In the present paper, the algorithm proposed by Giacopini et. al. [1], based on a mass-conserving formulation of the Reynolds equation using the concept of complementarity is suitably extended to include the effects of compressibility, piezoviscosity and shear-thinning on the lubricant properties. This improved algorithm is employed to analyse the performance of the lubricated small end and big end bearings of a connecting rod of a high performance motorbike engine. The application of the algorithm proposed to both the small end and the big end of a con-rod is challenging because of the different causes that sustain the hydrodynamic lubrication in the two cases. In the con-rod big end, the fluid film is mainly generated by the relative high speed rotation between the rod and the crankshaft. The relative speed between the two races forms a wedge of fluid that assures appropriate lubrication and avoids undesired direct contacts. On the contrary, at the con-rod small end the relative rotational speed is low and a complete rotation between the mating surfaces does not occurs since the con-rod only oscillates around its vertical axis. Thus, at every revolution of the crankshaft, there are two different moments in which the relative rotational speed between the con-rod and the piston pin is null. Therefore, the dominant effect in the lubrication is the squeeze caused by the high loads transmitted through the piston pin. In particular both combustion forces and inertial forces contribute to the squeeze effect. This work shows how the formulation developed by the authors is capable of predicting the performance of journal bearings in the unsteady regime, where cavitation and reformation occur several times. Moreover, the effects of the pressure and the shear rate on the density and on the viscosity of the lubricant are taken into account.

In this study, we evaluated the wear of different polymeric materials. The temperatures were also monitored near the articulating surfaces. Six pin-on-disc specimens made out from industrial grade Polyetheretherketone (PEEK), medical grade PEEK, Polyacetal, Ultra High Molecular Weight Polyethylene, Polyetherimide, and Polyphenylene Sulfide. The specimens were tested under ± 8° axial rotation and constant compressive load ranging from 50N–444N. The results of study show an increase in the wear and temperature with increased load. The PEEK-on-UHMWPE material combination outperformed all other tested material combinations in terms of volumetric wear.

A new multidirectional motion pin-on-disk (MPOD) apparatus was designed, built and validated. Multidirectional motion was proven to have influence on the wear behaviour due to the difference in shear stress, especially in biotribology experiments for prosthetic joint materials. This MPOD was designed to realize the ‘adhesive polishing’ effect observed in multidirectional sliding wear test. Following axiomatic design principle, several modules, such as loading unit, motion generation and pin guiding modules were developed according to the uncoupled design matrix. Force transducers were assembled separately in X and Y direction for precisely measuring, and a frequency control system was assembled to provide a wide range of rotation speed. Preliminary tests were performed by using ultra high molecular weight polyethylene pins against zirconium oxide disks, and the experimental results were analyzed and compared with those observed in unidirectional wear tester.

Some types of mating parts, such as exhaust valves and seats in diesel engines, must perform at elevated temperatures and in oxidizing environments, while at the same time resisting the effects of repetitive impacts and interfacial slip. The wear that takes place under such situations is the net result of a complex process that involves plastic deformation, tangential shear, and oxidation. Tribolayers form, are removed, and reform. An apparatus was designed to simulate the key aspects of elevated temperature wear of exhaust valves. Three degrees of motion: impact, slip, and rotation were taken into account. Two different test geometries were developed: (a) inclined cylindrical pins striking rounded corners, and (b) actual exhaust valve sealing surfaces striking the edges of flat blocks. The features of the high-temperature repetitive impact device are described, and examples of the wear scars produced by the two test configurations are presented.

