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Hornbuckle B.C.,Weapons and Materials Research Directorate | Rojhirunsakool T.,University of North Texas | Rajagopalan M.,Arizona State University | Alam T.,University of North Texas | And 6 more authors.
JOM | Year: 2015

The immiscible Cu-Ta system has garnered recent interest due to observations of high strength and thermal stability attributed to the formation of Ta-enriched particles. This work investigated a metastable Cu-1 at.% Ta solid solution produced via mechanical alloying followed by subsequent consolidation into a bulk specimen using equal channel angular extrusion at 973 K (700°C). Microstructural characterization revealed a decreased number density of Ta clusters, but with an equivalent particle size compared to a previously studied Cu-10 at.% Ta alloy. Molecular dynamic stimulations were performed to understand the thermal evolution of the Ta clusters. The cluster size distributions generated from the simulations were in good agreement with the experimental microstructure. © 2015, The Minerals, Metals & Materials Society (outside the U.S.).

Cooper G.R.,U.S. Army | Cooper G.R.,Weapons and Materials Research Directorate | Costello M.,Georgia Institute of Technology
Journal of Spacecraft and Rockets | Year: 2011

Payloads that behave like a liquid are carried onboard some projectile configurations, and it iswell established that the internal motion of a liquid payload can induce destabilizing moments on the projectile. This paper creates a method to include the effect of a liquid payload in the fight dynamic equations of motion, enabling trajectory simulations of projectiles with liquid payloads. To include this effect, liquid payload moments are added to the applied loads on the projectile. These loads are computed by solving the linearized Navier-Stokes equations for a projectile undergoing coningmotion.To highlight themethodology, trajectory simulation results are provided for an example projectile with different liquid payloads configurations possessing stable behavior while one exhibits catastrophic fight instability. Copyright © 2011 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.

Rogers J.,Georgia Institute of Technology | Costello M.,Georgia Institute of Technology | Hepner D.,U.S. Army | Hepner D.,Weapons and Materials Research Directorate
Journal of Guidance, Control, and Dynamics | Year: 2011

The use of inexpensive, commercially available thermopiles sensors for roll orientation estimation of spinning bodies is explored. The sensors convert observed thermal gradients into an electrical signal well suited for onboard data acquisition and real-time signal processing. An environmental model emulating sensor stimulus for a sixdegree-of-freedom body is generated given standard atmospheric and typical ground conditions. When sensor characteristics are included, the fully developed model can be used to generate accurate sensor output as a function of Euler angles and altitude. Outputs from the model are then shown to compare favorably with experimental flight data, capturing the predominant and nearly sinusoidal signal variation as the projectile rolls. An extended Kalman filter algorithm is offered, which enables real-time roll angle and roll rate estimation using solely thermopiles as feedback. Example results demonstrate that the algorithm yields reasonably accurate roll information. Finally, a trade study demonstrates that roll error is further mitigated as the number of thermopile sensors is increased. This research shows that thermopiles could be useful in a diverse multisensor constellation as a convenient absolute inertial roll reference.

Silton S.I.,U.S. Army | Silton S.I.,Weapons and Materials Research Directorate
33rd AIAA Applied Aerodynamics Conference | Year: 2015

The present study was undertaken to better understand the impact of the canard trailing vortex flow interactions on the aerodynamics of short length-to-diameter, fin-stabilized munitions when canards are deflected for pitch or yaw control. Advanced computational aerodynamic techniques were applied. Results indicated that the projectile trim angle remained at 6° for the pitch control canard deflections investigated. The trim angles were due to both positive canard pitching moments as well as increases in pitching moment for both the tail fins and body components due to interaction effects. For yaw control canard deflections, results show that significant yaw control can only be obtained at angles of attack prior to canard stall due to the individual local canard angles of attack. The effect of the canard trailing vortex interactions on the tail fin aerodynamics was greatest at small angles of attack. Canard-body interactions were most affected by the local flow; canard trailing vortices were not a contributor. © 2016, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.

Silton S.I.,U.S. Army | Silton S.I.,Weapons and Materials Research Directorate
29th AIAA Applied Aerodynamics Conference 2011 | Year: 2011

A computational study has been undertaken to predict the static aerodynamic coefficients and dynamic derivatives of the standard 0.50-cal army projectile using multiple simulations that are collectively called the virtual wind tunnel technique. Computational solutions have been completed and validated against experimental range data for a wide range of Mach numbers to include subsonic, transonic, and supersonic flight regimes. It was found that steady-state methodologies can be used to obtain the static aerodynamic coefficients and most of the dynamic derivatives with good agreement. However, the accurate prediction of the Magnus moment coefficient in the transonic and subsonic flight regimes remains problematic. Further investigation of grid resolution, including refined wake region, boundary layer growth rate and circumferential resolution, for the steady-state simulations, time-accurate, moving mesh RANS simulations, and LNS simulations have been completed without significant improvement seen in the prediction of the Magnus moment coefficient. The discrepancy in Magnus moment coefficient prediction is large enough that it appears to affect the predicted flight dynamics of the projectile.

McAllister Q.P.,University of Delaware | Gillespie Jr. J.W.,University of Delaware | Vanlandingham M.R.,Weapons and Materials Research Directorate
Journal of Materials Research | Year: 2012

An instrumented indentation method is established to accurately measure the local elastic-plastic material properties of a single fiber by accounting for the additional sources of compliance associated with fiber indentation. The Oliver-Pharr instrumented indentation data analysis method is compared for indentation of a standard, planar fused silica sample and in the radial direction of homogeneous, isotropic E-glass fibers of two different diameters. Compliance contributions from substrate deflection and other nonindentation-related fiber deflections are quantified and shown to be negligible. The added compliance observed is attributed to the lack of constraint due to the finite geometry of a curved fiber surface. This compliance contribution is accounted for by using a proposed area correction to capture the geometry of the curved fiber-probe contact combined with a structural compliance correction. Implementation of these corrections to experimental indentation curves results in accurate measurements of the fiber elastic modulus and hardness. © 2011 Materials Research Society.

Weingarten N.S.,Weapons and Materials Research Directorate | Rice B.M.,Weapons and Materials Research Directorate
Journal of Physics Condensed Matter | Year: 2011

Molecular dynamics (MD) simulations using a recently developed first-principles-based embedded-atom-method (EAM) potential are used to simulate the exothermic alloying reactions of a Ni/Al bilayer initially equilibrated at 1200K. Simulations are performed in the isobaric-isoenthalpic (NPH) ensemble, which provides insight into the influence of pressure on atomic mixing and the subsequent alloying reaction. For pressures lower than 8GPa, the mechanism of mixing is the same: as mixing and reaction occur at the interface, the heat generated first melts the Al layer, and subsequent mixing leads to further heat generation after which the Ni layer melts, leading to additional mixing until the alloying reactions are completed. However, for simulations at pressures higher than 8GPa, the reaction does not occur within the time interval of the simulation. The results will be compared with our previous simulations of a Ni/Al bilayer using a different interatomic potential, which predicts substantially different pressure-dependent melting behavior of the pure components. This comparative study suggests that pressure-dependent melting behavior of components of reactive materials can be used to influence reaction rates and mechanisms. © 2011 IOP Publishing Ltd.

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