At present, the general NDT method (nondestructive testing) centers around the testing processes, instruments and criteria of the defects which have already yielded and developed into large cracks. Needless to say, the present NDT is insufficient with regard to the inspection of fatigue cracks because from the analysis of LEED, RHEED and AES, it is known that fatigue crack sources are tiny, sometimes even with no initial observable signs. When external forces are exerted, however, they will develop into cracks in a short period of time and bring about the break of metals.

We have come to find out that the phenomenon of partial separation in metals, which refers to the over-concentration of chemical composition and the variation of metal structures, would arouse fatigue cracks. Therefore, the partial separation area may in a sense, be regarded as one of the fatigue crack sources and its early inspection will, in a certain degree, prevent unexpected disasters from taking place.

This humble article aims at the research for partial separation areas by means of various methods, such as sound resistance, conductivity rate, magnetic conductivity rate and the variation of B-H curves.