We have presented an application of the modified Moving Particle Semi-implicit (MPS) method for squeeze film flows. In addition to calculating the flow field of a squeeze film using the full Navier-Stokes equations, this method has the advantage of being meshless, which gives it the capability of analyzing dynamic and/or highly transient squeeze films by discretizing the domain as a series of particles and numerically analyzing inter-particle interactions. Although past literature has indicated the MPS method in its original form to be unstable in terms of its calculation of pressure, a modified algorithm was implemented to provide agreement between the numerical results and the analytical solutions.

This study presents and discusses how the lubricant film flows in and around the dimples of a textured surface. Currently some authors assume that the emptying of the dimples starts in their front edge (according to the lubricant’s flow), but several tests, with different texturing densities and distances, have showed that this behavior can only be seen in the first row of dimples or, if distance is long enough, in the following rows. However, in those cases where rows are closely distributed (high texturing densities) the emptying of the dimples shows two lateral fronts instead of a frontal one. The study led to the following conclusions: the way pockets are emptied depends on their distribution and position in the dimples’ array; frontal emptying phenomenon is only present at first row dimples or when distance between rows is long enough; when surrounding pockets modify how the lubricant reaches the dimple, the frontal emptying phenomenon becomes a bi-edged one, with two emptying fronts instead of one; as surface texturing requires a huge number of pockets at usually high texturing densities, it can be asserted than the frontal emptying phenomenon is not the most common one even though it’s the one that several authors use to study the emptying phenomenon.

This study investigates surface changes during scuffing in a dry condition. In the test a ball-on-disc apparatus was used, in which a rotating sapphire disc was loaded to a stationary steel ball. The contact area was directly observed and recorded by a digital camera attached to a microscope during the test. The variations in frictional force were synchronously measured with the capturing of images of the camera. After the test, the hardness of the scuffed steel ball were measured at different points in the contact area. The direct observation of the contact area shows that areas of macro plastic flow appeared from the trailing side of the contact area with a dramatic increase in frictional force. The macro plastic flow areas were changed, resulting in a dramatic expansion of the contact area. During the dramatic expansion, the friction coefficient kept a high constant value of about 0.4. The hardness distributions of the scuffed steel ball showed that the hardness was smaller at the tailing side of the contact area, in which macro plastic flows started, than that at the leading side. On the other hand the temperature rise calculated by a simple temperature estimation model was insufficient to cause the hardness reduction.

The lubricant applied to the disk in a hard drive is a critical component for head-disk interface reliability. In Heat Assisted Magnetic Recording (HAMR), the heat supplied to the disk by the laser will add new thermal considerations to lubricant performance. Investigations into how the lubricant behaves at the small time and length scales seen in HAMR systems need to be conducted numerically. Published works on HAMR lubricant modeling have considered only the van der Waals contribution to disjoining pressure, commonly called the dispersive component, and do not consider the film thickness dependence of viscosity. However, lubricants with reactive end groups such as Fomblin Zdol are widely used, and such simple disjoining pressure and viscosity models do not capture certain lubricant behavior. We have developed a simulation tool that incorporates film thickness dependencies of viscosity and polar and dispersive disjoining pressure into a continuum lubrication model. We investigate the effect of initial thickness on lubricant flow and evaporation under HAMR write conditions considering both components of disjoining pressure and thin-film viscosity. Simulation results indicate the effect of including polar disjoining pressure depends on the initial lubricant thickness. The inclusion of viscosity thickness dependence does not affect simulation results under scanning laser conditions but will be important in reflow simulations.

Owing to the fast technological developments, the operating conditions of the machines are becoming very stringent, exact and more demanding. Various journal bearing designs have been developed to prevent the undesired effect of bearing whirl. An example of a successful design is the four-lobe multirecess journal bearing. The bearing which having four curved segments that referred to as four lobes is the four-lobe multirecess journal bearing. Further, as the 4-lobe journal bearing is expected to run over a number of cycles during its lifetime, it is subjected to several start/stop operations. These transient periods causes the bearing bush to wear out between the recesses and significantly affects the bearing performance. The modified Reynolds equation governing the flow of lubricant in the clearance space of bearing have been solved including the combined effects of three aspects, the worn effect, the misalignment angle and offset factors, using an iterative scheme based on FEM and Newton-Raphson method. The simulated results have been presented for a wide range of offset factor δ, wear depth parameter, journal misalignment factors (φ, Ψ) and external load. The simulated results suggests that it is an imperative to account for the effect of wear along with misalignment of journal in order to predict the performance of the bearing accurately. Further, it has been observed that in general as the value of offset factor increases the static and dynamic performance of the 4-lobe four pocket worn misaligned hybrid journal bearing compensated with orifice restrictor is clearly affected as compared to similar four pocket unworn aligned hybrid circular journal bearing. Further the bearing having offset factor δ = 1.2 improves the stability due to increase in the bearing stiffness and reduced magnitude of the cross-stiffness components.

