Expansion of superheated metals

Abstract

The short interval of an exploding-wire expansion characterized by rapid rise of resistance, voltage, and electrically deposited energy is studied using time-correlated image-converter photographs, x-ray shadowgraphs, and electrical measurements from identical explosions. Striations in density of the molten expanding core appear concurrently with the electrical signature of the vaporization expansion wave and shortly before billows appear on the boundary surface of the expanding vapor cloud. Even though resolution and penetration do not allow correlation between individual striations and billows, this concurrence suggests that striations are a product of the vaporization process. Arguments are given to show that skin effect and pinch effect do not initiate striation. The same cannot yet be said of Joule heating dependent on the inverse fourth power of radius. Thus striation spacing may reflect underlying departures from uniformity in radius or in microcrystalline structure of the wire.

Evaporation of metals by high-density (107 A � cm?2) electrical currents

“…Then the particles of the material move exclusively in the radial direction, and distribution of current and electromagnetic field can be obtained in the approach of thin wire [ 13]: the intensity of magnetic field H has only an azimuthal component, and the density of current j has only a component along the axis of the wire. It should be noted that applicability of the one-dimensional model for the regimes with the characteristic current density of the order of 10 7 A. cm -2 and higher is confirmed by many experiments [14][15][16][17][18].…”

Current-induced thermal stresses in a metal cylinder

“…The copper cylinder experiences a time-independent, tensile hoop stress near the surface and a compressive hoop stress near the center of the cylinder. The largest tensile hoop stress occurs at the surface of the cylinder, which can cause the fragmentation of the cylinder and lead to the breakage or explosion of metallic wires at high electric current, as observed by Bennett et al 23 From Fig. 2, one can find that the time-independent, surface hoop stress strongly depends on the frequency of the alternating current and decreases with the increase in the angular frequency.…”

Formation of thin films using pulse power and electromagnetic repulsion forces

“…10 at late stages of discharge, when the current was damped down to very low values, many kinks appeared. During an early stage of plasma development, the lateral expansion velocities were in the range from 1.2ϫ 10 3 to 2.0ϫ 10 3 m / s. 3 There was some spread in these velocity values most likely caused by deterioration in the sharpness of electronic focus owing to the strong luminosity of the plasma. 3,5,6,10,22 It has been suggested that thermally induced stress or other wave phenomena cause the fragmentation.…”

“…When conditions on the outer surface of the wire inhibit development of surface ionization, discharge can only take place in the interior of the wire. 3,5,6,10,22 It has been suggested that thermally induced stress or other wave phenomena cause the fragmentation. 2 Shadows of thin wires in the photographs shown in Fig.…”

“…There have been many experimental studies [1][2][3][4][5][6][7][8][9][10][11] and numerical calculations on the physics of electrically exploding wires [12][13][14][15][16][17][18][19] as well as studies for various applications including electrothermal-chemical guns, [20][21][22] electromagnetic rail guns, 23 fuses, 24 and Z-pinches for x-ray generators. Thin metal films with strong adhesion to plastic surfaces were formed using a metal plasma produced by applying pulse power.…”