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Articles 1 - 12 of 12
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Studies Of Damage Tolerance In Automated Fiber Placement Based Heterogeneous Meso-Architectured Carbon/ Epoxy Composite Laminates., Karan Kodagali
Studies Of Damage Tolerance In Automated Fiber Placement Based Heterogeneous Meso-Architectured Carbon/ Epoxy Composite Laminates., Karan Kodagali
Theses and Dissertations
Traditional unidirectional (UD) carbon fiber-reinforced polymer matrix composites manufactured via automated fiber placement (AFP) are widely used in aerospace structures. While heterogeneous at the micro-scale, these materials are homogeneous at the meso-scale (ply-scale). The major limitation is its limited toughness, poor damage tolerance/impact resistance capability and the inability to sufficiently redistribute stresses, resulting in strength-toughness tradeoffs, making them susceptible to impact damage. From previous studies, there is an understanding that fiber architecture has a first order effect on the damage tolerance. Introducing new discontinuous/heterogeneous meso-scale architectures, through an optimal merger of material and structure, can result in unprecedented property improvements …
A Constitutive Material Model For Simulating Texture Evolution And Anisotropy Effects In Cold Spray., Creston Michael Giles
A Constitutive Material Model For Simulating Texture Evolution And Anisotropy Effects In Cold Spray., Creston Michael Giles
Theses and Dissertations
Cold spray has seen rapid advancement since its inception and has shown significant potential as a method of additive manufacturing. However, the large plastic deformation and repeated heating/cooling cycles that the material undergoes during the cold spray process can result in gradients in material structure and large residual stresses. The purpose of this study is to extend the existing EMMI material model to include anisotropic material response through the use of orientation distribution functions to predict residual stresses and anisotropy resulting from cold spray and similar additive manufacturing processes. Through the use of a finite element simulation, yield surfaces for …
Characterization Of Anisotropic Materials Using Scattered Field Measurements, Hirsch M. Chizever
Characterization Of Anisotropic Materials Using Scattered Field Measurements, Hirsch M. Chizever
Theses and Dissertations
This research uses monostatic far-zone scattered field measurements to estimate the permittivity of biaxial materials at X-Band. Utilizing Radar Cross Section (RCS) measurement techniques, this effort examines the efficacy of whole-sample TEM illumination in the estimation of anisotropic permittivity, in contrast with traditional subsample illumination methods. The research examines the impact that dielectric supports have on measurement error and uncertainty in permittivity estimates. Following an incremental approach, the research first demonstrates successful estimation of permittivity for isotropic spheres followed by a Teflon isotropic cube. Finally, the method is applied to uniaxial and biaxial cubes whose anisotropic permittivity is validated through …
Solution Anneal Heat Treatments To Enhance Mechanical Performance Of Additively Manufactured Inconel 718, David J. Newell
Solution Anneal Heat Treatments To Enhance Mechanical Performance Of Additively Manufactured Inconel 718, David J. Newell
Theses and Dissertations
The nickel-based superalloy Inconel 718 (IN718) is an excellent candidate among aerospace alloys for laser powder-bed fusion (LPBF) manufacturing. As-built LPBF IN718 has a vertically aligned columnar (001) microstructure which translates into orthotropic mechanical behavior. The post-process heat treatments for IN718 were developed 60 years ago for wrought and cast processes and do not mitigate the columnar microstructure of the LPBF process. Recrystallization is required to remove the columnar microstructure, which would allow for parts to be fabricated on different machines or in different orientations but still achieve the same properties. This research investigated the microstructure of LPBF IN718 as …
Towards Modeling The Anisotropic Behavior Of Polycrystalline Materials Due To Texture Using A Second Order Structure Tensor, Brandon Chandler Templin
Towards Modeling The Anisotropic Behavior Of Polycrystalline Materials Due To Texture Using A Second Order Structure Tensor, Brandon Chandler Templin
Theses and Dissertations
A material model capable of reproducing the anisotropic behavior of polycrystalline materials will prove to be useful in simulations in which directional properties are of key importance. The primary contributor to anisotropic behavior in polycrystalline materials is the development of texture through the rotation and alignment of slip systems due to plastic deformation. A large concentration of aligned slip systems will influence the glide of dislocations in the respective global deformation direction resulting in a directionally dependent flow stress. The Evolving Microstructural Model of Inelasticity (EMMI) is modified to account for evolving anisotropy due to the development of texture. Texture …
Multimessenger Approach To Search For Cosmic Ray Anisotropies, Larry David Buroker
Multimessenger Approach To Search For Cosmic Ray Anisotropies, Larry David Buroker
Theses and Dissertations
The origin of the highest energy cosmic rays is still unknown. The discovery of their sources will reveal the workings of the most energetic astrophysical accelerators in the universe. Recent international efforts have brought us closer to unveiling this mystery. Possible ultra-high energy cosmic ray sources have been narrowed down with the confirmation of an "ankle" and the GZKlike spectral feature at the high-end of the energy spectrum. A clear resolution of the ultra-high energy mystery calls for the search of anisotropies in the distribution of arrival directions of cosmic rays. In this thesis, we adopt the so-called "multi-messenger" approach …
