Fracture Mechanics Analysis and Fatigue Crack Growth Life Assessment for a Gas Turbine Blade Using FEM

In this paper, the fracture analysis and fatigue crack growth life assessment for a gas turbine blade of the hot gas path is studied. At first, applying FEM analysis using ANSYS software, the stress analysis for the turbine balde with no crack in the case of of steady state full load condition has been performed. In this way, thermomechanical loadings, i.e., rotational speed, temperature and pressure distributions are all included in the analysis. From the outcome results the critical regions on the blade airfoil surfaces having high stresses are recognized. Then, after modeling the crack in these regions the fatigue crack growth life assement analysis has be done. To do this, using ANSYS software the crack stress intensity factors (KI) for the cracks with different dimensions has been calculated. Having on hand the obtained values for KI in conjucture with the specified graph for the crack growth rate, i.e., (da/dN) vs. the.crack intensity factor for the blade material, the cyclic crack growth rate for the cracks with different dimension ratios (a/c) can be obtained. Finally, using numerical integration method, the number of cyles Nf to reach the critical crack depth value (af) for the turbine balde has been calculated.