Wright-Patterson Air Force Base

About: Wright-Patterson Air Force Base is a other organization based out in Wright-Patterson AFB, Ohio, United States. It is known for research contribution in the topics: Laser & Microstructure. The organization has 5817 authors who have published 9157 publications receiving 292559 citations. The organization is also known as: Wright-Patterson AFB & FFO.

Effect of microstructure on fatigue and tensile properties of the gamma TiAl alloy Ti-46.5Al-3.0Nb-2.1Cr-0.2W

Abstract: The relationships between the microstructure and tensile and axial load-controlled fatigue properties of the alloy Ti-46.5Al-3.0Nb-2.1Cr-0.2W (atomic per cent) have been studied. Two different microstructures, i.e. duplex (grain size, 20 μm) and fully lamellar (grain size, 300 μm), were produced, through two-step forging and subsequent heat treatments, giving similar yield strengths at room temperature. The fracture strains at room temperature were about 1.1% and 2.9% for the materials with the fully lamellar and the duplex microstructures respectively. At 600 °C, the duplex material shows a 15% higher fatigue strength than that of the fully lamellar material. At this temperature, the gamma alloy of both microstructures reaches high ratios of the fatigue strength at 10 7 cycles to the ultimate tensile strength (UTS), i.e. about 0.95. At 800 °C, the fully lamellar material exhibits higher fatigue strength values above 10 5 cycles, and both microstructures result in a two-stage behavior, in contrast to the test at 600 °C. The second stage features the characteristic conventional fatigue behavior, with a broad amplitude stress range, while the first stage is characterized by a narrow band of fatigue stress levels near the UTS. The fracture modes for the duplex material showed a general trend from transgranular to intergranular failure with increasing temperature. For the fully lamellar material, a change from predominantly translamellar failure to a mixture of inter lamellar and translamellar failure was observed, resulting in a microscopically and macroscopically rough fracture surface. The strain rate sensitivity of the fully lamellar material was negligible in the temperature range tested.

Exploring the Potential of Nucleic Acid Bases in Organic Light Emitting Diodes

Abstract: : Naturally occurring biomolecules have increasingly found applications in organic electronics as a low cost, performance-enhancing, environmentally safe alternative. Previous devices, which incorporated DNA in organic light emitting diodes (OLEDs), resulted in significant improvements in performance. In this work, nucleobases (NBs), constituents of DNA and RNA polymers, are investigated for integration into OLEDs. NB small molecules form excellent thin films by low-temperature evaporation, enabling seamless integration into vacuum deposited OLED fabrication. Thin film properties of adenine (A), guanine (G), cytosine (C), thymine (T), and uracil (U) are investigated. Next, their incorporation as electron-blocking (EBL) and hole-blocking layers (HBL) in phosphorescent OLEDs is explored. NBs affect OLED performance through charge transport control, following their electron affinity trend: G A C T U . G and A have lower electron affinity (1.8 2.2 eV), blocking electrons but allowing hole transport. C , T , and U have higher electron affinities (2.6 3.0 eV), transporting electrons and blocking hole transport. A-EBL-based OLEDs achieve current and external quantum efficiencies of 52 cd A 1 and 14.3%, a ca. 50% performance increase over the baseline device with conventional EBL. The combination of enhanced performance, wide diversity of material properties, simplicity of use, and reduced cost indicate the promise of nucleobases for future OLED development.

Electronic properties and optical-absorption spectra of GaAs-Al x Ga 1-x As quantum wells in externally applied electric fields.

Abstract: A study of the electronic and optical properties of GaAs-${\mathrm{Al}}_{\mathrm{x}}$${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$As quantum wells in external electric fields is presented using a theory which incorporates valence-subband-mixing effects. Electric-field-induced changes in the conduction- and valence-subband structure, exciton binding energies, exciton oscillator strengths of both allowed (\ensuremath{\Delta}n=0) and forbidden (\ensuremath{\Delta}\ensuremath{ e}0) transitions, and the total absorption spectrum are calculated. Optical transitions associated with several conduction and valence subbands are considered. Computed electronic and optical properties are found to be the result of an interplay between the effects of the overlap of electron and hole envelope wave functions and the valence-subband mixing. Valence-subband mixing results in a large splitting of the Kramer's degeneracy in a quantum-well system in the presence of an electric field. The electric-field-induced changes in the computed exciton binding energies and oscillator strengths are caused mainly by the variation of the degree of overlap between the electron and hole wave functions. The foregoing results are compared with those obtained assuming no valence-band-mixing effects and are shown to be both qualitatively and quantitatively different. A brief comparison of our results with available experimental data is presented.

Swelling of Composite Laminates

Abstract: : The swelling behavior of a graphite/epoxy (AS/3501-5) is shown to be described by a model which is based on the assumption that the swelling is negligible until the moisture concentration reaches a threshhold value and then increases linearly thereafter. The model also provides a means of measuring the volume fraction of voids. The analytical results, which take into account the curing stresses, are compared with the experimental data for the transverse and thickness strains of symmetric laminates as well as for the warpage of unsymmetric laminates. The initial absorption on virgin specimens facilitates the subsequent diffusion and the residual stresses appear to be responsible for the absorption being slower than the desorption during the early stages of moisture conditioning. Warpage of unsymmetric laminates is discussed in light of the cracks found in constituent plies. Finally derived is a temperature-relative humidity relationship which renders the graphite/epoxy composite laminates free of residual stresses. (Author)