| 摘要 |
PURPOSE:To improve the reliability of a fatigue test by saturating the periphery of a cracking magnetically with a DC magnetic field and detecting magnetic flux from the cracking part. CONSTITUTION:A DC power source 5 supplies a current to an exciting coil 4 to saturate the periphery of the cut part 1b of the test-piece 1 magnetically. Here, magnetic flux leaks from the bottom surface of the cut part 1b or a test-piece part forming the cracking, but a load is placed repeatedly to vary the shape of the cracking, so the leaking magnetic flux varies, and consequently voltages are induced across sensor coils 61-6n. Their signals are amplified by amplifiers 71-7n and inputted to LPFs 81-8n, but their AC components, i.e. repeatedly applied frequency components of the load are removed to obtain only a DC component regarding the depth of the cracking. Then a computing element 9 reads this signal and then calculates the cracking depth from an input signal from a table to obtain the depth of the cracking position corresponding to the respective coils, so that it is recorded on a recorder 10. Thus, the reliability of the fatigue test is improved.
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