THERMAL STRESSES FOR AN INFINITE BODY WITH A SPHERICAL CAVITY WITH TWO RELAXATION TIMES

Thermoelastic interactions caused in a homogeneous and isotropic infinite body with a spherical cavity are considered for the two different theories of generalized thermoelasticity, that is, Lord, and Shulman's theory and Green and Lindsay's theory. Analytical expressions for the temperature, displacement, and thermal stress fields are obtained; and the results are compared with the classical dynamical coupled theory.     

Failure Investigation of Spline-Shaft of an Under Slung Crane

Investigation of the causes of premature failure of a spline-shaft used in the hoist gear box assembly of an under slung crane has been presented. The investigation consisted of visual inspection, chemical analysis, characterization of microstructures by optical and scanning electron microscopes, energy dispersive spectroscopy (EDS), and hardness measurement. Visual observation of the fracture surface of the shaft revealed multiple cracks all of which initiated at the sharp corners of the spline. Fractography of the shaft showed striations confirming fatigue. The chemical composition of the shaft was found to be close to EN-24 grade of hardened and tempered steel which is specified as per IS 5517. Microstructural examination showed branched-out cracks and few of them were associated with oxide layer or scale which was confirmed by EDS analysis. Since the shaft was not exposed to high temperature in service, formation of scale along the crack suggested that it was pre-existing in the component. Base matrix of the shaft revealed bainitic microstructure. Hardness values were found to be lower than that obtained for EN-24 grade in hardened and tempered condition. Analyses of the results suggest that the component suffered from fatigue under reversed torsional loading, which initiated at pre-existing cracks in the component.     

Microstructure and electrical characterisations of K-modified PLZT

Potassium-modified PLZT [Pb_0.92(La_{1 – z}K_z)_0.08(Zr_0.60Ti_0.40)_{0.98 + 0.04z}O₃ (z = 0.0, 0.1, 0.3, 0.5, 0.7)] ceramics were synthesised using sol-gel technique. Preliminary structural and microstructural parameters were determined using XRD, SEM and TEM techniques. Detailed studies of dielectric properties at 10 kHz in a wide temperature range suggest that the compounds have diffuse phase transition of second order. Studies of spontaneous polarisation, pyroelectric and piezoelectric properties yielded data for devices.     

Ferrofluid Lubrication of a Journal Bearing Considering Cavitation

Ferrohydrodynamic lubrication in journal bearings by considering cavitation boundary conditions is studied. It is assumed that the magnetization vector is not parallel to the magnetic field vector. Various bearing characteristics have been studied and it is seen that qualitative behavior of these characteristics remains similar to that in the case of non-ferromagnetic fluid. However, a significant quantitative enhancement of these characteristics is observed.     

Conditioning of sludge produced through chemical treatment of radioactive liquid waste – Operating experiences

At Centralised Waste Management Facility (CWMF) 160 m³ of radioactive chemical sludge, generated from treatment of several batches of category-II and category-III radioactive liquid wastes by chemical precipitation method was stored in clariflocculator (CF) for downstream processing. The sludge needed conditioning before disposal. The analysis of the sludge samples collected at different radial locations and depths from the CF showed suspended solid content of 2.37–13.07% and radioactive content of gross β–γ 5000–27,000 Bq/g and α 100–600 Bq/g. After comparing different options available for conditioning of the sludge based on their technological and economical aspects, it was decided to dewater it using centrifuge before fixing in cement matrix with additives. Process Control Laboratory of CWMF studied the process in detail to optimize the relevant parameters for fixation of the concentrate obtained from centrifuge. Based on these results, conditioning of the stored sludge was undertaken.     

Combined experimental and analytical method for a realistic seismic qualification of equipment

The seismic qualification of equipment/structures are, in general, carried out either exclusively by analysis or exclusively by testing using a shake table. The analytical methods have the risk of the model not being a true reflection of the structure unless very elaborate modelling techniques are used. Even with an elaborate model there are many idealisations made which may not actually be realised in practice. The shake-table testing, avoids the modelling deviations to a large extent, but is also not without drawbacks. The important ones are the cost and the availability of a shake table of the required size and capacity. The shake-table testing is also carried out on the isolated equipment without the piping/structural connections from other components. The present paper suggests a combined experimental and analytical method on the ‘as installed’ equipment as an attractive alternative which overcomes the above drawbacks. In contrast to the existing practice of using the experimental results just to validate the analytical model, the suggested method uses the experimentally obtained dynamic characteristics of the ‘as installed’ equipment to obtain the response to the design seismic load. The paper brings out through an example of a simple storage tank which is too heavy for a shake table, the large deviations in its actual behaviour vis-à-vis an idealised analytical model.     

Model-based identification of rotating machines

Over the decades, vibration-based condition monitoring has become well accepted and widely used to identify faults in rotating machines. However, the quantification of faults may require a significant number of tests to be carried out which may be time consuming and costly, if not impossible, by experiments alone. In the recent past, it has been observed that model-based identification has played a significant role in the rapid resolution and quantification of faults. The paper seeks to give an overview of the recent developments in this field which has considerable practical importance.     

Single step synthesis of GdAlO3 powder

A novel method for preparation of nano-crystalline gadolinium aluminate (GdAlO₃) powder, based on combustion synthesis, is reported. It was observed that aluminium nitrate and gadolinium nitrate exhibit different combustion characteristics with respect to urea, glycine and β-alanine. While urea was proven to be a suitable fuel for direct formation of crystalline α-Al₂O₃ from its nitrate, glycine and β-alanine are suitable fuels for gadolinium nitrate for preparation of its oxide after combustion reaction. Based on the observed chemical characteristics of gadolinium and aluminium nitrates with respect to above mentioned fuels for the combustion reaction, the fuel mixture composition could be predicted that could lead to phase pure perovskite GdAlO₃ directly after the combustion reaction without any subsequent calcination step. The use of single fuel, on the other hand, leads to formation of amorphous precursor powders that call for subsequent calcination for the formation of crystalline GdAlO₃. The powders produced directly after combustion reactions using fuel mixtures were found to be highly sinterable. The sintering of the powders at 1550 °C for 4 h resulted in GdAlO₃ with sintered density of more than 95%. T.D.