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Full-Text Articles in Engineering
Degradation Of Carbon Fiber Reinforced Polymer And Graphite By Laser Heating, Nicholas C. Herr
Degradation Of Carbon Fiber Reinforced Polymer And Graphite By Laser Heating, Nicholas C. Herr
Theses and Dissertations
The availability of high power, diode pumped solid state and fiber lasers at powers 10 kW and shorter wavelengths (1.07 micrometer) has invigorated the development of tactical laser weapons. This shift to tactical missions greatly increases the variety of potential targets including carbon fiber reinforced polymers and related materials. The complexity of laser-material interactions has driven a historical reliance on live-fire testing and empirical models, but this becomes more difficult as the number of target materials grow. This dissertation combines thermal imagery and existing thermal models of the fire response of composite materials to develop a hybrid modeling approach of …
Effect Of Stress Ratio On Fatigue Crack Growth Rate At Notched Hole In 7075-T6 Aluminum Alloy Under Biaxial Fatigue, Reja Alshahrani
Effect Of Stress Ratio On Fatigue Crack Growth Rate At Notched Hole In 7075-T6 Aluminum Alloy Under Biaxial Fatigue, Reja Alshahrani
Theses and Dissertations
This research investigates the behavior of fatigue crack growth rate in both laboratory air and saltwater (3.5% NaCl) environments for notched cruciform specimen made from 7075-T6 aluminum alloy sheet at different stress ratios. With biaxility ratio of 1, and frequency of applied load of 10 Hz, the crack growth behavior was investigated under in-plane biaxial tension-tension fatigue with 0.1, 0.5, 0.7 stress ratios and then compared them to study the effect of stress ratio on the crack growth rate. Finite Element Analysis (FEA) was used to calculate cyclic variation of stress intensity factors (delta K) at the crack tips. The …
Corrosion Fatigue Crack Growth Behavior At Notched Hole In 7075-T6 Under Different Biaxial Stress Ratios, Khalid A. Alghamdi
Corrosion Fatigue Crack Growth Behavior At Notched Hole In 7075-T6 Under Different Biaxial Stress Ratios, Khalid A. Alghamdi
Theses and Dissertations
This thesis presents the results of a study to quantify the effects of biaxial loading on fatigue crack behavior in both air and saltwater (3.5% NaCl) environments from pre-cracked notched circular hole in a 7075-T6 cruciform specimen using a fracture mechanics approach. With stress ratio of R = 0.5, the crack growth behavior was investigated under fatigue loading with 0.5, 0, -0.5, and -1 biaxial stress ratio lambda. The crack propagation was monitored using optical microscopy. Finite Element Analysis was performed using the different stress ranges and stress ratios with various crack sizes to compute of stress intensity factors (delta …
Microfacet Wavelength Scaling Of The Brdf, Samuel E. Freda
Microfacet Wavelength Scaling Of The Brdf, Samuel E. Freda
Theses and Dissertations
The bidirectional reflectance distribution function (BRDF) describes realistic scattering of light off materials by relating incident irradiance to outbound radiance. One popular class of BRDF models assumes a surface is comprised of tiny microfacets. The drawback of microfacet BRDFs is that they often no not contain specific material parameters and neglect wavelength effects. Wave optics BRDF expressions, however, can describe wavelength effects at the expense of being more computationally cumbersome. Previous work of following a Beckmann-Kirchhoff derivation of BRDF, then relating wave optics BRDF coordinates to microfacet coordinates led to a complicated, but versatile, BRDF. In this work, the infinite …
The Effects Of Ionizing Radiation And Oxidizing Species On Strains Of Deinococcus Radiodurans Lacking Endogenous Oxidative Protection Methods, Dylan L. Klawuhn
The Effects Of Ionizing Radiation And Oxidizing Species On Strains Of Deinococcus Radiodurans Lacking Endogenous Oxidative Protection Methods, Dylan L. Klawuhn
Theses and Dissertations
Multiple strains of Deinococcus radiodurans were transformed, creating knockout mutations in genes responsible for manganese ion transport, manganese and copper/zinc super-oxide dismutase, and bacillithiol synthesis. These mutated strains were then irradiated with ~20,000 Gys. The results showed that the mutated strains had a higher sensitivity to ionizing radiation, those responsible for bacillithiol synthesis having an increase in sensitivity 3000 times more than wild type Deinococcus radiodurans. In addition to radiation the mutated strains were also exposed to paraquat, an oxidizing herbicide. Strains missing manganese super-oxide dismutase showed increased sensitivity.
