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.

The Chemistry of Deformation: How Solutes Soften Pure Metals

Abstract: Solutes have been added to strengthen elemental metals, generating usable materials for millennia; in the 1960s, solutes were found to also soften metals. Despite the empirical correlation between the "electron number" of the solute and the change in strength of the material to which it is added, the mechanism responsible for softening is poorly understood. Using state-of-the-art quantum-mechanical methods, we studied the direct interaction of transition-metal solutes with dislocations in molybdenum. The interaction increases dramatically with increasing electron number and strongly influences the mechanisms responsible for plasticity in these materials. Our quantitative model explains solution softening of metals by using changes in energy and stress scales of plasticity from solutes.

Hot deformation and microstructural damage mechanisms in extra-low interstitial (ELI) grade Ti–6Al–4V

Abstract: The hot deformation behavior of extra-low interstitial (ELI) grade Ti–6Al–4V alloy with Widmanstatten preform microstructure over wide temperature (750–1100oC) and strain rate ranges (0.001–100 s−1) has been studied with the help of processing maps. In the lower temperature and strain rate regime (850–950°C and 0.001–0.1 s−1), globularization of the lamellar structure occurs while at higher temperatures (980–1100oC) the β phase exhibits large-grained superplasticity. The tensile ductility reaches peak values under conditions corresponding to these two processes. A dip in ductility occurs at the β transus and is attributed to a possible nucleation of voids within prior β grains. At lower temperatures and strain rates below about 0.1 s−1, cracking at the prior β grain boundaries occurs under mixed mode conditions. At strain rates higher than 1 s−1 and temperatures lower than about 950oC, the material exhibits a wide regime of flow instabilities. On the basis of these results, a temperature–strain rate window for hot working this material without microstructural defects is identified.

Load-adaptive crystalline–amorphous nanocomposites

Abstract: Advances in laser-assisted deposition have enabled the production of hard composites consisting of nanocrystalline and amorphous materials Deposition conditions were selected to produce super-tough coatings, where controlled formation of dislocations, nanocracks and microcracks was permitted as stresses exceeded the elastic limit This produced a self-adjustment in the composite deformation from hard elastic to quasiplastic, depending on the applied stress, which provided coating compliance and eliminated catastrophic failure typical of hard and brittle materials The load-adaptive concept was used to design super-tough coatings consisting of nanocrystalline (10–50 nm) TiC grains embedded in an amorphous carbon matrix (about 30 vol%) They were deposited at near room temperature on steel surfaces and studied using X-ray photoelectron spectroscopy, X-ray diffraction, scanning electron microscopy, Raman spectroscopy, nanoindentation and scratch tests Design concepts were verified using composition–structure–property investigations in the TiC–amorphous carbon (a-C) system A fourfold increase in the toughness of hard (32 GPa) TiC–a-C composites was achieved in comparison with nanocrystalline single-phase TiC

Carbon nanofiber paper for lightning strike protection of composite materials

Abstract: Carbon fiber reinforced polymer matrix composites have been increasingly used for aircraft structures. Such relatively low-conductivity composite materials need to be engineered with lightning strike protection to achieve lightning tolerance comparable to metallic components. This study developed a specialty paper made of carbon nanofibers and nickel nanostrands as a surface layer on the composite panels and explored potential replacement for existing lightning strike protection materials. The porous, flexible, non-woven papers of nanofibers and nanostrands were first prepared by the papermaking process. They were then incorporated onto the surface of carbon fiber reinforced polymer composites through resin transfer molding process. A method of applying a temporary surface barrier on the paper was developed to prevent the infused resin from breaching the paper’s surface. This minimized the resin on the composite panel’s surface and allowed its surface conductivity to remain high. The lightning strike tests conducted on these composite panels showed that lightning strike tolerance correlated to the surface conductivities of composite panels.

Large-Eddy Simulation of Supersonic Cavity Flowfields Including Flow Control

Abstract: Large-eddy simulations of supersonic cavity flowfields are performed using a high-order numerical method. Spatial derivatives are represented by a fourth-order compact approximation that is used in conjunction with a sixth-order nondispersive filter. The scheme employs a time-implicit approximately factored finite difference algorithm, and applies Newton-like subiterations to achieve second-order temporal and fourth-order spatial accuracy. The Smagorinsky dynamic subgrid-scale model is incorporated in the simulations to account for the spatially underresolved stresses. Computations at a freestream Mach number of 1.19 are carried out for a rectangular cavity having a length-to-depth ratio of 5:1. The computational domain is described by 2.06×10 7 grid points and has been partitioned into 254 zones, which were distributed on individual processors of a massively parallel computing platform. Active flow control is applied through pulsed mass injection at a very high frequency, thereby suppressing resonant acoustic oscillatory modes