磁気ひずみ効果を利用した残留応力測定に関する研究

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Macroscopic analysis of initial and residual stress is necessary for design and inspection of steel structures for safety's sake. The X-ray method has been employed for such analysis, though it requires extensive experience and high skill together with rather expensive apparatus. A magnetic method is developed here with a U-shaped probe for the purpose which is based on the "magnetostriction effect". Since the permeability is a function of the stress of a steel test piece due to the eflect, the inductance of a coil around the U-shaped probe, made of high permeability material, is a function of the stress of the piece to which the probe is attached. The change in the inductance is detected effectively by an alternating current bridge having the probe on the piece and another probe on a dummy test piece as bridge sides. The dummy piece has to be of the same material and stress-free by heat treatment. A calibration curve of the bridge output and the stress should be prepared employing two test pieces after heat treatment. Comparison of stress data with the probe, σ_m, and those with wire strain gauges, σ_s, gives fairly good accordance as shown below : σ_s=(1±0.06)σ_m+(0.6〜2) kg/mm^2. The second term, 0.6〜2kg/mm^2, depends on kinds of steel. Though this method allows simple and handy measurement of the compressional stress, the method cannot be apllied directly for the case of tensile stress since the output is a two-valued function of the stress. Therefore, another method is devised to overcome the defect. Since the output of the transversal stress is found to be about three times larger than the output of the tensile stress and it is one-valued function, the tensile stress can be measured by rotating the probe by 90 degrees and employing another calibration curve. The method gives results which is fairly close to those measured with strain gauges with diflerences of the same order stated above. Above study leads to the measurement of two-dimensional stress by rotating the probe around its axis. Therefore, the "shear-difference method", developed in the analysis of the photo-elasticity, is studied and examined here for its application to this method theoretically. Since this indicates possibility of obtaining two-dimensional stress distribution by measuring the directions of principal axes and the difference of two principal stresses, experiments have been performed for the cases of compression-compression, compression-tension and tension-tension using various kinds of steel. Comparison of the results with those by the strain gauge method also shows good accordance withn 2kg/mm^2for stress less than 30 kg/mm^2. Simiilar comparison is also mode for welded test pieces andthis gives somewhat larger difference of about 4 kg/mm^2. Above studies indicate that magnetic non-destructive measurements with the probe developed here is effective for practical usage in macroscopic measurements of initial and residual stresses.
独立行政法人海上技術安全研究所の論文
1980-01-31

磁気ひずみ効果を利用した残留応力測定に関する研究

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