Dynamic behavior of an explosive opening switch

Abstract

This paper summarizes an investigation into the dynamic behavior of explosive opening switches, which are used in power compression circuits for railgun research. During switch operation, a primacord is ignited at one end of the switch, and a detonation wave propagates down the primacord along the length of the switch. It is assumed that all locations along the length of the primacord detonate simultaneously, a line detonation. A twodimensional Eulerian hydrocode was executed to simulate the early-time dynamics of the explosive switch.Three different opening switch element geometries were considered: a circular extemal shape with a round intemal hole, a faceted (or hexagonal) extemal shape with a round internal hole, and a circular extemal shape with a round internal hole that has four intemal notches directed along predetermined shear planes. The results provide insight into the pressures, stresses, and strains experienced at various locations in the switch. I. INTRODUC~IONMany railgun energy storage systems (e.g., homopolar generators or batteries) require an inductor/opening switch for power compression [l-31. The opening switch is a critical component, and one of the primary reasons inductive systems have not been embraced for rapid-fire railguns is the lack of maturity of opening switch technology. There are several options for opening switches that have been considered including mechanical [4], solid-state [5], and explosive [6]. Mechanical switches, which utilize sliding contacts for commutation, seem to have a practical limit of approximately 1 MA current and a 0.1 volt-second commutation capability [6], and solid-state switches capable of handling the required commutation energy are currently unreasonably large and expensive. Consequently, most inductively driven railguns have utilized explosive opening switches.Significant experimental progress has been made with explosive opening switches [6], and they are now routinely utilized at several laboratories around the country. The electrical characteristics of explosives switches have been studied theoretically [7,8], and calculations to determine the velocity of the break-out links [l] have been performed. However, an understanding of explosive switch dynamic processes is incomplete, and such an understanding is required if efficient design improvements are to be made.Recently, attempts to simulate the dynamic behavior of the switch have been undertaken utilizing a two-dimensional hydrocode [9,10]. While these calculations did indicate the potential of hydrocode calculations for explosive switch modeling, they were preliminary and the discussion of the results was limited. The purpose of this paper is to extend these previous efforts and advance the understanding of the This work was supported in part Contract No. F08635-91-C-0001.Wright Laboratory and SDIO under dynamic processes that occur during the opening of an explosive switch. * Aasfollows. In Section II a brief description of an explosive switch is presented, and in Section 111 the computational mo...