The Distribution Mechanism On Preload Of Bolt Group And Modal Characteristics Of Low Pressure Turbine Shaft And Disc

The performance of bolt assembly between the low pressure turbine shaft and disc is directly related to the assembly performance and the operation of the whole machine.And the connection effect of bolt group is related to many factors,including the size of the connecting parts,material of the connecting parts and the bolts,the tightening process of the bolt group,etc.The control precision and the distribution uniformity of bolt preload are the key points of the whole bolt assembly.Because of the large number of connecting bolts between the aero engine shaft and disc and great pretension of bolts,the elastic interaction between bolts has a certain influence on the residual preload of bolts.Because of these connection characteristics,the performance of bolt connection can't be ignored in the dynamic analysis,and it needs an effective and feasible method to equal the dynamic characteristics of bolt group connection,in order to improve the accuracy of the calculation results of the whole dynamic connections.This paper is divided into four parts.The first and second part is about the elastic interaction in the process of bolt assembly.The third and fourth part is about the influence of the equivalent treatment of the bolted joints on the dynamic characteristics of the shaft,and the influence of the different preload on the mode characteristics of the discThe second chapter,based on the study of the elastic interaction mechanism and the actual project,an interaction model of multi axis bolt tightening process is established in accordance with the elastic deformation compatibility condition.In addition,in order to improve the accuracy of the dynamic calculation of the multi bolt joints,considering the influence of the bolted joint surface,the dynamic model is established.The distribution law of contact stress of bolt joint surface is analyzed,and the basic theory of modal analysis is introduced.The third chapter,the bolt connection structure model of shaft and disc is established in the finite element.The influence of the material properties,the size of the disc,the distribution of the bolt holes,the tightening process,and the constraint of the disc on the elastic interaction between the bolted joints are analyzed qualitatively by means of numerical simulation.In this project,the assembly bench of the low pressure turbine shaft and disc of the aero engine is set up,in order to verify the elastic interaction mechanism between the bolt groups,and analyze the influence of elastic interaction on the residual preload of bolt group.The fifth chapter,the dynamic model of bolted joint surface is established based on the related theory.The measured surface pressure is further converted into the equivalent stiffness of bolted joint.And then plug it into the spring-damping unit of the model.Finally,the simulation results of the finite element model are compared with the experimental data to verify the feasibility and accuracy of the equivalent treatment of the stiffness of bolted joints by the spring-damping element method,and correctness of the stiffness of joint surface calculated by the actual surface pressure.The sixth chapter,the relationship between bolt preload and the stiffness of joint surface is established based on related theory.The effects of the stiffness and the distribution of the bolted joint surface on the modal frequencies are analyzed.And the effects of different fastening processes on the dynamic characteristics of the low pressure turbine shaft and disc were tested.