already proposed to study cavitation in fluid mechanics. It is shown how the widely used Jakobsson–Floberg–Olsson (JFO) / Elrod–Adams (EA) mass flow conservation model can be compared with this new model. Moreover, the new model can incorporate the variation of the viscosity in the cavitation region and allows the pressure to fall below a cavitation pressure. Numerical computations show that discrepancy with JFO/EA is mostly associated with light loading condition, starved situation or viscosity effects.

Study of the Influence of Heat Convection Coefficient on Predicted Performance of a Large Tilting-Pad Thrust Bearing

Abstract: Part of the heat generated by the shearing of the lubricating film during operation of a hydrodynamic bearing is transferred to the bearing components. In the case of the pad, which is usually fully submerged in the lubricating oil, heat is further transferred at the pad free walls to the oil by convection. This mechanism causes a thermal gradient in a pad and, consequently, its thermal deflection. In large hydrodynamic thrust bearings, thermal deflection of the pads is an important phenomenon influencing bearing performance. For such bearings, pad distortion can reach the level of hydrodynamic film thickness and can significantly change the bearing’s properties. In this paper, the study of the influence of the heat convection coefficient on the predicted performance of a large hydrodynamic thrust bearing is presented. Two sets of convection coefficients at the pad free surfaces are investigated with the use of thermo-elasto-hydrodynamic (TEHD) calculations. An analysis is carried out for the Itaipu hydro turbine thrust bearing with the outer diameter equal to 5.2 m, which is one of the biggest hydro power plants in the world. The results of the theoretical predictions are compared to the measured data collected during bearing operation.

Real-Gas Effects in Foil Thrust Bearings Operating in the Turbulent Regime

Abstract: In this study, an elastohydrodynamic model was created for predicting the pressure field in a compliant thrust bearing assembly lubricated by high pressure CO2. This application is of significance due to ongoing research into the closed-cycle supercritical CO2 turbine as a high-efficiency alternative to steam turbines. Hardware development for this concept has been led by Sandia National Laboratories, where turbomachinery running on gas foil thrust and journal bearings is being tested. The model accounts for the fluid velocity field, hydrodynamic pressure, and frictional losses within the lubrication layer by evaluating the turbulent Reynolds equation coupled with an equation for structural deformation in the bearings, and the fluid properties database RefProp v9.0. The results of numerical simulations have been compared with empirical correlations, with reasonable agreement attained. Of particular interest is the contrast drawn between the performance of high pressure CO2 as a lubricant, and ambient pressure air. Parametric studies covering a range of fluid conditions, operating speeds, and thrust loads were carried out to illustrate the value of this model as a tool for improved understanding and further development of this nascent technology.

Foil Bearing Design Guidelines for Improved Stability

Abstract: Experimental evidence in the literature suggests that foil bearing-supported rotors can suffer from subsynchronous vibration. While dry friction between top foil and bump foil is thought to provide structural damping, subsynchronous vibration is still an unresolved issue. The current paper aims to shed new light onto this matter and discusses the impact of various design variables on stable foil bearing-supported rotor operation. It is shown that, while a time domain integration of the equations of motion of the rotor coupled with the Reynolds equation for the fluid film is necessary to quantify the evolution of the rotor orbit, the underlying mechanism and the onset speed of instability can be predicted by coupling a reduced order foil bearing model with a rigid-body, linear, rotordynamic model. A sensitivity analysis suggests that structural damping has limited effect on stability. Further, it is shown that the location of the axial feed line of the top foil significantly influences the bearing load capacity and stability. The analysis indicates that the static fluid film pressure distribution governs rotordynamic stability. Therefore, selective shimming is introduced to tailor the unperturbed pressure distribution for improved stability. The required pattern is found via multiobjective optimization using the foil bearing-supported rotor model. A critical mass parameter is introduced as a measure for stability, and a criterion for whirl instability onset is proposed. It is shown that, with an optimally shimmed foil bearing, the critical mass parameter can be improved by more than two orders of magnitude. The optimum shim patterns are summarized for a variety of foil bearing geometries with different L/D ratios and different degrees of foil compliance in a first attempt to establish more general guidelines for stable foil bearing design. At low compressibility (λ < 2), the optimum shim patterns vary little with bearing geometry; thus, a generalized shim pattern is proposed for low compressibility numbers.

