Acoustic Emission during Fatigue Testing of Pressure Vessels

It is known that the basic mechanism of fatigue crack growth in ductile pressure vessel steels, which is repetitive blunting and re-sharpening of the crack tip, is a weak acoustic emission (AE) source. On the other hand, a large number of AE events occur during cyclic crack growth. Most AE events are caused by repetitive friction at the fracture surfaces, but these AE events show relatively weak correlation with the crack growth velocity. In the paper it is shown, based on examples – fatigue crack growth starting from an artificial weld defect, cycling of a natural crack defect, crack initiation and growth in gas cylinders - which information can be gained by relatively simple analyses of the AE data from cyclic pressure tests.