Monitoring the velocity of the insulator-metallic phase transition in aluminium powder under shock loading

Abstract

This paper describes a novel and miniature probe for monitoring the velocity of the phase transition in aluminium powder under shock loading. Experimental results are presented that could suggest an explanation for the phenomena that are involved, and the possible consequences of these on the design of flux-compression generators are discussed.

Experimental study of shock-wave magnetic cumulation

“…Another mechanism of shock-wave magnetic cumulation was proposed in [28,35,36]. According to this mechanism, noticeable electrical conductivity emerges in an elastic precursor propagating in the powder ahead of the main shock-wave front.…”

“…The conclusion about the presence of a precursor [36] was made on the basis of readings of the gauge located in the aluminum powder. The gauge was a thin manganin wire wound onto a plastic rod.…”

“…3], but the approximation of the velocity by an exponential dependence at small times yielded ≈5 km/sec. Novac et al [36] believed that such a high velocity testified to the presence of a precursor in which the powder became conducting. The phase velocity of the wave was determined in [36] by means of differentiation of electrical resistance of the gauge.…”

“…The phase velocity of the wave was determined in [36] by means of differentiation of electrical resistance of the gauge. In addition to the ambiguous treatment of the experimental data described [36] (among all, because the differentiation operation is sensitive to noise), the influence of the disturbing wave in the plastic rod was, apparently, ignored.…”

“…Let us compare the results of [28,35,36] with available data on shock compressibility of aluminum powders obtained by different experimental methods [30][31][32][33]37]. The elastic precursor was not registered for such materials, and shock-wave velocity was found to be a linear function of particle velocity.…”