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A Study on Evaluation of Strain Behavior near Crack Tip by Self-Generated Magnetic Field from Externally Applied Stress

Abstract. The easy and accurate nondestructive examination technique is demanded today. The NDE uses the magnetostriction of the materials to evaluate the materials. In general, materials are magnetized to engage in the NDE test. In this study, we measured the leakage magnetic flux density of crack tip vicinity without magnetizing or demagnetizing the material. We used the stainless steel for the test specimen since it is widely used and it has both ferromagnetic and non-ferromagnetic properties. We found the leakage magnetic flux densities increased in crack tip neighborhood as the load to the ferromagnetic material was increased. The stress intensity factor and the leakage magnetic flux density have the linear relationship. The leakage magnetic flux density increased similarly for non-ferromagnetic material in crack tip neighborhood. We confirmed that we could detect and evaluate the strain of the defect by measuring the stress-generated magnetic signal of the material with the low magnetic field tesla meter. Our new NDE technique would be very effective to the defect evaluation without costly manners.