Technique to Assess Aging of Propellant Grain

Physical properties of composite propellants used in solid rocket motors change significantly with age. To predict the margin of safety and to reevaluate the remaining service life, the structural integrity analysis of solid propellant grains of aged rocket motors is pa-formed at various stages of their life span. To have the reliable results from these analyses, it is mandatory to use the current physical properties of the propellant at the time of analysis. Change in physical properties due to aging is more significant at exposed surfaces. Traditional methods of assessing current physical properties may not truly represent the properties of the batch. The paper presents a novel technique to measure the stress strain response at the exposed surface of propellant grain using a miniature testing device. This specially designed device is able to measure the stress response while the propellant surface is compressed at a constant rate. This measured stress strain behavior is then co related with the physical properties measured by routine tensile tests of the similar type of propellant which is aged artificially. It is observed that there exists an excellent correlation between the measured stress values by the sensor and physical properties measured by uni axial tensile test. This nondestructive technique provides properties of propellant grains of all the motors in the batch comprehensively. The technique is safe as well as economical as compared to the traditional methods.