A Parametric Analysis of the Thermal Shear Localization in Elastohydrodynamic Lubrication Films

2005 ◽  
Vol 128 (1) ◽  
pp. 79-84 ◽  
Author(s):  
L. Chang
Keyword(s):  
Elastohydrodynamic Lubrication ◽  
Shear Localization ◽  
Dimensionless Group ◽  
Thermally Induced ◽  
Critical Range ◽  
Group Parameter ◽  
High Degree ◽  
Range Of Values ◽  
Lubricant Viscosity ◽  
Newtonian Behavior

Experiments and computer simulations have revealed some unusual results of elastohydrodynamic lubrication (EHL) associated with a high degree of thermally induced inhomogeneous shear across the lubricant film, or thermal shear localization. The results include the development of a sizable film dimple in the central EHL region and a dramatic reduction in EHL traction. In this study, a theoretical analysis is carried out to determine the conditions under which the thermal shear localization may develop in EHL films. For a Newtonian lubricant obeying the Barus law of viscosity, a dimensionless group-parameter is identified that fully governs the degree of the thermal inhomogeneous shear. Results are presented that show the critical range of values of this parameter corresponding to the onset of the shear localization. The analysis is also extended to lubricants with non-Newtonian behavior. Results suggest that the same dimensionless group-parameter may be used to measure the degree of the shear localization when the lubricant viscosity in the parameter is replaced by an effective viscosity that accounts for the non-Newtonian effect.

A Parametric Analysis of the Thermal Shear Localization in EHL Films

2005 ◽  
Author(s):  
L. Chang
Keyword(s):  
Elastohydrodynamic Lubrication ◽  
Shear Localization ◽  
Dimensionless Group ◽  
Theoretical Formulation ◽  
Thermally Induced ◽  
Critical Range ◽  
Group Parameter ◽  
High Degree ◽  
Range Of Values ◽  
Lubricant Viscosity

Experiments and computer simulations [1] have revealed some unusual results of elastohydrodynamic lubrication (EHL) associated with a high degree of thermally induced inhomogeneous shear across the lubricant film, or thermal shear localization. The results include the development of a sizable film dimple in the central EHL region [2] and a dramatic reduction in EHL traction [3, 4]. In this study, a theoretical analysis is carried out to determine the conditions under which the thermal shear localization may develop in EHL films. For a Newtonian lubricant obeying the Barus law of viscosity, a dimensionless group-parameter is identified that fully governs the degree of the thermal inhomogeneous shear. Results are presented that show the critical range of values of this parameter corresponding to the onset of the shear localization. The analysis is also extended to lubricants with non-Newtonian behavior. Results suggest that the same dimensionless group-parameter may be used to measure the degree of the shear localization when the lubricant viscosity in the parameter is replaced by an effective viscosity that accounts for the non-Newtonian effect. Reference [5] presents details of the theoretical formulation and results analysis.

scholarly journals Effects of non-Newtonian lubricants and elastic coating on transient elastohydrodynamic lubrication at impact squeeze loading

2019 ◽  
Vol 11 (7) ◽  
pp. 168781401986607
Author(s):  
Li-Ming Chu ◽  
Yuh-Ping Chang ◽  
Hsiang-Chen Hsu
Keyword(s):  
Elastohydrodynamic Lubrication ◽  
Flow Index ◽  
Transient Pressure ◽  
Academic Innovation ◽  
Pressure Profiles ◽  
The Impact ◽  
Peak Increase ◽  
Ball Motion ◽  
Lubricant Viscosity ◽  
Peak Value

This study explores the effects of non-Newtonian lubricants on elastohydrodynamic lubrication with coating at impact and rebound loading using power law lubricants. The coupled transient modified Reynolds, rheology, elasticity deformation, and ball motion equations are solved simultaneously, thus obtaining the transient pressure profiles, film shapes, normal squeeze velocities and accelerations. The effect of the flow index ( n) is equivalent to enhancing the lubricant viscosity, also enlarging the damper effect. The simulation results reveal that the film thickness, the primary peak, and the secondary peak increase with increasing the flow index. The greater the flow index is, the earlier the dimple form, and the smaller the maximum value of the impact force is. The rebounding velocity and the peak value of acceleration increase with decreasing the flow index. Moreover, this research possesses academic innovation and industrial application.

Theoretical Investigation in Transient Elastohydrodynamic Lubrication of Reciprocating Motion in Air Compressor Piston Pin

2012 ◽  
Vol 622-623 ◽  
pp. 1821-1825
Author(s):  
Khanittha Wongseedakaew
Keyword(s):  
Friction Coefficient ◽  
Reynolds Equation ◽  
Initial Conditions ◽  
Elastohydrodynamic Lubrication ◽  
Approximation Technique ◽  
Air Compressor ◽  
Compressor Piston ◽  
Minimum Film Thickness ◽  
Bearing Materials ◽  
Lubricant Viscosity

This paper presents the effect of squeeze motion to elastohydrodynamic lubrication (EHL) in piston pin of air compressor with non-Newtonian lubricants based on a Carreau viscosity model. The time dependent modified Reynolds equation and elasticity with initial conditions were formulated and solved numerically using a multigrid multilevel with full approximation technique for a piston pin. Effects of bearing materials and liquid properties were examined. The results show that minimum film thickness and friction coefficient increases when lubricant viscosity increases. At the same time, for increasing of elastic modulus of bearing bushing the friction coefficient decreases.

