Mechanical Properties Of Bolted Connection Structure Under Real Contact Surface Topography

Bolted joints are widely used in the complex rotor connections in aeroengine.Precise prestress and pre-deformation of the tightened joint are the key insurance of the whole engine's stability and reliability,which are achieved by the turning of the nut through torque control generally.The bolted joint,however,is a complex contact system,the geometric deviations resulting from machining errors will unavoidably enlarge the preload deviation.If lacking related mechanism study,not only the engine vibration may become out of tolerance,the engine optimization will also become hard to promote resulting from lack of guidance.Moreover,the formation of bolt residual torque still lacks a theory basis,which will lead to an incomplete performance prediction of bolted joint,leaving hidden dangers.Aiming towards the problems mentioned above,in this study,geometric deviations are introduced into the formation analysis of bolt preload and residual torque,and the deviation range of these two parameters is obtained while given geometric tolerance.At last,the variation law of bolt residual torque under working conditions is also researched in addition.First,based on the torque-preload relationship during tightening process,through effects of geometric deviations including non-parallel bearing surface,pitch and thread angle deviation on contact pressure,the equivalent friction radius and torque components are analyzed,based on which the influence of geometric deviations on bolt preload is obtained.In order to simulate the tightening process of bolted joint under geometric deviations,a parametric finite element model is established.Through the three-dimensional real thread tightening simulation,the tightening process of bolted joint under geometric deviations is analyzed,and the precision of this simulation on bolt preload is then verified by tightening experiment.Based on the above study,we continued to study the formation mechanism of bolt residual torque during releasing process of tightening torque.Through consideration of torque component radio and torsional stiffness radio,the influence of geometric deviation on residual torque is analyzed.Then,the influence of geometric deviation parameters and non-geometric deviation parameters on residual torque is obtained by finite element simulation,and the accuracy of the model for residual torque simulation is also verified by tightening experiment.In order to further study the variation of bolt residual torque under working conditions,we propose the assumption of non-uniform deformation flange under shearing loading and analyzes the relationship between residual torque variation and flange deformation.Through finite element simulation,the influence of bolt position,number of bolts and geometric parameters of flange on the variation of residual torque is obtained.In the uniaxial tension experiment,the accuracy of the simulation model on flange deformation was verified.In this study,the geometric deviations of the contact surface are introduced into the formation analysis of bolt preload and residual torque,which improves the understanding of the assembly process under multiple input errors,providing guidance for active design to improve the assembly accuracy.The research of this paper also involves the variation of internal stress and contact status of bolt joints,which also provides a theoretical basis for the study of tightening process for bolt group and performance degradation of bolted joint under geometric deviations.