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Joyce P.J.,U.S. Naval Academy | Brown L.P.,U.S. Naval Academy | Landen D.,Institute for Advanced Technology | Satapathy S.,Institute for Advanced Technology
Conference Proceedings of the Society for Experimental Mechanics Series | Year: 2011

Castings of metal matrix composites are of potential interest as high strength, high wear resistance conductors. This paper examines the high-strain-rate strength of a tungsten-carbide (WC) filled aluminum bronze alloy (C95400) selected for its good combination of good electrical and thermal conductivity and high mechanical strength, toughness, and wear resistance. A functionally graded material with high wear resistance at the surface was fabricated by centrifugal casting which uses a rotating mold to deposit the high density WC particles at the outer surface while retaining the bulk electrical and thermal conductivity of the bronze alloy for conducting applications. In this paper we evaluate the effects of the WC particles on the dynamic material behavior of the material in the range 500 s -1 to 5000 s -1. The electromagnetic ring expansion technique was used to obtain a nearly uniform uniaxial tensile stress in a thin ring specimen. The dynamic stress-strain response was evaluated as a function of WC particle content. The technique worked satisfactorily in the pure bronze region of the casting but in the WC filled region near the surface the conductivity was too low to effectively launch the ring specimens. ©2010 Society for Experimental Mechanics Inc.

Gard M.,Institute for Advanced Technology | Levinson S.J.,Institute for Advanced Technology | Ferraro S.B.,Institute for Advanced Technology | Jimenez J.A.,Texas State University
IEEE Transactions on Plasma Science | Year: 2012

The small-caliber launcher (SCL) is a 2-m-long railgun with a 1-in bore. The gun line houses 91.5-in (232.4 cm) rails with a 1.25 in × 0.25 in thickness. A need was determined to characterize the gun line for maximum performance of exit velocity, peak velocity, and efficiency by using factorial experiments with linear regression modeling. In this paper, a 2 k factorial experiment was designed and conducted in order to study the effect of key design factors (i.e., charge voltage, armature mass, and starting location) on the performance of the SCL. This statistical method enables the efficient and accurate characterization of the joint effects of these design factors on the SCL. Analysis of variance indicates that a combination of low armature mass (i.e., 49 g), high charge voltage (i.e., 12 kV), and short starting location (i.e., 29.6 cm) maximizes the SCL's exit velocity, peak velocity, and efficiency. Furthermore, some interactions between these factors were found to cause significant statistical effects on SCL performance. © 2011 IEEE.

Guillot M.J.,University of New Orleans | McNab I.R.,University of Texas at Austin | McNab I.R.,Institute for Advanced Technology
Journal of Spacecraft and Rockets | Year: 2013

Several launch methods have been proposed to economically deliver small payloads (~10 kg) into low Earth orbit at a high launch rate including gun launch concepts using electromagnetic and light gas guns. The traverse through the atmosphere subjects the launch vehicle to high aerodynamic heating loads, requiring the launch vehicle to incorporate a thermal protection system if the payload is to survive atmospheric transit. Additionally, small rocket motors are required to insert the payload into low Earth orbit. The objective of this effort is to apply the Advanced Ballistic Reentry System Shape Change Code to study ballistic and lifting trajectories of a nominal 10 kg launch package launched from a 16 km airborne platform using sphere-cone and elliptical aeroshells. The computer code was modified to incorporate lift and drag coefficients numerically computed using the modified Newtonian method and approximate quadrature to extend the capability of the code to compute lifting trajectories and ablation of elliptical aeroshells. In the first part of the study, total ablated mass and internal temperature distribution of the aeroshell for ballistic trajectories are quantified, assuming both laminar and turbulent flow, over a range of launch parameters relevant to gun launch. Total thermal protection system and propellant mass needed for orbital circularization are computed to serve as a baseline for the lifting trajectories. The second part of the study focuses on computing trajectories without ablation to quantify the reduction in propellant mass that can be obtained by employing aerodynamic lift. Optimal trajectories are sought that minimize total parasitic mass for 200 km orbital insertion. Results indicate that thermal heating is manageable with a passive thermal protection system and that lifting trajectories reduce propellant mass requirements over ballistic trajectories. Copyright © 2012 by the American Institute of Aeronautics and Astronautics, Inc.

McDonald J.,Institute for Advanced Technology | Hsieh J.,University of Texas at Austin | Satapathy S.,Institute for Advanced Technology
IEEE Transactions on Plasma Science | Year: 2011

One innovative approach for producing functionally graded tungsten/copper composites involves infiltrating a porous tungsten structure with molten copper. The porous structure is created by sintering tungsten powder to create an initial porous preform and then connecting the preform to the anode of an electrochemical cell. The porosity increases with time as the tungsten oxidizes in the alkaline electrolyte. The rate of porosity increase depends on the local value of electric-potential difference between the electrode and electrolyte, while the local electrical properties are a function of the porosity. Therefore, the porosity distribution, which determines the material-property gradient of the resulting material, can be modeled by a system of coupled equations describing porosity and electric potential. The present work develops a numerical tool capable of predicting the evolution of porosity in the rectangular-slab geometry (the extension to cylindrical-shell and elliptical-shell geometries is straightforward). Analysis of the results suggests that the shape of the gradient can be varied by adjusting parameters such as initial porosity and current density. © 2010 IEEE.

