Assignment allocation and simulated annealing algorithms for cell formation

In this paper a nonlinear mathematical programming model is developed for cell formation that identifies part families and machine groups simultaneously with no manual intervention or subjective judgement. The objective of the model is minimization of the weighted sum of the voids and the exceptional elements. Changing weights for void and exceptional elements aids the designer with a systematic generation of different solutions, i.e., forming large loose cells or small tight cells. An assignment allocation algorithm (AAA) and a simulated annealing algorithm (SAA) are developed to solve the model. AAA and SAA compare favorably with many well-known procedures for the problems tested. AAA is less computer-intensive and hence large problems with 400 parts and 240 machines were solved with AAA in less than a minute on Sun Sparc station. However, AAA is sensitive to the initial machine grouping solution input to the algorithm. SAA gives consistent results but requires more computational time.     

Machine loading in flexible manufacturing systems considering routeing flexibility

The key competitive strength of a manufacturing system lies in its flexibility, which represents the ability to respond effectively to changing circumstances. Flexible manufacturing systems (FMSs) react appropriately to change. The relevance of a particular type of flexibility depends upon the system and problem being considered. In this paper, the machine loading problem in a flexible manufacturing system is addressed. The loading problem is concerned with the allocation of part operations and required tools to the machines, so as to optimise some objective(s) subject to some technological constraints. Several objectives have been considered in the past such as maximisation of the utilisation of resources, minimisation of processing and tooling costs and maximisation of throughput rates. In such procedures, it is quite probable that a rigid loading schedule is obtained and in cases of machine breakdowns and tool failures alternate routeings are often not available. Therefore, in this paper, we develop a mathematical model which considers maximisation of the production routeings available for the parts and hence increases the routeing flexibility. The model is illustrated by examples.     

The Effect of Lithium Disilicate Ceramic Surface Neutralization on Wettability of Silane Coupling Agents and Adhesive Resin Cements

This in vitro study was aimed to evaluate the possible changes in wettability of an etched glass ceramic surface to silane primers, adhesive resin and resin cement when the surface had been neutralized by a special neutralizing agent after etching. Rectangular shaped specimens were cut from the CAD blocks of an e-max lithium disilicate glass ceramic, cut specimens were sequentially polished and ultrasonically cleaned. All the specimens were etched for 20 s with 5% hydrofluoric acid and ultrasonically cleaned. Specimens were randomly assigned to one control group (without neutralization) and one treatment group (with neutralization) having 20 specimens each. The specimens of each group were further divided into two subgroups having 10 specimens each and tested to determine the effect of neutralizing agent on wettability of experimental and commercial silanes. Each subgroup specimen was tested for wettability to adhesive resin and commercial resin cement. Data were analyzed using two-way ANOVA. Neutralizing the ceramic surface did not show a significant effect on wettability to the silanes and the resin based materials, but the experimental silane showed better wettability than the commercial silane. The adhesive resin had statistically significant lower contact angle (high wettability) values than the commercial resin cement. The results of the current study suggested that the neutralizing agent did not have an impact on the wettability of the etched ceramic. However, there were differences in wetting properties of the silane primers, and adhesive resin versus resin composite luting cements.     

Bulk temperature estimation during wear of a polymer composite pin

Various models have been proposed to estimate the bulk temperatures along the axis of a pin wearing against a disc in a pin-on-disc tribometer. These have been generally addressing the estimation of temperature for monolithic materials. The current investigation addresses the estimation of the bulk temperatures for a composite material using the rule of mixtures and corroborates the same with experimental verification.     

Development of cladding materials for sodium-cooled fast reactors in India

Sodium-cooled fast reactors are an important component of India’s move towards energy security. The Fast Breeder Test Reactor (FBTR) has been successfully operated for over 22 years, and the construction of a Prototype Fast Breeder Reactor (PFBR) has been taken up. Future development of Fast Reactor technology depends to a large extent on the economics, safety and waste management issues. The targets important for economics have been identified as reduction in capital costs, higher burn-up fuels, higher temperatures of operation, longer life and higher breeding ratios. These targets can be achieved with significant improvements in performance of materials, especially of Alloy D9 (15Cr-15Ni-0.2Ti), a titanium modified austenitic stainless steel, currently used for fuel cladding. Through research programmes implemented to improve the void swelling resistance of Alloy D9, it has been established that certain solute additions are essential in association with thermomechanical treatments for conferring swelling resistance. Research work conducted on refinement of Alloy D9 composition and thermomechanical treatments aimed at understanding irradiation effects, corrosion, mechanical properties and weldability at IGCAR Kalpakkam along with modelling studies for the prediction of weld behaviour is reported in the present paper. It is concluded that a significant rise in fuel burn-up can be achieved with the use of a new generation “InD9” alloy for fuel cladding.     

