Influence of tilt angle of plate on friction and transfer layer—A study of aluminium pin sliding against steel plate

In the present investigation, unidirectional grinding marks were attained on the steel plates. Then aluminium (Al) pins were slid at 0.2°, 0.6°, 1.0°, 1.4°, 1.8°, 2.2° and 2.6° tilt angles of the plate with the grinding marks perpendicular and parallel to the sliding direction under both dry and lubricated conditions using a pin-on-plate inclined sliding tester to understand the influence of tilt angle and grinding marks direction of the plate on coefficient of friction and transfer layer formation. It was observed that the transfer layer formation and the coefficient of friction depend primarily on the grinding marks direction of the harder mating surface. Stick-slip phenomenon was observed only under lubricated conditions. For the case of pins slid perpendicular to the unidirectional grinding marks stick-slip phenomenon was observed for tilt angles exceeding 0.6°, the amplitude of which increases with increasing tilt angles. However, for the case of the pins slid parallel to the unidirectional grinding marks the stick-slip phenomena was observed for angles exceeding 2.2°, the amplitude of which also increases with increasing tilt angle. The presence of stick-slip phenomena under lubricated conditions could be attributed to the molecular deformation of the lubricant component confined between asperities.

Pressure and thermally induced stages of wear in dry sliding of a steel ball against an aluminium-silicon alloy flat

Wear of etched near-eutectic aluminium silicon alloy slid against a steel ball under ambient is explored. The sliding velocity is kept low (0.01 m/s) and the nominal contact pressure is varied in a 15-40 MPa range. Four stages of wear are identified; ultra mild wear, mild wear, severe wear and post severe oxidative wear. The first transition is controlled by the protrusions of silicon particles, projecting out of the aluminium alloy matrix. Once these protrusions disappear under pressure and sliding, oxidation and bulk energy dissipation mechanisms take over to institute transitions to other stages of wear. The phenomenological characteristics of wear stages are explored using a variety of techniques including nanoindentation, focused ion beam milling, electron microscopy, X-ray photoelectron spectroscopy (XPS), energy dispersive X-ray spectroscopy (EDS) and optical interferometry. (c) 2010 Elsevier B.V. All rights reserved.

Raman spectrum of guanidinium aluminium sulphate hexahydrate

The Raman spectrum of guanidinium aluminium sulphate hexahydrate also known as ‘GASH’ which is a ferro-electric crystal and has strong hydrogen bonds has been recorded. 38 Raman lines have been identified in the spectra of GASH. The O-H stretching mode is found to be very much influenced by the hydrogen bond and they appear over a widely extended region from 2240–3600 cm.−1 It can therefore be concluded that all the O-H bonds are hydrogen bonded and some of them are quite strong. The Raman lines due to the N-H vibrations appear with the normal frequency shifts indicating thereby that N-H bonds are not hydrogen bonded. These conclusions are fully supported by the results obtained from the X-ray crystal structure analysis of GASH. The principal vibrations of the Al-(OH2)6 groups have also been identified.

Intraseasonal response of mixed layer temperature and salinity in the Bay of Bengal to heat and freshwater flux

Buoy and satellite data show pronounced subseasonal oscillations of sea surface temperature (SST) in the summertime Bay of Bengal. The SST oscillations are forced mainly by surface heat flux associated with the active break cycle of the south Asian summer monsoon. The input of freshwater (FW) from summer rain and rivers to the bay is large, but not much is known about subseasonal salinity variability. We use 2002-2007 observations from three Argo floats with 5 day repeat cycle to study the subseasonal response of temperature and salinity to surface heat and freshwater flux in the central Bay of Bengal. About 95% of Argo profiles show a shallow halocline, with substantial variability of mixed layer salinity. Estimates of surface heat and freshwater flux are based on daily satellite data sampled along the float trajectory. We find that intraseasonal variability of mixed layer temperature is mainly a response to net surface heat flux minus penetrative radiation during the summer monsoon season. In winter and spring, however, temperature variability appears to be mainly due to lateral advection rather than local heat flux. Variability of mixed layer freshwater content is generally independent of local surface flux (precipitation minus evaporation) in all seasons. There are occasions when intense monsoon rainfall leads to local freshening, but these are rare. Large fluctuations in FW appear to be due to advection, suggesting that freshwater from rivers and rain moves in eddies or filaments.