Granular flows have been proposed as an alternative lubrication mechanism to conventional liquid lubricants in sliding contacts due to their ability to carry loads and accommodate surface velocities. Their load carrying capacity has been demonstrated in the experiments of Yu and Tichy [1]. Alternate lubrication techniques are becoming necessary due to the failure of conventional liquid lubricants in extreme temperature environments, and their promotion of stiction in micro-/nanoscale environments. Yet, understanding granular behavior has been difficult due to its non-linear and multiphase behavior. Cellular Automata (CA) has been shown to be a viable first order approach to modeling some complex aspects of granular flow. Previous work by the authors successfully modeled granular shear with a CA model [2]. Additional work combined CA computational efficiency with particle dynamics to effectively model collision events. This work builds upon and modifies the prior CA modeling approaches by adding friction modeling and spin of particles. This modification maintains the computational efficiency of CA, while increasing accuracy of the predicted granular flow properties, such as speed, solid fraction, and granular temperature. The current work compares the CA model with friction and spin physics relations to the authors’ prior CA model which neglected friction. Both CA models are also evaluated against experimental data to quantify the benefits of including friction and spin in the CA modeling approach for granular flows.

The tribological behaviour of Stellite 6, Tribaloy 700 and Tribaloy 400C have been studied during self-mated unlubricated rotational sliding between 20 to 600°C, at 3ms −1 for 1 hour using scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDX). Testing was conducted using a specially designed wear rig in which bearings and shafts of the materials were machined and tested within a furnace. Tribaloy 700 exhibited high bearing wear rates for all temperatures. Tribaloy 400C and Stellite 6 bearing wear rates generally decreased with temperature until very low wear rates were recorded at 600°C. The bearing wear rates appeared to be related to the formation of wear resistant oxide films often known as ‘glazes’. Adherent ‘glazes’ formed on Tribaloy 400C and Stellite 6 at 450°C and 600°C. However, ‘glazes’ formed on Tribaloy 700 showed poor adherence to the substrate causing high wear rates.

Residual stresses due to machining are the results of the thermo-mechanical history of the piece/tool interface. The magnitude and the gradient of stress play a key role for the surface integrity. A thermo-mechanical model has been developed. It allows simulating the rolling/sliding contact between an elastic tool in rotation along its own axis and an elastic-plastic flat in translation. The analysis includes the effects of both the normal and tangential loading. Frictional heating is also considered. The model is based on a semi-analytical method and the transient 3D contact problem is fully solved. Compared to the finite element method the computing time is reduced by several orders of magnitude. This technique has already been successfully applied to the simulation of running-in and wear, and to fretting wear, and a first attempt to simulate residual stress and strain due to the contact between a grinding tool and a work piece is made here. First results are presented for various stationary and transient thermo-mechanical loading histories.

The model of a lubrication problem involving a Newtonian fluid with the contaminant particle smaller than the minimum film thickness is developed. The interaction of fluid and particle is considered in the model. The behavior of a particle in the lube oil is also studied. The lube oil is regarded as the continuum phase, and the lubrication problem is solved by the modified Reynolds equation to determine the film pressure and velocity. The dynamics of a particle in the lubricant are studied using Newton’s second law to determine the particle velocity, angular velocity and displacement. The effects of the particle motion including translation and rotation on lubrication characteristics are analyzed. The effect of relative velocity between particle and oil on the pressure is also discussed. The results indicate that the particle motion has a significant effect on the film pressure distribution. When the particle velocity is lower than the film velocity, the motion of particle causes a significant pressure increase. This high pressure only lasts a short time if the particle rotation is neglected. However, when considering the particle rotation, the high pressure will last a much longer time.

A MEMS device with a configuration similar to that of a micro-bearing was developed to study the friction behavior of the curved sidewall surfaces. This friction testing device consists of two sets of actuators for normal motion and rotation, respectively. Friction measurements were performed at the curved sidewall surfaces of single-crystal silicon. A general model was developed for the equivalent tangential stiffness of the bush-flexure assembly at the contact point by reducing a matrix equation to a one-dimensional formulation for the purpose of using a recently developed quasi-static stick-slip model. The measurement results show that the coefficient of static friction exhibits a nonlinear dependence on the normal load. The true coefficient of static friction was determined by fitting the experimental friction curve.

Spin-off experiments for PFPE Z25 were conducted by using a 3.5 inch disk at a constant speed of 10,000 rpm. The initial film thickness was set to about 2.4 nm for all the experiments while temperature was changed in a wide range. It is found that the rheological behavior of the film is quite different from that expected from the continuum. A novel model based on Fick’s law of diffusion was proposed, which is called the layer molecular dynamic diffusion (LMDD) model. The theoretical prediction was compared with the experimental results and a good agreement was obtained, verifying the effectiveness of the model.

