Effect of valency on material removal rate in electrochemical machining of aluminium

Material removal rate (MRR) of aluminium work piece has been obtained by electrochemical machining using NaCl electrolyte at different current densities and compared with the theoretical values. It has been observed that resistance of the electrolyte solution decrease sharply with increasing current densities. The over-voltage of the system initially increases and then attains a saturation value with increasing current densities. The material removal rate, determined experimentally, almost corresponds to theoretical value with Al³⁺ state. On the other hand, taking into account over-voltage, MRR comes out be 72%. It appears that removal of a fraction of aluminium occurs in Al⁺ which subsequently gets converted into Al³⁺ through a series chemical reactions. A mechanism of such chemical reactions is proposed.     

A general higher-order shell theory for compressible isotropic hyperelastic materials using orthonormal moving frame

The primary objective of this study is threefold: (1) to present a general higher-order shell theory to analyze large deformations of thin or thick shell structures made of general compressible hyperelastic materials; (2) to formulate an efficient shell theory using the orthonormal moving frame, and (3) to develop and apply the nonlinear weak-form Galerkin finite element model for the proposed shell theory. The displacement field of the line normal to the shell reference surface is approximated by the Taylor series/Legendre polynomials in the thickness coordinate of the shell. The use of an orthonormal moving frame makes it possible to represent kinematic quantities (e.g., the determinant of the deformation gradient) in a far more efficient manner compared with the nonorthogonal covariant bases. Kinematic quantities for the shell deformation are obtained in a novel way in the surface coordinate described in the appendix of this study with the help of exterior calculus. Furthermore, the governing equation of the shell deformation has been derived in the general surface coordinates. To obtain the nonlinear solution in the quasi-static cases, we develop the weak-form finite element model in which the reference surface of the shell is modeled exactly. The general invariant based compressible hyperelastic material model is considered. The formulation presented herein can be specialized for various other nonlinear compressible hyperelastic constitutive models, for example, in biomechanics and other soft-material problems (e.g., compressible neo-Hookean material, compressible Mooney–Rivlin material, Saint Venant–Kirchhoff model, and others). A number of numerical examples are presented to verify and validate the formulation presented in this study. The scope of potential extensions are outlined in the final section of this study.     

Effects of binder on recovery stamp charged coke making process

The optimum stability of coal cake is essential for producing good quality of coke in stamp charged coke making process. A suitable binder named as ‘X7’ was identified to improve the stability of coal cake, oven throughput, coke quality and reduce specific energy consumption for stamp charged coke making process. Laboratory results show that addition of ‘X7’ in coal blend up to 0.10–0.50 percentage, improved the mechanical strength of coal cake by 3.0–5.0 percentage. Six hundred kg pilot plant trials show that addition of binder in the base coal blend improved coke quality in terms of CSR, M ₄₀ and AMS significantly. Coke plant trials also show that ‘X7’ addition (0.10%) in base coal blend improved coke quality in terms of CSR (1.25 point), M ₄₀ (0.9 point) and AMS (1.70 mm). Addition of ‘X7’ increased Coke End Temperature up to 24°C during plant trials. The increased in temperature saved energy approximately 11 000 Gcal and reduce CO₂ emission by at least 10 000 T/Annum.     

A frequency dependent transmission line model for a counterpoise

This paper has proposed a methodology to obtain a frequency dependent distributed‐parameter model for a buried bare conductor employing a time‐domain fitting from measured transient voltages and injected currents. The transient characteristic impedance and propagation function are expressed by a rational function in a z‐plane and a genetic algorithm (GA) has been used as an optimization tool. Frequency dependence of the per unit line parameters (RLGC) is derived from the obtained propagation parameters. Simulation results by the proposed model agree well with that from the measured results. © 2006 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Unsteady computation of flow field and convective heat transfer over tandem cylinders at subcritical Reynolds numbers

Unsteady flow and convective heat transfer over single and two tandem cylinders at constant-heat-flux condition in subcritical range of Reynolds number was numerically investigated. Two-dimensional computations were performed by adopting 3-equation k-kl-ω turbulence model using a commercial software FLUENT®. The aim was to investigate the capabilities of k-kl-ω turbulence model for collective flow and heat transport conditions past cylindrical bodies and then to identify a critical spacing ratio for the maximum heat transport. The center-to-center spacing ratio (L/D) was varied in the range from 1.2 to 4.0. Instantaneous path lines and vorticity contours were generated to interpret the interaction of shear layer and vortices from upstream cylinder with the downstream cylinder. Comparison of pressure coefficients, fluctuating and average lift as well as drag coefficients, Strouhal number and the local and average Nusselt numbers with the available literatures indicated a reasonably good agreement. The combined outcome of flow field and heat transfer study revealed a critical spacing ratio of L/D = 2.2. Based on the present investigation, a correlation has been suggested to calculate overall average Nusselt number of the two cylinders placed in tandem.