Hydrogenation of Benzaldehyde over Palladium Intercalated Bentonite Catalysts: Kinetic Studies

Bentonite, a 2:1 type swellable phyllosilicate clay mineral having exchangeable inorganic cations in the interlamellar space to nullify their charge deficiency was used to generate palladium nanoparticles. It was found that 1% w/w palladium nanoparticles were generated in the interlamellar space using adsorption excess technique. The synthesized catalysts were characterized by using XRD, TEM, BET surface area analysis, and AAS. The modified clay catalysts were tested for their catalytic activity towards the hydrogenation of benzaldehyde to benzyl alcohol in liquid phase using a high-pressure reactor at various temperatures and pressures. High selectivity (100%) towards the desired product of benzyl alcohol was achieved with conversion over 80% in all cases. These results showed different hydrogen dependency for the reaction at various temperatures. The kinetics of the reaction was studied using Langmuir Hinshelwood single site model. The rate constant was determined using pseudo first-order kinetics and activation energy for benzaldehyde hydrogenation was calculated at various temperatures using Arrhenius equation and was found to decrease with increase in temperature.     

Response surface methodological study of esterification of lactic acid with palmitic acid catalyzed by immobilized lipases from Mucor miehei and porcine pancreas

X _s), enzyme/substrate (E/S) ratios (X _e) and incubation time (X _t) on the preparation of palmitoyl lactic acid using Mucor miehei lipase (MML) and porcine pancreas lipase (PPL). Experimental ester yields were found to be in good agreement with predictions. In the case of MML, the ester yield was found to increase with X _e and X _t and a maximum yield of 27 mM was obtained at X _e=128 activity units(AU)/mM of substrate, X _s=64–74 mM and X _t=72 h. In the case of PPL, the ester yield was found to increase with increases in X _e and X _s. Optimum conditions for PPL were X _e=45 AU/mM, X _s=85–90 mM and X _t=72 h, at which the maximum ester yield of 15 mM was obtained. Received: 14 April 1999 / Revised version: 2 September 1999     

Thermodynamics of surfaces and adsorption in the Fe-C-S-O system

Surface tension experiments have been conducted on Fe-C-S-O alloys using the sessile drop technique at 1823, 1873, and 1923 K in a purified argon atmosphere. The experimental data indicate lowering of surface tension values for alloys with low carbon and oxygen contents relative to the corresponding tenary Fe-S-O system of comparable compositions. The data exhibit an increasing trend of the surface tension values as a function of carbon and oxygen contents and temperature of the melt. Modified Butler’s equations have been used in conjunction with the consistent thermodynamic relations for a dilute quaternary system to calculate the surface tensions and adsorption functions of the system. The calculated values are in excellent agreement with those of the experimental data for compositions having lower oxygen at 1823 K, however, the values for the alloys containing higher oxygen contents depart from those of the experimental data. The calculated surfact tension values agree within 150 mN/m with those of the experimental data at 1873 K. The agreement, in general, has been favorable despite the constraints involved in the calculations as discussed in the text.     

Isothermal oxidation of TiAl alloy

Isothermal oxidation behavior of Ti-48.6 at. pct Al alloy was studied in pure dry oxygen over the temperature range 850 °C to 1000 °C. The oxidation was essentially parabolic at all temperatures with significant increase in the rate at 1000 °C. Effective activation energy of 404 kJ/mol was deduced. The oxidation products were a mixture of TiO₂ (rutile) and α-Al₂O₃ at all temperatures. An external protective layer of alumina was not observed on this alloy at any of the temperatures studied. A layered structure of oxides was formed on the alloy at 1000 °C.     

Characterization of Al2O3/ZrO2 nano multilayer thin films prepared by pulsed laser deposition

Microstructural characterization of pulsed laser deposited Al₂O₃/ZrO₂ multilayers on Si (1 0 0) substrates at an optimized oxygen partial pressure of 3 × 10⁻² mbar and at room temperature (298 K) has been carried out. A nanolaminate structure consisting of alternate layers of ZrO₂ and Al₂O₃ with 40 bi-layers was fabricated at different zirconia layer thicknesses (20, 15 and 10 nm). The objective of the work is to study the effect of ZrO₂ layer thickness on the stabilization of tetragonal ZrO₂ phase for a constant Al₂O₃ layer thickness of 5 nm. The Al₂O₃/ZrO₂ multilayer films were characterized using high temperature X-ray diffraction (HTXRD) in the temperature range 298–1473 K. The studies showed that the thickness of the zirconia layer has a profound influence on the crystallization temperature for the formation of tetragonal zirconia phase. The tetragonal phase content increased with the decrease of ZrO₂ layer thickness. The cross-sectional transmission electron microscope (XTEM) investigations were carried out on a multilayer thin films deposited at room temperature. The XTEM studies showed the formation of uniform thickness layers with higher fraction of monoclinic and small fraction of tetragonal phases of zirconia and amorphous alumina.