The influence of crack breathing and imbalance orientation angle on the characteristics of the critical speed of a cracked rotor

Muãoz-Abella

Lat. Am. j. solids struct.

et al. 2014

In this paper we present the numerical analysis of the quasi-static behavior of an unbalance cracked shaft with straight and elliptical cracks considering an eccentric mass. The rotation of the shaft has been simulated by considering different angular positions to complete one rotation. The influence of the mass eccentricity in the opening of the crack has been studied considering different angles of eccentricity. The study of the partially opening/closing of the crack in the rotation of the shaft under the influence of the eccentric mass is analyzed. The work allows us to know the influence of the unbalance in the crack breathing mechanism and will help to predict the influence of this behavior on the values of the Stress Intensity Factor and on the propagation of cracks.

Section: Finite Element Model Of a Cracked Shaftmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Quasi-static numerical study of the breathing mechanism of an elliptical crack in an unbalanced rotating shaft

Muãoz-Abella

Lat. Am. j. solids struct.

et al. 2014

“…A few studies have been recommended where the weight-only breathing models may not be suitable for lightweight rotors, vertical rotors or rotors operating around their critical speed of rotation [21,22], as there is significant influence from dynamic loads. Rubio et al [13,17] highlighted the influence of the eccentricity on the breathing behavior in a rotating cracked shaft in terms of crack opening percentage and stress intensity factor.…”

Section: Introductionmentioning

confidence: 99%

Crack breathing behavior of unbalanced rotor system: A Quasi-static numerical analysis

Hossain¹,

Wu²

2018

J. vibroeng.

Abstract. Crack opening and closing during shaft rotation of a cracked rotor system have long been a focus of many previous studies. Previously published modeling work in the literature uses weight-governed crack breathing model for very large rotor systems. However, for lightweight or vertical or lightly damped rotors the opening and closing statuses of a crack are not always weight dominated as there is significant influence from dynamic loads. Further, the dependence of the breathing mechanism on the crack location has not been investigated yet. In this paper, the crack breathing behavior of an unbalanced shaft at the different crack location of a rotating shaft is investigated. A three-dimensional finite element model, consisting of a two-disk rotor with a transverse crack, is used. Finite element model is simulated using ABAQUS/Standard. Crack breathing behavior is found to strongly depend on its axial position, angular position, depth ratio, unbalanced force ratio and angular position. Two different crack breathing regions along the shaft length are identified, where unbalanced shaft stiffness may be larger or smaller than the balanced shaft, depending on the unbalance force orientation, magnitude and crack location. Further, four specific crack locations along the shaft length have been identified, where the crack remains fully closed or open or just behaves like in the balanced shaft. The results suggest that more accurate prediction of the dynamic response of cracked rotors can be expected when the effects of unbalance force and individual rotor physical properties on the crack breathing have been taken into account.

“…Rotating machines are extensively used in industry, such as the compressors, rotors in manufacturing machines, steam and gas turbines, generators, and pumps [12][13][14]. Fatigue cracking of rotor shafts is an important phenomenon that can lead to severe damage and great economic loss if not detected in time, especially for the highly connected and automatic production system in the Industry 4.0 factory.…”

Section: Introductionmentioning

confidence: 99%

Experimental Dynamic Analysis of a Breathing Cracked Rotor

Guo

Yan

Bergman

2017

Chin. J. Mech. Eng.

Crack fault diagnostics plays a critical role for rotating machinery in the traditional and Industry 4.0 factory. In this paper, an experiment is set up to study the dynamic response of a rotor with a breathing crack as it passes through its 1/2, 1/3, 1/4 and 1/5 subcritical speeds. A cracked shaft is made by applying fatigue loads through a three-point bending apparatus and then placed in a rotor testbed. The vibration signals of the testbed during the coasting-up process are collected. Whirl orbit evolution at these subcritical speed zones is analyzed. The Fourier spectra obtained by FFT are used to investigate the internal frequencies corresponding to the typical orbit characteristics. The results show that the appearance of the inner loops and orientation change of whirl orbits in the experiment are agreed well with the theoretical results obtained previously. The presence of higher frequencies 2X, 3X, 4X and 5X in Fourier spectra reveals the causes of subharmonic resonances at these subcritical speed zones. The experimental investigation is more systematic and thorough than previously reported in the literature. The unique dynamic behavior of the orbits and frequency spectra are feasible features for practical crack diagnosis. This paper provides a critical technology support for the self-aware health management of rotating machinery in the Industry 4.0 factory.