The elastohydrodynamic lubrication of piston rings

1983 ◽  
Vol 386 (1791) ◽  
pp. 409-430 ◽  
Keyword(s):  
Film Thickness ◽  
Combustion Chamber ◽  
Diesel Engines ◽  
Elastohydrodynamic Lubrication ◽  
Cylinder Liner ◽  
Piston Rings ◽  
Lubrication Regimes ◽  
Piston Seal ◽  
Cylinder Liners ◽  
Lubricant Viscosity

The piston seal that separates the hostile environment of the combustion chamber from the crankcase that contains the lubricant is an essential machine element in reciprocating engines. The sealing force pressing the piston rings against the cylinder liner varies with the combustion chamber pressure to form an effective self-adjusting mechanism. The conjunctions between piston rings and cylinder liners are thus subjected to cyclic variations of load, entraining velocity and effective lubricant temperature as the piston reciprocates within the cylinder. Recent theoretical and experimental studies have confirmed that piston rings enjoy hydrodynamic lubrication throughout most of the engine cycle, but that a transition to mixed or boundary lubrication can be expected near top dead centre. The purpose of the present paper is to examine the suggestion that elastohydrodynamic lubrication might contribute to the tribological performance of the piston seal, particularly near top dead centre. The mode of lubrication in eight four-stroke and six two-stroke diesel engines is assessed in terms of the dimensionless viscosity and elasticity parameters proposed by Johnson (1970), and the associated map of lubrication régimes. The survey indicates unequivocally that elastohydrodynamic action can be expected during part of the stroke in all the engines considered. In the second part of the paper a detailed examination of the influence of elastohydrodynamic action in one particular engine is presented to confirm the general findings recorded in the study of lubrication régimes. Current analysis of the lubrication of rigid piston rings already takes account of the variation of surface temperature along the cylinder liner and its influence upon lubricant viscosity. It is shown that, when the enhancing influence of pressure upon viscosity is added to the analysis of rigid piston rings, the predicted cyclic minimum film thickness is more than doubled. Full elastohydrodynamic action, involving both local distortion of the elastic solids and the influence of pressure upon viscosity, results in a fourfold increase in film thickness. It is further shown that it is necessary to take account of the variation of squeeze-film velocity throughout the lubricated conjunction at each crank angle if reliable predictions of film shape and thickness are to be achieved. It is thus concluded that the wave of elastic deformation, which ripples up and down the cylinder liners many times each second in diesel engines, together with the associated local elastic deformations on the piston rings themselves, combine with the influence of pressure upon lubricant viscosity to enhance the minimum oil film thickness in the piston seal by elastohydrodynamic action.

Measurement of Boundary Lubricant Viscosity at Metal-Deformation Pressures (3000 Atmospheres, 20 Tons/Sq In.)

1967 ◽  
Vol 89 (3) ◽  
pp. 272-281 ◽  
Author(s):  
G. W. Rowe
Keyword(s):  
Boundary Lubrication ◽  
Flat Surface ◽  
Hydrodynamic Lubrication ◽  
Elastohydrodynamic Lubrication ◽  
Wire Drawing ◽  
Average Pressure ◽  
Boundary Lubricant ◽  
Metal Deformation ◽  
Local Pressures ◽  
Lubricant Viscosity

In many metalworking operations, such as rolling and wire drawing, the average pressure acting between the workpiece and the tool will be of the order of the yield stress of the metal, usually 20–50 tons/sq in. The lubricant temperature may also rise by 60 deg C or more. Any consideration of hydrodynamic lubrication in these operations should thus take account of the large viscosity changes which may occur under such pressures and temperatures. In addition, it is probable that the rate of shear will be important [1], but this will not be considered in this paper. Local pressures of the same order are developed in typical boundary-lubrication apparatus using a hemispherical slider on a flat surface under kilogram loads [2]. Information on the pressure and temperature coefficients of viscosity for lubricants is therefore important also in studies of boundary lubrication and elastohydrodynamic lubrication [3], especially in the presence of boundary additives [4]. This paper describes a simple apparatus for viscosity measurement at temperatures up to 70 deg C and pressures up to 20 tons/sq in. (3000 atmospheres) or with future modifications up to 45 tons/sq in., together with some results for fluids with and without boundary additives.