Investigation of Protein Adsorption Mechanism and Biotribological Properties at Simulated Stem-Cement Interface

Abstract: Debonding of the stem–cement interface occurs inevitably for almost all stem designsunder physiological loading, and the wear debris generated at this interface is showingan increasing significance in contributing to the mechanical failure of cemented total hipreplacements. However, the influence of protein adsorption onto the femoral stem and thebone cement surfaces has not been well taken into consideration across previous in vitrowear simulations. In the present study, the protein adsorption mechanism and biotribo-logical properties at the stem-cement interface were investigated through a series of fric-tional tests using bone cements and femoral stems with two kinds of surface finishes,lubricated by calf serum at body temperature. The friction coefficient was dependent onthe surface finish of the samples, with an initial much lower value obtained for the pol-ished contacting pairs followed by a sudden increase in the friction coefficient withregard to the tests performed at higher frequencies. The friction coefficient did notchange much during the tests for the glass-bead blasted contacting pairs. In addition,proteins from the calf serum were found to adsorb onto both the femoral stem and thebone cement surfaces, and the thickness of the physically adsorbed proteins on thepolished metallic samples was more than 10lm, which was measured using an opticalinterferometer and validated through a vertical scanning methodology based on Ramanspectroscopy. An initial protein adsorption mechanism and biotribological properties atthe stem-cement interface were examined in this study, and it suggested that wear at thestem-cement interface may be postponed or reduced by tailoring physicochemical proper-ties of the femoral components to promote protein adsorption.[DOI: 10.1115/1.4023802]Keywords: stem-cement interface, biotribology, surface characterization, proteinadsorption

A Study on the Tribological Characteristics of a Magneto-Rheological Elastomer

Abstract: Research on the applications of magneto-rheological (MR) elastomers in mechanical engineering has greatly expanded, whereas the performance of MR fluids in tribology has rarely been investigated. In this study, the tribological characteristics of an MR elastomer are identified in order to improve tribological performance with the activation of a magnetic field. Microscopic changes in the surface and in the MR particles are investigated. The friction and wear of an MR elastomer is measured using a pin-on-disc tester under applied and unapplied magnetic fields. In addition, the linear sliding friction of an MR elastomer with respect to different velocities and loads is measured using a linear sliding tester.

Wear Simulation of Metal-on-Metal Hip Replacements With Frictional Contact

Abstract: Preclinical wear evaluation is extremely important in hip replacements, wear being one of the main causes of failure. Experimental tests are attractive but highly cost demanding; thus predictive models have been proposed in the literature, mainly based on finite element simulations. In such simulations, the effect of friction is usually disregarded, as it is considered not to affect the contact pressure distribution. However, a frictional contact could also result in a shift of the location of the nominal contact area, which can thus modify the wear maps. The aim of this study is to investigate this effect in wear prediction for metal-on-metal implants. Wear assessment was based on a purpose-developed mathematical model, extension of a previous one proposed by the same authors for metal-on-plastic implants. The innovative aspect of the present study consists in the implementation of a modified location of the nominal contact point due to friction, which takes advantage of the analytical formulation of the wear model. Simulations were carried out aimed at comparing total and resurfacing hip replacements under several gait conditions. The results highlighted that the adoption of a frictional contact yields lower linear wear rates and wider worn areas, while for the adopted friction coefficient (f=0.2), the total wear volume remains almost unchanged. The comparison between total and resurfacing replacements showed higher scaled wear volumes (wear volume divided by wear factor) for the latter, in agreement with the literature. The effect of the boundary conditions (in vivo versus in vitro) was also investigated remarking their influence on implant wear and the need to apply more physiological-like conditions in hip simulators. In conclusion although friction is usually neglected in numerical wear predictions, as it does not affect markedly the contact pressure distribution, its effect in the location of the theoretical contact point was observed to influence wear maps. This achievement could be useful for increasing the correlation between numerical and experimental simulations, usually based on the total wear volume. In order to improve the model reliability, future studies will be devoted to implement the geometry update by combining the present model to finite element analyses. On the other hand, further experimental investigations are required to get out from the wide dispersion of wear factors reported in the literature.

Modeling and Analysis of the Meshing Losses of Involute Spur Gears in High-Speed and High-Load Conditions

Abstract: A first-principle based mathematical model is developed in this paper to analyze the meshing losses in involute spur gears operating in high-load and high-speed conditions. The model is fundamentally simple with a few clearly defined physical parameters. It is computationally robust and produces meaningful trends and relative magnitudes of the meshing losses with respect to the variations of key gear and lubricant parameters. The model is evaluated with precision experimental data. It is then used to study the effects of various gear and lubricant parameters on the meshing losses including gear module, pressure angle, tooth addendum height, thermal conductivity, and lubricant pressureviscosity and temperature-viscosity coefficients. The results and analysis suggest that gear module, pressure angle, and lubricant pressure-viscosity and temperature-viscosity coefficients can significantly affect the meshing losses. They should be the design parameters of interest to further improve the energy efficiency in high-performance, multistage transmission systems. Although the model is developed and results obtained for spur gears, the authors believe that the trends and relative magnitudes of the meshing losses with respect to the variations of the gear and lubricant parameters are still meaningful for helical gears. [DOI: 10.1115/1.4007809]

