Temperature Histories of Small Metallic Fragments Trapped in Propelling Charges

摘要

Small metallic fragments can be trapped in combustible cartridge cases duringmanufacture and released into the interior-ballistic flow upon combustion of the case. Such particles may survive the interior-ballistic cycle and pose an ignition threat to the case of the next round or to unburned combustion gases mixing with air as the breech is opened. In this report the particle temperature is computed at the time of projectile exit, making use of the one-dimensional code IBHVG2 to characterize the interior-flow. The fragment is assumed to be released at the instant of case burnout and its trajectory along the flow streamline computed approximately in order to quantify the heat-transfer rate. Uncertainties in particle drag are treated by examining maximum, average, and minimum values. Aluminum and steel fragments are considered and temperature histories computed as a function of fragment mass, shape, and initial axial location. It is found that, for fragments imbedded in the outer-radius of the combustible case, only very small fragment sizes completely vaporize. Fragments initially located near the breech are ones most likely to remain in the gun chamber after firing and these particles can achieve temperatures in excess of 2000 C. A complete assessment of the ignition threat posed by these fragments will require the development of experiments to test the susceptibility of combustible-case materials to fragments of combined size and temperature similar to those computed in this report. (Author) (ttl)