Abstract
Fatigue crack in a rotary shaft is a common failure observed in rotor systems. Since vibration of the shaft causes alternating fatigue loads, the crack propagates slowly. Meanwhile, the propagating crack may cause nonlinear or unstable vibration of the rotor system. In fact, growth of the crack and vibration of the shaft are coupled with each other. Hence, it is necessary to study the fatigue degradation behavior of the cracked rotor accounting for this coupling effect. In this paper, a coupling model of rotor vibration and crack growth is established through dynamic theory and fracture mechanics, and a sequential iterative procedure is proposed to solve the coupling model. Then, the competing degradation failure mode of the cracked rotor is analyzed with regard to the rapid crack growth failure and the unstable vibration failure. And degradation measures are proposed based on the competing degradation failure criterion. At last, degradation behaviors with the coupling effect of nonlinear vibration behavior and multiple parameters including rotation speed, unbalance eccentricity and orientation angle, and damping are investigated by numerical simulation. The results indicate that nonlinear vibration behavior and multiple parameters have considerable influence on the degradation behaviors, which present complex regularity. The findings are of significance to guide the safety design of the rotor system for long time operation and help to the further research on prognostics and lifetime prediction.
Highlights
Rotary machinery is a kind of common mechanical structure, which is widely used in industry equipments
Because of the rotary motion, the rotor suffers from the alternating fatigue loads. e initiation and further propagation of the fatigue crack are caused subsequently. e presence and propagation of the crack lead to nonlinear, complicated, or even unstable vibration behavior and the performance degradation of the rotor, which may cause severe damage to mechanical components or even catastrophic accidents
It is difficult to provide simplified experience formulas illustrating the complex relationship between the crack size and the system stiffness and the relationship between the vibration responses and the fatigue loads. ese relationships are required to be revealed by corresponding physical models. erefore, with all the above considerations, it is of great significance to establish a specific and applicable fast-slow coupling model of the cracked rotor and to analyze the degradation behavior with the coupling effect of nonlinear vibration behavior and multiple parameters
Summary
Rotary machinery is a kind of common mechanical structure, which is widely used in industry equipments. Crack growth causes slow decrease of the stiffness and variation of the dynamic characteristics of a cracked rotor system, which leads to fatigue degradation. Erefore, with all the above considerations, it is of great significance to establish a specific and applicable fast-slow coupling model of the cracked rotor and to analyze the degradation behavior with the coupling effect of nonlinear vibration behavior and multiple parameters. One is to establish the fast-slow coupling model accounting for nonlinear dynamics of the cracked rotor and the fatigue propagation of the transverse surface crack. En, the degradation measure of the cracked rotor is defined based on the competing degradation failure criterion which accounts for both the unstable vibration of the rotor and the rapid growth of the crack. The degradation behaviors with the coupling effect of multiple parameters of the rotor system including rotation speed, unbalance eccentricity and orientation angle, and damping are analyzed through numerical simulation and several new findings are reported
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