Stress Intensity Factor Calculations for the Compressor Blade with Half-Elliptical Surface Crack Using Raju-Newman Solution

This paper presents results of the stress intensity factor calculations for the compressor blade including a half-elliptical crack, subjected to vibration. In this analysis, the Raju-Newman empirical solution for stress intensity factor calculations in the rectangular plate with a half-elliptical flaw was used. The bending stress used in the Raju-Newman solution was computed for the real blade using the finite element method. The K-factor values were calculated only at one point of the crack front, where the crack tip contacts the free surface, because the crack length during experimental investigations was measured just in this direction. In order to determine the stress intensity factors for different crack sizes, ten diverse flaws in the blade were defined. Results of the experimental fatigue tests performed for the blade without preliminary defects showed that the cracks developed from the convex blade surface. On the blade fracture, the beach marks typical of the fatigue damage were visible. The dimensions of cracks in the rectangular plate were defined based on the beach marks shape. In the next part of the work, the stress intensity factor values were used as an input data into the Paris-Erdogan equation. As a result of this calculation, the crack growth rate for the compressor blade vibrating at constant amplitude was estimated. The results obtained were finally compared with the results of the experimental crack growth analysis performed for 1st stage compressor blades of the helicopter turbo-engine.