Applied Mechanics and Materials Vols. 110-116

Abstract: The present work attempts to overcome underlying assumptions in traditional Taguchi based optimization techniques highlighted in literature. Taguchi method alone fails to solve multi-response optimization problems. In order to overcome this limitation, exploration of grey relation theory, desirability function approach, utility theory etc. have been found amply applied in literature in combination with Taguchi method. But aforesaid approaches relies on the assumption that individual response features are uncorrelated i.e. independent of each other which are really impossible to happen in practice. The study takes into account this response correlation and proposes an integrated methodology in a case study on optimization of multiple bead geometry parameters of submerged arc weldment. Weighted Principal Component Analysis (WPCA) has been applied to eliminate response correlation and to convert correlated responses into equal or less number of uncorrelated quality indices called principal components. Based on individual principal components a Multi-response Performance Index (MPI) has been introduced to derive an equivalent single objective function which has been optimized (maximized) using Taguchi method. Experiments have been conducted based on Taguchi’s L25 Orthogonal Array design with combinations of process control parameters: voltage, wire feed, welding speed and electrode stick-out. Different bead geometry parameters: bead width, bead height, penetration depth and HAZ dimensions have been optimized. Optimal result has been verified by confirmatory test. The study highlights effectiveness of the proposed method for solving multi-objective optimization of submerged arc weld.

Abstract: In the recent development of LED technologies and market growth of LED luminaries, further study is needed in order for LEDs to replace the current incandescent bulb. Because of the LED radiation pattern, and it being a point-type light source, LED luminaries must employ similar and different methods than those of other luminaries in order to achieve a uniform irradiance. The methods presented in this paper can fasten the production of luminaries while cutting cost and still make luminaries with over 80% uniform irradiance. To achieve these methods reflectors, of 97% reflectivity, of multiple shapes and angles are combined with different arrays of LEDs. All luminaries are constructed using SolidWorks, and then ray data is simulated in TracePro commercial software. The final luminaries are then manufactured and the simulated results are compared and verified with experimental results. The purpose of this paper is to create luminaries for different situations that are affordable to produce while maximizing light efficiency.

Abstract: X-Ray Computed Tomography (CT) scanning is an effective method for estimating the porosity of various engineering materials and biomedical specimens such as tissue scaffolds and bones. However, the scanning and analysis parameters play a significant role in the accuracy of the porosity value determined from CT scan. This paper presents details of an investigation carried out to understand the effect of system parameters, namely the voxel size, X-ray focal spot size and segmentation threshold, on the estimated porosity by taking an example of safety-critical foam used for impact protection applications. Different voxel resolutions and focal spot sizes are selected in a total of 12 scanning tests and the effect of segmentation threshold is analyzed on each of these tests. The study indicates that the obtained porosity value is greatly influenced by the choice of voxel size at larger spot sizes and less influenced at smaller spot sizes. The threshold also has significant effect on the porosity value, especially at larger voxel sizes.

Abstract: Withdrawn due to double publication.

Abstract: Analytical expressions for the temperature rise in a semi-infinite workpiece due to the heating with CW and repetitive laser pulse irradiation have been derived. It has been shown that the soaking time at a temperature above the phase transformation temperature, on which the homogeneity of microstructure and the depth of hardening depend, can be increased by heating with repetitive laser pulses. Experimental results of surface hardening of high-carbon steel with repetitive laser pulses showed higher depth of hardening and better microstructure homogeneity compared to those with continuous wave laser.

Abstract: A rapid optical inspection system for rapid measuring the surface roughness of titanium dioxide (TiO2) thin films is developed in this work. The incident angle of 60° is a good candidate for measuring surface roughness of TiO2 thin films and y = 90.391x + 0.5123 is a trend equation for predicting the surface roughness of TiO2 thin films. Roughness average (Ra) of TiO2 thin films (y) can be directly deduced from the peak power density (x) using the optical inspection system developed. The results were verified by white-light interferometer. The best measurement error rate of the optical inspection system developed can be controlled about 8.8%.The saving in inspection time of the surface roughness of TiO2 thin films is up to 83%.

Abstract: A numerical study of the magnetohydrodynamic (MHD) flow in a square cavity filled with porous medium is presented by Lattice Boltzmann Method (LBM). The left and right vertical walls of the cavity are kept at constant but different temperatures while both the top and bottom horizontal walls are insulated. The effects of the controlling parameters involved in the heat transfer and hydrodynamic characteristics are studied in detail. The results show that heat and mass transfer mechanisms and the flow characteristics inside the enclosure depend strongly on the strength of the magnetic field and Darcy number. The average Nusselt number decreases with rising values of the Hartmann number while this increases with increasing values of the Darcy number.

Abstract: The present study investigates the relationship of process parameters in electro-discharge diamond face grinding (EDDFG) of tungsten carbide and cobalt composite (WC-Co). The central composite rotatable design had been utilized to plan the experiments and response surface methodology (RSM) was employed for developing experimental models. Analysis on machining characteristics of EDDFG was made based on the developed models. In this study, wheel RPM, current, pulse on-time, and duty factor are considered as input process parameters. The process performances such as material removal rate (MRR) and average surface roughness (Ra) were evaluated. Analysis of variance test had also been carried out to check the adequacy of the developed regression models. The observed optimal process parameter settings are wheel RPM of 1500, current of 6.9029 A, pulse on-time of 137. 8208 µs, and duty factor of 0.79 for achieving maximum MRR and minimum Ra; finally, the results were experimentally verified. A good agreement is observed between the results based on the RSM model and the actual experimental observations. The error between experimental and predicted values at the optimal combination of parameter settings for MRR and Ra lie within 6.18% and 12.33%, respectively.

Abstract: Finite element models had been developed considering radiative and conductive heat transfer [1]. This work consist application of such models for nuclear waste disposal containers. The temperature of enclosure walls are predicted with the help finite element method. This is useful in determining material properties of enclosure that will be suitable under required criteria. Heat transfer characteristics and temperature behavior of the enclosure walls is investigated by changing parameters such as absorption coefficient and emissivity of walls. Comparison with the experimental work show that the present heat transfer model works well for the prediction of thermal behavior of the enclosure in the actual nuclear waste disposal containers.

Abstract: We determine the critical current density of the superconductor having an array of hole exposed under electric current and under a perpendicular magnetic field. It is assumed that the inner holes sides are accounted in the de Gennes boundary condition while outer edge is in contact with vacuum. The critical current calculation was done after solving time dependent Ginzburg-Landau equation and evaluating the electric voltage. The enhancement factor of the critical currents due to the boundary condition is discussed.