Analysis On Sealing Properties And Vibration Failure Mechanism Of Aviation Ferrule Pipeline Fittings

Aviation hydraulic system is an important mechanical and electrical system,which connects pump source and actuator by high pressure fluid,thus realizing different control tasks of aircraft.Due to its better pressure and impact resistance,as well as good vibration resistance and high reliability,ferrule pipeline fittings is widely used in aviation hydraulic pipeline system.At present,90%of the problems of "running,risking,dripping and leaking,in aviation pipeline system are related to the sealing properties of pipeline fittings,and the problems urgently needed to be solved in engineering are assembly method of pipeline fittings,mechanism of influence of fluid on sealing properties of pipeline fittings,low pressure and no pressure leakage of pipeline fittings,sealing failure of pipeline fittings caused by vibration of pipeline system and vibration fatigue reliability of pipeline fittings.Under the support of 973 project and enterprise cooperation project,aiming at the actual demand of improving sealing properties and vibration fatigue reliability of aero hydraulic ferrule pipeline fittings,the assembly method of pipeline fittings and the influence of high pressure fluid and pulsation fluid on the sealing properties of pipeline fittings are developed based on multi-scale model of pipeline fittings.The fretting fatigue and seal failure mechanism of pipeline fittings are studied under the foundation excitation vibration environment of hydraulic pipeline system.The vibration fatigue reliability of pipeline fittingss is analyzed based on the fatigue test of pipeline fittings.The main research contents and results are as follows.Based on the measured data of the rough surface of each part of pipeline fittings,a multi?scale model of pipeline fittings is established with rough surface,which realizes accurate computation of the sealing properties of pipeline fittings.The sealing properties of pipeline fittings and the influence of the ferrule properties are obtained during the tightening process.Comparing with the tightening test and calculation results during tightening process,the reasonable assembly torque of pipeline fittings is obtained.A multi-scale contact model of pipeline fittings is established considering high pressure pulsating fluid.Based on the calculation of multi-scale model of pipeline fittings,the law of the influence of high pressure pulsating fluid on the sealing properties of pipeline fittings are obtained,and the leakage mechanism of pipeline fittings is revealed after unloading of high pressure fluid,and the assembly method of pipeline fittings is proposed under high pressure fluid.In additon,it can be seen that the sealing area of pipeline fittings increases with the increase of fluid pressure,and high pressure fluid could improve the sealing reliability,the sealing properties of pipeline fittings fluctuates periodically under the action of pulsating fluid and the sealing properties of fittings is limited under the influence of pulsation fluid.Based on the equivalent mass method,the model simplification of complex pipeline fittings system is studied,which provides a concise and accurate research method for vibration properties of complex pipeline fittings system.The validity of the simplified method is verified by experiments.Based on the simplified model of pipeline fittings system,the vibration stress response of pipeline fittings dangerous points is obtained by calculation and test.The cyclic vibration load of dangerous points of pipeline fittings system is defined under vibration environment,which provides the load for next chapter.The vibration failure mechanism of pipeline fittings is explored under vibration environment.The evolution process of vibration failure of pipeline fittings is obtained based on the accelerated vibration test of pipeline fittings system,which reveales the fretting fatigue of pipeline fittings is the main cause of seal failure.Then,the load of pipeline fittings under vibration conditions is taken as load input variable,and the statistical results of vibration fatigue test data of pipeline fittings is taken as strength input variable.Based on the concept of minimum order statistics,a reliability model for pipeline fittings is established under vibration load,and the statistical processing method of random truncation data is used to verify the reliability model of pipeline fittings.In view of the structural properties and sealing forms of ferrule pipeline fittings,a multi-scale contact model is proposed for analyzing the sealing properties of pipeline fittings.The influence of high pressure pulsating fluid on the sealing properties of pipeline fittings is clarified,and the assembly method of pipeline fittings is achieved under high pressure fluid.The vibration failure mechanism of pipeline fittings is revealed.A reliability model for predicting pipeline fittings system is established under vibration load.This paper provides a scientific basis and reference for the practical application of pipeline fittings by combining theory with experiment.