Mechanism of low-temperature deformation in quenched aluminium-magnesium alloys

The dislocation mechanisms for plastic flow in quenched AlMg alloys with 0.45, 0.9, 2.7 and 6.4 at. % Mg were investigated using tensile tests and change-in-stress creep experiments in the temperaturhttp://eprints.iisc.ernet.in/cgi/users/home?screen=EPrint::Edit&eprintid=28109&stage=core#te range 87° -473° K. The higher the magnesium content in the alloy, the higher was the temperature dependence of flow stress. The alloys showed no perceptible creep in the vicinity of room temperature, while they crept at lower as well as higher temperatures. The most probable cause of hardening at temperatures below ∼ 200° K was found to be the pinning of dislocations by randomly distributed solute atoms, while athermal locking of dislocations by dynamic strain ageing during creep was responsible for the negligibly small creep rate in the room temperature range.

Clustering kinetics in aluminium-silver alloys

Resistometric studies of isochronal and isothermal annealing of an Al-0.64 at.% Ag alloy have given a value of 0.13 ± 0.02 eV for the silver-vacancy binding energy and 0.55 ± 0.03 eV for the migration energy of solute atoms.

Electron-metallographic studies of precipitation in an aluminium-zinc-magnesium alloy

The mechanism of sub-microscopic precipitation in an Al-Zn-Mg alloy selected for its maximum response to ageing has been studied by a standardized oxide-replica technique in a 100 kV. Philips Electron Microscope. Contrary to earlier conclusions, examination of the oxide replicas has been shown to reveal details of the precipitation process almost as clearly as the thin-foil transmission technique. The reported formation of spherical Guinier-Preston zones followed by the development of a Widmanstaetten pattern of precipitated platelets has been confirmed. The zones have, however, been shown to grow into the platelets and not to dissolve in the matrix as reported earlier. The precipitation process has been correlated with the Hardness/Ageing Time curve and the structure of the precipitates has also been discussed.

Polarisation studies on the Raman spectra of cubic crystals - Part II: Calcium fluoride and potassium aluminium sulphate

Polarisation characters of the Raman lines of calcium fluoride (fluorspar) and potassium aluminium sulphate (alum) were investigated under the following conditions. Unpolarised light was incident normally on a face of the crystal making an angle 22.5° with a cubic face and the light scattered transversely along a cubic axis was analysed by a double image prism kept with its principal axes inclined at 45° to the vertical. Under these conditions the depolarisation factors of the Raman lines belonging to the totally symmetric (A), the doubly degenerate (E) and the triply degenerate (F) modes should be respectively =1, >1 and <1. The characteristic Raman line of CaF2 at 322 cm-1 exhibited a depolarisation value less than 1, showing thereby that the corresponding mode is a triply degenerate one (F). The Raman lines observed in the spectrum of K-alum were also classified and the results were compared with those given by previous investigators using standard crystal orientations.

Studies on phosphorus oxychloride and aluminium chloride complex

1. Anhydrous aluminium chloride reacts with phosphorus oxychloride to give a complex with a composition AlCl3.2 POCl3 which can be prepared in the form of a free flowing powder. 2. The phosphorus oxychloride-aluminium chloride complex in nitrobenzene dissociates into AlCl3.POCl3 and POCl3 as indicated by the cryoscopic measurements. 3. The solution of the complex in nitrobenzene has a higher specific conductivity than the corresponding electrical conductivities of individual components. Similar higher electrical conductance is observed when the two components are mixed in nitrobenzene in different proportions. 4.When a solution of anhydrous aluminium chloride in nitrobenzene is titrated conductometrically against a solution of phosphorus oxychloride in nitrobenzene, a limiting value in the conductivity is reached at point corresponding to the molecular composition, the components in the ratio of 1:2 AlCl3: POCl3 in solution. 5. The absorption maxima of the complex in nitrobenzene solution differ from the absorption maximum of the individual components.

Design of first- and second-order sliding mode observers for induction motors using a stator-flux model

We extend current research in the area of 'sensorless' control of induction motors by presenting two observers based on first- and second-order sliding mode control theories for the simultaneous estimation of flux and speed. We base the observers on the stator-flux model of the motor instead of the usual rotor-flux model mainly because of the uncertain rotor resistance that plays a significant role in the latter. By designing the observers as if they are sliding mode controllers, we lend the properties of parameter insensitive closed-loop dynamics and finite time convergence to the stator flux and speed estimation schemes. We also present simulation and experimental results to validate the operation of the observers.

Analysis of Flux Fringing for High-Frequency AC Inductor Design

Design of high-frequency inductors for purposes like Active Front End (AFE) converter filters involves analytical calculations based on methods like area product approach and accurate graphical methods. Once a core with an area product is selected the subsequent calculations of inductance and peak operating flux requires the estimation of reluctance of the magnetic circuit. This in turn demands an estimate of the fringing that will happen in the air gap of the inductor. In this paper we have looked at analytical methods for evaluating fringing flux and compared it with results from finite element method. Different levels of details of modelling the inductor is first considered for this purpose. The end results are compared with experimental measurements of inductance. It is shown that simple fringing flux model can provide accurate models for the inductor design.