交流電位差法による短い表面き裂長さの測定

抄録

An alternating current (ac) potential technique was developed for the measurement of short surface cracks in smooth specimens of a ferromagnetic material. For a constant crack length, the potential difference (E₀) between two probes located across the crack was found to be directly proportional to the operating ac frequency. The relation between E₀ and crack length (α) changed specimen by specimen, because the value of E₀ was very sensitive to placement of lead wires for potential measurement. The relation of ΔE₀(=E₀-E_0I) vs. a, however, was uniquely determined, independent of specimen, where E_0i Was the potential difference for a reference crack length, e. g., initial crack length. Therefore, surface crack lengths were able to be determined through the equation for ΔE₀ vs. a. Best accuracy was obtained for the operating ac frequency of 2 kHz in this study. In fatigue crack growth tests, the potential difference (E) was found to be a function of loading conditions. In this case, the crack length was calculated with good accuracy through the equation for ΔE₀ vs. a by substituting ΔE (=E-E_i) for ΔE₀, where E was the potential difference under loading, and E_i was the value at reference crack length.