Relaxation of preload in precision bolt connections and its impact on accuracy decline in gyroscopic systems under thermal vibration load

The precision of gyroscopes, as core components of inertial navigation systems, critically determines system accuracy and stability. Precision threaded connections, widely used for assembly, are highly susceptible to preload relaxation during repeated start-stop operations, affecting overall performance. However, the short-term relaxation behavior of preload under coupled external loads remains insufficiently understood. This study investigates the preload relaxation of precision threaded connections under thermo-vibrational loading. An improved Iwan-based tangential contact stiffness model is developed to characterize interface slip behavior and stiffness weakening. By combining numerical simulations with experimental validation, the relationship between tangential stiffness degradation and preload loss is quantified through an interface contact state parameter. Experimental results confirm preload relaxation and contact surface hysteresis. Analysis of the gyroscope rotor assembly reveals that a 9.5% increase in stiffness weakening rate under thermal-vibration loading correlates with a 23.7% rise in axial deviation. A strong positive correlation (up to 0.9691) between stiffness weakening and preload relaxation is established. The findings provide critical insights into the dynamic degradation mechanisms of threaded connections and offer theoretical guidance for improving the stability and signal accuracy of precision aerospace systems such as gyroscopes.