Search

In this paper, the cycloidal pin wheel drive mechanism of the secondary drive component of the rotary vector (RV) reducer is studied. Under the condition of grease lubrication, considering tooth profile modifications and machining errors, we established a three-dimensional load-bearing contact analysis model of a cycloid pinwheel transmission mechanism. We studied the time-varying contact characteristics of the gear teeth and dynamic joint surfaces of the inner and outer races of a crankshaft bearing. Considering the thermal effects, we proposed an analysis model of the lubrication characteristics of cycloid pinwheel transmission mechanisms. We also studied the thermal lubrication properties, such as load de-formation, lubrication film thickness, contact pressure and temperature increase at the lubrication contact area. The accuracy of the model was verified by temperature experiments on the inner raceway of an RV reducer bearing and the evolution law of the dynamic thermal lubrication characteristics of the inner and outer races of the crankshaft bearing, the meshing gear tooth pair and the whole process of single pin tooth meshing were revealed. This study provides an effective method for analyzing the temperature increases of the key joints of RV reducers. [ABSTRACT FROM AUTHOR]

Demand for micro-deep-drawn complex-shaped parts in biomedical, chemical analysis and microsystem technologies has been growing. Micro-deep drawing is a micro-plastic forming used to produce micro-parts from different materials. Researchers have worked upon several aspects of micro-deep drawing (MDD), namely the scaling effects, handling of micro-parts and process intermittency. The present work reviews some of these experimental and numerical studies on the MDD considering the size effects, forming limit diagram, parametric effect, lubrication and coating on punch and die surfaces. The topology modification of the deep drawing tool surface using macro/microstructured coated tool shows substantial potential for the lubricant-free micro-deep drawing. Further, micro-structuring of the blank via laser has emerged as another approach in the MDD process to reduce the effective contact area between tool and sheet and, hence, the friction forces. Finally, challenges and scope for further research in MDD are listed to implement these processes commercially. [ABSTRACT FROM AUTHOR]

AbstractGear tooth spalling is a typical tooth surface defects in gear transmission. The accurate calculation of the time-varying mesh stiffness of the gear pair with spalling defect under mixed elastohydrodynamic lubrication (EHL) plays an important role in tooth damage prediction and fault feature analysis. In this work, an improved time-varying mesh stiffness (TVMS) model of spalling faulty gear in mixed EHL line contact considering the coupled effect of rough surface topography is established. The proposed model considers the combined effect of spalling defect, surface roughness topography, and lubrication on the contact characteristics of the meshing interface to obtain a revised contact stiffness, which is further used to determine the comprehensive TVMS. The cylindrical contact coefficient for curved meshing interface with spalling fault is derived and incorporated into the statistical micro-contact Greenwood and Williamson model (GW model) to obtain the asperity contact stiffness. The revised contact stiffness at the rough faulty gear interface is obtained from the parallel action of the asperity contact stiffness and oil film stiffness under load-sharing concept. The dynamic responses of the gear system are analyzed using the established mesh stiffness model through the six degrees of freedom translational-torsional dynamic model, in which the dynamic meshing force is calculated iteratively using the transit surface topography and geometrical parameters along the line of contact instead of a quasi-static meshing force. Effects of multi-parameters as surface roughness, spalling fault size, and lubricant on the mesh characteristics and dynamic responses of the gear system are further investigated and discussed. [ABSTRACT FROM AUTHOR]

