Foil gas bearings are self-acting, compliant-surface hydrodynamic bearings that usually use air or other process gas as their working fluid or lubricant. Foil gas bearings are made of one or more bump foils, which are compliant surfaces of corrugated metal, and one or more layers of top foil. Because foil gas bearing performance parameters, such as load capacity, are dominated by foil material and foil geometric designs, numerical models have been developed to predict the bearing’s performance based on these characteristics. However, previous models often simplify bump foil as elastic foundation with constant stiffness and neglect top foil altogether. Further, they typically use the Reynolds equation to simplify the fluid solution. In this study, ANSYS software is used to build a 3D, fully-coupled, fluid-structure-interaction model for a foil gas bearing to predict key performance parameters such as load capacity and journal attitude angle. The model’s results show good agreement with previously published test data. This not only demonstrates the feasibility of 3D fully coupled fluid-structure-interaction model for a conventional foil bearing using commercial codes, but also shows modeling capability for future generations of foil gas bearing.

Quick response and rheological properties as a function of magnetic field are well known features of MR fluids which inspire their usage as brake materials. Controllable torque and minimum weight of brake system are the deciding functions based on which the viability of the MR brake against the conventional hydraulic brake system can be judged. The aim of this study is to optimize a multi-disk magneto-rheological brake system considering torque and weight as objective functions and geometric dimensions of conventional hydraulic brake as constraints. The electric current accounting magnetic saturation, MR gap, number of disk, thickness of disk, and outer diameter of disk have been considered as design variables. To model the behavior of MR Fluid, Bingham and Herschel Bulkley models have been compared. To implement these models in estimating the braking torque a modification in shear rate dependent component has been proposed. The overall design of MR brake has been optimized using a hybrid (Genetic algorithm plus gradient based) optimization scheme of MATLAB software.

The purpose of this study was to investigate the effect of cooling contact surface temperature of the test cylinder when a rise in contact temperature over 100 degree C occurs during boundary lubrication tribological testing. The Hertzian contact pressure in a ball on cylinder tests will be optimized with respect to the contact temperature using Design of Experiment (DOE) software. Several boundary lubrication tests were conducted to study the behavior of 0.1 P% (phosphorus percentage) plain ZDDP oil in the presence of 0.4% FeF 3 under two different rotational speeds (lower stage of 100 rpm for the first 5000 revolutions and higher stage of 700 rpm until failure or 100000 revolutions whichever comes first). The one rotational speed of 700 rpm until failure will be compared to the two speed stages under a contact cooling surface temperature and different contact loads (2.77GPa–3.8Gpa Hertzian contact pressures). The two different speed stages indicate better performance under an extreme contact load and a lower contact surface temperature; whereas higher contact surface temperature and lower load are needed for the one speed stage of 700 rpm cycle.

The thermal elastohydrodynamic analysis of lubrication is applied to investigate the influence of misalignments of the meshing members on lubrication in spiral bevel gears. The calculation is based on the simultaneous solution of the Reynolds, elasticity, energy, and Laplace’s equations. The full thermal EHD lubrication analysis is applied, therefore, the oil viscosity variation with respect to pressure and temperature and the density variation with respect to pressure are included. By using the corresponding computer program, the influence of pinion’s running offset and axial adjustment errors, and angular position error of pinion axis on maximum oil film pressure and temperature, EHD load carrying capacity, and on power losses in the oil film is investigated. On the basis of the obtained results it can be concluded that the EHD load carrying capacity and the friction factor are very sensitive to misalignments of the mating members in the spiral bevel gear pair, the friction factor is reduced by the increase of EHD load carrying capacity and vise versa, and the maximum inlet oil temperature is almost insensitive to the misalignments.

Tribology and solid mechanics are essential when studying engine lubrications. Very reproducible boundary lubrication tests were conducted as part of Design of Experiment software (DOE) to study the behavior of fluorinated mix in developing environmentally friendly (reduced P and S) anti-wear additives for future engine oil formulations using ball on cylinder testing protocol. In this study fully formulated oil and ZDDP plain oils were tested under the protocol of two cycles. A 100 rpm cycle was used for the first 5000 revolutions and a 700 rpm cycle was used until failure or 100000 revolutions whichever comes first. All tests were generated under extreme boundary lubrication (Hertzian contact pressure of 2.72 GPa). Design of Experiment (DOE) with 2 level factorial was used to investigate the failure and wear responses with respect to fluorinated mix interactions in plain and fully formulated oils. The two cycle’s tests indicate better performance than the one cycle test. Findings indicate that the most significant factors, affecting friction and wear are fluorinated mix concentrations together with oil formulation.