McDonald J.,Institute for Advanced Technology | Hsieh K.-T.,Institute for Advanced Technology | Satapathy S.,Institute for Advanced Technology
IEEE Transactions on Plasma Science | Year: 2011

Current flow in the neighborhood of sharp conducting edges and corners is encountered in many applications of computational electromagnetics. Some examples include resonant cavities and waveguides of rectangular shape, cracks in metal components in nondestructive testing, and the edges and corners of the railarmature contact in an electromagnetic launcher. Although the number of analytical solutions to such problems is small, it is generally believed that such solutions often involve singularities, high gradients, or discontinuities in one or more field components near the edge or corner. It has been demonstrated that the so-called edge elements can provide much more accurate predictions of global quantities (like resonant frequencies and scattering parameters) in the case of full-wave electromagnetics when field discontinuities or singularities are present. They have also been shown to better represent field discontinuities at material interfaces in magnetostatics and reentrant corners in low-frequency electromagnetics. This feature of edge elements is due to their ability to allow necessary jumps in field components at geometric or material discontinuities, as opposed to nodal elements, with the Coulomb gauge enforced, which can overconstrain the fields in certain situations. The main question of interest in this paper is whether edge elements give a similar advantage in the representation of current diffusion around a sharp edge. Both edge- and node-based formulations are considered, and the results are discussed. © 2010 IEEE.

Wetz D.,Institute for Advanced Technology | Landen D.,Institute for Advanced Technology | Satapathy S.,Institute for Advanced Technology | Surls D.,Institute for Advanced Technology
IEEE Transactions on Dielectrics and Electrical Insulation | Year: 2011

In high-energy pulsed power applications, the metallic conductors are expected to heat up significantly due to resistive losses. In the pulsed case, materials exposed to short loading times, from 0.1 s to 100ms behave different from those exposed to long loading times, 1 min to 1 h [1-4]. With this in mind, it is important to understand the mechanical properties of metals when they are heated rapidly so that the correct mechanical properties are considered when designing high-energy experiments where the thermal and mechanical stresses are high. An expanding ring experiment, similar to the one originally designed by Gourdin et al[5-7] has been set up at the Institute for Advanced Technology (IAT) to test such mechanical properties. In Gourdin's work the ring specimen under test sits radially around the center of a primary coil that is driven with a current pulse from a near critically damped RLC circuit. The ring expands and fragments due to the induced electromagnetic forces. In order to determine material properties at elevated temperatures, an inductive heating source has been developed to rapidly heat the ring specimen to temperatures as high as the melting temperature in 10's of milliseconds, immediately prior to the application of electromagnetic expansion forces. The data generated will quantify the sensitivity of material properties to the rate and duration of heating in commonly used materials for development and validation of appropriate constitutive equations. © 2011 IEEE.

Chakravarthy K.M.,University of Texas at Austin | Watt T.J.,Institute for Advanced Technology | Bourell D.L.,University of Texas at Austin
IEEE Transactions on Plasma Science | Year: 2011

One of the difficulties associated with electromagnetic launch is the lack of diagnostic tools capable of surviving the in-bore environment. In railguns, the principal diagnostics are current and voltage measurements, in addition to magnetic field (B-dot) sensors. X-rays and high-speed video are often taken of projectiles after exit, but imaging the in-bore performance of armatures has been limited. In those cases where high-speed cameras have been used to look down the bore of the launcher, the short depth of field ultimately limits their usefulness. High-speed video has been used to look at solid armatures from the side, though this has been limited to either stationary or hybrid solid/plasma armatures. In most cases, laboratory railguns are surrounded by high-strength laminated steel containments that preclude the kind of visual access required for imaging. The University of Texas at Austin and the Institute for Advanced Technology have performed experiments using a modified containment system that allows real-time imaging of the armature as it is accelerated down the launcher. Numerous tests were performed using aluminum armatures on copper and copper-alloy rails at currents up to 150 kA and observed velocities up to around 300 m/s. Grayscale imaging of the armature was performed using a Phantom imaging camera and a 10-ms high-intensity flash lamp, which provided frame rates in excess of 40 000 pps and integration times down to 2 μs. Successful imaging of the armaturerail interface was observed for a variety of test conditions including solid-state and transitioned armaturerail contacts. In addition to providing direct evidence of overall armature behavior, video was used to independently measure projectile velocity, which is usually inferred from relatively coarse B-dot measurements. © 2010 IEEE.

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