Lubricants are usually utilized to decrease wear, reduce friction, and release heat. Although the lubrication approximation originated from thin-film studies, it has limitations because of continuum mechanics assumptions. To overcome these limitations, for the first time, this article employs a hierarchical multiscale approach to study the frictional sliding contact considering elastohydrodynamic lubrication. This multiscale model consists of a molecular model of lubricant and a continuum model of sliding contact components. Specifically, the molecular dynamics method is used at the nanoscale to model the lubricant and analyze the friction coefficient in contacted surfaces. Through MD simulation, the effects of hydrocarbon chain lengths, temperature, and sliding velocity on a constant friction coefficient are studied in this article. The calculated friction coefficients from the molecular model are passed to the continuum model, in which the finite element method is employed to conduct stress and strain analysis of the sliding contact components. Although variations in the frictional sliding response are invariably coupled with the friction coefficients, the molecular-to-continuum hierarchical approach enables us to isolate the relative contributions from the chemical formulation of the lubricant and the temperature. This approach has further potential implications for the evaluation of tribological damage. The results demonstrate that an increase in temperature or the chain length of lubricant hydrocarbon molecules can significantly decrease the friction coefficient and, as a result, reduce contact shear stress, plastic deformation, and pile-up height. [ABSTRACT FROM AUTHOR]

The key function of lubricants is to reduce the friction, wear, and heat between the parts that are in contact with each other. The main applications of the lubricants are to control temperature, and reduction in wear and corrosion of the machinery. Keeping in mind the importance of lubrication and its applications in varied machines. The goal of this research is to inspect the heat transmission impact in the magnetohydrodynamic flow of Jeffrey liquid near a stagnation point through a lubricated surface. Lubrication is accomplished by a shear-thinning liquid. The velocity, continuity, and shear stress, amalgamated with power-law fluids, are used to develop interfacial conditions. The exclusivity of the anticipated model is the inclusion of variable thermal conductivity and diffusion coefficients in the existence of homogeneous-heterogeneous reactions. Using the Keller–Box finite-difference approximation approach, the numerical results are accomplished. The outcomes are portrayed and tabulated in the form of diagrams and tables, respectively. It is witnessed that a greater magnetic field affects the fluid flow velocity and the drag force coefficient. Moreover, it is also inferred that the heat transfer rate dwindled for the greater thermal conductivity parameter. Authentication of the presented model is also part of this investigation. [ABSTRACT FROM AUTHOR]

In order to analyze the bearing wear in the spindle system considering different speed and load conditions, a four-bearing spindle system was investigated. Two different working conditions, Case I and Case II, are considered. Case I condition has lower spindle speed and higher external loads and preload than Case II condition. Based on Archard model, a new wear depth model of angular contact ball bearing is presented which takes into account the influence of lubrication on bearing wear. The wear depths of inner and outer raceways for angular contact ball bearings are calculated based on the motion parameters and contact parameters of ball elements which are obtained by spindle system model. The effects of spindle speed, angular misalignment, external load and surface roughness on the wear depths of bearings are comparatively studied. Increasing spindle speed at Case I condition can significantly increase bearing wear. Angular misalignment may be beneficial to individual bearing, but overall, no angular misalignment is the most beneficial to spindle system. The change rate of wear depth of bearing raceway with external loads at Case I condition is much greater than that at Case II condition. The surface roughness can significantly affect the bearing wear in the spindle system, especially at Case I condition. [ABSTRACT FROM AUTHOR]

Falling-film hydrodynamics and heat transfer, a cutting-edge technology, has been widely used in a variety of industrial applications, including desalination and refrigeration. In this study, a two-dimensional and two-phase model was developed to examine the microscopic flow mechanism and transient flow characteristics. Film thickness varies with sprinkle density in the impingement, propagation, and accumulation zones, with the thinnest film appearing between 90° and 140°. In both the unsteady and steady cases, the film thickness over the stabilizing tube is nearly the same. Due to the acquired momentum of the liquid film, the propagation time for the test tube was also shorter than that of the stabilizing tube. Low sprinkle density results in dry regions; high sprinkle density results in mal-distribution, the formation of recirculation zones beneath the tubes, air cavities in the flow field, wavy disturbances in the liquid profile, and fluid waste. Furthermore, as the liquid sprinkle density increases, the developed recirculation zones and air cavities beneath the tubes expand and become modified. A sprinkle density can be set just above the minimum value to achieve steady-state film thickness. The findings can be used to improve flow characteristics and avoid over commitment and insufficient liquid supply. [ABSTRACT FROM AUTHOR]

