RESISTANCE CHANGES CAUSED BY VAPORIZATION WAVES IN EXPLODING WIRES
ARMY BALLISTIC RESEARCH LAB ABERDEEN PROVING GROUND MD
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The marked increase in electrical resistance occurring at temperatures above melting can be explained by assuming a vaporization, expansion wave proceeding radially inward from the wire surface. This wave reduces the conducting cross section of the wire, thereby increasing the resistance. A theoretical fluid dynamical model of an expansion wave involving a phase change from liquid to wet vapor is investigated this analysis shows the expected velocity of small amplitude waves to be very close to the experimental value cited above. The theory predicts both the onset of the wave and the wave speed as a function of deposited energy up to the critical temperature. Beyond critical temperature, where the liquid to vapor expansion does not apply, the wave speed should be only a function of deposited specific energy. The experimental data for copper wires under a variety of conditions are found to correlate to a single curve thus, the supposed resistance anomaly in high temperature copper wires is explained.
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