The phase shift of an ultrasonic pulse at an oil layer and determination of film thickness

An ultrasonic pulse incident on a lubricating oil film in a machine element will be partially reflected and partially transmitted. The proportion of the wave amplitude reflected, termed the reflection coefficient, depends on the film thickness and the acoustic properties of the oil. When the appropriate ultrasonic frequency is used, the magnitude of the reflection coefficient can be used to determine the oil film thickness. However, the reflected wave has both a real component and an imaginary component, and both the amplitude and the phase are functions of the film thickness. The phase of the reflected wave will be shifted from that of the incident wave when it is reflected. In the present study, this phase shift is explored as the film changes and is evaluated as an alternative means to measure oil film thickness. A quas i-static theoretical model of the reflection response from an oil film has been, developed. This model relates the phase shift to the wave frequency and the film properties. Measurements of reflection coefficient from a static model oil film and also from a rotating journal bearing have been recorded. These have been used to determine the oil film thickness using both amplitude and phase shift methods. In both cases, the results agree closely with independent assessments of the oil film thickness. The model of ultrasonic reflection is further extended to incorporate mass and damping terms. Experiments show that both the mass and the internal damping of the oil films tested in this work have a negligible effect on ultrasonic reflection. A potentially v ery useful application for the simultaneous measurement of reflection coefficient amplitude and phase is that the data can be used to negate the need for a reference. The theoretical relationship between phase and amplitude is fitted to the data. An extrapolation is performed to determine the values of amplitude and phase for an infinitely thick layer. This is equivalent to the reference signal determined by measuring the reflection coefficient directly, but importantly does not require the materials to be separated. This provides a simple and effective means of continuously calibrating the film measurement approach

Cavitation in internal flows of liquid jet through a throat

The interaction of a liquid with the surrounding air produces unstable waves that disintegrate the liquid into droplets, which is known as liquid atomization. The common internal flow of a liquid atomization nozzle experiences a single-phase flow but might turn into a multiphase flow with the existence of cavitation. Cavitation in internal flow has gotten a lot of attention because of the positive and negative consequences it can have depending on the application. One such advantageous result is that cavitation has been used to promote the atomization of liquid jets by causing gas bubbles in the atmosphere to collapse. Most of the past research on cavitation has focused on the exit orifice’s constant cross-section area. The current study investigates the effect of throat location and geometry on cavitation characteristics. Filtered water was used as the simulation fluid. The high-speed shadowgraph technique was applied to record the images of the internal flow patterns. The placement of the throat was discovered to have a substantial impact on the status of the cavitation. Cavitation began at the inlet of the throat when the throat was placed at the uppermost part of the exit orifice. However, when the throat is placed in the middle of the exit orifice, the cavitation begins at the end of the throat. Four cavitation regimes were identified, namely developing, mixed, super and sudden expansion cavitation. Furthermore, it was found that the discharge coefficient depends on the cavitation’s state and length, except when the cavitation is in the supercavitation regime

Observations of Film Thickness Profile and Cavitation Around a Journal Bearing Circumference

The film formation in a journal bearing and the extent of the cavitated region is an important contribution to load carrying capacity. In the present work, an ultrasonic method has been used to measure the film thickness profile around the circumference of an operating journal bearing. The reflection of an ultrasonic pulse at an oil layer can be used to determine the film thickness. A transducer was mounted inside a hollow shaft and the signal passed through slip rings. The journal bearing was run at a series of loads and rotational speeds. The transducer continuously pulsed and received as it swept around the bush circumference. This enabled the full film thickness profile to be established. In the converging region the predicted film shape agrees well with predictions from classical lubrication theory. When cavitation occurs, the presence of oil-air and aluminum-air interfaces disrupts the ultrasonic signal. Evidence of cavitation appearance is very clear from the measurement results. The minimum film thickness, the attitude angle, and the onset of cavitation are compared with theoretical solutions

Measurement of circumferential viscosity profile in stationary journal bearing by shear ultrasonic reflection