Elastomers are the class of materials that are widely used in a variety of industrial, commercial, and consumer applications due to their unique mechanical properties, including high elasticity, high flexibility, and high resilience. However, there are many challenges in machining of elastomers such as poor surface finish, build up of heat, degradation of elastomers, etc. To overcome these challenges, cryogenic cooling assistance has been introduced as a means of improving the machinability of elastomers. This paper presents a soft computing approach for optimizing the surface roughness and cutting force during turning of elastomers under different lubrication conditions. Three types of elastomers, namely Nitrile Rubber (NBR), Polyurethane Rubber (PU), and Neoprene Rubber (CR), are studied, and a cryogenic fluid delivery system is employed to improve the machining process. Taguchi's L27 array is used to vary the input parameters, and a Back-Propagation Artificial Neural Network (BPANN) model is developed to predict the cutting force and surface roughness. The cutting force and surface roughness are analyzed under different cooling conditions, cutting speeds, feeds, and depths of cut for various elastomers. The results show that changes in cutting conditions significantly affect the cutting force and that the type of lubrication used affects the cutting force by altering the material's physical properties. Cutting force is significantly influenced by cutting conditions, and NBR requires the highest cutting force compared to PU and CR. Further, at a cutting speed of 55 m/min, a feed of 0.11 mm/rev, and a depth of cut of 0.25 mm, the cutting force for NBR (85.1 N), while for PU (75.1 N) and CR (80.3 N), respectively. Finally, with LN2 lubrication conditions, the Cutting Force decreased by 45% and Surface Roughness decreased by 16.9%. This study provides insights into the factors affecting the elastomer machining process, which can be useful for optimizing the machining process parameters and improving machining efficiency. [ABSTRACT FROM AUTHOR]

As operating under quite high bearing speed with quite narrow clearance, the slip effect generally inevitable exists and closely relates to the performance of Gas Journal Bearing (GJB). However, singly the conventional macroscopic method may not be capable of fully exploring the influence of slip effect and seize tiny details such as slip velocity and flow vortex. In this article, both the Lattice Boltzmann Method (LBM) and the Reynolds equation method are applied to analyze the distributions of lubricant viscous dissipation heat, velocity, slip velocity, pressure, journal position and film thickness versus different operating parameters at multiscale. It shows that the slip effect weakens the squeezing function on lubricant film, reduces the viscous dissipation heat peaks, consumes the maximum pressure peaks, and decreases the bearing capacity, which is more obvious at larger Knudsen number. At higher bearing speed, the high viscous dissipation heat and pressure zone rapidly magnifies, in contrast, under larger bearing load, the high viscous dissipation heat zone concentrates. [ABSTRACT FROM AUTHOR]

In the rotating parts of large mechanical equipment, the existence of friction and wear will inevitably cause energy consumption and loss. Coating a layer of solid lubricating material on the surface of mechanical equipment is an effective means to reduce friction and wear. In this study, for the first time, a composite film with high mechanical and lubricating properties was prepared by hot-pressing the mixture of graphene oxide (GO), polyethylene glycol (PEG), and polyvinyl alcohol (PVA). Its structure and properties were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), Raman spectroscopy (Raman), and thermogravimetric analysis (TGA). The lubrication and tribological properties of GO-PEG-PVA composite film and other single films under different lubrication conditions were analyzed. The lubrication characteristics of GO-PEG-PVA composite film under oil lubrication were discussed in detail. The results show that the surface coating with GO-PEG-PVA can ensure a lower friction coefficient, especially in the condition of oil lubrication, the friction coefficient is 82% lower than that without oil film. The hot pressing process ensures that the surface morphology will not produce large shear deformation. The lubrication mechanism and lubrication model were discussed in detail, and the concept of improving surface lubrication performance by co-lubrication was put forward. [ABSTRACT FROM AUTHOR]

