A Novel Method to In-Situ Characterize Fatigue Crack Growth Behavior of Nickel-Based Superalloys By Laser Thermography

BackgroundNickel-based superalloys are key materials for aero-engine hot-end components, and fatigue is one of their most typical failure forms. In the field of fatigue research, in-situ characterization of crack growth behavior is crucial, and more intuitive and accurate characterization methods need to be developed.ObjectiveIn this work, to better understand their fatigue crack growth behavior, we have developed new methods for in-situ characterization of crack growth behavior using laser thermography detection technique.MethodsAccording to the thermal images of sample surfaces captured during the fatigue process, a method for positioning crack tip based on Prewitt edge detection is proposed, and a novel parameter, i.e., the crack opening temperature gradient (COTG), is defined to evaluate the crack closure effect.ResultsBased on the variation characteristics of COTG with load rate, the crack initial opening load rate (CIOLR) and crack opening load ratio (COLR) can be determined under different fatigue cycles. The results show that CIOTG and COTG tend to decrease with increasing fatigue cycles.ConclusionThis work provides a visual and quantitative in-situ method for crack detection and characterization of the crack closure effect in fatigue testing.