Influence of Minimum Quantity Lubrication on Friction Coefficient and Work-Material Adhesion During Machining of Cast Aluminum With Various Cutting Tool Substrates Made of Polycrystalline Diamond, High Speed Steel, and Carbides

Abstract: Due to the increasing emphasis on environmental constraints, industry works on how to limit the massive use of lubricants by using the micro-pulverization of oil in machining processes and, especially, in the machining of aluminum alloys for the automotive industry. The success of a machining operation is dependent on a friction coefficient and weak adhesion with the tool-work material interface. This paper aims at identifying the influence of cutting tool substrates (high speed steel (HSS), carbide, polycrystalline diamond (PCD)) and of minimum quantity lubrication (MQL) on the friction coefficient and on adhesion in tribological conditions corresponding to the ones observed in the cutting of aluminum alloys (sliding velocity: 20-1500 m/min). An open ball-on-cylinder tribometer, especially designed to simulate these tribological conditions through Hertz contact, has been used. It has been shown that HSS and carbide substrates lead to large friction coefficients (0.8–1) and substantial adhesion in dry conditions, whereas PCD substrates would lead to lower average friction coefficient values (0.4–0.5) and very limited adhesion, which proves the necessity of using PCD tools in the dry machining of aluminum. It has also been shown that the application of MQL leads to a large decrease of the friction coefficient (0.1–0.2) and eliminates almost all traces of adhesions on pins for any substrates, which shows that MQL is an interesting compromise between dry machining and flood cooling.

Four-Point Contact Ball Bearing Model With Deformable Rings

Abstract: In many applications, such as four-point contact slewing bearings or main shaft angular contact ball bearings, the rings and housings are so thin that the assumption of rigid rings does not hold anymore. In this paper, several methods are proposed to account for the flexibility of rings in a quasi-static ball bearing numerical model. The modeling approach consists of coupling a semianalytical approach and a finite element (FE) model to describe the deformation of the rings and housings. The manner in which this weak coupling is made differs depending on how the structural deformation of the ring and housing assemblies is injected into the set of nonlinear geometrical and equilibrium equations in order to solve them. These methods enable us to account for ring ovalization, ring twist, and raceway opening (including change of conformity) since a tulip deformation mode of the ring groove is observed for high contact angles. Either the torus fitting technique or mean displacement computation are used to determine these geometrical parameters. A comparison between the different approaches allows us to study, in particular, the impact of raceway conformity change. The loads used in this investigation are chosen in order that the maximum contact pressure (the Hertz pressure) at the ball-raceway interface remains below 2000 MPa, without any contact ellipse truncation. For the ball bearing example considered here, relative differences of up to 30% on the axial displacement, 10% on the maximum contact pressure, and 10% on the contact angle are observed by comparing rigid and deformable rings for a typical loading representative of the one encountered in operation. Despite the local change of conformity, which becomes significant at high contact angles and for thin ball bearing flanges, it is shown that this hardly affects the internal load distribution. The paper ends with a discussion on how the ring and housing flexibility may affect the loading envelope when the truncation of the contact ellipse is an issue.

Influence of Surface Roughness Lay Directionality on Scuffing Failure of Lubricated Point Contacts

Abstract: The influence of roughness lay directionality on scuffing failure is studied considering different roughness lay direction combinations of the contacting surfaces of a ball-on-disk contact. Using a recently developed scuffing model Li et al., (2013, “A Model to Predict Scuffing Failures of a Ball-On-Disk Contact,” Tribol. Int., 60, pp. 233–245)., the bulk temperature and flash temperature are predicted for each roughness lay combination within the load range from 0.76 GPa to 2.47 GPa in a step-wise manner under the rolling velocity of 10 m/s and slide-to-roll ratio of −0.5 to show substantial impacts of roughness lay directionality on scuffing resistance performance (SRP). It is found (i) the lay direction combination that results into contacts of asperities with small contact radii leads to increased local contact pressures and frictional heat flux, reducing SRP; (ii) the continuous asperity contact along the sliding direction leads to continuous surface temperature rise and lowers SRP; and (iii) the lubricant side leakage caused by the pressure gradient in the direction normal to the sliding direction leads to reduced SRP. With these main mechanisms in effect, the SRP of a contact decreases as the deviation between the roughness texture orientations of the two surfaces increases. The surfaces with their roughness lay directions both perpendicular to the sliding direction exhibits best SRP. The surfaces with one roughness lay direction positioned in line with the direction of sliding and the other positioned perpendicular to the sliding direction shows worst SRP.