Energy and environment are of major concern in internal combustion engine component design. The piston ring-cylinder liner (PRCL) contact plays an essential part in design and is highlighted in this study. In fact, the rings ensure the sealing property, reducing the environmental impact by avoiding lubricant contamination (blow-by) and lubricant consumption. Unfortunately, when sealing, the rings generate between 11 to 24% of the friction losses in an internal combustion engine [1], thus reducing the energy efficiency of the engine. The cylinder liner surface features a special micro-geometry, a classical one is the cross-hatching pattern, obtained by honing. This texturing acts as a micro-bearing, oil reservoir and debris trap. Understanding the influence of texture parameters as groove depth and width or angle, will allow tribological improvements of the PRCL contact. The 2D transient Reynolds equation has to be solved for this kind of surface. The statistical method using the Patir and Cheng [2] flow factors is widely used. This approach lumps the different components of the surface (grooves and plateaux) and does not consider the roughness directionality. Methods decoupling both components, like the homogenization method [3] are also used. Another alternative is to use a deterministic model on measured surfaces, but this is a “hugely” expensive approach. Multigrid methods [4] are used to drastically reduce the calculational cost. The aim of the current study is to facilitate the understanding of measured surface calculations. Hence, analytical surfaces are used. They allow a flexible handling of the cross-hatching parameters. The plateaux are perfectly smooth and the grooves are sinusoidally shaped. The top ring is modelled using a parabolic profile. Periodic boundary conditions are used in the orthoradial direction and zero pressure conditions (Dirichlet) in the axial direction. To investigate the effect of different parameters, various imposed film thicknesses are applied and the mean load carrying capacity (LCC) over time is calculated. When representing the LCC corresponding to each parameter compared to the smooth LCC, as a function of the logarithm of the minimum film thickness, the curves are quite linear for small values of the film thickness and then for larger values they converge to 1.

Understanding granular flows has always been important for predicting natural phenomena such as rockslides and soil erosion, as well as industrial processes such as coal-based fossil fuel systems and solids processing. As such, it becomes important to understand granular flows from both a classical granular flow and tribological perspective. Inherently important in the study of granular flows is the study of the individual particle level interactions, which define the global behavior of the flow. The current work examines both the coefficient of restitution (COR) and coefficient of friction (COF) for various material combinations. COR and tribological experiments are performed on various sphere and plate (disk) materials, such as low carbon steel, tungsten carbide (WC), and NITINOL 60.

Discrete Model is based on the description of the physical state (velocity, position, temperature, magnetic moment, electric potential ..) of a large number of discrete elements that form the media to be studied. It is not basedon a continuous description of the media. Thus, it is particularly well adapted to describe media evolution driven by discontinuous phenomena like the description of multi fracturation followed by debris flow like wear study. Recently, the use of discrete model has been widened to face problem encountered with complex rheological behavior and/or multi-physical behavior. Multi-physical problems face complex mathematical formulation because of the mixing of different families of differential equations when continuous approach is chosen. With the discrete model, each particle has a physical state and state evolution is due to local physical particle interaction: it is often much simple to write. From the beginning of the years 2000, this method has been widely applied for the study of tribological problems. Wear has been investigated[1], thermo-mechanical behavior of a contact[2], subsurface damage due to surface polishing[4]… Recently, it has been shownhow quantitative results can be obtained with this method[4]. To help and promote research in this area, a platform GranOO has been developed under a C++ environment and is distributed under thefree GPL license. The goal of this platform is to offer to researchers, especially in the tribology domain, a numerical and easy to use environment to facilitate the access to Discrete Element simulations. The main aspect of this platform ispresented in the extended abstract and some applicationsgiven as examples. Details can be found on url www.granoo.org.

A model-based diagnostic to detect and assess faults is applied to gearboxes. Signals measured from a gearbox were compared to corresponding signals from simulations. The gearbox simulation model includes dynamics of input, lay and output shafts, gear bodies, bearings, and kinematics and tribology of gear tooth contacts. These were assembled into a systems model via bond graphs. To make simulations emulate measurements, the model’s parameters were “tuned”. A direct physical correspondence between parameters and real system elements locates faults. Considered was gear tooth cracking. Faults disturb normal flow of power and signal through a machine. Viewing the gearbox as a communications channel, and applying information theory theorems to the perturbed signals permitted assessment of the gearbox’s functional health.

