The technique of using a Hall generator to plot the flux-leakage due to flaws was established in Frankford Arsenal Report No. R-1581 of February 1961, "Investigation of Hall-Effect Devices for Flaw Detec¬tion in Ferrous Materials". This effort was extended to study artificial flaws simulating the random slopes and depths encountered in real sur¬face cracks. Improvements have been developed in the test instrumenta¬tion to allow photographic records to be made via cathode-ray oscilloscope presentations. Determination of vertical flaw depths greater than 30 mil* was found to be feasible as in earlier studies. The direction of flaw in¬clination from the vertical can be determined exactly; the actual angle of inclination can be only roughly determined for all cases. As. exact indication of flaw angle was obtained in about 24% of the cases where the flaw specimens were nearly perfect.
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