An inspection of fatigue crack extension based on strain information

Detection of fatigue crack initiation and growth behavior of a blind holed specimen is carried out by means of the strain interference method. The strains on the center axis of the hole are used for the determination of the strain function h. The crack initiation can be detected using the waveform of the strain function h. The waveform of h of the precracking can be distinguished from that of the postcracking. The depth of penetration of the crack into the specimen thickness can also be inspected using the waveform of the strain function h. Such variations of the waveform are based on the crack tip opening and closing behavior. Furthermore, the approximate estimation of crack length is carried out using the waveform of the strain function hh measured at the maximum stress point.