A method for the measurement of hydrodynamic oil films using ultrasonic reflection

The measurement of the thickness of an oil film in a lubricated component is essential information for performance monitoring and control. In this work, a new method for oil film thickness measurement, based on the reflection of ultrasound, is evaluated for use in fluid film journal bearing applications. An ultrasonic wave will be partially reflected when it strikes a thin layer between two solid media. The proportion of the wave reflected depends on the thickness of the layer and its acoustic properties. A simple quasi-static spring model shows how the reflection depends on the stiffness of the layer alone. This method has been first evaluated using flat plates separated by a film of oil, and then used in the measurement of oil films in a hydrodynamic journal bearing. A transducer is mounted on the outside of the journal and a pulse propagated through the shell. The pulse is reflected back at the oil film and received by the same transducer. The amplitude of the reflected wave is processed in the frequency domain. The spring model is then used to determine the oil film stiffness that can be readily converted to film thickness. Whilst the reflected amplitude of the wave is dependent on the frequency component, the measured film thickness is not; this indicates that the quasi-static assumption holds. Measurements of the lubricant film generated in a simple journal bearing have been taken over a range of loads and speeds. The results are compared with predictions from classical hydrodynamic lubrication theory. The technique has also been used to measure oil film thickness during transient loading events. The response time is rapid and film thickness variation due to step changes in load and oil feed pressure can be clearly observed

Oil film measurement in polytetrafluoroethylene-faced thrust pad bearings for hydrogenerator applications

There is a growing trend in the replacement of the babbit facing in thrust pad bearings with a composite polytetrafluoroethylene (PTFE) surface layer. The PTFE-faced bearings have been shown to allow a greater specific pressure, reduce thermal crowning, and, in some cases, negate the need for an oil-lift (jacking) system. These designs of bearing require new methods for the measurement of oil film thickness both to assist in their development and for plant condition monitoring. In this work, an ultrasonic method of oil film measurement is evaluated for this purpose. An ultrasonic transducer is mounted on the back face of the thrust pad. Pulses are generated and transmitted through the pad material, bonding interlayer, and PTFE surface layer. The proportion of the wave that reflects back from the oil film layer is determined. This is then related to the oil film thickness using a series of calibration experiments and a spring stiffness model. In practice, the reflected signal is difficult to distinguish, in the time domain, from other internal reflections from the pad. Signals are compared with reflections when no oil film is present and processing is carried out in the frequency domain. Experiments have been performed on a full size PTFE-faced thrust pad destined for a hydroelectric power station turbine. The instrumented pad was installed in a test facility and subjected to a range of loading conditions both with and without oil lift. Although there were some problems with the robustness of the experimental procedure, oil films were successfully measured and used to study the effect of the oil-lift system on film formation. © IMechE 2006

An ultrasonic approach for contact stress mapping in machine joints and concentrated contacts

The measurement of pressure at a contact in a machine part is important because contact stresses frequently lead to failure by seizure, wear or fatigue. While the interface might appear smooth on a macroscale, it consists of regions of asperity contact and air gaps on a microscale. The reflection of an ultrasonic pulse at such a rough contact can be used to give information about the contact conditions. The more conformal the contact, the smaller is the proportion of an incident wave amplitude that will be reflected. In this paper, this phenomenon has been used to produce maps of contact pressure at machine element interfaces. An ultrasonic pulse is generated and reflected at the interface, to be received by the same piezoelectric transducer. The transducer is scanned across the interface and a map of reflected ultrasound (a c-scan) is recorded. The proportion of the wave reflected can be used to determine the stiffness of the interface. Stiffness correlates qualitatively with contact pressure, but unfortunately there is no unique relationship. In this work, two approaches have been used to obtain contact pressure: firstly by using an independent calibration experiment, and secondly by using experimental observations that stiffness and pressure are linearly related. The approach has been used in three example cases: a series of press fitted joints, a wheel/rail contact and a bolted joint