We derive an extension of the Maugis-Dugdale-Johnson-Greenwood model for 2D adhesive Hertzian contact to viscoelastic materials. This results in extremely simple approximate results for the maximum amplification of the pull-off due to viscoelastic effects, for arbitrary form of the viscoelastic linear properties. In particular, we assume that the initial loading state is fully relaxed, and unloading occurs at very large pulling speeds. We show that the maximum amplification (of the order of E I / E R 2 / 3 , the ratio between instantaneous and relaxed modulus to the 2/3 power) is only reached for large and soft cylinders, namely, large enough (relaxed) Tabor-Maugis parameters λ of the order of the order of E I / E R , and therefore typically much larger than the Tabor-Maugis parameters to have a "short-range" JKR adhesion regime in quasi-static conditions, which is λ ∼ 1. The results agree well with recent numerical ones by Muser-Persson, but there is an shift factor in the Tabor-Maugis parameter which requires further study and may depend on initial contact area. [ABSTRACT FROM AUTHOR]

Attempts have been made to use air-vortex cotton-blended spun yarn of 30s and 40s count as sewing thread by using 2.9% and 5.9% concentrations of lubricant. No systematic study has been conducted as of now for vortex because all the sewing threads used in the garment industry are produced from ring yarn. Yarn strength, elongation, hairiness, dry heat shrinkage, yarn abrasion, snarling of yarn after heat setting, loop strength, and knot strength of air-vortex-spun sewing threads have been studied. It is observed that the sewing thread made with 5.9% concentration of lubricant performs better in comparison to that made with a 2.9% lubrication level. Seam strength and efficiency of different types of seams made by air-vortex sewing threads have also been studied. Flat and lapped seams are found to produce higher seam strength and seam efficiency. Seam strength and efficiency improve with an increase in the concentration of lubricant in both 30S and 40S yarn. [ABSTRACT FROM AUTHOR]

In this study, the effects of surface roughness and thermal on slider bearings with turbulent fluid film were examined using the Streamline Upwind Petrov–Galerkin (SUPG)-Finite Element Method. Using the assumption that roughness is stochastic and has a Gaussian random distribution, one-dimensional transverse and longitudinal surface roughness models were taken into consideration. The texture of the surface's irregularity is changed into a regular domain for computational efficiency. To derive the modified Reynolds equation for turbulent lubrication, the Ng-Pan turbulent model is used. For all local Reynolds values, the pressure distribution of the combined effect is less than the thermal and surface roughness influences of the one-dimensional longitudinal surface roughness, which is a reduction of 16% in load-carrying capacity performance and 3% decrease in friction force, for non-parallel (w = 0.4) between the surface roughness effect and the combined effect condition, respectively. However, the pressure distribution of the thermal effect is smaller than the combined and surface roughness effects in the transverse, one-dimensional roughness model for all local Reynolds values, which is a reduction of 33% in load–carrying capacity performance and 13% decrease in friction force, for non-parallel (w = 0.4) between the surface roughness effect and the thermal effect condition, respectively. Moreover, the combined effects at various temperatures are examined. As a result, the load-carrying capacity performance is better in the case where the pad temperature is lower than the slider in both longitudinal and transverse models. The performance of a slider bearing will generally be improved by taking surface roughness and the coefficients of turbulent lubrication equations into account. Tables and figures were used to present the results. [ABSTRACT FROM AUTHOR]

Based on mixed thermal-elastohydrodynamic lubrication, the dynamic contact of ball bearings with worn band is investigated, and the film thickness, pressure, profile and interfacial temperature are analyzed. The temperature-pressure-viscoelastic equation of lubricant is constructed. The surface roughness, the elastic deformation and the worn band are included in the film thickness. The discretization method and compound iteration method are combined to solve the problem. Through numerical examples, the distribution and contour of film thickness, pressure and temperature with consideration of surface roughness and worn band are discussed, and the point contact with lower entrainment speed is found. [ABSTRACT FROM AUTHOR]

We develop a lubrication-type model of contact line motion on a surface patterned by an array of square patches of decreased wettability. The model accounts for evaporation of the liquid due to surface heating, as well as effects of surface tension and disjoining pressure. Stick-slip motion and strong interface deformations are found from the simulations. The height of the capillary ridge becomes spatially nonuniform when the stable contact line travels over the region of decreased wettability. Coupling between the surface pattern and intrinsic contact line instability is investigated. For the weak evaporation limit, the model predictions are compared to previous studies of contact line dynamics under isothermal conditions. [ABSTRACT FROM AUTHOR]

