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PROPOSED METHOD OF CORRECTING MAGNETIC RECORDING BORESCOPE RESULTS FOR DETECTOR LIFT-OFF VARIATIONS
ARMY MATERIALS AND MECHANICS RESEARCH CENTER WATERTOWN MA
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The functional dependence of leakage field strength, associated with a crack-type defect, on the distance from the crack has been experimentally determined. Field strength measurements were used to generate empirical expressions relating the leakage field strength to lift-off distance. Equations were written for the normal and horizontal field components and the partial derivative of the horizontal component of the field strength with respect to horizontal distance from the crack, based on the assumption of a semicircular field pattern. Comparison of calculated values and the experimental data demonstrated that, over the range of interest, the semicircular field assumption adequately describes the field. Results of the analysis of the leakage field surrounding a crack suggested a method of correcting for the uncontrollable variations in lift-off which occur during magnetic recording borescope inspection of large caliber gun tubes. Curves required to make these corrections have been established for two specific types of detectors and a procedure for making the correction utilizing these curves is presented. Practical application of the correction to gun tube inspection is considered.
APPROVED FOR PUBLIC RELEASE