Viscosity is the most important lubricant property that affects bearing performance. It controls the film thickness that is established during operation. In this study, an ultrasonic method was used to measure the viscosity profile around a static journal bearing by using shear reflection coefficients. The technique introduced was found to be promising and acceptable results were obtained for certain regions of the journal bearing circumference. It proved to be critical to use the right model for determining viscosity from the layer response to a shear ultrasonic pulse. This study serves as a preliminary work for developing viscosity measurement in a rotating journal bearing

Fuzzy logic based model to predict maximum oil-film pressure in journal bearing

Oil-film pressure response is one of the key parameters that describe the operating conditions in hydrodynamic lubrication regimes. In the present study, a fuzzy logic model is developed to predict the maximum oil-film pressure in hydrodynamic plain journal bearing. In the development of predictive model, journal bearing parameters of rotational speed, bearing load and oil-feed pressure are considered as model independent variables. For this purpose, a number of experiments, based Box-Behnken experiment Design technique (BBD), are performed to observe the maximum oil-film pressure values. The results revealed that the model is able to predict maximum oil-film pressure adequately

Wear properties of nanosilica filled epoxy polymers and FRP composites

This paper is aimed to determine the wear properties of nanosilica filled epoxy polymers and FRP composites. Woven fiberglass has been deployed as the reinforcement material. The fibers were mixed with three different percentages of nanosilica-modified epoxy resin, i.e: 5wt%; 13wt%; 25wt%, in order to fabricate the desired samples of FRP composites. The effect of nanosilica on wear properties was evaluated using dry sliding wear and slurry tests. The results show that increasing the amount of nanosilica content has reduced the amount of accumulated mass loss. It was found that the FRP laminates with 25wt% of nanosilica have the highest wear resistance. The nanosilica filled fiber reinforced polymer composites have a high potential in tribological application such as ball bearing housing and snow sleds

Flexural response of nanoclay-modified epoxy polymers

Epoxy resin is one of the most common polymer matrices, used in a wide range of applications. Cured epoxy exhibits brittle behaviour and low fracture toughness when subjected to mechanical loadings. The aim of this work was to study the effect of nanoclay on the flexural stress-strain response and flexural properties of Epikote 828 and aerospace grade-Cycom 977 polymers. Three-point bending tests were conducted on two polymer nanocomposite systems which contained 1-5 wt-% montmorillonite nanoclays. The white clay powder used in this study had a mean dry particle size of 8-10 μm before the mechanical stirring or milling process was performed. It was found that the slope of the stress-strain curves increased with increasing nanoclay content. This indicates that nanoclay enhanced the flexural modulus of the epoxy. The results showed that the degree of reinforcement depends on the degree of nanoparticles dispersion in the epoxy

Literature survey on manufacturing alumina/aluminum MMC by stir casting and their wear behaviors with and without solid lubrication

Alumina (Al2O3) particles are used to incorporate into the aluminum either through liquid, semi liquid or solid-state processing condition because they could provide, high strength, high modulus, and hardness properties com-pared to those without the reinforcement. Some major problems such as wettability, porosity, and poor dispersion of particles from the view of processing conditions to produce the aluminum metal matrix composites are brought forward in this paper with several techniques for improvising. Many works had shown success of mitigating wear through the incorporation of alumina into aluminum with several degree of weight losses, depending on the produced composites properties. These, however, are still considered high when compared to those with the incorporation of solid lubricant such as carbon nanotube (CNT) or graphite which is our major concern for future development. This paper reviews several aspects that are needed during stir casting upon mixing the alumina particulates with the molten aluminum and so when solid lubricants are added. This paper is also aimed to provide a preliminary and specific guide for a researcher to initiate an experimental work, tailoring a niche area in alumina-aluminum metal matrix composite fabrication and wear testing by adjusting the angle of deposition to 45°, the improved coatings can be achieved especially at the uneven threat part of the bolt. The hardness was also found to be higher at the alignment of 45° angle. Keywords: Stir casting · Alumina · SiC · Aluminum · Metal matrix composite · Wea