Dual‐Off‐Axis Composite Beam for Interfacial Stress Sensors With Tension‐Compression Sensing and Intrinsic Thermo‐Mechanical Decoupling

Solid rocket motors (SRMs) operate under severe thermo‐mechanical loads, generating complex interfacial stresses that induce debonding and trigger catastrophic ignition failures. Current sensors are limited by their inability to conduct bidirectional monitoring and severe multi‐physics cross‐interference, rendering dynamic tracking of the pure (temperature‐decoupled) stress signals highly challenging. To overcome these bottlenecks, a dual‐off‐axis composite beam architecture is proposed to develop an in situ temperature‐self‐compensating interfacial stress sensor. Delivering bidirectional sensing, intrinsic safety, and distributed monitoring, its fundamental innovation involves symmetrically integrating pre‐stretched fiber Bragg gratings (FBGs) onto the upper and lower surfaces of a clamped‐clamped beam. Under interfacial stress, the two FBGs exhibit opposing strain responses. Combined with optical differential demodulation, this design eliminates temperature‐induced common‐mode interference and enables high‐fidelity reconstruction of the pure stress signal. In a wide‐range alternating thermal field spanning tens of degrees Celsius, the sensor exhibits an average residual temperature sensitivity coefficient of ≤ 2 × 10 − 7 °C − 1 . Calibrated via a novel elastic‐medium uniform‐loading method, the sensor demonstrates exceptional metrics: high linearity (R 2 > 0.998) across a ±1 MPa measurement range, a resolution of ≤0.001 MPa, and outstanding durability over 5000 cycles. Finally, real‐time capture of debonding evolution in simulated charges alongside system‐level demonstrations validates its engineering robustness in complex thermo‐mechanical environments.