Micro-cantilever beam are now widely used in modern micro and nano devices. This device includes micro-switches and microscopes which are operated by atomic force. The dynamic analysis of cantilever beams is of critical prior to manufacturing of the beams. Dynamic analysis is carried out using an energy technique based on Galerkin method and pull-in parameters are to be found out for prismatic cantilever. In squeeze film damping the air present between movable beam and fixed beam behave as squeezed fluid and producing the damping effect which lead to reducing in displacement. In case of fringing field the line of action of electrostatic force do not remain perpendicular at the boundaries. The effect of damping due to Squeeze film and fringing field on dynamic performance of beam is studied and found out the pull-in factors and matched with the published outcomes. This area opens novel opportunities for structural optimization of electrostatic micro-beams. [ABSTRACT FROM AUTHOR]

Skid-resistance performance of a runway greatly influences aircraft landing safety. A wet runway significantly increases the incidence rates of aircraft overrun. To study the influence of the skid-resistance performance of a runway on aircraft landing, a co-simulation method is proposed. First, a finite element (FE) model of the local tire-water film-runway simulation is established to obtain the combination coefficient-slip ratio curve of a tire on a wet runway. Second, a global model of an Airbus A320 virtual prototype (VP) is created. Then, on the basis of fuzzy control theory, a two-dimensional (2D) fuzzy controller of the aircraft AB is established. The friction coefficient-slip ratio curve of the tire on the wet runway obtained in the local simulation is introduced into the full-scale hydroplaning simulation model of the aircraft. Finally, the global-local multiscale simulation method is used to analyze the skid-resistance behaviour of the aircraft on three types of runways. It is found that the increase of water film thickness of the pavement and the increase of the grounding speed cause the attenuation of the friction coefficient of a runway, finally causing the reduction of the deceleration rate of the aircraft and the increase of the braking distance. [ABSTRACT FROM AUTHOR]

The paper presents the numerical solution of line contact thermal elastohydrodynamic lubrication (EHL) with bio-based lubricant. The model comprises Reynolds equation, film thickness, load balance and energy equations with appropriate boundary conditions by incorporating viscosity–pressure–temperature and density–pressure–temperature relations. Second-order finite difference scheme is used for the discretised form and their equation. The multigrid method with full approximation scheme is used to solve the Reynolds equation along with multilevel multi-integration method for film thickness equation. The pressure, film thickness and temperature distributions for two rolling velocities and various loads with a bio-based lubricant are presented in detail. The present findings yield a reduction in the minimum film thickness for high speed. Details of pressure spike as a function of relevant parameters are given. The results are compared with earlier findings based on different methods. [ABSTRACT FROM AUTHOR]

Lubricated contact performance can be improved by using a textured surface as well as a hydrophobic surface. A procedure to obtain the optimal partially textured journal bearing combined with the hydrophobic coating is presented through the computational fluid dynamics (CFD) codes. In this study, lubricated hydrophobic textured contacts with and without cavitation modeling are discussed. The cavitation phenomena in the lubricant is modeled using a multiphase model of “mixture” to obtain a realistic condition. The effect of dimple depth, as well as the eccentricity ratio, on the tribological performance, is of particular interest. It is found that the tribological performance is greatly influenced by the multiphase flow cavitation scheme. When cavitation modeling is taken into account, higher load support is noted. Furthermore, the simulation results show that a hydrophobic textured surface with a shallow depth (d/hmin<1) seems to be better for enhancing the tribological performance. Meanwhile, for the case of the low eccentricity ratio, there is an optimal dimple depth giving the highest load support. The findings explored in this work can be considered as a theoretical basis to increase the performance of hydrophobic textured journal bearing. [ABSTRACT FROM AUTHOR]