     

Experimental evaluation of waste plastic oil and its blends on a single cylinder diesel engine

Journal of Mechanical Science and Technology - The aim of the present work to investigate the performance of oil derived from the waste plastic on diesel engine. Waste plastic fuel (WPF) is derived...     

Some basic aspects of electromagnetic radiation during crack propagation in metals

Measurements of the electromagnetic radiation (EMR) emitted during crack propagation and fracture and the effect of modes of fracture, physical properties and high temperature on the characteristics of emitted EMR from metals have been discussed. It has been observed that all the three modes of fracture give rise to EMR emission; however, the relative amplitude in tearing mode is very low. A linear variation of EMR peak voltage with bond energy has been observed while frequency varies parabolically with bond energy. Both these curves indicate that no EMR emission or negligible EMR emission is expected in metals having bond energy <270 kJ/mole. EMR characteristics decrease with increase in lattice parameter. Higher tensile strength metals emit stronger EMR signals. Experiments conducted at high temperatures validate the prediction of Molotskii that an increase in specimen temperature should decrease the EMR frequency. One additional but important observation has been that while the EMR peak amplitude decreases with increase in temperature in steel, it increases with increase in temperature in copper.     

Magnetic Hysteresis Loop Technique as a NDE Tool for the Evaluation of Microstructure and Mechanical Properties of 2.25Cr–1Mo Steel

This study intends to understand the effect of short-term overheating on microstructure modifications, and variation in mechanical and magnetic properties of boiler tubes. It is based on the hypothesis that short-term overheating on boiler tubes leads to microstructural changes degrading their mechanical properties, thus resulting in their failure. As part of this study, fresh 2.25Cr–1Mo boiler tube samples were heat treated in the range of 700–950 \(^{\circ }\hbox {C}\). Magnetic hysteresis loop (MHL) measurements were carried for the non-destructive evaluation (NDE) of the mechanical properties that get altered due to microstructural modifications. For comparison, MHL was also carried out on a service-exposed boiler tube, which had failed due to short-term overheating. The magnetic parameters were correlated with the change in microstructure and micro-hardness of the samples. A decrease in coercivity, remanence, maximum induction and micro hardness were found at the lower soaking temperatures, due to: easy magnetic domain wall and dislocation motions for the stress relaxation; annihilation and recovery of dislocations; increase in inter carbide distance; and the decrease in the number density of carbides for the coarsening of carbides. A subsequent increase in coercivity, remanence and maximum inductions along with hardness are due to the nucleation and growth of fresh bainitic phase, obstructing the magnetic domain wall and dislocation motion. A drastic decrease in coercivity for the service-exposed tube is due to the transformation of MX type carbides to \(\hbox {M}_{23}\hbox {C}_{6}\) type and accumulation of such carbides at the grain boundaries along with the decrease in number density of the carbides. The presence of scale has less effect on the coercivity, but its demagnetizing effect largely decreases the remanence and maximum induction. The results of the study show that the MHL can be a suitable NDE technique for the evaluation of change in microstructure and degradation of mechanical properties in power plant steels.     

Integral Model for Development of Instant Interface Temperature at Time <Emphasis Type="Italic">τ</Emphasis> = 0<Superscript>+</Superscript> of Cylindrical Solid Additive-Bath System

Closed-form solution derived from the integral model for the instant interface temperature θ _e between the cylindrical-shaped additive and the growing frozen layer of the bath material onto the additive immediately after the immersion of the additive in the bath indicates this temperature dependence on the property ratio B and the Stefan number S _t . Increasing B (0 ≤ B ≤ ∞) or decreasing S _t (∞ ≥ S _t ≥ 0) raises θ _e from the initial temperature of the additive to the freezing temperature of the bath material, and for S _t →0, 0 ≤ B ≤ ∞, it assumes the expression \( {{\theta}}_{e} = \sqrt {6B} /\left( {3 + \sqrt {6B} } \right). \)