This paper presents a numerical investigation into the dynamics and pressure distribution of a full hydrostatic bearing with six pockets. The pockets are rectangular and the effects of their depth are investigated by choosing a deep pocket type (0.25in) and a shallow one (0.01in), respectively. Parametric studies are partitioned in operational and geometric. The operational ones include the effects of bearing eccentricity and shaft rotation speeds. The geometric ones are the concentric clearance and the pocket depth. Whether deep or shallow the pockets have the same footprint projected base. It was found that the pocket’s depth causes the pressure to be either uniform across the pocket (deep pocket) or vary (shallow) in a ramp increasing in the direction of rotation. In both cases a Raleigh step effect is observed at the downstream edge of the pocket. More interestingly, in the convergent region the hydrodynamic effect on the lands creates pressures that are significantly higher than those in the hydrostatic pockets when the rotational speeds are high. It was found that for narrow clearance the effect of pocket depth on cross-coupled and direct stiffness is negligible, while for the large clearance the stiffness decreases with the increase in the pocket depth. For either type of pocket the stiffness increases with eccentricity and rotation whether the concentric clearance is large or small.

An oil lubricated wave bearing has been tested on a new rig for fluid film journal bearings at NASA Glenn Research Center in Cleveland, Ohio, USA. The tests are intended to evaluate the rig possibilities of running without misalignment. Data recorded under steady-state conditions included oil flow rate, input, output and oil supply temperatures, and shaft position. Two sets of data were collected: i) by varying the load to 9000 N at a constant shaft rotation speed of 8,000 RPM and ii) by varying the speed from 9,000 to 12,000 RPM at constant load of 6,700 N. The temperatures of the metal sleeves were also recorded. Vibration levels at four locations were displayed and recorded. These measurements indicated that damping from the wave bearings provides significant attenuation of the vibration generated by the air turbine that drives the rig.

Spherical bearings have been used successfully in engines for some years. The spherical bearing geometry allows a simplified axisymmetric piston design; gradual rotation of the piston and rings results in axisymmetric sidewall wear, temperature distribution and thermal expansion. A previously-described concept engine design incorporating a spherical joint piston was based on an existing production engine with a conventional cylindrical piston pin. Previously-developed finite element lubrication analysis methods are applied to both designs and predictive comparisons made.

A reduction of vibrations in mechanical seals increases the life of the seals in centrifugal pumps by minimizing fatigue damage. Mechanical seals consist of two smooth seal faces. One face is stationary with respect to the pump. The other rotates. Between the faces a fluid film evaporates as the fluid moves radially outward across the seal face. Ideally, the film evaporates as it reaches the outer surface of the seal faces, thereby preventing leakage from the pump and effectively lubricating the two surfaces. Relative vibrations between the two surfaces affect the fluid film and lead to stresses on the seal faces, which lead to fatigue damage. As the fluid film breaks down, impacts between the two seal faces create tensile stresses on the faces, which cycle at the speed of the motor rotation. These cyclic stresses provide the mechanism leading to fatigue crack growth. The magnitude of the stress is directly related to the rate of crack growth and time to failure of a seal. Related to the stress magnitude, vibration data is related to the life of mechanical seals in pumps.

In this study, a new developed tribological multi-function simulator system, SHU-MFS is firstly introduced. By changing of the holder, a hip joint simulator and a POD tester can be generated in the new system. The simulator is designed not only for wear tests of the total hip prostheses, but also applicable in common tribological study. As to the module of hip joint simulator, this design can be described as having the basic motion components in human hip joints. A frequency control system is developed to offer a wide range of rotation frequency so as to provide proper experiments towards different groups. In the POD part, eight precision-made pins are generated and an advanced computer system is built up to measure the friction coefficient of the test samples.

