Research on Interaction of Multiple Cracks and Nondestructive Evaluation by Means of Electromagnetic Techniques

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1. A method was proposed for simplified nondestructive evaluation of two-dimensional multiple cracks by means of the d.c.potential drop technique. A new methodology was introduced to calculate the potential drop by using terms representing the interaction between cracks. The analysis was able to be done with personal computer in a short time.2. A method was proposed for simplified nondestructive evaluation of multiple cracks by means of the d.c.potential drop technique for a subregion containing some cracks. The distribution of the potential drop for cracks in a subregion was calculated based on simplified analysis of crack interactions.3. A method was proposed for simplified nondestructive evaluation of three-dimensional multiple cracks by means of the d.c.potential drop technique. The potential drop was expressed by utilizing terms representing the interaction between cracks and considering the effect of the side walls.4. A method was proposed for simplified nondestructive evaluation of multiple cracks by means of measurement of magnetic field produced in the air by d.c.current flow in a material. The change in magnetic flux density due to three-dimensional multiple surface cracks was expressed by using terms representing the interaction between these cracks.5. As an example of three-dimensional radiated multiple cracks, formation of multiple minute defects, i.e., void formation in metal line was investigated. It was found that the atomic flux divergence formulated to predict void formation was the parameter dominating the void formation. By utilizing the parameter, nondestructive evaluation of void formation in metal line by means of electrical resistance measurement was enabled.Finally, it is noted that the summary of the techniques developed in this research program has been presented as an invited paper "NDE of Multiple Cracks by Electromagnetic Techniques" at the 4th Far East Conference on NDT.