Radiation Effects On An Active Ytterbium-Doped Fiber Laser, Adam C. Poulin
Radiation Effects On An Active Ytterbium-Doped Fiber Laser, Adam C. Poulin
Theses and Dissertations
This is the first published research focused on the impact of gamma and mixed gamma/neutron radiation on an actively lasing ytterbium-doped fiber laser. While the gain medium of the ytterbium-doped fiber laser was irradiated, the power was measured in-situ and the spectrum was recorded intermittently. Two radiation sources were used, a 60Co cell and a reactor. Three irradiation experiments were conducted per radiation source; pristine fibers were used for the first two experiments, and fibers from the second experiment were re-irradiated for the third experiment. The results indicate that as the total dose increased linearly with time, the laser …
Creep Of Hi-Nicalon™ S Ceramic Fiber Tows At 700°C In Air And In Silicic Acid-Saturated Steam, Matthew W. Piper
Creep Of Hi-Nicalon™ S Ceramic Fiber Tows At 700°C In Air And In Silicic Acid-Saturated Steam, Matthew W. Piper
Theses and Dissertations
Aircraft structural and engine components are subjected to elevated temperature and steam environments during operation. Turbine blades experience particularly harsh conditions that are approaching the operating temperature limits of current Nickel-based superalloys even with active cooling. Ceramic matrix composites (CMCs), which demonstrate high specific strength and specific stiffness and maintain these properties at elevated temperatures such that active cooling is not required, are prime candidates to replace superalloys as the materials for turbine blades. Ceramic matrix composites are composite materials that consist of a ceramic matrix with fiber reinforcement. This research investigated a silicon carbide (SiC) fiber, Hi-Nicalon™ S, which …
Radiation Effects In Thin Film Hexagonal Boron Nitride, Nathaniel M. Kaminski
Radiation Effects In Thin Film Hexagonal Boron Nitride, Nathaniel M. Kaminski
Theses and Dissertations
The radiation response of 2 nm and 12 nm hexagonal boron nitride (hBN) thin film insulators was studied using metal insulator semiconductor (MIS) devices. Current-voltage, capacitance-voltage, and impedance spectroscopy measurements were compared to quantify changes in hBN resistance due to radiation damage. MIS devices exposed to a gamma total dose deposition of 3.1 Mrad(Si) from a Co- 60 source exhibited a small increase in hBN resistance and no observable C-V shift associated with charge trapping. MIS devices irradiated with 4.5 MeV silicon ions showed no significant resistivity decrease to a threshold fluence of 1 ×1012 for the 2 nm …
Characterization Of 2d Jammed Granular Memristive Copper Arrays, Len L. Kedrow
Characterization Of 2d Jammed Granular Memristive Copper Arrays, Len L. Kedrow
Theses and Dissertations
A novel sensor made of jammed granular memristive copper spheres was explored in an effort to develop a protection technology that could be used in non-proliferation treaty monitoring. The micro-copper spheres were annealed for various times at a constant temperature. SEM, EDS, and XPS were used to characterize the growth of the oxide coating. Electrical characterization of the device was done by confining the granular copper spheres to a two-dimensional plane using a unique test fixture capable of measuring I-V curves at the boundary of the circuit board using tungsten pillar electrodes. Electroforming of the copper spheres produced soft dielectric …