Failure analysis of TGB housings of helicopters

All the three TGB housings had fatigue crack at the fillet of the lug fusing area with the temperature sensor – locating boss. Fractographic and microstructural studies confirmed that the fatigue crack initiation was due to presence of stress raisers at the fillet region. The stress raisers have resulted either during machining or were present in the casting itself. Analysis also shows that the incorporation of the temperature sensor – locating boss had made the lug vulnerable for early fatigue crack initiation. A detailed analysis of the failure is presented in this report. A few recommendations are made for enhancing the fatigue life of the component