Computational Analysis of Fatigue Crack Growth based on Stress Intensity Factor Approach in Axial Flow Compressor Blades

Gas turbine compressor blades are subjected to centrifugal, gas bending and vibratory loads. This repeated loading and unloading can reduce the life of compressor blades. This research aims at the estimation of fatigue crack growth and fatigue life of various three dimensional crack in a compressor blade considering the stress intensity factor calculations for a half-elliptical crack, subjected to centrifugal loading. Static stress analysis was carried out to ascertain the critical region or crack zone of the blade. The maximum Von - Mises stress was found at the fillet region near the root of the blade, the predicted state of stress has helped in identifying the region of singularity which may lead to crack initiation. Finite Element Method was used to evaluate the range of stress intensity factor solutions in the blade with a half-elliptical flaw. Semi-elliptical crack lengths ranging from 0.2 mm to 6 mm were considered in the crack zone. Stress intensity factor was evaluated for different rotational velocity of 5000, 10000 and 20000 rpm. The stress intensity factor range obtained is employed to predict fatigue crack growth behavior and fatigue crack life estimation by using Paris law. The maximum Mode I stress intensity factor of 61.4 Mpa√m was found at the surface interception point, for a crack length of 6 mm and crack depth of 2.4 mm. With the increase in rotational velocity of 5000 rpm, 10000 rpm and 20000 rpm, fatigue crack length growth rate was estimated to be and 1.95 x 10-09, 1.65 x 10-07 m/cycle and 4.15 x 10-05 m/cycle and the fatigue crack propagation life was estimated to be of 4.3 x 108 cycles, 7.3 x 106 cycles and 5 x 103 cycles respectively. It was concluded that at the surface crack interception point, fatigue crack growth rate increases with increase in crack depth and the fatigue crack propagation life tends to decrease with increase in the rotational velocity of the compressor blade.