THE STRESS-STRAIN STATE AND DURATION UNTIL FRACTURE OF ROTATING DISKS IN CREEP
The stress-strain state and duration until fracture are calculated for a two-stage behavior of a rotating disk with a hyperbolic surface shape under creep. The first stage is the damage accumulation and beginning of fracture in a certain body’s area where the accumulated damage reaches a critical value. The second stage is the fracture front spreading and a complete destruction of the body. It is assumed that the fracture front propagates axisymmetrically, the fracture is brittle. The calculation method consists in the fact that the unsteady creep problem is reduced to a similar problem within the assumption of a steady material creep. In order to obtain a valid solution, it is necessary to multiply the known solution of the steady creep by some functions of the coordinates and time. To find these functions, we obtain the corresponding system of equations. We investigate the duration of stages depending on the creep kinetic theory version in the statement of Yu.N. Rabotnov and L.M. Kachanov. According to the calculations, the dependence of the second stage duration to the first stage duration can be from tenth to several tens of percent depending on the applied load, the surface shape and the size of the inner hole of the disc. With a decrease in the radius of the disc’s inner hole, the second stage duration can be comparable with the first one. In all the studied cases the first stage duration in the Rabotnov’s model is higher than on the Kachanov’s one; the dependence of the second and the first stage duration in the Rabotnov’s model is smaller than in the first stage of the Kachanov’s model. The analysis of the fracture front movement showed that the main time of the second stage (about 75-85 % according to the Kachanov’s model and 85-90 % according to the Rabotnov’s model) is 20 % of the working part of the disk radius.