A Three-Dimensional Navier-Stokes–Based Numerical Model for Squeeze-Film Dampers. Part 1—Effects of Gaseous Cavitation on Pressure Distribution and Damping Coefficients without Consideration of Inertia

Even though most published results detailing damper behavior consider only the liquid phase, the cavitation process in the lubricant film, when it happens, is critical for the damper's performance. A number of modeling approaches, such as the half-Sommerfeld and Elrod models, were proposed in order to account for the effects of cavitation on the pressure generation, without directly simulating the cavitation process. Based on the experimental data, a few other homogeneous cavitation models have also been developed. All these models are based on the classical Reynolds equation. In this article, a three-dimensional numerical model is developed and validated in connection with the operation of a two-phase squeeze-film damper. The full Navier-Stokes equations (NSE), coupled with a homogeneous cavitation model, is solved to simulate the flow of the two-phase lubricant film and the associated pressures. The pressure variation on the journal surface and the gas concentration distribution in the lubricating fluid (cavitated region) will be presented. The damping coefficients predicted by the NSE model are compared to the ones that resulted from the application of the Reynolds equation.     

Specific Film Thickness—A Closer Examination of the Effects of EHL Film Thickness and Surface Roughness on Bearing Fatigue

Analysis of literature bearing-fatigue life results shows that fatigue life is not a simple function of the widely accepted specific film thickness, λ, which is the ratio of the EHL film thickness h to composite surface roughness [sgrave]. Instead, the influence of film thickness on bearing life increases with increasing surface roughness; at about 0.20 micrometer (8 microinch) composite roughness life increases with the square root of h while at about 0.46 micrometer (18 microinches) life increases with h squared.

The negative effect of surface roughness on bearing life appears to be relatively independent of film thickness. This suggests that surface roughness affects fatigue life by some mechanism in addition to the degree of interaction of asperities through an intervening EHL film. Additional test results are needed to confirm this point.     

Rheological Behavior of Greases: Part I—Effects of Composition and Structure

The aim of this work is to show the correlation between grease rheological behavior and its composition and structure (base oil viscosity, soap nature, and concentration).

A rheological investigation was carried out under the controlled stress mode. The results, obtained over different time intervals, show that grease behaves like a non-Newtonian viscoelastic material, with a narrow linear domain.

The soap nature and concentration are the dominant parameters when grease is submitted to low shearing. This was confirmed by TEM observations: the closer networks gave the highest rheological properties. Base oil viscosity influenced grease behavior only under high strain rates.

Some properties are discussed with respect to their influence on the contact replenishment, which is a critical point for mechanism lifetime prediction.

Finally, the authors suggest using rheometry as an alternative technique to standardized methods. Yield stress varies in the same way as penetration does, but is further influenced by the sample macrostructure.     

Effects of Gas Composition,Humidity and Temperature on the Tribology of the Head/Disk Interface—Part II: Model and Analysis

A qualitative model for the effect of water condensation on the frictional behavior of unlubricated and lubricated carbon-overcoated disks is presented. The model suggests that for unlubricated disks adsorbed water acts as a lubricant, protecting the unlubricated disk surface from direct solid/solid contact and direct exposure to the environment. For lubricated disks, the interaction between adsorbed water and lubricant molecules seems to be responsible for the effect of humidity on the frictional behavior of lubricated disks. The effect of temperature on the frictional behavior of the head/disk interface is discussed in terms of surface energy, lubricant viscosity and mobility.     

Antiwear Film Formation by ZnDTP,Detergent, and Dispersant Components of Passenger Car Motor Oils—Part II: Effects of Low-Molecular-Weight Dispersant on Film Formation

Passenger car motor oils (PCMOs) are undergoing a rapid evolution. Studies have found that some exhaust emission catalysts may be deactivated by phosphorus, largely derived from zinc dialkyldithiophosphate (ZnDTP), the mainstay antiwear and antioxidant agent in PCMO formulations for the past 50 years. Consequently, future engine oils will contain significantly reduced phosphorus levels. Since ZnDTP is the dominant antiwear and antioxidant in current PCMOs, lower phosphorus content will impact engine oil formulation strategies.

To better understand the effects of ZnDTP reduction on wear control, electrical contact resistance (ECR) studies have been carried out on blends containing ZnDTP, detergent, and low-molecular-weight (LMW) succinimide dispersant. In contrast to previous results obtained with high-molecular-weight (HMW) dispersant, the combination of ZnDTP and LMW dispersant gave an ECR trace closely resembling that of ZnDTP alone. Thus, the chemical structure of the succinimide dispersant can have a profound effect on ZnDTP antiwear film formation. ECR experiments on three-way combinations of ZnDTP + LMW succinimide dispersant + overbased phenate detergent provided a much better film than that from a similar formulation using an HMW succinimide dispersant. This study demonstrates that the ECR experiment is sensitive to the chemical structures of components controlling the function of modern PCMOs, making ECR a convenient tool to optimize the performance of the remaining ZnDTP in lower phosphorus PCMO formulations.     

