Fatigue crack growth prediction in a gas turbine casing

Some gas turbines casings are very susceptible to involve cracking in critical points. According to studies, thermal fatigue specified as the main reason of creation of cracks. This approach is to predict the fatigue life of the detected crack on the edge of eccentric pin hole of a heavy duty gas turbine casing, which is one of the most probable positions for crack initiation and propagation. The crack position and direction was determined, by using non-destructive tests. Distribution of outer surface temperature was measured by using thermography method and for the measurement of inner surface ten thermocouples were installed inside the casing wall. The temperature data was applied as boundary condition in finite element simulation by using Abaqus software. Stress distribution of the casing was calculated in accord to engine work cycle and then, fatigue crack growth was predicted by using ZENCRACK fracture mechanics code. The analysis results showed that the crack growth rate will decrease gradually and after periods of time while stress intensity factor values will reach the Threshold value, the crack propagation will stop. CTOD and J-Integral methods were implemented for calculating the fracture mechanics quantities and Paris model was used to estimate the fatigue life.