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.

Computational Aeroelasticity: Success, Progress, Challenge

Abstract: This article asserts a much broader dee nition of the term, one in whichCAEencompassesalllevelsofaeroelasticanalysis.Aeroelastic tools based on both linear unsteady aerodynamics and nonlinear CFD methods have been developed and successfully applied. We refer to both of these methodologies as components of CAE. Likewisestructuralmodelingassimpleasbeamtheorytostate-of-the-art e nite element modeling (FEM) have been incorporated into aeroelastic tools, and these techniques should also be included under the CAE heading. It is not the intention of this article to provide an exhaustive history of the development and application of CAE over the past 70 years. Rather, the subject will be examined in the context of two primary themes: 1) aeroelastic problems requiring theoretical

Microstructural Influences on Very-High-Cycle Fatigue-Crack Initiation in Ti-6246

Abstract: The fatigue behavior of an alpha + beta titanium alloy, Ti-6Al-2Sn-4Zr-6Mo, has been characterized in the very-high-cycle fatigue (VHCF) regime using ultrasonic-fatigue (20 kHz) techniques Stress levels (σ max) of 40 to 60 pct of the yield strength of this alloy have been examined Fatigue lifetimes in the range of 106 to 109 cycles are observed, and fatigue cracks initiate from both surface and subsurface sites This study examines the mechanisms of fatigue-crack formation by quantifying critical microstructural features observed in the fatigue-crack initiation region The fracture surface near the fatigue-crack-initiation site was crystallographic in nature Facets, which result from the fracture of primary alpha (α p ) grains, are associated with the crack-initiation process The α p grains that form facets are typically larger in size than average The spatial distribution of α p grains relative to each other observed near the initiation site did not correlate with fatigue life Furthermore, the spatial distribution of α p grains did not provide a suitable means for discerning crack-initiation sites from randomly selected nominal areas Stereofractography measurements have shown that the facets observed at or near the initiation sites are oriented for high shear stress; ie, they are oriented close to 45 deg with respect to the loading axis Furthermore, a large majority of the grains and laths near the site of crack initiation are preferentially oriented for either basal or prism slip, suggesting that regions where α p grains and α laths have similar crystallographic orientations favor crack initiation Microtextured regions with favorable and similar orientations of α p grains and the lath α are believed to promote cyclic-strain accumulation by basal and prism slip Orientation imaging microscopy (OIM) indicates that these facets form on the basal plane of α p grains The absence of a significant role of spatial clustering of α p grains, coupled with the observation of regions of microtexture on the order of 300 to 500 μm supports the idea that variability in fatigue life in the very-high-cycle fatigue regime results from the variability in the nature (intensity, coherence, and size) of these microtextured regions

X‐ray powder diffraction of polymer/layered silicate nanocomposites: Model and practice

Abstract: X-ray powder diffraction in reflection (Bragg-Brentano parafocusing geometry) is extensively used to characterize the structure of polymer/layered silicate nanocomposites (PLSNs). The large basal spacings (d 001 > 2.0 nm) necessitates the collection of data at scattering angles (2θ) of less than 10°. The calculation of an ideal scattering profile for PLSNs provides an avenue to ascertain the influence of experimental parameters and the arrangement, organization, concentration, and composition of constituents on the experimentally observed pattern. This enables better experimental technique, more complete utilization of the scattering data, insight into inconsistencies between scattering and microscopy, and minimization of incorrect interpretation or overinterpretation of data. Because of the strong θ dependence of theoretical and experimental factors at low values of 2θ, careful sample preparation and data evaluation are necessary and should be complemented by microscopic observations, especially for PLSNs with low volume fractions of organically-modified layered silicates (OLS) that are suspected of having exfoliated morphologies. X-ray powder diffraction in reflection alone is insufficient to completely characterize and ascribe PLSN morphology.