This article deals with the finite differential method of static performance of a foil journal gas bearing. A foil bearing is a self acting hydrodynamic device, which separates stationary and rotating components of high speed rotating machinery by a fluid film of air or other gaseous lubricant. The present work concentrates on common approach in foil bearing in calculating the carrying capacity for a given shaft position (figure-1). During this work the external load is fixed and related shaft position is investigated. For steady operating characteristics such as minimum film thickness and load capacity predicted for the foil bearing. The system of governing equation is solved numerically with FDM by a computer program written in the MATLAB computing environment. A generalized hydrodynamic analysis is conducted to systematically analyses the effect like bearing speed is discussed.

Surface roughness has a significant affect on adhesion. We used a single-asperity model to describe a smooth tip in contact with a rough surface and predicted that an optimal size of asperity will yield a minimum of adhesion. Experimentally, adhesive forces on silicon wafers with varying roughness were measured using AFM cantilevers with varying tip radii. It was found that minima do exist, and for all tip radii, the adhesion falls significantly for roughness greater than 1–2 nm and drops at higher roughness for larger tips. In addition to RMS roughness, the roughness exponent is another important parameter for the characterization of rough surfaces and its affect on adhesion was also investigated. We developed computer programs to simulate a set of fractal rough surfaces with differing roughness exponents. The adhesive forces between an AFM tip and the fractal surfaces were calculated and the adhesion was seen to decrease as the roughness exponent increases. This work should help minimize MEMS stiction and progress the understanding of nanoscale contact mechanics.

The full thermal EHD lubrication analysis is applied, therefore, the oil viscosity variation with respect to pressure and temperature and the density variation with respect to pressure are included. By using the corresponding computer program, the influence of oil viscosity, pressure-viscosity and temperature-viscosity exponents, supplied oil temperature, speed and minimum oil film thickness on maximum oil film pressure and temperature, EHD load carrying capacity, and on power losses in the oil film is investigated. Small part of the obtained results is presented and discussed.

To improve calculation of the oil supply to the main and conrod bearings in the combustion engine, it is possible to simulate plain bearings on a coupled elasto-hydrodynamic basis while allowing for partial-fill states. In an effort to advance the extended simulation technique, software has been developed by the Institute for Machine Components and Design (IMK) at the University of Kassel and validated in experiments. This paper describes the simulation software that has been developed, including the resultant findings on the lubricating oil requirement.

This paper illustrates the effect of misalignment on performance of cement kiln partial journal bearing. The performance parameters include minimum film thickness, load carrying capacity, power loss and dynamic coefficients such as elastic coefficients and damping coefficients. The bearing analyses have been carried out using a commercial rotor dynamics software package.

A significant component of our understanding of cartilage mechanical behaviour is the ability to model its response to various types of mechanical loading, for which we require detailed knowledge of cartilage material properties. The Finite Element Analysis software ABAQUS is renowned for the ability to model poroelastic materials using the soil consolidation theory . In this research, ABAQUS has been used to model and investigate the mechanical behaviour of articular cartilage, mainly using indentation and unconfined compression techniques. A biphasic model of articular cartilage was first created and subsequently modified to incorporate more detailed material descriptions. Various material constitutive laws (and mechanical properties), accounting for the strain dependent permeability of the porous matrix, solid viscoelasticity and transverse isotropy, have been adopted to produce increasingly sophisticated models. The presence of collagen fibril networks embedded in the solid has been also considered and Fibril Reinforced Elastic and Viscoelastic models produced. A salient feature of these models is their ability to simulate fibril stiffening by replicating the nonlinear fibrillar response. In this paper, we provide an overview of the state-of-art modelling techniques adopted to simulate cartilage behaviour. The comparative study performed by the authors provides a critical assessment of the effectiveness of such techniques.

