Study On Fatigue Test And Stress Control Techniques Of Aircraft Hydraulic Pipelines

The aircraft hydraulic system piping vibration problem is the main problem that always troublesthe technical staff. With a new generation of aircraft hydraulic system pressure getting higher andhigher, the flow getting larger and larger, and the structure getting more and more complex, theproblem is getting increasingly outstanding. Many aircrafts at home and abroad have had a similarfailure. Currently, in the development process of the new aircraft, the faults such as pipe breakage andoil leak at pipe joint are very frequent. According to the statistical information, the piping fault hasbecome the main fault of aircraft failure.To avoid the fatigue cracks produced in the pipe use, and to improve the aircraft security andreliability, fatigue test research for pipe is studied in this paper, such as the assembly quality testingand evaluation, as well as research work for pipe vibration suppression and some other aspects, themain results are as follows:（1）The failure rules caused by fatigue is studied to improve the fatigue strength of the materialin order to avoid or delay the occurrence of fatigue damage. The fatigue test for the aircraft pipematerial LF2M is conducted. The S-N curve is plotted and the fatigue limit of the material is obtained.The material fatigue limit is amended, and the fatigue limit of the pipe structure is obtained. Then, thefatigue test for real pipe is carried out, and the two results are compared. The results shows thatfatigue limit of aircraft piping design should refer to the experimental results.（2）First, the simulation analysis for assembling stress of pipe is carried out, in order to figureout the change of the pipe modal frequency caused by assembling stress. Then the simulationexperiment for assembling stress of pipe and the modal test are carried out, in order to verify theeffect law of assembling stress on pipe modal frequency. Finally, the natural frequency test on theactual aircraft pipe is conducted by means of hammering method, and the results show that theassembling stress of pipe has certain influence on pipe modal frequency.（3）Based on the dynamic vibration absorber thought, a new spring type of dynamic vibrationabsorber for pipe system vibration attenuation is designed. First the structure is designed and theparameters of the vibration absorber are selected. Then the finite element model of the pipeline systemis set up to analyze the harmonic response of before and after the installation of the damper. Finally,the experimental verification is conducted.