Fatigue Assessment of Brazed T-Joints Based on Damage Tolerance Including Residual Stress Effects

The fatigue crack growth behavior of a brazed joint is characterized by a Paris-exponent that is much higher than the one of bulk metals, which means that brazed components have only a short residual fatigue life after the initiation of a fatigue crack. Therefore, the threshold of fatigue crack growth of brazed joints is of particular importance in the fatigue analysis of brazed components and needs to be understood well. Residual stresses have to be considered in crack growth analysis in the threshold regime. The corresponding effects are explored experimentally and theoretically. The stress intensity factors due to the residual stresses in a brazed T-joint of compressor impellers were measured by using the cut compliance method. It was found that residual stresses are present but relatively small. They do not affect the endurance stress significantly. A concept for an endurance analysis of a brazed T-joint that includes imperfections and residual stresses is suggested.