The research work presents the study of a heterostructured surface acoustic wave (SAW) resonator consisting of an interdigital transducer (IDT), lithium niobate (LN), and silicon (Si) substrate. In the proposed structure, Silicon is the base substrate, above it layer of LN is placed then IDT is designed on it. The presented analysis includes the variation of the quality factor and electromechanical coupling coefficient with the change in the width of the piezoelectric layer. The electromechanical coupling coefficient (K2), quality factor (Q-factor), velocity, resonance, admittance, and anti-resonance frequency have been studied for the thickness of the different layers of LN film. The higher quality factor of one port SAW devices reduces the energy loss and the K2 of the devices indicates faster energy conversion. The Q-factor and K2 are found to be depending on the thickness of LN, resonance, and anti-resonance frequency. [ABSTRACT FROM AUTHOR]

The research work presents the study of a heterostructured surface acoustic wave (SAW) resonator consisting of an interdigital transducer (IDT), lithium niobate (LN), and silicon (Si) substrate. In the proposed structure, Silicon is the base substrate, above it layer of LN is placed then IDT is designed on it. The presented analysis includes the variation of the quality factor and electromechanical coupling coefficient with the change in the width of the piezoelectric layer. The electromechanical coupling coefficient (K2), quality factor (Q-factor), velocity, resonance, admittance, and anti-resonance frequency have been studied for the thickness of the different layers of LN film. The higher quality factor of one port SAW devices reduces the energy loss and the K2 of the devices indicates faster energy conversion. The Q-factor and K2 are found to be depending on the thickness of LN, resonance, and anti-resonance frequency. [ABSTRACT FROM AUTHOR]

The paper presents steady isothermal elastohydrodynamic lubrication (EHL) of elliptical contact with Roelands pressure–viscosity model over varying rotational speed. The governing Reynolds and film-thickness equation for elliptical contact in roller bearings are analysed by using multigrid method with full approximation scheme. The non-dimensional pressure distribution and film-thickness for elliptical contacts are obtained. The distinct friction models appropriate to lubricants in contact regions are predicted. The result shows that rolling contact weariness does not occur on the surfaces with longitudinal roughness and wear or scraping exists in circular EHL contacts with entrainment along major axis to that of minor axis. The computation predicts that minimum film thickness, central film thickness and elastic deformation increase as the rotational speed increases. The computed results are compared with earlier finding which are in good agreement. [ABSTRACT FROM AUTHOR]

The boron occupies an important place on contributions and its usage is getting widespread. Although the use of boron-added mineral oils serves to reduce friction, environmental risks can not be totally removed. It is necessary to improve the properties of biological oils used for additives so that they can compete with mineral oils technically. In the study, the use of liquid boron as an additive for engine lubrication oil together with vegetable oil was investigated experimentally in two diesel engines. Experiments were first carried out using mineral lubrication oil in the engine, and then the experiments were repeated using mineral base oil with additives in the second engine with the same technical characteristics as the first engine. Basically, the study was performed in the fields of engine performance (torque, power, consumption per hour, specific fuel consumption) and exhaust emissions (CO, CO2, HC, O2, SO2, NOx). As a result, it was concluded that the engine, in which boron and mineral oil with wild mustard oil were used, provided more significant fuel saving than in the engine with additive-free mineral oil, and no significant change was seen in the engine performance, also they showed similarities in terms of exhaust emissions. [ABSTRACT FROM AUTHOR]

Ball-in-socket metal on metal (MOM) contacts were analysed using the Abaqus Finite Element package to simulate dry contact between the acetabular cup and the femoral head. Different cup thicknesses of 4, 6, 8, and 10 mm were considered using a polyurethane foam block support system. Elastohydrodynamic lubrication (EHL) analyses were developed for the contacts using three different approaches to specify the contact. These were (i) A simple model based on the radii of relative curvature, (ii) An equivalent contact model developed so that its dry contact area and maximum pressure replicated the values obtained from the FE analysis, and (iii) A modified version of (ii) that also ensured equivalence of the gap shape outside the contact area. Published in vivo information for the hip joint contact forces over the walking cycle was used to specify the operating conditions for the EHL analysis. The analysis method was found to be effective for all points of the walking cycle for cases where the cup thickness exceeded 5 mm and modelling approach (ii) was identified as satisfactory. For a cup thickness of 4 mm, membrane action began to emerge in the FE analyses so that such contacts behaved in a different way. [ABSTRACT FROM AUTHOR]