Since being originally introduced, cylindrical rolling element bearings have been significantly improved, in terms of their performance and working life. A major objective has been to decrease the Hertz contact stresses at the roller–raceway interfaces, because these are the most heavily stressed areas in a bearing. It has been shown that bearing life is inversely proportional to the stress raised to the ninth power (even higher). Investigators have proposed that under large normal loads a hollow element with a sufficiently thin wall thickness will deflect appreciably more than a solid element of the same size. An improvement in load distribution and thus load capacity may be realized, as well as contact stress is also reduced considerably by using a bearing with hollow rolling elements. Since for hollow rolling element no method is available for the calculation of contact stresses and deformation. The contact stresses in hollow members are often calculated by using the same equations and procedures as for solid specimens. This approach seems to be incorrect. Recently, the Finite Element Analysis (FEA) has been successfully used to evaluate contact problems for the roller bearings. Investigations have been made for hollow rollers in pure normal loading. Different hollowness percentages ranging from 0% to 90% have been analysed in FEA software to find the optimum percentage hollowness which gives minimum stress and finally longest fatigue life.

A computer program for dynamic analysis of ball bearings, in which a simple mixed lubrication model for the retainer/race and retainer/ball contact is incorporated, is developed and retainer instability in reaction wheel bearings is investigated. Results show that an increase in the amount of oil promotes the instability and that a retainer with rectangular pockets is more stable than one with circular pockets.

The objective of the 2006–07 Virginia Tech Turbocharger Project was to obtain and analyze vibrations data from different bearing designs. The supporting tasks were divided amongst various sub-teams; a turbocharger team, an engine test operating team, a dynamometer team, and an ADRE software team. The turbocharger team has successfully developed a procedure for disassembly and reassembly of the turbocharger. A consistent and well-documented assembly procedure has ensured turbocharger operation free from human error. Consistency in the rebuild process is vital to properly compare vibration data with the different shaft bearings. The most important aspect of this reassembly is the torque applied to the tie-bolt nut. This torque causes the tie-bolt to stretch, and this stretch must be accounted for because it is a measure of preload force on the compressor wheel. The team designed and made a stand to carefully apply this torque on the tie-bolt nut without creating a bending moment. The original stock bearings were used for the first turbocharger rebuild to see if the rebuild procedure would lead to similar data. Two other bearings have been tested and analyzed. This paper will give a brief overview of the results to date.

An analysis of double arched ball bearing which considers centrifugal forces and gyroscopic effects is performed. Based on operating conditions of a 5 DOF inner ring and Coulomb friction model, the conventional bearing theory is extended from 2 to 3 or 4 contact points. The commonly control criterion of ball bearing by the inner or outer raceway is debatable and is known to fit with difficulty with experimental data. In addition when more than two contact points are involved it becomes obsolete. The paper presents a mathematical model to describe the complex ball bearing internal kinematics under the effect of the external working conditions. Lubricant thickness is taken into account in geometrical equations and the non-linear system of this quasi-static model is solved by a Newton-Raphson method. The 3D model is first validated through comparisons with published data for conventional or single arched ball bearings. Results are also compared to those provided by the commercial software RBL4. The analysis of a double arched ball bearing is finally performed and the complex motion of the ball highlighted.

Conventional method of performing Elasto-hydrodynamic Lubrication (EHL) analysis on a partial arc bearing involves simplification of actual physical model and developing complex codes. This paper presents the overall EHL analysis of a radialy adjustable single 60° partial arc bearing using the sequential application of Computational Fluid Dynamics (CFD) and Computational Structural Dynamics (CSD). Here the coupled field analysis uses the capabilities of commercially available Finite Element Software ANSYS/FLOTRAN and the technique of Fluid Structure Interaction (FSI). The pressure field has been obtained using CFD considering the flow to be laminar. Stress distribution and deformation in the pad due to resulting pressure force is obtained using Finite Element Method (FEM), satisfying the boundary conditions. The stress distribution indicates the critical points in the pad. In this paper the static characteristics of radialy adjustable single 60° partial arc bearings are predicted for different eccentricity ratios and length to diameter (L/D) ratios. The results show reasonable agreement in general.

