Digital Image Correlation Measurements of Strain in Solid Propellant Grains Under Confining Pressure: Methodology and Results

Accurate monitoring of the effect of confining pressure on grain deformation is crucial for assessing the structural integrity of solid rocket motors during ignition. In this work, we develop a grain strain measurement system based on the digital image correlation technique. The system utilizes a 45° reflector combined with strategic illumination from a light source, enabling real‐time collection of grain inner surface data under confining pressure within the narrow cavity of the grain. Circumferential strain measurements of the inner surface are conducted at five confining pressure points on ring‐shaped specimens resembling the columnar grain. The findings indicate that the circumferential strain of the specimens continues to increase during the holding stage of the gas pressurization process. Furthermore, we extend the application of this test system to a subscale motor. The comparison between the experimental and simulation results reveals that the relative error in the variation of circumferential strain on the inner surface of grain within 10 MPa pressure loading is below 8%. The methods and conclusions presented in this study are instrumental in providing a reference for the fine structural integrity analysis and the storage life estimation of solid rocket motors.