Nonlinear bonding analysis of bolt connection and secondary tightening strategy

The tightening process of aero-engine rotor bolt involves a nonlinear bonding stage, which poses challenges in achieving accurate control of the pre-tightening force using the way of torque control. This study proposes a secondary tightening control strategy that offers high precision and adaptability for controlling the bolt pre-tightening force based on the snug point. Firstly, we provide a detailed description of the variable stiffness process during the nonlinear bonding stage of bolt, based on theories related to bolt tightening relationship and the joint surface contact model. Secondly, we design methods for extracting the snug point and calculating the target rotation angle through Monte-Carlo model and the linear goodness of fit evaluation mechanism. Thirdly, we experimentally investigate the effectiveness of this secondary tightening strategy using the typical connection section of aero-engine rotor flange bolt as our experimental object. The results indicate that applying this secondary tightening strategy can effectively mitigate uncertainties caused by nonlinear bonding and reduce errors resulting from variations in bolt structure and external conditions. Compared to torque method and torque–angle method, employing this secondary tightening strategy reduces the standard deviation of pre-tightening force from 1.875 and 1.031 to 0.536, thereby minimizing dispersion in pre-tightening force level. Additionally, it reduces maximum deviation of pre-tightening force from 30.9% and 20.1% to 2.8%, significantly improving the control accuracy of bolt tightening.