Performance of a self-lifting linear air contact

An investigation into the performance of a self-levitating linear air bearing that functions on the squeeze film principle was conducted and a detailed set of results describing its floating characteristics at various operating parameters is presented. Experimentally assessed performance of the bearing was compared with performance predicted by a computer model of the bearing

Surface damage resulting from rolling contact operating in magnetic field

This paper describes the effects of magnetic field in rolling contact tests of steel by using a two-disc configuration and the investigation of mechanisms involved. Two contact conditions, namely pure rolling and rolling with 10% sliding were used together with 0.4 and 1.1 Tesla horizontal static magnetic fields created by permanent magnets. Results of optical and scanning electron microscope observations point out that finer wear particles and smoother worn surfaces are produced in the presence of a magnetic field. It is proposed that finer wear particles result from the movement of subsurface crack initiation towards the surface due to the action of magnetic field

Squeeze-film levitation characteristics of plates excited by piezoelectric actuators

A small mass is levitated by a vibrating plate with an arrangement of four piezoelectric actuators that generate a squeeze-film in the gap between the plate and the mass. Different arrangements of actuators and plate design are explored using simulation in order to produce better performance

Plate actuator vibration modes for levitation

The design of an aluminium or steel plate of various thicknesses for achieving levitation of a small aluminum disk is investigated by simulation using ANSYS. Each plate design is excited by an arrangement of four hard piezoelectric actuators driven with an AC voltage, which produces a centre displacement for generating a squeeze-film in the gap between the vibrating plate and the disk. Physical experiments show levitation conditions for one of the designs

Present state of knowledge of the upper atmosphere: An assessment report; processes that control ozone and other climatically important trace gases

The state of knowledge of the upper atmosphere was assessed as of January 1986. The physical, chemical, and radiative processes which control the spatial and temporal distribution of ozone in the atmosphere; the predicted magnitude of ozone perturbations and climate changes for a variety of trace gas scenarios; and the ozone and temperature data used to detect the presence or absence of a long term trend were discussed. This assessment report was written by a small group of NASA scientists, was peer reviewed, and is based primarily on the comprehensive international assessment document entitled Atmospheric Ozone 1985: Assessment of Our Understanding of the Processes Controlling Its Present Distribution and Change, to be published as the World Meteorological Organization Global Ozone Research and Monitoring Project Report No. 16

Morphology of surface damage resulting from static and dynamic contacts

Contact fatigue damages resulting either from static or dynamic contact are of interest for understanding the failure modes and mechanisms leading to improvement of the components’ performances in tribological applications. The objective of this research was to ascertain how and to what extent the counterface materials, loading conditions, contact configuration, lubrication, and the environment affect the failure behaviours of material under static and dynamic contact fatigue loading. An experimental ball-on-flat test configuration was employed for both static and dynamic contact fatigue testing. In house designed test rig was used to study static cyclic loading contact fatigue behaviours of brittle polymethylmethacrylate (PMMA) in contact with balls made of different materials, i.e. Si3N4, steel, aluminium, bronze and PMMA in dry and oil-lubricated conditions. A modified four ball test machine was used to study dynamic rolling contact fatigue behaviours of thermally sprayed molybdenum and titanium coatings in contact with steel balls in dry and seawater conditions. The static contact fatigue and the dynamic contact fatigue test results revealed that counterface material, loading magnitude, lubricant and the environment play a vital role in controlling failure modes and the extent of damage. In static contact fatigue, adhesive strength of the interface was the key factor controlling damage of the PMMA plate in both dry and oil-lubricated conditions. In dry conditions, three failure modes, i.e. adhesive wear, ring cracks, and radial cracks controlled the damage of PMMA to a different degree for each combination of materials. Whereas, the damage of each combination in oil-lubricated conditions was affected by the extent of three failure modes, i.e. adhesive wear, radial cracks and abrasive wear. In dynamic contact fatigue tests, adhesive wear and inter-lamellar cracking were the major failure modes controlling damage of molybdenum coating and titanium coating in dry contact conditions while abrasive wear, corrosion and lubrication controlled damage processes in seawater conditions.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

