Detecting Fatigue Crack Initiation by Strain Interference Method. (IV). Monitoring Fatigue Crack Initiation by Strain Information.

Usually, the fracture accident of a machine equipment originates in the notched section. However, it is very difficult to monitor the fatigue crack initiation for all parts of the machine equipment. In this study, a method of detecting and monitoring fatigue crack initiation in the notched section of running machine equipment is proposed. Fatigue crack initiation can easily be detected by the observation and analysis of the waveform of the strain function composed of the strains in the vicinity of the notch, because the waveform of the strain changes its shape after the crack initiation. In the present study, the crack initiation under the constant or fluctuating stress amplitude was monitored using the specimen with a small hole. It was found that the crack initiation can be detected when the crack length reaches about 1mm.