Breathing characteristics of rotor cracks based on time-varying centroid position.

On the basis of material and fracture mechanics theory, the flexible matrix and stiffness matrix of crack elements are derived using the strain energy release rate and the Timoshenko beam element model of six degrees of freedom. In accordance with the geometric relationship between the opening and closing of crack, time-varying centroid coordinates of the crack are fixed by neutral axis theory, and the position of the crack closing line is obtained depending on the time-varying centroid coordinates, which describe the crack's breathing characteristics. On this basis, a time-varying centroid coordinate model is proposed and compared with the sinusoidal model, the Gaozhu model, and the zero-stress intensity factor model. Results show that the proposed model has more coupling characteristics. Finally, the flexibility matrix of oblique, straight, and semielliptical crack elements is derived, and the breathing mechanism of three kinds of cracks is studied. [ABSTRACT FROM AUTHOR]