The Analysis of the Lubrication Condition and Friction Losses of a Single Acting Cross Head Guide Shoe of a Low Speed Cross Head Diesel Engine: Part II — A Practical Model for the Determination of the Oil Film Thickness

The cross head guide shoe plate of a large diesel engine operates under a large normal force which presses it against the rails between which it executes both axial and transverse motion. In order to ensure the safe operation of an unconventional bearing such as the guide shoe system of the cross head engine, an algorithm that can be used to predict accurately the oil film thickness that can be achieved for all the engine's operating regimes, is invaluable. A solution of the three dimensional form of Reynolds differential equation can provide the requisite oil film thickness. However, with even the availability of very fast computers and large computer storage capacity this solution for a large axial bearing such as the guide shoe becomes impractical in terms of computation time and computer core requirements. This paper describes alternative simplified algorithm for accurate prediction of the oil film thickness developed in the guide shoe bearing at different operating regimes of the engine.     

A Model for Rolling Bearing Life with Surface and Subsurface Survival—Tribological Effects

Until now the estimation of rolling bearing life has been based on engineering models that consider an equivalent stress, originated beneath the contact surface, that is applied to the stressed volume of the rolling contact. Through the years, fatigue surface–originated failures, resulting from reduced lubrication or contamination, have been incorporated into the estimation of the bearing life by applying a penalty to the overall equivalent stress of the rolling contact. Due to this simplification, the accounting of some specific failure modes originated directly at the surface of the rolling contact can be challenging. In the present article, this issue is addressed by developing a general approach for rolling contact life in which the surface-originated damage is explicitly formulated into the basic fatigue equations of the rolling contact. This is achieved by introducing a function to describe surface-originated failures and coupling it with the traditional subsurface-originated fatigue risk of the rolling contact. The article presents the fundamental theory of the new model and its general behavior. The ability of the present general method to provide an account for the surface–subsurface competing fatigue mechanisms taking place in rolling bearings is discussed with reference to endurance testing data.     

The Effects of Roughness on Piston Ring Lubrication—Part II: The Relationship between Cylinder Wall Surface Topography and Oil Film Thickness

In this investigation, a theoretical piston ring/cylinder wall model has been utilized to study the dependence of the oil film thickness on surface roughness shape and amplitude, as well as on engine operating conditions. For a given roughness, a plateau honed cylinder wall surface was found to produce a thinner oil film. It has also been shown that the small crosshatch angle used when honing the cylinder wall produces surfaces that enhance hydrodynamic action.     

Classical EHL Versus Quantitative EHL: A Perspective Part I—Real Viscosity-Pressure Dependence and the Viscosity-Pressure Coefficient for Predicting Film Thickness

That classical elastohydrodynamic lubrication (EHL) is not a quantitative field can be illustrated by its failure to provide a consistent and rigorous definition of the viscosity-pressure coefficient. Indeed, if the pressure dependence of viscosity cannot be accurately described, then the viscosity-pressure coefficient cannot be defined. Classical EHL has employed fictional narratives to justify the pressure dependences that have been utilized. In this context, the purpose of this perspective article is to review specific and real needs from EHL and to show that data and models describing the viscosity-pressure dependence are already available and how they can properly be used. The final aim is to encourage researchers to change their philosophy of classical EHL to a quantitative approach, in which every hypothesis and every result, whether experimental or numerical, would be justified on the basis of acceptable physics.     

Different Approaches to the Investigation and Testing of the Ni-Based Self-Fluxing Alloy Coatings—A Review. Part 2: Microstructure,Adhesive Strength,Cracking Behavior,and Residual Stresses Investigations

After presenting general facts about Ni-based self-fluxing alloy coatings and describing the wear and corrosion studies in Part 1, Part 2 of the article deals with the review and systematization of the investigations on behavior of these coatings exposed to external mechanical loading (cracking behavior, adhesive strength, fatigue), residual stresses, and microstructure (particle state, phases, porosity, dilution, dissolution) considering the period from 2000 to 2013. The following deposition technologies are included: flame spraying, high-velocity oxy/air fuel spraying, detonation gun spraying, electric arc spraying, plasma spraying, plasma-transferred arc welding, and laser cladding. In addition to the review of investigations on microstructure and effects of external loading and residual stresses, reference is also given to papers describing the application of the Ni-based self-fluxing coatings, as well as to those in which these coatings were used as a reference material or an addition to obtain a composite coating.     

