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The dynamics of non-spherical vapour bubbles
(Fourth Australasian Conference on Hydraulics and Fluid Mechanics Organising Committee, 1971-11-29) Guy, TB; Ledwidge, TJ
An account is given of an experimental and theoretical study of the dynamics of a vapour bubble in sub-cooled water. The bubble is generated by transiently heating a thin constantan steel strip in which a cylindrical nucleation hole exists. A finite element computer solution to the transient, non- spherical growth of the bubble assumes the bubble surface to be inscribed by a large number of spheres of radii equivalent to the average of the principal radii of curvature at a point on the surface. The particular case of axial symmetry is considered here. The change of the surface topology of the bubble with time is taken to be that produced by the corresponding growth or collapse of the generating spheres. It is assumed that under the considered conditions, the energy exchange across the liquid-vapour interface is dominated by mass transfer and thus a considerable simplification in the interfacial energy exchange equations results. The mass transfer equation across the boundary is coupled to a modified form of the Rayleigh equation in which pressure gradient, surface tension and viscosity terms have been accounted for. The effect of a temperature field on the bubble shape and on the acoustic wave emitted by the bubble is examined and shown to be in reasonable agreement with the experimental dynamic pressure measurements.
Stress distribution in iron powder during die compaction
(Australian Nuclear Science and Technology Organisation, 2013-09-10) Kisi, EH; Wensrich, CM; Luzin, V; Kristein, O
Granular materials are extremely important in food production, minerals extraction, pharmaceuticals and powder metallurgy. They can be poured like a liquid and yet can support static shear stresses like a solid (mounds do not collapse), Granular materials are always locally and macroscopically inhomogeneous making algebraic constitutive models difficult to develop. Numerical analysis using continuum (finite element) or individual particle (discrete element) models are being widely explored [1,2]. However, there were previously no methods for their experimental validation. This paper reports the application of the neutron diffraction strain scanning method, originally developed for residual stress measurements within engineering components, to the problem of the stress distribution in granular Fe under a consolidating pressures Strains were measured in axial, radial, circumferential and an oblique direction using the neutron strain scanning diffractometer KOWARI at ANSTO(Sydney) and the full stress tensor as a function of position wvas able to be extracted (e.g. Fig l). Results will be presented for a both a straight Walled and a converging die. Typical results using the converging die are shown in Fig. l.
Residual stress in railway rails components measured by neutron diffraction
(Australian Nuclear Science and Technology Organisation, 2013-09-10) Paradowska, AM; Blomqvist, K; James, M
Rail degradation typically occurs through a combination of wear and rolling contact fatigue in the rail heads. Both of these degradation modes are associated with the plastic deformation and failure behaviour of rail steels. Increased rates of‘ degradation are associated with special trackwork such as switches and crossings, and insulated rail joints; these components therefore incur higher maintenance costs and shorter service lives compared to open rail. in response to the demand for increased axle loads and/or annual haulage rates, rail steel manufacturers are required to continuously develop improved rail materials, which can otter reduced rates of‘ degradation and extended maintenance intervals, while the rail infrastructure operators are required to continuously improve rail maintenance strategies. The presented work forms part of a PRE Ltd. collaboration research project on the application of non-destructive neutron diffraction residual stress measurements to the rail application. In this paper the measurements results of industrially important large-scale railway rail components such as bends and crossing, will be discussed,
Residual stresses in titanium aerospace components formed via additive manufacture
(Australian Nuclear Science and Technology Organisation, 2013-09-10) Hoye, N; Li, H; Cuiuri, D; Paradowska, A
Additive manufacturing (AM) using arc-wire based metal deposition has been suggested as one method to reduce the costs associated with production of titanium components, particularly within the aerospace sector. In the present study gas tungsten arc welding (GTAW) with automated wire addition was used to additively manufacture (AM) a representative thin-walled aerospace component from Ti-6AI-4V in a layer-wise manner. Residual strains, and hence stresses, were analysed quantitatively using neutron diffraction techniques on the KOWARI strain scanner at the OPAL research facility operated by the Australian Nuclear Science and Technology Organisation (ANSTO). Results showed that residual strains within such an AM sample could be measured with relative ease using the neutron diffraction method. Residual stress levels were found to be greatest in the longitudinal direction and concentrated at the interface between the base plate and deposited wall. Difficulties in measurement of lattice strains in some discrete locations were ascribed to the formation of the formation of localised texturing where α-Ti laths form in aligned colonies within prior β-Ti grain boundaries upon cooling. Observations of microstructure reveal 'basket-weave' morphology typical of welds in Ti-6AI-4V. Microhardness measurements show a drop in hardness in the top region of the deposit, indicating a dependence on thermal cycling from sequential welds. Time-of-flight neutron diffraction has been proposed to analyse stresses in both the α-Ti and β-Ti phases simultaneously as well as inter-granular strains. This study forms part of a wider investigation into the suitability of arc-wire based deposition techniques for the additive manufacture of titanium components.
Adsorption at a solid-liquid interface
(Saha Institue of Nuclear Physics, 2012-07-25) Gerth, S; Nelson, A; Klimczak, M; Steinrück, HG; Weißer, M; Magerl, A
Surfactants from tri-block copolymers are well known for the reduction of surface tension or friction at an interface. We investigate the tri-block copolymer Pluronic® P123 consisting of a central part of 70 propylene oxide (PO) units terminated by two end groups of 20 ethylene oxide (EO) units (E020 - PO70 — E020). In concentrated solutions above 27 weight percent (wtp) and at intermediate temperatures the micelles self-assemble into crystalline structures. In addition we found a near surface crystallization for a diluted P123 system below the critical temperature and concentration for bulk crystallization. Different chemical surface treatments (hydrophilic or hydrophobic) influence this near-interface ordering. The initiation of crystal growth is preferred at an attractive interface, whereas no layering of micelles is observable for a hydrophobic coating. The build up of a Bragg peak at Q w 0.05 A1 observed in reflectometry provides evidence for a micellar layering at the surface. We note, that this dense surface structure is present under conditions where there is no bulk crystallization. To access the stability of the surface layer, we have studied the destruction and the kinematic recovery of this surface layer under shear. To this end we have built a cone-plate shear device suitable for in-situ neutron reflectometry. The recovery of the adsorbed micellar layer in dependence of a previously applied shear rate, temperature and polymer concentration yields a nucleation time for layer growth. In addition, the structural fidelity of the adsorbed layer system is elucidated by the integrated Bragg intensity.

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