Detection Method and State Characterization of Lining Curing Process Based On Laser Ultrasound

ABSTRACT Hydroxyl‐terminated polybutadiene (HTPB) liners, as gel‐like substances, play a crucial role in bonding the casing and propellant within the combustion chamber of solid rocket engines. Real‐time monitoring and accurate determination of the HTPB liner's cured and semi‐cured states are essential for ensuring optimal engine charge quality. This study explores the application of laser ultrasonic technology to detect and characterize the curing process and state of the liner layer. First, numerical simulations and experimental validation were conducted to elucidate the propagation pathway of ultrasonic longitudinal waves in a steel‐lining‐steel three‐layer laminated sample. A calibration method was then developed to precisely determine the propagation time and velocity of longitudinal waves within the liner. This method enables the effective extraction of transition information during the liner's curing process. Finally, the evolution of nonlinear harmonics and modulation waves during the curing process was systematically investigated. By employing the bispectral analysis method, the third‐order spectral peaks of the harmonics were successfully extracted. These findings provide a robust approach for effectively characterizing the curing state of HTPB liners, thereby contributing to advancements in solid rocket engine manufacturing and quality control.