Generation of POD curves in the absence of service-induced cracked components – an experimental approach

Assessing the reliability of non-destructive testing (NDT) techniques in detecting in-service fatigue cracks is vital for ensuring the structural integrity of aero engines. However, the requirement of a large number of in-service failed components with numerous initiating fatigue cracks makes it a cost-intensive methodology. Hence, laboratory samples with electrical discharge machined (EDM) notches representing fatigue cracks have also been used for NDT reliability studies. However, probability of detection (POD), a measure of NDT reliability, is usually a function of all crack dimensions rather than only length. This limits the applicability of EDM notches (minimum width of notch ~0.3 mm) as artificial fatigue cracks for POD studies. The current study demonstrates the methodology of generating cracks under laboratory conditions in nickel-based superalloy samples (representative aero engine material), mimicking in-service conditions such as crack tightness as low as 1 μm, crack tortuosity, transgranular nature, crack branching and multiple initiation sites of cracks. POD curves generated using these samples are demonstrated and the feasibility of this approach is discussed.