Aerospace Engineering Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/2737
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Item MANUFACTURING TECHNIQUES FOR TITANIUM ALUMINIDE BASED ALLOYS AND METAL MATRIX COMPOSITES(2010) Kothari, Kunal B; Wereley, Norman M; Radhakrishnan, Ramachandran; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Dual phase titanium aluminides composed vastly of gamma phase (TiAl) with moderate amounts of alpha2 phase (Ti3Al) have been considered for several high temperature aerospace and automobile applications. High specific strength coupled with exceptional high temperature performance in the areas of creep and oxidation resistance makes titanium aluminides "materials of choice" for next generation propulsion systems. Titanium aluminides are primarily being considered as potential replacements for Ni-based superalloys in gas turbine engine components with the aim of developing more efficient and leaner engines with high thrust-to-weight ratio. As titanium aluminides lack room temperature ductility, traditional manufacturing techniques such as casting, forging and rolling are more expensive to perform. To overcome this, research over the past decade has examined powder metallurgy techniques such as hot-isostatic pressing, sintering and hot-pressing to produce titanium aluminides parts. Enhancements in these powder metallurgy techniques has produced near-net shape parts of titanium aluminides possessing a homogeneous and refined microstructure and thereby exhibiting better mechanical performance. This study presents a novel powder metallurgy approach to consolidate titanium aluminide powders. Traditional powder consolidation processes require exposure to high temperatures over a lengthy duration. This exposure leads to grain growth in the consolidated part which adversely affects its mechanical properties. A rapid consolidation process called Plasma Pressure Compaction (P2C) has been introduced and utilized to consolidate titanium aluminide powders to produce titanium aluminide parts with minimal grain growth. The research also explores the role of small alloying additions of Nb and Cr to enhance ductility of the consolidated parts. The grain size of the consolidated parts is further reduced in the sub-micrometer range by milling the as-received powders. Finally, a metal matrix composite with TiAl matrix reinforced with TiB was developed by first blending the matrix and the reinforcement powders and then consolidating the powder blend.Item Development and Validation of a Bidirectionally Coupled Magnetoelastic FEM Model for Current Driven Magnetostrictive Devices(2009) Graham, Frank; Flatau, Alison; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)A bidirectionally coupled magnetoelastic model (BCMEM) has been extended to include electric currents in its magnetic finite element formulation. This enables the model to capture the magnetoelastic behavior of magnetostrictive materials subjected to elastic stresses and magnetic fields applied not only by permanent magnets but also by current carrying coils used often in transducer applications. This model was implemented by combining finite element solutions of mechanical and magnetic boundary value problems using COMSOL Multiphysics 3.4 (Finite Element Modeling software) with an energy-based non-linear magnetomechanical constitutive model. The BCMEM was used to simulate actuator load lines and four point bending results for Galfenol, which were then compared to experimental data. The model also captured the ΔE effect in Galfenol. The BCMEM can be used to study and optimize the design of future current driven magnetostrictive devices.Item QUASI-STATIC CHARACTERIZATION AND MODELING OF THE BENDING BEHAVIOR OF SINGLE CRYSTAL GALFENOL FOR MAGNETOSTRICTIVE SENSORS AND ACTUATORS(2009) DATTA, SUPRATIK; FLATAU, ALISON B; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Iron-gallium alloys (Galfenol) are structural magnetostrictive materials that exhibit high free-strain at low magnetic fields, high stress-sensitivity and useful thermo-mechanical properties. Galfenol, like smart materials in general, is attractive for use as a dynamic actuator and/or sensor material and can hence find use in active shape and vibration control, real-time structural health monitoring and energy harvesting applications. Galfenol possesses significantly higher yield strength and greater ductility than most smart materials, which are generally limited to use under compressive loads. The unique structural attributes of Galfenol introduce opportunities for use of a smart material in applications that involve tension, bending, shear or torsion. A principal motivation for the research presented in this dissertation is that bending and shear loads lead to development of non-uniform stress and magnetic fields in Galfenol which introduce significantly more complexity to the considerations to be modeled, compared to modeling of purely axial loads. This dissertation investigates the magnetostrictive response of Galfenol under different stress and magnetic field conditions which is essential for understanding and modeling Galfenol's behavior under bending, shear or torsion. Experimental data are used to calculate actuator and sensor figures of merit which can aid in design of adaptive structures. The research focuses on the bending behavior of Galfenol alloys as well as of laminated composites having Galfenol attached to other structural materials. A four-point bending test under magnetic field is designed, built and conducted on a Galfenol beam to understand its performance as a bending sensor. An extensive experimental study is conducted on Galfenol-Aluminum laminated composites to evaluate the effect of