Design and Application of Flexible Stress Sensors for Monitoring the Mechanical State of Charge Interfaces

ABSTRACT Structural integrity calculations of solid rocket motor charges should be verified by monitoring the charges’ mechanical state. Through these measurements, failures such as debonding and cracking can be detected in real time, thereby establishing a data foundation for digital twin technology that combines virtual and real environments. Flexible media are proposed to mitigate the effects of embedded sensors on the stress‐strain field at the propellant–insulation interface. In this study, capacitive flexible sensors are introduced for measuring interface stress, and their working principle is presented. A finite element model of propellant rectangular specimens embedded with these sensors was established, thereby facilitating the tensile process. Rigid and flexible sensors were compared, revealing that flexible sensors significantly improve the stress state. The tensile results of sensor electrode plates and flexible interlayers with different material moduli were then investigated from the perspectives of measurement accuracy and stress‐strain fields. The obtained results show that the flexible interlayer modulus exerts a substantial influence on stress and strain within both the interlayer and the specimen, whereas the electrode plate's modulus has a smaller effect. A flexible interlayer modulus between 5 and 8 MPa was determined to provide optimal sensor performance. Moreover, an electrode plate modulus of approximately 3000 MPa was identified to maintain the favorable linearity of capacitance measurements. These findings offer a theoretical basis for the material selection, design, and engineering application of capacitive flexible stress sensors in solid rocket motors, thereby ensuring accurate measurements and minimizing interference with charge structural integrity.