applied fracture mechanics

Fracture Analysis of Generator Fan Blades 321Figure 12. (a) Typical micrograph showing a primary crack initiation site and (b) a crack nucleatingparticle at the origin of the crackFigure 13. Opened crack surface of blade No. 7Crack initiation and growth from the convex side and also decrease in the fatigue region incomparison with the fractured blades, prove that the fluctuation of the stresses and themaximum stress had been highly increased during the accident probably due to excessivevibrations.3.4. Stress analysis of the blades3.4.1. Steady state stressesThe most important stresses acting at the transition radius in the critical cross-section of theairfoils, under normal operating conditions, consist of a tensile stress component due tocentrifugal forces and a bending stress component introduced by the action of the air flowpressure. The tensile stress depends on the rotational speed (N, 50 revolutions persecond), mass of the airfoils (m, 0.51 kg), distance from the center of rotation (r, 0.615 m)