Membrane Properties Involved In Calcium-Stimulated Microparticle Release From The Plasma Membranes Of S49 Lymphoma Cells, Lauryl Elizabeth Campbell
Membrane Properties Involved In Calcium-Stimulated Microparticle Release From The Plasma Membranes Of S49 Lymphoma Cells, Lauryl Elizabeth Campbell
Theses and Dissertations
The mechanism of microparticle shedding from the plasma membrane of calcium-loaded cells has been investigated in erythrocytes and platelets. Recent studies have revealed the physiological and clinical importance of microparticle release from nucleated cells such as lymphocytes and endothelium. The experiments of this study were designed to address whether simple mechanisms discovered in platelets and erythrocytes also apply to the more complex nucleated cells. Four such mechanisms were addressed: potassium efflux, transbilayer phosphatidylserine migration, cytoskeleton degradation, and membrane lipid order. The rate and amount of microparticle release in the presence of a calcium ionophore, ionomycin, was assayed by light scatter …
Anisotropy In The South Atlantic Anomaly, Shaun M. Easley
Anisotropy In The South Atlantic Anomaly, Shaun M. Easley
Theses and Dissertations
From June 2000 through July 2006, the TSX-5 satellite measured proton fluxes in the Earth’s magnetosphere using its CEASE instrument. A review of the satellite data by scientists at AFRL/VSBX revealed an unanticipated, recurring bi-modal structure in histograms of the proton counts. This research identified the bi-modal behavior as anisotropic in nature, and the result of two separate processes. At low altitudes the anisotropy was well described by the classic “East-West Effect.” Comparisons of the satellite data to simple analytical models are presented. At high altitudes, the anisotropy was the result of the detector measuring protons at different pitch angles …
Finite Element Modeling Of Crack Tip Plastic Anisotropy With Application To Small Fatigue Cracks And Textured Aluminum Alloys, Gabriel Petru Potirniche
Finite Element Modeling Of Crack Tip Plastic Anisotropy With Application To Small Fatigue Cracks And Textured Aluminum Alloys, Gabriel Petru Potirniche
Theses and Dissertations
For the characterization of crack advance in mechanical components and specimens under monotonic and fatigue loading, many engineering approaches use the assumption that the plastic deformation at the crack tip is isotropic. There are situations when this assumption is not correct, and the modeling efforts require additional correction factors that account for this simplification. The goal of this work is to study two cases where the plastic anisotropy at the crack tip is predominant and influences the magnitude crack-tip parameters, which in turn determine the amount of crack advance under applied loading. At the microstructural level, the small crack issue …
Efficient And Accurate Computation Of Non-Negative Anisotropic Group Scattering Cross Sections For Discrete Ordinates And Monte Carlo Radiation Transport, David W. Gerts
Theses and Dissertations
A new method for approximating anisotropic, multi-group scatter cross sections for use in discretized and Monte Carlo multi-group neutron transport is presented. The new method eliminates unphysical artifacts such as negative group scatter cross sections and falsely positive cross sections. Additionally, when combined with the discrete elements angular quadrature method, the new cross sections eliminate the lack of angular support in the discrete ordinates quadrature method. The new method generates piecewise-average group-to-group scatter cross sections. The accuracy and efficiency for calculating the discrete elements cross sections has improved by many orders of magnitude compared to DelGrande and Mathews previous implementation. …
Measuring The Effects Of Soil Parameters On Bidirectional Reflectance Distribution Function, Pushkar Shrikant Pradhan
Measuring The Effects Of Soil Parameters On Bidirectional Reflectance Distribution Function, Pushkar Shrikant Pradhan
Theses and Dissertations
Remote sensing data acquisition often requires a revisit to the same target. Therefore, it is not always possible to have the same illumination and viewing conditions. Bidirectional Reflectance Distribution Function (BRDF) is an attempt to predict the reflectance of an object for any given viewing and illumination geometry by explaining the interaction of the incident energy with the target object, the medium lying between the source and the target, and the interaction of the reflected energy with the medium between the target and the sensor. In this study various factors affecting BRDF were explored. Various factors contribute to this characteristic …
Characterization Of Spatial And Temporal Anisotropy In Turbulent Mixing Layers Using Optical Techniques, Patrick J. Gardner
Characterization Of Spatial And Temporal Anisotropy In Turbulent Mixing Layers Using Optical Techniques, Patrick J. Gardner
Theses and Dissertations
The optical aberrations induced by mixing layers of dissimilar gases are recorded and analyzed in order to characterize the spatial and temporal properties of the flow. Laser light was propagated through a mixing layer of Helium and Nitrogen gas, having velocities of 8.5 m/sec and 1.5 m/sec, respectively. The light was propagated in a direction perpendicular to the plane of the mixing layer. The mixing layer was evaluated in two experimental regimes: free turbulent mixing, where the mixing layer spreads into the surrounding air; and channel flow, where the mixing layer is confined to a rectangular channel. The optical perturbations …