Ultrasonic assembly of anisotropic short fibre reinforced composites

AbstractWe report the successful manufacture of short fibre reinforced polymer composites via the process of ultrasonic assembly. An ultrasonic device is developed allowing the manufacture of thin layers of anisotropic composite material. Strands of unidirectional reinforcement are, in response to the acoustic radiation force, shown to form inside various matrix media. The technique proves suitable for both photo-initiator and temperature controlled polymerisation mechanisms. A series of glass fibre reinforced composite samples constructed in this way are subjected to tensile loading and the stress–strain response is characterised. Structural anisotropy is clearly demonstrated, together with a 43% difference in failure stress between principal directions. The average stiffnesses of samples strained along the direction of fibre reinforcement and transversely across it were 17.66±0.63MPa and 16.36±0.48MPa, respectively

Ultrasound as an experimental tool for investigating engineering contacts

Within the science of Tribology, there are few tools which practically and effectively allow the measurement of conditions at an interface. This paper describes an ultrasonic technique for measuring interface parameters. Ultrasound is an ideal measurement medium, as it has good transmission through most solids, is unaffected by surface oxide layers, is non-destructive, safe and portable. If an interface is modelled as a stiff spring, an equation can be derived which predicts the frequency profile of the reflected ultrasound. By performing a Fourier transform upon the ultrasonic echo from the interface, the stiffness of that interface can be calculated. The stiffness can be used to infer the behaviour of asperity contacts within the interface. In this work the stiffness of a metal interface over 10 loading cycles was measured, showing the effects of plasticity and adhesion. Results are also presented showing how first plastic loading cycles exhibit asperity creep and how over a number of cycles shakedown is achieved. Finally, a Hertzian ball-on-flat contact was scanned and the ultrasonic reflection profile obtained

Galaxy And Mass Assembly (GAMA): Panchromatic Data Release (far-UV-far-IR) and the low-z energy budget

We present the Galaxy And Mass Assembly (GAMA) Panchromatic Data Release (PDR) constituting over 230 deg2 of imaging with photometry in 21 bands extending from the farUV to the far-IR. These data complement our spectroscopic campaign of over 300k galaxies, and are compiled from observations with a variety of facilities including: GALaxy Evolution eXplorer, Sloan Digital Sky Survey, Visible and Infrared Telescope for Astronomy (VISTA), Wide-field Infrared Survey Explorer, and Herschel, with the GAMA regions currently being surveyed by VLT Survey Telescope (VST) and scheduled for observations by Australian Square Kilometer Array Pathfinder (ASKAP). These data are processed to a common astrometric solution, from which photometry is derived for ∼221 373 galaxies with r < 19.8 mag. Online tools are provided to access and download data cutouts, or the full mosaics of the GAMA regions in each band. We focus, in particular, on the reduction and analysis of the VISTA VIsta Kilo-degree INfrared Galaxy data, and compare to earlier data sets (i.e. 2MASS and UKIDSS) before combining the data and examining its integrity. Having derived the 21-band photometric catalogue, we proceed to fit the data using the energy balance code MAGPHYS. These measurements are then used to obtain the first fully empirical measurement of the 0.1–500 μm energy output of the Universe. Exploring the cosmic spectral energy distribution across three time-intervals (0.3–1.1, 1.1–1.8, and 1.8–2.4 Gyr), we find that the Universe is currently generating (1.5 ± 0.3) × 1035 h70 W Mpc−3, down from (2.5 ± 0.2) × 1035 h70 W Mpc−3 2.3 Gyr ago. More importantly, we identify significant and smooth evolution in the integrated photon escape fraction at all wavelengths, with the UV escape fraction increasing from 27(18) per cent at z = 0.18 in NUV(FUV) to 34(23) per cent at z = 0.06. The GAMA PDR can be found at: http://gama-psi.icrar.org/

Galaxy And Mass Assembly (GAMA): data release 4 and the z < 0.1 total and z < 0.08 morphological galaxy stellar mass functions

Galaxie

The use of dry coupling in ultrasonic nondestructive testing

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