Embeddable structural sensors for SHM of solid rocket motor grains

Structural Health Monitoring is essential in that any event that may compromise the solid rocket motor must be detected. The magnitude, position and time of any imposed event that may damage the propellant grain, bonding system or integrity of the case must be detected and identified for safe operation of the motor. The current embedded sensor technology has been developed to monitor the effect of these events on the propellant grain. Normal bond stress and temperature can be measured using DBST sensors and the output interpreted to confirm integrity. It has been shown that the presences of de-bond and cracks can be determined. Current work is in progress to establish if these embedded sensors can be used to determine position and size of such defects. The stress distribution in a typical propellant grain also has a shear component particularly near the ends and around any flaps, slots or stress relieving devices. This can be the critical stress under certain loads and in complex geometries. Therefore, a recent addition to the range is a sensor to measure shear stress in the same body as the DBST. Motors can be stored for long periods before being used so the sensor system must also be reliable and stable for at least twenty years of operation. Similar sensors stored for ten years have shown little change and tests are being undertaken to establish the confidence that the sensor system will last the life of the motor. This paper will review the recent development and testing of these embeddable sensors, and results to date will be discussed.