Vibration Characteristics Analysis And Crack Identification Of An Aeronautical Hydraulic Straight Pipe With Slant Crack

Aeronautic hydraulic pipeline system is an important channel for medium transmission and energy transmission.The hydraulic pipeline has various shapes,staggered layers,and a large number,and the external load it bears is very complicated.Therefore,the hydraulic pipeline system has become one of the aircraft components with a high failure rate.As an important accessory device of aero-engines,the hazards of cracks in hydraulic pipelines are more serious than general failures.Therefore,the research on the method of establishing the crack model and the method of dynamic modeling of the hydraulic straight pipe system has important scientific research significance and engineering application value.This paper uses a combination of numerical calculation and experimental testing to study the technical problems in the identification of the crack parameters and the analysis of the vibration characteristics of the aeronautic hydraulic straight pipe.The main research contents are as follows:(1)Based on the theory of linear fracture mechanics and the principle of strain energy release,the crack area is discretized into a series of tiny strips that are approximately trapezoidal.Considering the influence of shear force and shear coefficient,the local flexibility coefficient induced by slantcracks under different external forces is derived.Based on Matlab software,the local flexibility coefficient is calculated by numerical integration method,and the influence of crack depth,crack angle and crack position on the local flexibility coefficient is analyzed.It makes up for the gap in the existing local flexibility theory in the analysis of hydraulic pipeline structure cracks,and provides a theoretical basis for the crack detection and vibration characteristics analysis of aero hydraulic straight pipes.(2)According to the deduced expression of the local flexibility coefficient caused by the slant crack,the total flexibility inversion method is used to calculate the stiffness matrix of the crack element,so as to establish the finite element model of aeronautic hydraulic straight pipe with slant crack fault.A modal test study of slant cracked hydraulic pipelines has been carried out.The test results show that the natural frequency obtained by the finite element model established by the local flexibility coefficient is in good agreement with the test value.Through the established finite element model of slant crack aeronautic hydraulic straight pipe,the influence of crack parameters on inherent characteristics is analyzed.The contour map method is used to realize the fault diagnosis of slant crack and the quantitative judgment of position and depth,which provides a new way for the quantitative diagnosis of aeronautic hydraulic pipeline crack fault.(3)Using the dynamic model of the slant crack hydraulic straight pipe established in this paper,the vibration response of the slant crack hydraulic pipeline system is calculated by the Newmark-β numerical integration method.The vibration characteristics of the pipeline under the pump source harmonic excitation are compared with numerical calculation and experimental test.The effects of crack depth,crack angle,and plunger pump speed on the vibration response characteristics are discussed in detail.The results show that as the crack depth increases,the vibration response of the hydraulic straight pipe increases.The vibration response of hydraulic straight pipe is affected by the change of crack angle.The amplitude for vibration response of hydraulic straight pipe is minimum when the crack angle is close to 0°.The larger the crack angle,the more significant the influence of cracks on vibration response of hydraulic straight pipe.Under different rotate speeds,the amplitude for vibration response of hydraulic straight pipe with straight cracks is larger than that with slant ones.