Pin joints are used in many items of industrial machinery where two structural members are required to articulate. A pin is assembled between typically four bushes. As the members articulate the pin rotates relatively slowly inside the bushes. A hydraulic test machine has been developed to load and articulate a 56 mm diameter pin held in four bushes, typical of that found in earth moving machinery and aircraft landing gear. The rig is capable of applying realistic loads and speeds of articulation, whilst measuring torque and angular displacement. The test machine design and operation is described. The pin joint is lubricated with mineral oil based grease. Joint rotation is relatively slow and hydrodynamic calculations predict that the joint operates in the boundary regime. During a single cycle the torque remains largely constant, with a static friction peak at the beginning and end of the cycle. Measurements of the torque during articulation demonstrate friction coefficients varying from 0.02 to 0.12 depending on the rotational speed. The contact stress distribution between the pin and bushes was estimated by an ultrasonic method. An ultrasonic pulse was sent through the hollow pin and reflected back from the pin-bush interface. High contact pressures causes conformity between the pin and bush and so the wave passes through. The proportion of the sound wave reflected was used to estimate the contact stress distribution. The results showed how the stress is maximum in the outer bushes and over a 60° arc of the pin. The results of the study can be used to understand how pin joints function and how they may be optimised.

Chemical-Mechanical Polishing is used to polish silicon wafers in the manufacturing of integrated circuits. Wafers are pressed, electronics side down, onto a rotating pad that is flooded with a slurry containing abrasive particles. The slurry is entrained in the interface and the abrasive particles slide against the silicon and polish it. Our previous work has shown that subambient pressures develop at the silicon/pad interface and we have measured this pressure and its distribution over the wafer surface (1). However, our experiments have been limited to those conditions where the pad rotates and the wafer slides on the pad but the wafer itself does not rotate. Our experiments showed a skewed pressure distribution. This paper describes experiments and pressure distribution measurements where the wafer, as well as the pad/platen is rotated (2). Specifically-designed wireless electronic transmitters and receivers were built and used to measure the interfacial pressures at the silicon/pad interface. Subambient stress maps and temperatures have been measured and Figure 1 shows an example of a skewed pressure distribution when the silicon is not rotated and Figure 2 shows the pressure distribution for the same wafer while it is rotating. The subambient pressures develop over a 2 second time period from when the rotation started. The pressure distributions are symmetric in spite of the lean and tilt of the wafers. The rotational speed and other variables have a big influence on the polishing rate and this will be discussed in the talk.

A thin micro-motor has been developed comprising a molded polymeric rotor disk with cylindrical sleeve that functions as solid lubrication bearing. It is designed to overcome the frictional resistance and to provide vibration damping in the rotation. Accelerated ageing was conducted on this bearing system to assess the tribological endurance of plastic against surface wear. It was demonstrated that the wear resistance property of the plastic material can be significantly improved with Tetrahedral Amorphous Carbon coating for more than 1×10 9 continuous cycles. The experimental results provide indication of good reliability for using polymeric material in small rotational mechanism.

Many approaches have been used to control the reverse pumping effect in radial lip seals. One of those is the use of oriented triangular micro-asperities on the shaft of the seal. This extended abstract presents areal surface parameter measurements from a lip seal with triangular micro-cavities oriented towards the direction of rotation. Surface parameters in the roughness, hybrid and functional groups are presented. The measurements are then discussed and placed in the context of radial lip seal performance.

A dynamic analysis tool for calculating cage stress in needle roller bearings under planetary motions was developed to examine the mechanism of rising cage stress. This analysis considers three degrees of freedom of a cage and rollers and two degrees of freedom of a planetary gear in two-dimensional model. Moreover, the elastic deformation of the cage is implemented to determine the cage stress by using a Component-Mode-Synthesis method. In order to validate this dynamic analysis, two needle roller bearings with different structural cage strengths were tested in a planetary gear system. In cases where the weaker cages were damaged, the analyzed stress of the cages nearly reached or exceeded the material fatigue strength. This high stress was observed when a roller passed the load zone collided with the pocket bar due to the centrifugal force of planetary motion. The maximum cage stress increased with the carrier rotation speed and the stress of the damaged weaker cage only exceeded the fatigue strength in the experimental range of carrier speed. These results indicate that the dynamic model is effective and valid for the current application.