X-Ray Absorption Study of the Effect of Calcium Sulfonate on Antiwear Film Formation Generated From Neutral and Basic ZDDPs: Part 1—Phosphorus Species

Zinc dialkyldithiophosphates (ZDDPs) from very effective antiwear films in boundary lubrication applications. In most cases, however, the ZDDPs do not work alone. They are formulated with many other additives to provide the performance required by today's modern oils. X-ray absorption near-edge spectroscopy (XANES) has been used to study the antiwear films formed from the commonly used combination of ZDDP and calcium sulfonate in both neutral and basic forms. The results are presented in two papers: Part 1 for the phosphorus species and Part 2 for the sulfur species. XANES showed conclusively that in the presence of LOB (low overbased) or HOB (high overbased) calcium sulfonate under sliding conditions, ZDDPs do not form long-chain polyphosphates that have been associated with antiwear action. Instead, short-chain polyphosphates calcium phosphate are formed. The relative amounts of calcium phosphate formed depend on the ester group of the ZDDP: aryl > n-alkyl > sec-alkyl. Interestingly, this order of ester groups is inversely related to the antiwear effectiveness of the ZDDPs. Thus, it is probable that the addition of either LOB or HOB calcium sulfonate to ZDDP will result in a decrease in antiwear effectiveness of the additive mixture compared to the ZDDP by itself. Wear data support this conclusion. It is suggested that the elimination of long-chain polyphosphates and the formation of calcium phosphates in the tribofilm leads to this decrease in antiwear effectiveness, the latter by abrasion of the antiwear film.     

A Mixed Lubrication Model for Journal Bearings with a Thin Soft Coating—Part I: Contact and Lubrication Analysis

Soft coatings are used extensively in industry for contact friction reduction, particularly during the running-in period. A numerical model is developed for contact and lubrication analysis of some soft coating coated bearings in mixed fluid lubrication. The model is applied to determine oil film thickness, contact pressure, and the friction coefficient of the coated bearings in contact with a hard journal surface. The contact of tin-coated 339 Al-Si alloy bearings with case hardened steel is analyzed using the developed model.     

Effects of Strain-Induced Martensitic Transformation on the Solid Particle Erosion Behavior of Fe–Cr–C–Ni/Mn Austenitic Alloys

The effects of Ni and Mn concentrations and also the impact velocity on the solid particle erosion behavior of Fe?C12Cr?C0.4C?CxNi/Mn (x?=?5 and 10) alloys were investigated with respect to strain-induced martensitic transformation. The critical strain energy (CSE), which is defined as the energy required to initiate the martensitic transformation increased with increasing Ni and Mn concentrations. As the impact velocity decreased, the solid particle erosion resistance of the low CSE alloy improved compared to that of the high CSE alloy under the given ranges of impingement angles and impact velocities. This result was most likely due to an increase in the volume fraction of martensite that formed during the solid particle erosion test in the low CSE alloy when the impact velocity was decreased.     

A study on the energy efficiency improvement of greenhouses — with a focus on the theoretical and experimental analyses

Most greenhouses in Korea are made according to European weather conditions, which leads to very low solar energy efficiency under the domestic weather conditions. Thus, greenhouses in Korea should be adapted to the regional weather conditions to improve their energy efficiency. This paper investigates the current greenhouses in Korea. It also analyzes the problems arising from the greenhouses and offers alternatives for improving their energy efficiency based on measurements and a theoretical analysis. The elements of greenhouses were also investigated. When using a partially non-transparent insulation with heat storage mass between the indoor and outdoor air, the temperature difference became greater than 20°C during the daytime and greater than 5°C during the night, which will reduce the cost of fossil fuels.     

Influence of atmospheric humidity on abrasive wear — II. 2-body abrasion

Specimens of glass, steel, copper and an aluminium alloy were abraded on silicon carbide abrasive papers under controlled levels of atmospheric humidity. Under the testing conditions used, all materials show an increase in wear rate between 0 and 65% r.h. At higher humidity levels the softer materials show a decreasing wear rate, while the harder materials show a continuing increase. Atmospheric moisture decreases the fracture strength of the SiC abrasives. This results in improved cutting efficiency at low humidity and in grit deterioration at high humidity. The magnitude of the effect on wear rates is strongly dependent on experimental conditions, in particular load per abrasive, distance of contact with the specimen surface and supply of fresh abrasives.     

Hydrodynamic Effects on the Boiling Interface in a Misaligned,Two-Phase,Mechanical Seal—A Qualitative Study

A qualitative study of the hydrodynamic effect on the radius at which boiling occurs in two-phase, misaligned, mechanical seals with coning is presented. The more important parameters affecting the problem are identified and analyzed. It is found that hydrodynamic effects depend mainly on a modified Sommerfeld number. It is shown that in most practical cases the hydrodynamic effects can be neglected men at large face misalignment. It is further shown that the boiling interface in many cases is practically axisymmetric and at almost the same radius as for perfectly aligned faces. A factor that reduces the tendency to cavitate in misaligned, two-phase seals is also pointed out.