Study on the Fundamental Characteristics of the Θ Probe and Crack Monitoring Using This Probe Combined with the Caustic Method

概要

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The new Θ probe, which is used in eddy current testing, has various advantages compared to previous probes. In the present study, the fundamental characteristics of this probe are first investigated using commercially available aluminum plates. The effects of liftoff and the angle between the detecting coil and the flaw on the flaw signal are then clarified. The effects of the flaw dimensions on the flaw signal are also investigated, and it is shown that the amplitude reaches a constant value for a flaw depth of H>8 mm, a flaw width of W>7 mm, and a flaw length of L>20 mm, within the experimental conditions of the present study. Next, the monitoring of crack initiation under static loading and crack growth under the low cycle fatigue condition in the duralumin plates is attempted by applying the Θ probe combined with the caustic method. It is shown that the signal amplitude can be obtained when fracture is initiated under static loading. In addition, in the A7075 plate, the amplitude is increased at the fatigue crack growth rate of da/dN larger than 0.017 mm/cycle. Consequently, the possibility of crack monitoring using the Θ probe is confirmed.