Acoustic emission (AE) is a widely used non-destructive technique for real time monitoring. Over the past decades it has been used as an effective technique for the detection, characterization and location of fatigue cracks. The basic principle is based on the elastic energy emitted from crack propagation incidents under stress. The emitted elastic wave propagates through the continuous media and it is detected by sensors attached on the surface of the material. Fatigue cracks are one of the important damage phenomena in metallic structures in aerospace applications. Fatigue life under cyclic loading consists of three stages: stage I (crack nucleation), stage II (crack propagation) and stage III (failure). In this study, the fatigue crack propagation of Ti6Al- 4V four-point bending test specimens is studied during stage II. Two test specimens are used for this study, one corner notched sample and one unnotched sample. In order to monitor the crack propagation, two AE piezoelectric sensors are placed on one side of the specimen and crack propagation gauges are placed on the damage location areas as verification. The rate and the location of the recorded events is in good correlation to the crack growth rate and the position of the crack showing the potential of using AE for fatigue monitoring of this kind of test. Other AE parameters are also studied with respect to their efficiency for characterizing crack propagation, though care should always be taken for reflections and dispersion which inevitably distort the acoustic signals.
doi: 10.12783/SHM2015/186