Study On Loosening Regular Pattern Of Bolt Connection Of Low Pressure Turbine Shaft And Disc

Aeroengine,a typical high-speed,high-pressure,high-temperature and high-reliability operation characteristic,is known as "the pearl on the industrial crown".Bolt connection has the advantages of simple structure,compact connection,easy assembly and disassembly,So it's widely used in the connection structure of aeroengine.At present,although the low-pressure turbine shaft disc meets the assembly requirements after assembly,but after service,bolt loosening will occur and the connection status does not meet expectations.In order to ensure that the low-pressure turbine shaft disc connection can still meet the requirements after use,it is necessary to have a deeper understanding of the loosening rules of bolt connection after loading.This paper takes the bolt group of low-pressure turbine shaft disc as the research object,mainly from the force analysis of bolt connection,elastic interaction,loosening test and other aspects to explore the loosening rules of bolt connection structure.The research contents are as follows:Firstly,Analysis of the change of force between the end face of bolt and the contact part of thread under dynamic transverse load,and analysis of loosening of single bolt under transverse alternating load based on the concept of critical friction torque.Secondly,because of the high price of the existing single bolt lateral vibration loosening test machine,a single bolt lateral vibration loosening test machine and its supporting system are designed and built,and the single bolt preload is measured directly by the ultrasonic preloading system.The loosening experiments were carried out with preload as variables,and the experimental results were compared with the theoretical results.The accuracy of the theoretical model is verified,and different quantities are taken as independent variables for discrete analysis,and the influence of different independent variables on the loosening of single bolt is obtained.Thirdly,the multi-bolt load is equivalent to the single-bolt load,and the multi-bolt load is equivalent to the single-bolt load.Based on the theory of elastic interaction,the coefficient of interaction between bolts is calculated by the experiment of elastic interaction.Combined with the theoretical model of loosening of single bolt connection structure,the theoretical model of redistribution of pre-tightening force under the influence of interaction after the reduction of pre-tightening force of single bolt in bolt group is obtained.Finally,since there is no experimental equipment for multi-bolt loosening,a multi-bolt tension-bending-torsion combined loading loosening tester and its supporting system are designed and built for flange-type multi-bolt connection.On the basis of the size and load of low-pressure turbine shaft disc,a low-pressure rotor scale specimen is designed,and a multi-bolt tension-bending-torsion combined loading loosening test is carried out on the designed tester.Experiments verify the correctness of the theoretical model and propose the loosening law of multi-bolt connections under load.The above research can provide theoretical reference and experimental conditions for the study of single bolt and multiple bolt loosening.It has theoretical and practical significance to improve the assembly quality of aeroengine bolted structure,and can also provide reference for flange multi-bolt loosening test and research work.