A Thermohydrodynamic Analysis of Dry Gas Seals for High-Temperature Gas-Cooled Reactor

Abstract: A comprehensive analysis method is proposed to resolve the problem of simulating the complex thermoflow with two kinds of distinct characteristic lengths in a dry gas seal. A conjugated simulation of the complicated heat transfer and the gas film flow is carried out by using the commercial computational fluid dynamics (CFD) software CFX. By using the proposed method, three-dimensional velocity and pressure fields in the gas film flow and the temperature distribution within the sealing rings are investigated for three kinds of film thickness, respectively. A comparison of thermohydrodynamic characteris- tics of the dry gas seal is conducted between the sealed gas of air and helium. The latter one is used in a helium compressor for a high-temperature gas-cooled reactor (HTGR). From comparisons and discussions of a series of simulation results, it will be found that the comprehensive proposal is effective and simulation results are reasonable. Even under a hypothetical accidental condition, the maximum temperature rise in the dry gas seal is within the acceptable range of HTGR safety requirements. (DOI: 10.1115/1.4007807) In Luan and Khonsari's numerical study (9), the heat generation at the contact interface between seal rings, heat conduction into the rings, and heat convection into the surrounding fluid in the chamber were also considered. In Brunetiere and Modolo's paper (8), a correlation for the global Nusselt number for the rotating ring and the static disc was proposed, in which the Nusselt number is a function of the Reynolds number of the flow, Prandtl number, the ratio of the fluid, and material thermal conductivities. Also it concluded that the heat source was located in the contact between the rotating and the stationary rings and depended on the tempera- ture distribution in the solids. In all of the previous studies, the gas film between the rotating and stationary ring was simplified as a heat source, which made the problem simpler, but involved unreality of the model. However, since the gas film is approximately in the range of lami- nar flow, while the flow in the chamber is turbulent due to large distinct characteristic length, it is very difficult to resolve them in one calculation. In the present study, a comprehensive analysis method is pro- posed to resolve the problem of simulating a complex thermoflow with two kinds of distinct characteristic lengths in the dry gas seal by considering the effective factors step by step. Firstly, the flow in the gas film is resolved through the isothermal model. The fric- tion heat is obtained and it is assumed to be the heat source in the preliminary model. Secondly, a conjugate heat transfer method is employed in the preliminary model to evaluate the convective heat transfer coefficient between seal rings and the sealed me- dium, with a simplification that the gas film is a heat source and the friction heat is transferred into the sealing rings. Then, in the detailed model, an improved conjugate heat transfer method is proposed to simulate the physical nonisothermal flow field by using convective heat transfer coefficient calculated in the prelim- inary model as boundary conditions. Finally, the proposed method is employed to predict thermohydrodynamics of the dry gas seal in the sealed gas of helium, even under a hypothetical accidental condition. A comparison of thermohydrodynamic characteristics of the dry gas seal is also made between the sealed gas of helium and air. 1

Morton Effect Cyclic Vibration Amplitude Determination for Tilt Pad Bearing Supported Machinery

Abstract: This paper presents theoretical models and simulation results for the synchronous, thermal transient, instability phenomenon known as the Morton effect. A transient analysis of the rotor supported by tilting pad journal bearing is performed to obtain the transient asymmetric temperature distribution of the journal by solving the variable viscosity Reynolds equation, a 2D energy equation, the heat conduction equation, and the equations of motion for the rotor. The asymmetric temperature causes the rotor to bow at the journal, inducing a mass imbalance of overhung components such as impellers, which changes the synchronous vibrations and the journal’s asymmetric temperature. Modeling and simulation of the cyclic amplitude, synchronous vibration due to the Morton effect for tilting pad bearing supported machinery is the subject of this paper. The tilting pad bearing model is general and nonlinear, and thermal modes and staggered integration approaches are utilized in order to reduce computation time. The simulation results indicate that the temperature of the journal varies sinusoidally along the circumferential direction and linearly across the diameter. The vibration amplitude is demonstrated to vary slowly with time due to the transient asymmetric heating of the shaft. The approach’s novelty is the determination of the large motion, cyclic synchronous amplitude behavior shown by experimental results in the literature, unlike other approaches that treat the phenomenon as a linear instability. The approach is benchmarked against the experiment of de Jongh. [DOI: 10.1115/1.4007884]

Influence of Surface Waviness on the Thermal Elastohydrodynamic Lubrication of an Eccentric-Tappet Pair

Abstract: The effect of single-sided and double-sided harmonic surface waviness on the film thickness, pressure, and temperature oscillations in an elastohydrodynamically lubricated eccentric-tappet pair has been investigated in relation to the eccentricity and the waviness wavelength. The results show that, during one working cycle, the waviness causes significant fluctuations of the oil film, pressure, and temperature, as well as a reduction in minimum film thickness. Smaller wavelength causes more dramatic variations in oil film. The fluctuations of the pressure, film thickness, temperature, and traction coefficient caused by double-sided waviness are nearly the same compared with the single-sided waviness, but the variations are less intense.