Research On Dynamic Characteristics Of A Cracked Rotor And Diagnosis Method Of Crack

With the increasing demand of the industry,large-scale rotating machinery such as aero-engines and gas turbines are gradually developing in the direction of higher speed and power density.The complicated and demanding working environment puts forward higher requirements on the safety and reliability o f equipment.As the core component of the rotating machinery,once the irreversible damage such as wear and crack occurs,it will most likely cause the bending and fracture of the rotor,and even cause damage to the unit,causing serious economic losses and personal safety problems.Therefore,it is of great significance to study the fault characteristics of cracked rotors and extract relevant fault diagnosis criteria.Based on the theory of fracture mechanics,the stress intensity factors caused by cracks are first calculated.By establishing the relationship between stress intensity factor and strain energy release rate,the additional strain energy caused by cracks is obtained by integrating the crack region.The crack unit is obtained by Castingliano’s theorem.The flexibility matrix is added to obtain the stiffness moment of the crack element,and finally the resonance model of the crack is established based on the stress intensity factor zero method.At the same time,the finite element software ABAQUS is used to simulate the respiratory effect of the cracked rotor to verify the accuracy of the theoretical calculation.Considering the weakening of the rotor stiffness caused by the crack unit,the system dynamics equation is established.Taking the modeled aeroengine cantilever rotor as the object,the influence of crack depth,crack position and crack inclination on the dynamic characteristics of the rotor system is studied.The critical characteristics of the rotor and its peak characteristics are summarized.The subcritical resonance resonance of the crack rotor is analyzed.The variation of rotational speed,resonance peak,axial trajectory and acceleration response with crack parameters;the effects of support stiffness and crack element length on the response of cracked rotor system are also considered.Breathing cracks give the rotor a time-varying stiffness and therefore exhibit some nonlinearity.In this paper,based on the basic theory of nonlinear vibration,the nonlinear characteristics of the rotor system under different cracks,eccentricities and deviation angles are analyzed by the phase trajectory diagram,Poincare diagram and bifurcation diagram of the rotor system motion.Finally,the influence of the magnitude and phase of the unbalance force on the dynamic characteristics of the cracked rotor system and the unbalanced forces of different parameters and the mutual dominance between the cracks are studied.Considering the combined resonance phenomenon unique to the nonlinear system,the torsional pulse and the torsion are studied.Coupling dynamic characteristics of cracked rotor under external excitation such as harmonic,axial pulse,axial harmonic excitation and lateral harmonic excitation,and extract relevant rotor crack identification criteria.