Contact Of Crack Edges Research Articles

Simulation of the Propagation of Circumferential Crack in the Cylindrical Element Structure Exposed to Cyclic Loadings

The purpose of these studies was to work out the methods for the computation of crack development in the plate and axisymmetric elements of structures at cyclic loading for the plasto-elastic arrangement using the conception of the accumulation of scattered damages in the material. In the domain in question, we simulated the processes of alternating-sign plasto-elastic deformation and the material crack resistance was estimated using the fatigue test data for smooth specimens. Thermal and elastically-deformed states of the structure were determined for different loading modes using the finite elements method. The material damageability was assessed for the curves of low-cycle fatigue and for the range of plasto-elastic deformations on the route of probable crack propagation using the hypothesis of linear summation. As soon as a critical value of the damageability is achieved the crack is propagated stepwise for the specified step. As an example, consideration was given to the kinetics of circumferential crack in the cylindrical element exposed to the axial-symmetric cyclic loading. The contact of crack edges was taken into consideration for compressing loading semicycles. The obtained data agree with the data obtained using the Newman method. The suggested technique can be used for the estimation of survivability of the elements of steam turbines (heat rotor grooves at start-up-stop modes, blade and disk interlocks, etc.).

Deformation and Vibration-Induced Stress Intensity of a High-Temperature Turbine Rotor with a Breathing Transverse Crack

The vibrations of a double-seat weighty rotor of the steam turbine with a breathing transverse crack are examined in the field of operating environment temperatures. The 3D vibration model for the rotor with a breathing transverse crack is applied. The variable two-dimensional temperature field is found from the solution of nonstationary heat transfer problem. Its effect on the contact of crack edges on rotor vibrations was evaluated. The distribution of stress intensity factors along the crack front was established for different rotor positions. Fatigue crack extension modes are assessed.

Domain decomposition method for a model crack problem with a possible contact of crack edges

The scalar Poisson equation is considered in a domain having a cut with unilateral constraints specified on its edges. An iterative method is proposed for solving the problem. The method is based on domain decomposition and the Uzawa algorithm for finding a saddle point of the Lagrangian. According to the method, the original domain is divided into two subdomains and a linear problem for Poisson’s equation is solved in each of them at every iteration step. The solution in one domain is related to that in the other by two Lagrange multipliers: one is used to match the solutions, and the other, to satisfy the unilateral constraint. Examples of the numerical solution of the problem are given.