Creep-fatigue Crack Growth Rate Of P91 Steel And Growth Behavior Reserch

The engineering components used in such applications as power plants, petrochemical plants and aerospace systems operate cyclically. The operating cycle for these components typically consists of a startup phase followed by continuous high temperature operation under sustained load and eventually shutdown. The creep fatigue crack growth is a critical issue in the residual life assessment of such components. For the above problem, this topic take P91 steel as the research object, focus on two influence factors of creep-fatigue crack propagation:hold time and load frequency. On one hand, using high temperature damage mechanics, creep-fatigue crack propagation damage model was constructed, and compared with the corresponding experimental data and research the influence of hold time on creep-fatigue crack growth rate. On the other hand, through test research, analysis the effects of loading frequency on high temperature fatigue crack propagation rate.The main work and conclusions are summarized as follows:1) Based on damage mechanics, by modifying the Chaboche proposed stress controlled fatigue damage model, so it can describe the fatigue crack tip damage Df. Using ductility exhaustion theory describe the, the crack tip damage(Dc) under creep mechanism. When Dc and Df satisfy a certain mathematical relationship, creep-fatigue damage of the crack tip reaches the critical value. Creep-fatigue crack extend a unit, creep and fatigue crack propagation rate prediction model was got.For the established creep-fatigue crack growth rate forecast model, developed the corresponding creep- fatigue crack propagation simulation subroutines. Using Abaqus simulate P91 steel under 625 ℃ creep- fatigue crack growth rate for different hold time, and the creep-fatigue crack growth tests compared the simulate resulting rate, the results show good agreement between the simulate rate and test rate. This verified the validity of the model.2) Found that the crack growth rate increases with hold time. Comparative analysis of different fracture parameters association with creep- fatigue crack growth rate, discovery that (Ct)avg can be used for correlating crack growth rate. The crack propagation rate curves of fatigue/creep interaction at 625 ℃ could well be described by Saxena model under the condition of this test. This can be estimated high hold time or low hold time creep- fatigue crack growth rate3) Take P91 as the research object, test the effects of loading frequency on high temperature fatigue crack growth rate. Discovery that high temperature fatigue crack growth rate increases with decreasing load frequency. The high-temperature fatigue crack growth rate da/dN transform into (da/dt)nominai·Consider the influence of loading frequency on high temperature fatigue crack growth rate was got.