Internal fatigue crack propagation in a Ti-6Al-4V alloy: An in situ study

Environment effect on internal fatigue crack propagation studied with in-situ X-ray microtomography

“…In order to ensure internal crack initiation but also to know its precise location (to facilitate the µCT observation), an artificial internal notch is inserted inside the specimen by following the procedure described by [18,19]. It is also possible to add a narrow path -which is called chimney in the rest of this paper -to link the notch to the surface of the specimen to bring air to the internal notch.…”

“…It is also possible to add a narrow path -which is called chimney in the rest of this paper -to link the notch to the surface of the specimen to bring air to the internal notch. Discussion on the level of vacuum in the artificial notch with and without the optional laser-drilled chimney can be found in [19]. The notching procedure is illustrated in Figure 3 and the list of tested specimens is available in Table 2.…”

“…• One half-sheet is notched with the use of a femtosecond laser (which produces short and reduced interaction with the material) as described in [19]. This The notch dimensions are approximately 300×120×20 𝜇m (cf.…”

“…[41] have followed a crack that initiated from an internal casting defect in an Al alloy and [30] could detect an internal crack initiation from an inclusion in a Ni-based super-alloy also with this method. The present work is based on the experimental protocols presented by [27,18,19] who could observe internal crack propagation in a casting Al alloy and a Ti64 alloy using an in-situ synchrotron µCT technique.…”

“…To evaluate the influence of the environment, this study combines the artificial internal notch procedure described in [19] and the ultrasonic in-situ synchrotron setup developed by [27]. The artificial internal notches are known to be under vacuum conditions [18] unless a path is added to link the initiation site to the surface in order to bring air to the propagating crack [40].…”