The influence of magnetic field on wear in sliding contacts

The influence of the horizontal magnetic field has not been sufficiently studied in contrast to study activity on the influence of the vertical magnetic field by researchers. The reason was that the influence of horizontal magnetic field to change the wear mass loss of ferromagnetic materials is smaller compared to the vertical magnetic field. However, the influence of horizontal magnetic field on rolling contact changes the subsurface crack initiation point toward surface is postulated by a researcher. Therefore, it is significance finding out how the horizontal magnetic field influences the tribological characteristics. This thesis presents a study on the influence of the horizontal magnetic field on wear in sliding contacts contributes for ascertainment the effect and mechanism of horizontal magnetic field on tribological characteristics of sliding contacts, through the experimental approach.The static magnetic field with densities of 0 and 1.1 Tesla and different orientations was applied to different contact conditions, different surface modifications and two sliding frequencies, using a ball-on-plate contact configuration. In conclusion, the presence of magnetic field enhances the chemical adsorption between iron or oxide iron and oxygen, and causes the transition of adhesive wear to oxidative wear. Besides, the presence of magnetic field combined with low sliding frequency forms the bulging on the wear surface and weakens the prevailing wear mechanism due to the low frictional temperature. On the other hand, the presence of magnetic field combined with high sliding frequency induces the transition to the oxidative wear mechanism and reduces the wear. Also, distinctly different appearances of wear surface are created by different magnetic field orientations. In the lubricated sliding contact, the magnetic field causes the reduction of wear and induction of oxide. It is postulated that the presence of magnetic field enhances the oxygen adsorption on the wear track by iron wear particles and hence varies the tribological behaviour. The influence of magnetic field on carbon steel coating consists in changes of oxide iron layer and steel layer, alterations of mechanical properties of the coating, and decrease in the mass loss and the surface roughness on the dry sliding contact. All these could be suggested the influence of adhesive strength of the interface between the base material and coating.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Trends in stratospheric minor constituents

Photochemical models predict that increasing source gas concentrations are also expected to lead to changes in the concentrations of both catalytically active radical species (such as NO2, ClO, and OH) and inactive reservoir species (such as HNO3, HCl, and H2O). For simplicity, we will refer to all these as trace species. Those species that are expected to have increasing concentration levels are investigated. Additionally, the trace species concentration levels are monitored for unexpected changes on the basis of the measure increase in source gases. Carrying out these investigations is difficult due to the limited data base of measurements of stratospheric trace species. In situ measurements are made only infrequently, and there are few satelliteborne measurements, most over a time space insufficient for trend determination. Instead, ground-based measurements of column content must be used for many species, and interpretation is complicated by contributions from the troposphere or mesosphere or both. In this chapter, we examine existing measurements as published or tabulated

The effects of magnetic fields on rolling contact fatigue wear

The thesis describes the effects of the magnetic field in rolling contact tests of steel by using a two-disc machine and the investigation of its mechanism from contact stress analysis by using FEM and the agnetisation of a ferromagnetic substance. In the tests, two contact kinematic conditions, that is pure rolling and 10% rolling with sliding together with 1.1 and OAT [Tesla] of horizontal static magnetic fields created by permanent magnets were pplied. The results of optical and scanning electron microscopy observations show that finer wear particles and smoother worn surfaces are produced in the presence of the magnetic field. For the generation of the finer wear particles, it is considered necessary that the subsurface crack initiation point is moved towards the surface due to the magnetic field. Wear amounts of the discs are lowered III the magnetic fields under the pure rolling conditions. However, at 100/0 rolling with sliding, the wear amounts are increased in the magnetic fields even though finer particles and smoother surfaces are observed. Both tendencies are unified by calculating the number of cycles required to generate wear particles, which are reduced due to the magnetic field's presence. For these mechanisms, it is considered that domain walls near the contact region are caught by dislocations when the specimen is agnetised and part of the energy for magnetisation activates the dislocation movement resulting in crack initiation.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Modelling Influence of Poisson's Contraction on Squeeze Film Levitation of Planar Objects

Poisson's contraction effect is utilised to generate squeeze film levitation and is investigated through a computer model and validated experimentally. A finite element model (ANSYS) is verified by the experimental testing of five different plate designs. Each plate is subjected to uniaxial plain stress by an arrangement of two hard piezoelectric actuators bounded to the bottom of the plate and driven with DC and AC voltages. It is observed that a pulsating dimple or crest shape along the longitudinal axis in the central area of the plate is created due to Poisson's contraction, generating a squeeze-film between the plate and a levitated object. The separation distance between the floating planar object and the plate is analysed using computational fluid dynamics (ANSYS) and experimentally measured by a laser sensor. A good agreement has been found between model predictions and experimental results