magnetic field, bending moment and Galfenol-Aluminum thickness ratio on actuation and sensing performance. A generalized recursive algorithm is presented for non-linear modeling of smart structures. This approach is used to develop a magnetomechanical plate model (MMPM) for laminated magnetostrictive composites. Both the actuation and sensing behavior of laminated magnetostrictive composites as predicted by the MMPM are compared with results from existing models and also with experimental data obtained from this research. It is shown that the MMPM predictions are able to capture the non-linear magnetomechanical behavior as well as the structural couplings in the composites. Model simulations are used to predict optimal actuator and sensor design criteria. A parameter is introduced to demarcate deformation regimes dominated by extension and bending. The MMPM results offer significant improvement over existing model predictions by better capturing the physics of the magnetomechanical coupled behavior.Item Characterization and Modeling of the Magnetomechanical Behavior of Iron-Gallium Alloys(2006-08-31) Atulasimha, Jayasimha; Flatau, Alison; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Magnetostrictive Iron-Gallium alloys (Galfenol) demonstrate moderate magnetostriction (~350 ppm) under very low magnetic fields (~100 Oe), have very low hysteresis, high tensile strength (~500 MPa), high Curie temperature (~675°C), are in general machinable, ductile and corrosion resistant. Therefore, they hold great promise in active vibration control, actuation, stress and torque sensing in helicopters, aircrafts and automobiles. To facilitate design of magnetostrictive actuators and sensors using this material, as well as to aid in making it commercially viable, it is necessary to perform a comprehensive characterization and modeling of its magnetomechanical behavior. This dissertation addresses some of these issues, focusing primarily on quasi-static characterization and modeling of the magnetomechanical behavior of single-crystal FeGa alloys with varying gallium content and along different crystallographic directions, and studying the effect of texture on the magnetomechanical behavior of polycrystals. Additionally, improved testing and modeling paradigms for magnetostrictive materials are developed to contribute to a better understanding and prediction of actuation and sensing behavior of FeGa alloys. In particular, the actuation behavior (λ-H and B-H curves) for 19, 24.7 and 29 at. % Ga <100> oriented single crystal FeGa samples are characterized and the strikingly different characteristics are simulated and explained using an energy based model. Actuation and sensing (B-σ and є-σ curves) behavior of <100> oriented 19 at. % Ga and <110> oriented 18 at. % Ga single crystal samples are characterized. It is demonstrated that the sensing behavior can be predicted by the model, using parameters obtained from the actuation behavior. The actuation and sensing behavior of 18.4 at. % Ga polycrystalline FeGa sample is predicted from the volume fraction of grains close to the [100], [110], [210], [310], [111], [211] and [311] orientations (obtained from cross-section texture analysis). The predictions are benchmarked against experimental actuator and sensor characteristics of the polycrystalline sample.Item A HYBRID MODEL FOR FATIGUE LIFE ESTIMATION OF POLYMER MATRIX COMPOSITES(2006-01-20) Uleck, Kevin Ronald; Vizzini, Anthony J; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)A major limitation of current fatigue life prediction methods for polymer matrix composite laminates is that they rely on empirical S-N data. In contrast to fatigue life prediction methods for metals which are based on physical crack growth models, the heart of fatigue life models for composites is empirical S-N data for each specific material system and specific loading conditions. This implies that the physical nature and processes responsible for tensile fatigue are not well understood. In this work a mechanism-based approach is used to model the damage growth and failure of uniaxial polymer matrix composites under uni-axial tension-tension fatigue loading. The model consists of three parts: an initial damage model, a damage growth model, and a tensile failure model. The damage growth portion of the model is based on fracture mechanics at the fiber/matrix level. The tensile failure model is based on a chain of bundles failure theory originally proposed for predicting the static strength of unidirectional laminates using fiber strength distributions. The tensile fatigue life prediction model developed in this work uses static tensile strength data and basic material properties to calculate the strength degradation due to fiber-matrix damage growth caused by fatigue loading and does not use any experimental S-N data. The output of the model is the probability of failure under tensile fatigue loading for a specified peak load level. Experimental data is used to validate and refine the model and good correlation between the model and experimental data has been shown. The principal contribution of this work is a hybrid-mechanistic model for analyzing and predicting the tension-tension fatigue life behavior of uniaxial polymer matrix composites. This model represents the very foundation to build upon a comprehensive model for fatigue. It demonstrates the validity of the ideas as they apply to uniaxial laminates that may in turn be used to apply to more complex laminates. Additionally, because the model is mechanism based it can be used for evaluation of the effects of constituent property changes such as matrix stiffness and toughness, or environmental conditions such as temperature and moisture.