In Situ Monitoring of Internal Bore Deformation in Vertically Stored SRM Grains Using Flexible Resistive Strain Gauges

ABSTRACT Solid rocket motor (SRM) propellant grains are highly susceptible to creep under sustained gravitational loading during vertical storage, which poses a significant threat to their structural integrity. Reliable in situ monitoring of strain in the SRM propellant grain bore under these conditions remains a considerable challenge. This study introduces an innovative monitoring approach based on a flexible resistive strain gauge (FlexGauge) with an off‐axis serpentine configuration, specifically designed for deformation measurement and to match the modulus of viscoelastic propellants. Two full‐scale SRMs containing different propellant formulations were instrumented with FlexGauges bonded to the internal bore surfaces. Digital image correlation (DIC) was co‐located at the same positions to provide benchmark strain data. During a 90‐day period of vertical storage, strain was continuously recorded using a customized monitoring system capable of multi‐parameter acquisition, remote transmission, and visualization. The results show strong agreement between the FlexGauge and DIC measurements, with a maximum deviation of less than 4.25% for both axial and hoop strains. The system demonstrated high stability and reliability, enabling the first full‐scale acquisition of strain data consistent with the deformation patterns observed in vertically stored grains. The FlexGauge and accompanying monitoring system demonstrated effectiveness and reliability, and show strong potential for long‐term structural health monitoring and storage‐life assessment of SRM propellant grains.