In this work, the desensitising effect of water film on the diamond cutting of HMX crystal is studied by using reactive force field (ReaxFF) molecular dynamics simulations. The lubrication behavior, reaction kinetics, decomposition products and reaction pathways are particularly studied to reveal the underlying atomistic origins of desensitisation of wet-cutting system. Simulation results show that a film lubrication and its evolutionary behaviour occur at the nano-cutting interface. And forming a complete water-lubricating film is critical for improving thermal stability of the entire cutting system, which is correlated to tool sharpness, HMX properties and water-lubrication method in the actual cutting process. More interestingly, the mechanism of desensitising effect is confirmed to be that the nano-water film inhibits the C–O affinity between diamond tool and HMX, which makes the relatively stable symmetric cleavage of the main ring dominant in the initial decomposition of HMX. Although the type and evolution trend of the decomposition product is similar to that in dry cutting, the degree of decomposition and the severity of HMX are lower in wet-cutting, and the presence of water-lubricating film causes the transition of main dynamic mechanism function of the HMX from the self-catalysed mode into the random nucleation mode. [ABSTRACT FROM AUTHOR]

A semi-analytic solution is developed for heterogeneous elasto-plastic materials with inhomogeneous inclusions under elastohydrodynamic lubrication in point contact or line contact. The inhomogeneous inclusions within a material are homogenized as homogeneous inclusions with properly determined eigenstrains based on the equivalent inclusion method, and the surface displacements induced by these eigenstrains are then introduced into the gap between the contact bodies to update surface geometry. The accumulative plastic deformation is iteratively obtained by a procedure involving a plasticity loop and an incremental loading process. The model takes into account the interactions among the contact bodies, the embedded inclusions, and the plastic zones, thus leading to a solution of the surface pressure distributions, film thickness profiles, plastic zones, and subsurface stress fields. This solution is of great importance for the analysis of elasto-plasto damage of heterogeneous materials subject to lubricated contact. [ABSTRACT FROM PUBLISHER]

This work is concerned with the lubrication analysis of artificial knee joints, which plays an increasing significant role in clinical performance and longevity of components. Time-dependent elastohydrodynamic lubrication analysis for normal total knee replacement is carried out under the cyclic variation in both load and speed representative of normal walking. An equivalent ellipsoid-on-plane model is adopted to represent an actual artificial knee. A full numerical method is developed to simultaneously solve the Reynolds and elasticity equations using the multigrid technique. The elastic deformation is based on the constrained column model. Results show that, under the combined effect of entraining and squeeze-film actions throughout the walking cycle, the predicted central film thickness tends to decrease in the stance phase but keeps a relatively larger value at the swing phase. Furthermore, the geometry of knee joint implant is verified to play an important role under its lubrication condition, and the length of time period is a key point to influence the lubrication performance of joint components. [ABSTRACT FROM AUTHOR]

The tibial component of current knee prostheses made of ultra high molecular weight polyethylene (UHMWPE) has a high degree of wear that causes knee inflammation, prosthesis loosening and subsequent replacement in not more than 15 years. In order to know which UHMWPE material properties have more influence on wear, a steady state lubrication model with non-Newtonian synovial fluid has been studied through numerical solution. The results show that UHMWPE has a very high elastic modulus that makes difficult a well lubricated artificial joint and induces the formation of very thin lubricating films between the moving surfaces with the same magnitude of roughness components. This study shows that the use of deformable porous materials in the tibial component could cause the lubricating film thickness to be higher than the average roughness and the pressure levels to be lower than the one predicted for UHMWPE. These two facts imply friction and wear reduction. [ABSTRACT FROM AUTHOR]