Department of Mathematics Colloquium

University of Idaho

Fall 2011
Thursday,  September 1, 3:30-4:20pm, room TLC 030

Refreshments in Brink 305 at 3:00 p.m.

Numerical modeling of creep deformation and fracture
in heat-resistant steels


Gabriel Potirniche

Mechanical Engineering Department

University of Idaho


Heat-resistant alloys are used extensively in coal-fired power plants, as gas turbine materials for gas-fired power plants, or as reactor internals for nuclear power plants. With increasing demands imposed on structural materials operating at high temperatures, there is a growing need to predict the service life and reliability of components experiencing creep deformation and fracture. In this presentation two numerical models for the creep deformation and fracture of Cr-Mo heat resistant steels are introduced.

The first approach is strip-yield modeling, which is a numerical method to simulate crack growth under constant or variable amplitude loading. A numerical strip-yield model was developed to simulate creep crack incubation in heat-resistant steels. The time evolution of the plastic deformation ahead of a crack loaded in tension is modeled using a stress power law for the steady state creep stage. The evolution with time of the crack-tip plastic zone, crack-tip opening displacement and yield strength in the plastic zone are computed at constant temperature for center-crack panels.

The second approach is a micromechanical model developed for the evaluation of creep deformation and rupture times of modified Cr-Mo steels. Creep deformation in metallic materials is generally induced by the dislocation generation, motion, and annihilation. The evolution of dislocation density in the crystalline lattice was modeled by considering the generation and annihilation of single and dipole dislocations. In addition to the dislocation motion as a basis for creep deformation, there are other factors which are involved in the creep resistance of this type of steel. Among these, the most significant are precipitate coarsening, changes in the concentration of the solid solutions, void nucleation and crack formation. The evolution of these mechanisms during creep deformation was modeled by introducing specific continuum damage equations. Creep tests were also performed at several stress and temperature levels. The comparison of the numerical model results with the experimental data shows satisfactory agreement.