Development of transducer for measurement of internal dilation of solid propellant grain

Solid propulsion systems are an integral part of launch vehicles and missiles across the world. Structural margin of safety provides a measure of the ability of the solid propellant grain to meet various loads during its operational life. Using general purpose software packages for structural analysis, the structural margins of the propellant grains have been successfully predicted. But to validate the theoretically predicted margins, experimentally generated stress/strain data, at critical locations of the propellant grain are required. Our experiments to directly measure the strain by bonding strain gauges on the propellant grain have not yielded successful results. But by measuring the internal dilation of the propellant due to contraction while cooling, the hoop strain can be found out and thereby the margin of safety. In this paper, a technique to measure the internal dilation of solid propellant tube while cooling is explained. A special type strain gauge based displacement transducer was developed for this purpose.