This presentation describes ongoing research performed on a simple shear cell apparatus, previously described [1]. As a complement, discrete particle simulations and continuum models have been used to predict normal and shear forces in the ongoing experiments. The trends and orders-of-magnitude of the models and experiment are in basic agreement. Theoretical models used are constructed with basic principles, rather than curve fitting, to obtain effective properties of the mixture such as viscosity or conductivity. The experiment itself serves to determine the effects of shear rate, packing fraction, particle size and film thickness on the load carrying normal stress. Additionally, the frictional shear stress can be investigated. The working particulate medium within the apparatus consists of glass of aluminum spheres, poly-dispersed over four size increments, all less than 1.00 mm diameter. The upper annular disk is held stationary in a rotational sense by a force transducer, and applies predetermined normal stress values which vary according to a system of interchangeable counterweights. The lower transfer surface and the sidewalls of the annular ring are rotated by applied mechanical torque. Experimental trials consist of shear initiation, after which the trough velocity, film thickness, supporting load, and frictional torque are measured. From these measurements one can calculate the average shear rate, the average load-carrying normal stress, the average frictional shear stress, and the solids volume fraction. Such third body granular flow may apply to some solid lubrication mechanisms, and to applications such as smart clutches and dampers. The continuum theory presented is unique in that it addresses solid-like behavior and its transition to fluidized behavior. The discrete particle dynamics rely on the conceptual models of Iordanoff and colleagues [2]. Our findings are that the two theoretical predictions agree reasonably with the experimental results, suggesting validity of the approach. These results are promising, and may be used to further develop high level predictive models. Furthermore, similar methods of small scale experimental particle simulation can be used to develop simpler more usable continuum approaches.

Granular flows continue to be a complex problem in nature and industrial sectors where solid particles exhibit solid, liquid, and gaseous behavior in a manner which is often unpredictable locally or globally. In tribology, they have also been proposed as lubricants because of their liquid-like behavior in sliding contacts, and due to their ability to carry loads and accommodate surface velocities. The present work attempts to model a granular Couette flow in an annular shear cell using a lattice-based cellular automata (CA) computational modeling approach. The CA framework has the flexibility to employ rule-based mathematics and/or first-principle physics to rapidly model physical processes. The model developed in this work incorporates dissipative effects due to friction between particles and boundaries, in addition to particle spin. This new model also includes a rigorous treatment of boundary-particle interactions. Additional work has been done to account for the transfer of momentum through particle chains, allowing for the modeling of transitional granular flows, which consist of both kinetic and contact flow regimes.

State of the art of hydrodynamic journal bearing lubrication is realized by a significant oversupply with lubricant, causing energy losses due to fluid film friction in the unloaded areas of the bearing. Reducing the lubricant flow however may lead to overheating or collapse of the load carrying fluid film, both resulting in a complete failure of the journal bearing. A new approach to safely reduce the lubricant flow is presented in this paper, by using a broadband piezoelectric acoustic emission sensor to detect ultrasonic structure-borne noise, usually caused by metal-to-metal contact at boundary conditions. The method of structure-borne noise analysis has proven to be suitable for detecting the occurrence of solid friction [1–4]. By combining structure-borne noise analysis with a closed loop control of a proportional flow control valve a condition dependent lubricant flow can be set. Thus lubricant friction in the bearing is reduced and additionally electrical energy in the peripheral devices, such as pumps can be saved.

This paper describes an analytical study on gas transportation in radial shaft seal. A model is constructed in which seal surfaces with sinusoidal roughness, lubricant flow at the seal lip with gaseous cavity, dissolution of gas into and release of gas from the lubricant across double boundary films at gas-liquid interfaces, and convection of dissolved gas in the lubricant flow are considered. Polyalphaolefin as a lubricant, and helium, argon and carbon dioxide are assumed. The results demonstrate that the axial flow induced by surface roughness carries the gas, and that the gas flow through the lubricant film is proportional to the gas solubility coefficient, and the circumferential speed of the shaft, which agrees with the experimental finding for actual seals. The dependence of the gas flow on the axial flow of the oil and that on the boundary films are discussed.

While continuum-based approximations have had success modeling tribosystems with thick film powder flows, they do not predict the behavior of thin powder transfer films which can be worn away from the asperity region during mixed lubrication. This is especially the case for in situ self-replenishing transfer films in the form of compacted solids which are set up to undergo deposition and depletion simultaneously. Although control volume models have been developed to describe this type of tribosystem, very little is known about the wear mechanisms that govern the transfer film in sliding contact. The problem is highlighted through the sudden breakdown of the lubricant film which inevitably leads to interfacial starvation. This study examines evidence that will lead to a fundamental description of the deposition and depletion of powder transfer films by leveraging abrasive wear theory. Justification for this theory is provided by examining the relationship between the coefficient of friction (COF), wear rate, and atomic force microscope (AFM) images of wear interfaces; so that a more accurate model of an in situ self-replenishing solid lubrication process may be constructed.