This paper presents experimental studies on imbalance responses of a rotor supported by two flexure pivot tilting pad gas bearings with radial compliance. The radial compliance was aimed to accommodate large rotor centrifugal growth inherent with high speed operation. Frequency-dependent rotordynamic force coefficients calculated from developed software were used to predict critical speeds and onset speed of instability and compared with experimental results. Two results show very good agreement.

An explicit dynamic 2D finite element model of a composite under dynamic tribological loading is proposed. The software used for this kind of application manages contact conditions thanks to the Lagrange multipliers. The kind of contact is a deformable against rigid surface one. First of all due to ill-posedness of the classical Coulomb friction law, a regularized Coulomb friction law that allows local and global convergence of the models even under the presence of contact instabilities is proposed. This friction law is experimentally motivated and is similar to the simplified “Prakash-Clifton” law. In a second time the dynamic tribological behavior of the composite is studied by the mean of different models where the heterogeneities of the material are explicitly introduced. Those heterogeneous models stand for a description of the microscopic scale of the composite. A comparison is made between the results given by these heterogeneous models and the results obtained by the analysis of a homogeneous model. The elastic properties of the homogeneous model are obtained through classical homogenization process which is suitable here because the scale separation, difference between the size of the heterogeneities and the wavelength of the loading, is sufficiently important. The homogeneous model represents the macroscopic scale of the composite. Equivalence between heterogeneous models and the homogeneous one is straightforward if the contrast of Young’s modulus between the heterogeneities and the matrix is sufficiently low and if the local contact dynamic is stable. This equivalence has been observed for different contact instabilities like slip-separated, and stick-slip-separated ones. When the equivalence between the models is not ensured, because of high contrast of elastic properties for example, an adaptation of the dynamic parameter of the friction law is necessary to retrieve this equivalence. Finally the determination of the stresses and their evolution along the time in the heterogeneities and in the matrix is performed thanks to the relocalization process. This process is mixing dynamic analysis of the homogeneous models and fast static calculations on heterogeneous model. This process has already been applied to structures submitted to static loading but to our knowledge this is the first attempt to use it for dynamic contact problems. So this work highlights a full multi-scale approach for composite under dynamic contact with friction loading.

Air foil bearings have compliant elastic foundation to provide compliance to bearing surface and damping. The most widely used elastic structure is the corrugated bump foil. All the currently available formulas for the bump stiffness [1–3] do not consider bending moments at the bump supports and within the straight contact patch which connects the bumps. However, for continuous bump foils, bending moments at the support points where contact is made with the bearing sleeve cannot be neglected. This paper introduces a set of new formulations for stiffness of bump foils considering the bending moments at the support points. All the formulas were derived using computer algebra software. The results are compared with the result from other formula [3].

Engine designs require better fuel economy, lower NVH, and longer durability. Consequently, the understanding, analysis and design for lubricated engine components that have relative moving surfaces play an important role in this objective. As the GM corporate standard analytical tool for these components, FLARE has been under continuous improvements and validations since its first rollout from GMR in the late 80s. It has also been benchmarked with the best features available in the commercial software package and research literature. There are currently more than 20 standard work procedures directly involving FLARE as solver and its applications span over: • Rod, crank, cam and balance shaft journal bearings; • Connecting rod structure; • Piston structure and scuffing; • Engine mechanical friction; • Load calculation for engine block structural analysis; • Lube system analysis; • Noise analysis. There are three levels of analysis based on requirements. Namely, level one is used in initial design stage that finds solution by interpolating the curve-fitted equations. It requires the least information about the design and runs in seconds. In level 2, a more detailed solution can be obtained by solving mixed mass-conserving lubrication governing equations using FEM with the assumption of rigid bounding surfaces. Heat transfer can be taken into account in this level and above. Level 3 has the full capability, in addition to the features in level 2, the solution is coupled with the elasticity of surface/structure which can be obtained through offline structure FEM analysis. Higher level of analysis captures more physics but requires better understanding of the input parameters and careful interpretation of the results. The unique strength of FLARE is its detailed component level analysis capability. This presentation is an overview of the latest development on FLARE technology. It includes the physics captured in FLARE, integrated solution technique and some selected results for crankshaft bearings, floating piston pins, and piston/liner impact under partial film lubrication.