Bond-line stress and temperature sensors have been proposed in the past as a means to monitor the health of solid rocket motors. However, these previous works have only assessed the ability of these sensors to detect defects such as bond-line delaminations and bore cracks. In this work, the sensors were used to determine the effects of aging on the propellant modulus and the stress-free temperature. When composite propellants are cured, the molecular chains in the polymer entangle and cause shrinkage. This shrinkage causes stresses in the propellant at the cure temperature. Another cause of propellant stress is the differing coefficients of thermal expansion. Because the case and propellant have very different coefficients of thermal expansions, any cooling has an associated induced stress field in the propellant. Because the bond-line stress is linearly proportional to the temperature, the motor can be heated and cooled at 0.05°C/min while monitoring the bond-line stress. From these data, the stress-free temperature can be determined. These same data also produce estimates of the modulus. In this work, the analysis of the data showed a small decrease in the stress-free temperature and a moderate increase in the stiffness of the propellant, which correlates with the expected results.
Monitoring Modulus and Stress-Free Temperature with Health Monitoring Sensors
Journal of Propulsion and Power ; 35 , 2 ; 413-418
2019-01-11
6 pages
Article (Journal)
Electronic Resource
English
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