This paper proposes a contact model between a rigid sphere and an elastic plane covered with a thin liquid film. The elastic contact is determined by Johnson–Kendall–Roberts theory, which deals with the energy equilibrium of elastic and interfacial energies. In elastic contact under presence of thin liquid film, the energy needed to separate the two bodies is defined as the summation of the interfacial energy among the sphere, liquid, and plane. Capillary force affects the two bodies because a liquid bridge is formed between them. Shape of the liquid bridge, assumed by the Clark’s toroidal approximation, determines the capillary force. The hysteresis of the liquid contact angles and that of the liquid volume between loading and unloading processes are considered. In loading process, the liquid film is squeezed out from the contact area and accumulates at the contact edge with increasing the liquid contact angles. In unloading process, the accumulated liquid is dragged to the contact edge, and the contact angles decrease. An irreversible force curve is obtained from these two hystereses, and the effect of liquid bridge is discussed based on the calculated results. In addition, the adhesion-hysteresis mechanisms caused by the capillary force are discussed.
This research reports the scuffing failure phenomenon of piston ring–cylinder liner in pilot state bench tests. Initially, microhardness evaluation of chromium sprayed piston rings of functionally graded Aluminium A390 piston was conducted using a Vickers hardness Indenter following ASTM E-384 standard. The tribological characterization for dry sliding, simulating lubrication starvation was evaluated using reciprocating Universal Tribometer. For surface morphology and allied surface characterization, Energy Dispersive X-Ray spectroscopy integrated Scanning Electron Microscope was used. Substantially large volumes of wear depicting abnormal wear have been observed on the tribo-conjugate grey CI cylinder liner surfaces in sliding with chromium coating on SAE9254 grade steel substrate. This can be attributed to the considerable hardness gradient of tribopair in conjugation. With chromium coating having a conspicuous hardness edge over the CI cylinder liner, the extrusion and ploughing of the liner surface depict the abnormality in wear. The Coefficient of Friction (COF) under dry sliding with stepped load increments showed an unsteady state of friction and this performance is underrated for operation of any tribological system.
This paper evaluates a temperature variation between pulley sheaves and a metal push belt of an automotive Continuously Variable Transmission (CVT). In a study of wear mechanisms on pulley sheaves, one of the authors previously demonstrated a crystallographic phase transition from body-centered cubic (BCC) to face-centered cubic (FCC) in fine grains beneath a sliding surface of a pulley sheave which had been operated for certain period of time. Although prevailing metallurgy indicates that the transition needs a thermal history over the eutectoid point of the material, surface temperature on pulley sheaves have not been evaluated or reported. The authors therefore analyzed temperature variation on the pulley sheave under a same operating condition of the CVT as that the phase transition was discovered. The major technical problem was measurement methods used to obtain temperature distribution on the pulley surface where the clamp position of the V-belt changes continuously according to transmission ratios of the CVT. Uniquely developed infrared borescope enabled non-contact temperature measurements near the contact area during CVT operation. Measurement results were introduced to numerical calculation to predict the highest temperature on the power transmission area including subsurface area. The resultant highest temperature did not reach the eutectoid point of the material and indicated that single source of thermal energy did not occur in abovementioned phase transition. The findings generated our hypothesis that combination of energy sources, such as thermal dissipation due to power transmission, repeated impulsive forces due to contact and friction, and consequent generation of finer grain structure, enhances the phase transformation from BCC to FCC even under milder conditions than the thresholds of every single energy source.
Cage not only separates the rolling elements but play an essential role of lubricant supplier in solid lubricated rolling bearings, thereby lubricating the rolling contacts. In such bearings, whose service life can be significantly extended by targeted cage wear, a better understanding and a reliable prediction of the wear is necessary in order to achieve a further increase in the service life. In order to predict wear and eventually their life-time is a complex phenomenon as it involves several transfer processes taking place in the rolling and sliding contacts. The lifespan of such bearings can be determined by performing numerous lifetime experiments. Global lifetime model for solid-lubricated rolling bearings does not exist so far like a conventional bearing life model. Therefore, a dynamic simulation strategy based on Adams multibody simulation environment to predict and model wear at cage pocket interface have been proposed. An incremental wear simulation approach based on Fleischer wear law is introduced. Uniform global wear of the cage pocket depending on the recalculation of cage geometry and converted frictional energy for each wear increment is calculated. Simulation results show good accordance with the experimental results. The importance and suitability of such a wear simulation approach will be enunciated in this paper.
In an effort to further extend bearing life, the authors have attempted to acquire greater knowledge regarding lubricating grease behavior in a bearing. While conducting experiments, some kinds of difficulties commonly arise when attempting to observe grease behavior directly from the bearing exterior without removing seals and shields. Making a breakthrough such a troubling aspect, X-ray computed tomography (CT), which is one of the non-destructive inspection techniques, was employed and resulted in visualizing remarkable details of grease distribution in a resin ball bearing. Hydrodynamic grease transition from churning to channeling state was well revealed by the mixture distribution of urea and barium-based greases which have different properties of X-ray absorption capability. Furthermore, the three dimensional unsteady liquid-gas multi-phase flows analysis was performed. Hydrodynamic feature of grease was regarded as a non-Newtonian fluid, which shows a highly non-linear flow curve, and the constitutive equation of modified Bingham plastic model proposed by Papanastasiou was applied to rheological property. Through these novel experimental and calculation approaches, several new insights about grease behavior inside a ball bearing were brought out.
In refrigerant compressor, rolling bearings are lubricated with a mixture of oil and refrigerant. This has always represented a challenge for the bearing lubrication quality estimation (e.g. kappa or lambda parameters). Even if the dilution rate of the refrigerant is known, the exact effect on the lubricant film thickness remains doubtful due to the unknown piezo-viscosity and compressibility of the refrigerant and their variation with pressure and temperature. In the current paper, existing mixing laws for viscosity and piezo-viscosity are examined and adapted to better represent actual measurements. The results are compared with published Daniel plots showing reasonable agreement. Once this is done a modification to the bearing lubrication quality parameter kappa is proposed to better reflect the effect of the refrigerant on the lubrication quality of compressor rolling bearings. This is a first step in the direction of predicting the bearing life for this challenging application.