抄録
This paper describes surface crack detection by the alternating current potential drop (ACPD) method. A. C. potentials were measured for SUS304 and SS400 cracked specimens from 50Hz to 5kHz. The variation of potential with crack depth using sinusoidal a. c. for SUS304 did not depend on the frequency, but it did for SS400. The potential ratio measured using sinusoidal a. c. precisely agreed with that using rectangular a. c. in which a. c. potentials at many frequencies could be obtained by one measurement utilizing fast Fourier transformation. The increase in potential with increasing crack depth in experiments agreed with that calculated by the finite element method taking account of the skin effect.
