Papers by Author: Tom W. Coyle

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Authors: Hanif Montazeri, Fardad Azarmi, Tom W. Coyle, Javad Mostaghimi
Abstract: Sandwich structures are widely used, especially in areas where the performance of conventional materials is simply not adequate. Sandwich components achieve the same structural performance as conventional materials with weight savings of up to 75 %. They are basically made from two thin skins (faces) and a lightweight thicker core. Their structural, physical, and mechanical characteristics can be tailored based on service requirements by selection of different materials and manufacturing processes. In this study, the geometry and property of each separate component is utilized to the structural advantage of the whole assembly. Although Lagrangian method has been widely applied in other engineering disciplines, it has received less attention for optimization of sandwich components. The Lagrangian method is therefore introduced and expanded to find solutions for multipurpose design problems. This new optimization approach will enable us to find analytical solutions for complicated design problems which were conventionally solved by utilizing graphical methods. This paper aims to present a generic optimization method which can be used in the variety of applications in this field.
Authors: F. Azarmi, A. Moradian, J. Mostaghimi, Tom W. Coyle, L. Pershin
Abstract: There is a growing interest in use of the nickel-based alloy Inconel 625 coatings due to its ability to improve base materials high temperature properties. Thermal spraying methods such as Air Plasma Spraying (APS) can be considered as a convenient method to deposit this material. The present work deals with APS deposited Inconel 625 structures consisting of huge number of individual splats formed by impacting molten droplets on substrates during spraying process. It is clear that the splat formation mechanism which dominates its size, cohesion, and boundaries highly influences the microstructure of the coating. This paper presents a developed numerical technique performed to simulate splat formation using a three dimensional model. In this method flow field is solved by Finite Volume Method (FVM) and free surfaces are determined from Youngs’ Volume of Fraction method (VOF). Finally, the model prediction is correlated with the actual splat geometries.
Authors: Tom W. Coyle, E. Garcia, Z. Zhang, Lu Gan
Abstract: Plasma spray deposition of hydroxyapatite (HA) coatings is a well established commercial process. When deposited on metallic substrates, these coatings have been shown to promote bone fixation and osteconductivity. A concern with current coatings is the formation of relatively large debris particles during resorption. The size of the debris is related to the particle size of the powder injected into the plasma during the deposition process. The use of solution precursors or dispersions of fine particle size powders as the feedstock for plasma spraying has been shown to produce submicron/nanocrystalline structured coatings from relatively inexpensive precursors. Nanocrystalline HA coatings may improve the resorption of the coating in the body, avoiding the irritant effect of large particles which may be seen in current thermal sprayed HA coatings. We have explored the use of sols prepared from several different precursors as the feedstock for the plasma spray deposition of HA coatings on Ti6Al4V substrates, employing statistical design of experiments to establish optimal deposition conditions. We report on the formation and the characteristics of the coatings as a function of the deposition parameters. The presence of different Ca-P crystalline and amorphous phases was assessed by X-ray diffraction analysis. The coating microstructure was characterized by scanning/transmission electron microscopy. The suitability of the technique to coat biomedical implants is discussed.
Authors: Judy Ue, R.M. Pilliar, R.A. Kandel, Tom W. Coyle, M.D. Grynpas
Abstract: Sodium-doped CPP was synthesized using three dopant sources (sodium carbonate, sodium hydroxide and sodium phosphate). These materials were analyzed by XRD to determine phase composition and by differential thermal analysis to identify phase transition temperatures. Sintering of resulting glass powders showed that both dopant source and dopant concentration affects sinter neck formation and crystallinity. The open porosity of sodium phosphate and sodium carbonate doped samples at 0.1 Na2O/CaO sintered at different temperatures changed significantly. Crystallization of the construct during sintering was noted at temperatures lower than expected.
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