Localization of Dwell Fatigue Cracks in Ti‐6242 Alloy Samples

An in‐situ ultrasonic guided wave technique is employed for real‐time monitoring of crack initiation and evolution during dwell, cyclic fatigue and creep tests of Ti‐6242 alloy samples. Ultrasonic signals are acquired continuously during the test at different levels of fatigue load using a high‐speed data acquisition system. The initiation time and growth history of primary and multiple secondary cracks are assessed. Localization of the secondary cracks is performed by both the in‐situ ultrasonic method and an ultrasonic immersion scanning method which we call “vertical C‐scan” (VC scan). The VC scan is developed for imaging small cracks aligned normal to the fatigue sample axis. The fusion of ultrasonic and microradiographic images exhibits good agreement in crack location. Joint use of the three techniques provides location, shape, and size of the secondary cracks.