Browsing by Subject "Railgun"
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Item A MULTI-STAGE DISTRIBUTED ENERGY PLASMA ARC RAILGUN(2010-12) Karhi, Ryan W.; Mankowski, John J.; Giesselmann, Michael G.; Bayne, Stephen B.; Rasty, Jahan; McNab, Ian; Wetz, David A.The development process pertaining to the design, fabrication, coding, and testing of multi-stage distributed energy plasma arc railguns are presented. In collaboration on an Air Force Office of Scientific Research (AFOSR) funded Multidisciplinary University Research Initiative (MURI) project, the Center for Pulsed Power and Power Electronics (P3E) at Texas Tech University is responsible for developing and investigating a functional scale model of a multi-stage distributed energy store (DES) railgun to analyze its effectiveness to suppress a restrike phenomenon and increase plasma armature railgun performance [1]. The term “restrike” denotes the formation of an electrical breakdown in the railgun bore some distance behind a traveling plasma armature. The formation of this secondary arc reduces the driving force on the primary armature and has led to a velocity ceiling of approximately 6 km/s on all breech-fed plasma armature railguns. Numerous solutions have been theorized as viable methods of restrike prevention but lack experimental verification. The primary objective of our research team within the MURI effort is to experimentally test Dr. Jerry Parker’s theoretical restrike suppression technique [2] that was developed at Los Alamos National Laboratory in the 1980’s. The project tasks are organized to identify potential problematic issues and verify theoretical concepts before implementation of a full scale system.Item A multistage distributed energy bench-top electromagnetic launcher(Texas Tech University, 2006-12) McDaniel, Bryan; Mankowski, John J.; Giesselmann, Michael G.A multi-stage energy distributed bench-top electromagnetic launcher is a way of testing the re-striking issues, which affect the velocity of the armature, associated with an electromagnetic launcher. Additional advantages of the multi-stage energy distributed scheme include a reduction in resistive losses and less residual inductive energy stored in the rails. An electromagnetic launcher is also known as a railgun. The bench top railgun used in a two stage energy distributed system sets the parameters and design for a five stage energy distributed system. The tests done on the five stage energy distributed system demonstrated real time switching of downstream stages. In addition to instrumentation control, diagnostics were built including Rogowski coils, B-dots, and a flux ruler. After the solid armature tests were completed, construction was started on a free running arc experiment. The results from this experiment will set up the parameters and design for a multi-stage energy distributed free running arc railgun.Item Effect of electro-mechanical loading in metallic conductors(2010-12) Gallo, Federico Guido; Ravi-Chandar, K.; Mear, Mark E.; Satapathy, Sikhanda S.; Liechti, Kenneth M.; Landis, Chad M.The development of high powered electro-magnetic devices has generated interest in the effect of combined electromagnetic and mechanical loading of such structures. Materials used in high-current applications – aluminum alloys and copper – are subjected to heat pulses of short duration (in the range of a few hundred microseconds to a few milliseconds); immediately following or along with such heat pulses, these materials are also subjected to large mechanical forces. In previous work reported in the literature, ejection of material from the vicinity of preexisting defects such as cracks, notches or discontinuities have been observed resulting from short-duration high-intensity current pulses; after a series of pulses, permanent deformation and weakening of intact material has also been reported. But a lack of complete understanding of the effects of short duration current pulses hinders the assessment of the reliability of such conductors in high energy applications. Therefore, an investigation was undertaken to examine the behavior of electromagnetically and mechanically loaded conductors. This work investigates the effects of short-duration, high-current-density pulses in combination with viii mechanical loading. The aim is to develop a theoretical model to describe the resulting mechanical response. The model is to provide a characterization of the possible effects of thermally-induced plastic strains on metals loaded beyond or just below their yield strength or below the critical stress intensity factor. In the experiments reported here, two types of specimens, undamaged and damaged, were subjected to combined electromechanical loads. Undamaged specimens were used to observe thermally-induced plastic strains - strains not caused by an increase in mechanical loading, but rather resulting from the reduction of yield strength and post-yield stiffness due to the increase in temperature. The experiments were conducted such that it would be possible to develop a model that would conclusively account for the observed material behavior. The second sets of specimens were weakened a priori by the introduction of a crack in order to study the influence of such crack-like defects on the electrical and mechanical fields, and to produce a safe design envelope with respect to the loading conditions. Failure was found to occur due to melting triggered by joule heating; a quantitative criterion based on current concentration and heat accumulation near the crack tip has been developed based on these experimental results.Item An experimental and computational study of magnetic sawing in a railgun(2006-12) Melton, David Michael; Ravi-Chandar, K.Magnetic sawing is a phenomenon that can severely damage electrical conductors carrying high current densities. It occurs at flaws in the conductor, such as cracks or notches, or at any other location where the current becomes concentrated, and it can cut deeply into or completely through the conductor. This thesis studies the process experimentally using a railgun, a form of electromagnetic launcher. The research achieves two main objectives. The first is to develop and test a computational model to predict and avoid the onset of magnetic sawing damage. The second is to experimentally observe and characterize the progression of the damage as greater amounts of energy are supplied by the current. Finally, there is a discussion of the relative contributions to magnetic sawing damage by mechanical and thermal effects.Item Experimental investigation of the effects of electrical currents in small-scale contact regimes(2010-08) Manley, Matthew Halperin; Ravi-Chandar, K.; Satapathy, SikhandaRailguns undergo excessive wear between the projectile and the electromagnetic launcher rails due to the hypersonic relative motion and very large current density involved. The wear effects at the small-scale on the rail-armature interface are not well known but need to be examined in order to support the development of a multishot launcher. Proposed contact regimes in the surface asperity interactions include solidsolid contact, liquid-metal lubricated contact, and arcing. In the present work, a modified Mesoscale Friction Tester (MFT) equipped with a probe and substrate was used to investigate experimentally the arcing and friction conditions that the rail-armature interface would experience. Copper probes with a range of radii of curvature were electrochemically etched and polished to submicrometer roughness. The minimum electrode distances for arcing to occur was found in air at atmospheric pressure and led to a modified Paschen curve where field emission of electrons was the dominant physical mechanism as opposed to Townsend avalanche of ionized gas. Arcing erosion was studied by varying the current, number of strikes, dwell time, and nearest electrode positions horizontally and vertically. Copper-copper friction with a constant normal force resulted in reduced wear when applying a constant current between the electrodes.Item Intrumentation and control of electromagnetic launchers(2007-08) Karhi, Ryan W.; Mankowski, John J.; Dickens, James C.; Hemmert, David J.The instrumentation and control of electromagnetic launch technology is presented. All of the experimental work and theory presented refer to one specific type of launcher know as a railgun. Two railgun projects supported by the AFOSR are described. One is an STTR phase 1 contract to develop a fast transient control system for solid state switching of numerous capacitor banks for implementation on a railgun. The other is a MURI project in collaboration with the IAT at the University of Texas for low cost access to launch micro-satellites into orbit. A project goal for both funded projects was to design and test control systems for the application of multi-stage railgun timing control. This relatively new area of railgun research is attributed to the need for complex multi-stage systems. The paper starts with control systems for proof of principle solid armature experiments and ends with a controlled asynchronous free-running arc distributed energy system.