Experimental study of alternating current stress measurement under a uniaxial stress

The alternating current stress measurement (ACSM) which is developed from alternating current field measurement(ACFM) is a new and effective electromagnetic non-destructive testing method with greatly application potential for stress measurement. Using this technology to detect the magnetic field disturbance on the specimen caused by the stress can realize the assessment for the degree of stress concentration. In the present paper, the relationship of stress and induced magnetic field was studied by tensile experiments of 20# low carbon steel. Experiment results which are extremely valuable show when the tensile force is less than the yield strength of the specimen, the percentage change of testing signal in the vertical direction of stress can be up to 8% and higher than that in the parallel direction. When the tensile force increases from 0kN to 40 kN, which can exceed the yield strength, the percentage change of testing signal in the vertical direction increases dramatically and can be up to 26%, while that in the parallel direction can be up to 23% too, which can effectively detect the degree of stress concentration of the ferromagnetic specimen. Meanwhile, a mathematical model of the relationship between stress and induced magnetic field was builded under the external magnetic field according to the principle of ferromagnetics, which can provide a reasonable interpretation for experiments.