A Detection Method of Overloading History during Fatigue Crack Propagation Stage

In the present study a detection method of an overload application during stress cycles under constant amplitude was investigated. Also, the effect of a tensile overload was shown at three stress ratios: R = 0, -1.5, in order to understand the effects of R on crack propagation after an overload. At a baseline of R = 0, after an overload retardation in the crack propagation was observed. However, in the case of R = -1.5, the fatigue crack growth rate actually accelerated after a tensile overload. That behavior of crack propagation was tried to be detected by the information of strain waveform h; h = εy + 1.2λεx, where, εy and εx are the local strains at the specimen axis, and λ is the strain range ratio Δεy/Δεx. The waveform shape of h was changed after the overloading. Also, the application of an overload can be detected by the variation of the strain range ratio λ. Specially, the present method is useful for cases of the crack propagation stage under negative R conditions.