This paper introduces a research oriented numerical model used to simulate the fluid flow in a grinding process. Some of the most important features of the model are described, along with some results obtained. Distributions of temperatures, pressures and flow rates in and around grinding region are obtained in great detail. These results are essential in studying the influence of the fluid on the grinding process, as well as in determining the best fluid composition and supply parameters for a given application. The results agree well with global flow rates and temperature values found in literature and show the feasibility of 3-D simulations in grinding applications.

Milling hardened steels has emerged as a key technology in mold and die manufacturing industries. In cutting, a portion of work material is pushed upward by the tool rake face to form the chip while the other portion below this layer is ploughed under the cutting edge to become the machined surface. Although the ploughed material is a very small fraction of the uncut chip thickness, it determines surface integrity after machining. In this study, a 3D finite element simulation model of milling hardened AISI H13 tool steel (HRC 50) has been developed to study material deformation under the cutting edge of a milling insert. The ploughed depth in the range of 0.6 μm to 3.0 μm is used to study the material flow under the cutting edge. Friction between the cutting edge and workpiece surface has a significant influence on the ploughed depth. Different coefficients of friction are used to study their effects on stresses/strains and temperature during ploughing. The Johnson-Cook model is used to model the plastic behavior of workpiece material. The 3D finite element analysis gives an insight into some key issues in a milling process. The FEA model illustrates the effects of micro cutting edge geometry on pile-up in front of the cutting edge, transient stresses and temperatures, and a transition from ploughing to cutting in a milling process.

A steam generator tube of a nuclear power plant is damaged by a fretting phenomenon caused by flow induced vibrations (FIV). In this work, the surface of the tube was coated with CrN or TiN as a measure to improve performance of the fretting wear resistance. Fretting wear regime was classified by determining a phase difference between friction and relative displacement signals and contact characteristics were analyzed. As a result, coating increased the friction coefficient. At a lower load, contact condition shifted from gross slip to stick slip.

A new model for predicting the flow behavior in long journal bearing films in the transition regime (Taylor and wavy vortex regimes) was previously proposed by the authors. This paper presents the experimental verification. A comparison between the experimental and numerical results of the Torque–Speed graphs is presented with good agreement between the numerical and experimental data for the Couette, Taylor and pre-wavy regimes. In the wavy and turbulent regime, the magnitude of the numerically obtained data is larger than the corresponding measured torques, but the difference is confined to below 14%. A comparison between experimental and numerical flow patterns is also presented. The results match well in general, except that experimentally, a pre-wavy regime was identified. The latter is characterized by the disappearance of the Taylor vortices, while numerically the Taylor vortices are only distorted and the wavy vortices are formed in this regime.

This paper studies the numerical development of flow patterns and pressure profiles inside a hybrid Rayleigh step thrust bearing (HRSB) where the working magnetohydrodynamic (MHD) fluid is subject to an imposed magnetic field. This hybrid type bearing stems from integrating two classical component: the modified Rayleigh step (variable depth) and the hydrostatic feed entering at the center of the circular thrust bearing. The parameters used in this study consist of one geometric parameter, the Rayleigh step aspect ratio (depth to length ratio) and two dimensionless operational parameters, (i) the Reynolds number based on the hydrostatic fluid jet velocity entering the restrictor (Re jet ) and the Reynolds number based on the smooth upper plate angular speed (Re plate ). The numerical results are obtained using the commercially available package ANSYS (CFX) [4], which utilizes the full three-dimensional Navier-Stokes equations for the steady-state incompressible MHD fluid with constant properties. Results to be presented will will contain both vector and pressure fields within the Rayleigh step profile and on the smooth lands.

The PTT-OLROYD-B model for solute-solvent mixtures introduces visco elastic effects by way of five parameters, namely Deborah number De, a viscosity ratio r, a viscosity, a parameter related to the convected derivation and an elongation parameter κ. Asymptotic expansion is used to gain a description of the flow in the thin film situation. Two cases are considered depending of the relative magnitude of the parameters De and κ with respect to the thickness ratio. In the first situation, the elongation effects disappear at the limits and the constitutive law of the film flow is a double Newtonian Rabinowisch model whose parameters are completely described by those of the original 3-D model. In the second case in which the elongation parameter is of order zero with respect of the film thickness ratio, however small, a perturbation procedure allows to retain this parameter in the asymptotic constitutive law. This law appears to be a small modification of the double Newtonian Rabinowisch law. Last a new numerical procedure is proposed. Numerical examples will be presented for 3-D flows.