Andra Sabău | Hyperion University (original) (raw)
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Papers by Andra Sabău
Materials Science Forum, 2008
In this study, the foundation is being developed for the numerical simulation of the processes th... more In this study, the foundation is being developed for the numerical simulation of the processes that determine the oxide scale exfoliation behavior of the steam-side surfaces of superheater and reheater tubes in a steam boiler. Initially, the assumptions concerning the base state for calculating oxide strains also were critically examined. The state of stress-strain of an oxide growing on the inside surface of an externally-heated tube was considered for the conditions experienced in a boiler during transition from full-to partial-load operation. Since the rate at which the oxide grows is an important consideration, it was necessary to determine the appropriate temperature to use in the oxidation rate calculations. The existence of a temperature gradient through the tube, and the cyclic nature of the boiler operation (temperature and pressure) were considered; the growth temperature of the oxide was taken to be the oxide surface temperature. It was determined that the commonly-used approach for accounting for geometrical effects when calculating stress-strain development in a growing oxide scale of using the analogy of an infinitelylong flat plate gave sufficiently different results than when using a cylindrical geometry, that the latter was adopted as the preferred calculation procedure. Preliminary calculation of strains developed in multilayered oxides formed on alloy T22 as a function of boiler operating conditions indicated the magnitude of the strains in each layer; the large strain gradients between the layers inferred the importance of the detailed scale morphology in determining the mode of exfoliation.
Journal of Applied Mechanics, 1996
ABSTRACT The dynamics of a gas permeable contact lens during blinking are analyzed. The contact l... more ABSTRACT The dynamics of a gas permeable contact lens during blinking are analyzed. The contact lens is considered to be a planar, circular, porous disk of specified permeability. On one side, the lens is in solid contact with the eyelids, while on the other, it is separated from the corneal surface by a thin tear film. The rigid-body dynamics of the lens are coupled with the fluid dynamics of the tear film, and a velocity slip condition is imposed at their interface. The coupled system of ordinary and partial differential equations is solved by a combination of analytical and numerical techniques subject to boundary conditions and physical constraints limiting the duration and extent of the motion of the lens. In addition to the contact lens aspect ratio, this work investigates the effects of those variables that characterize the porous nature of the lens such as the Darcy number and the effective slip coefficient. The motion of a permeable contact lens can be controlled by a proper choice of the lens material microstructure. In fact, analysis of the results indicates that the motion of the lens is enhanced by lower values of the slip coefficient and higher values of the Darcy number, independent of the lens thickness. In addition, it is found that thicker lenses as well as thicker tear films cause the lens to move faster.
DOP-26 iridium alloy cups are used for fuel cladding for radioisotope power systems. The cups are... more DOP-26 iridium alloy cups are used for fuel cladding for radioisotope power systems. The cups are deep drawn and recrystallized prior to final fabrication operations. This study characterizes the plastic deformation of cups during a sizing operation following the recrystallization heat treatment. The purpose of the sizing operation is to achieve the specified roundness, diameter, and radius dimensions of the
Materials Science Forum, 2008
In this study, the foundation is being developed for the numerical simulation of the processes th... more In this study, the foundation is being developed for the numerical simulation of the processes that determine the oxide scale exfoliation behavior of the steam-side surfaces of superheater and reheater tubes in a steam boiler. Initially, the assumptions concerning the base state for calculating oxide strains also were critically examined. The state of stress-strain of an oxide growing on the inside surface of an externally-heated tube was considered for the conditions experienced in a boiler during transition from full-to partial-load operation. Since the rate at which the oxide grows is an important consideration, it was necessary to determine the appropriate temperature to use in the oxidation rate calculations. The existence of a temperature gradient through the tube, and the cyclic nature of the boiler operation (temperature and pressure) were considered; the growth temperature of the oxide was taken to be the oxide surface temperature. It was determined that the commonly-used approach for accounting for geometrical effects when calculating stress-strain development in a growing oxide scale of using the analogy of an infinitelylong flat plate gave sufficiently different results than when using a cylindrical geometry, that the latter was adopted as the preferred calculation procedure. Preliminary calculation of strains developed in multilayered oxides formed on alloy T22 as a function of boiler operating conditions indicated the magnitude of the strains in each layer; the large strain gradients between the layers inferred the importance of the detailed scale morphology in determining the mode of exfoliation.
Journal of Applied Mechanics, 1996
ABSTRACT The dynamics of a gas permeable contact lens during blinking are analyzed. The contact l... more ABSTRACT The dynamics of a gas permeable contact lens during blinking are analyzed. The contact lens is considered to be a planar, circular, porous disk of specified permeability. On one side, the lens is in solid contact with the eyelids, while on the other, it is separated from the corneal surface by a thin tear film. The rigid-body dynamics of the lens are coupled with the fluid dynamics of the tear film, and a velocity slip condition is imposed at their interface. The coupled system of ordinary and partial differential equations is solved by a combination of analytical and numerical techniques subject to boundary conditions and physical constraints limiting the duration and extent of the motion of the lens. In addition to the contact lens aspect ratio, this work investigates the effects of those variables that characterize the porous nature of the lens such as the Darcy number and the effective slip coefficient. The motion of a permeable contact lens can be controlled by a proper choice of the lens material microstructure. In fact, analysis of the results indicates that the motion of the lens is enhanced by lower values of the slip coefficient and higher values of the Darcy number, independent of the lens thickness. In addition, it is found that thicker lenses as well as thicker tear films cause the lens to move faster.
DOP-26 iridium alloy cups are used for fuel cladding for radioisotope power systems. The cups are... more DOP-26 iridium alloy cups are used for fuel cladding for radioisotope power systems. The cups are deep drawn and recrystallized prior to final fabrication operations. This study characterizes the plastic deformation of cups during a sizing operation following the recrystallization heat treatment. The purpose of the sizing operation is to achieve the specified roundness, diameter, and radius dimensions of the