Reduced double-minimum potential curves for XY3 pyramidal molecules

1985 ◽  
Vol 50 (7) ◽  
pp. 1519-1536 ◽  
Author(s):  
Vladimír Špirko ◽  
Svatopluk Civiš ◽  
Stanislav Beran ◽  
Petr Čársky ◽  
Jürgen Fabian
Keyword(s):  
Experimental Data ◽  
Ab Initio ◽  
Degree Of Approximation ◽  
Potential Functions ◽  
Potential Curve ◽  
Wide Range ◽  
Minimum Potential ◽  
High Degree ◽  
Range Of Values ◽  
Potential Curves

The reduced potential curve (RPC) method used by Jenc and Pliva for studying the diatomic potentials is adapted for three-parameter studies of the inversional double-minimum potential functions of XY3 pyramidal molecules. Reduced double-minimum potential curves (RDMPC's) of the first, second and third row hydrides (CH3-, NH3, OH3+; SiH3-, PH3, SH3+; GeH3-, AsH3, SeH3+) are constructed using CNDO/2 and ab initio MBPT(2) theoretical potentials. The theoretical RDMPC's corresponding to a group of isoelectronic hydrides coincide to a high degree of approximation, so that they can be represented by a single curve. Furthermore, there is a nearly perfect coincidence between the theoretical RDMPC's of the first row hydrides and the ammonia experimental RDMPC (the only curve known experimentally). To illustrate a practical use of the proposed RPC approach, several approximants to the genuine phosphine potential are constructed (over a wide range of values for the inversion motion coordinate) by combining the available experimental data and the calculated RDMPC's. The resulting potentials exhibit a very close coincidence.

scholarly journals State of the art of friction modelling at interfaces subjected to elastohydrodynamic lubrication (EHL)

Friction ◽  
2020 ◽  
Vol 9 (2) ◽  
pp. 207-227
Author(s):  
Zhuming Bi ◽  
Donald W. Mueller ◽  
Chris W. J. Zhang
Keyword(s):  
State Of The Art ◽  
Computational Modelling ◽  
Elastohydrodynamic Lubrication ◽  
Contact Surfaces ◽  
Friction Prediction ◽  
Hydrodynamic Behaviors ◽  
Lubricant Viscosity ◽  
Film Lubrication ◽  
Friction Modelling ◽  
Fluid Film Lubrication

AbstractElastohydrodynamic lubrication (EHL) is a type of fluid-film lubrication where hydrodynamic behaviors at contact surfaces are affected by both elastic deformation of surfaces and lubricant viscosity. Modelling of contact interfaces under EHL is challenging due to high nonlinearity, complexity, and the multi-disciplinary nature. This paper aims to understand the state of the art of computational modelling of EHL by (1) examining the literature on modeling of contact surfaces under boundary and mixed lubricated conditions, (2) emphasizing the methods on the friction prediction occurring to contact surfaces, and (3) exploring the feasibility of using commercially available software tools (especially, Simulia/Abaqus) to predict the friction and wear at contact surfaces of objects with relative reciprocating motions.

Effects of Load, Squeeze Velocity, Viscosity on Pure Squeeze EHL Motion Using Optical Interferometry

2017 ◽  
Vol 739 ◽  
pp. 164-168
Author(s):  
Li Ming Chu ◽  
Jaw Ren Lin ◽  
Yuh Ping Chang
Keyword(s):  
Film Thickness ◽  
Interference Fringe ◽  
Contact Region ◽  
Elastohydrodynamic Lubrication ◽  
Static Condition ◽  
Microscopic Mechanism ◽  
Experiment Method ◽  
Interferometry Method ◽  
Fringe Patterns ◽  
Lubricant Viscosity

This paper presents a novel experiment method to investigate the microscopic mechanism of the oil film under the pure squeeze elastohydrodynamic lubrication (EHL) motion. An optical EHL squeeze tester is used to measure the interference fringe patterns of the contact region. In order to show the dimple thickness clearly, the grayscale interferometry method is employed to obtain the film thickness map. In addition, the effects of squeeze speed, load, and lubricant viscosity on the dimple film thickness are explored under a quasi-static condition.

scholarly journals Investigation of Thermally Induced Deterioration Processes in Cold Worked SAF 2507 Type Duplex Stainless Steel by DTA

Crystals ◽  
2020 ◽  
Vol 10 (10) ◽  
pp. 937
Author(s):  
Tibor Berecz ◽  
Éva Fazakas ◽  
Enikő Réka Fábián ◽  
Péter Jenei ◽  
János Endre Maróti
Keyword(s):  
Stainless Steel ◽  
Duplex Stainless Steel ◽  
X Ray Diffraction ◽  
Thermally Induced ◽  
Σ Phase ◽  
Hardness Tests ◽  
Strain Induced Martensite ◽  
Kissinger Plot ◽  
Cold Worked ◽  
High Degree

Thermally induced deterioration processes were studied in cold worked (up to 60% deformation) SAF 2507 type super-duplex stainless steel (SDSS) by differential thermal analysis (DTA). DTA results revealed two transformations. Parent and inherited phases of these transformations were examined by other methods too, such as micro-hardness tests, optical metallography and X-ray diffraction (XRD). Finally, these transformations were identified as the formation of α’- and σ-phases. Formation of strain-induced martensite (SIM) and recrystallization were not experienced until 1000 °C, despite high degree of cold working. Activation energies of the σ-phase precipitation and α’-phase formation were determined from the Kissinger plot, through DTA measurements—they are 275 and 220 kJ/mol, respectively—in good agreement with the values found in the literature.

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