Abstract
As an ignored physical property, the metal magnetic memory signal has the potential for non-destructive testing in the future. To get the variation characteristic of magnetic signals under different loads, the normal components of surface spontaneous magnetic signals Hp(y) of the Q235 I-steel column were measured online. In this paper, the variation law of Hp(y) with stress was investigated in the position of the point of contraflexure and stress concentration. The physical mechanism between its magnetic property and mechanical property was established at the elastic and plastic stages. Experimental results show that Hp(y) reaches the extreme value in the position of stress concentration, where the magnetic field gradient K presents the zero-crossing phenomenon along with the peak–peak value phenomenon on the left and right sides. In the position of the point of contraflexure, when the Hp(y) curve reaches the extreme value, the corresponding equivalent uniaxial stress σeq is 54 MPa, which is in good agreement with the Jiles–Atherton (J–A) model. Characteristic parameters Kmax, ζ, and η can reflect the extent of damage of the specimen. In the position of stress concentration, Hp(y) values decrease sharply at the early plastic stage. The analysis shows that the distribution regularity of Hp(y) at the elastic stage is in good agreement with the J–A model. The modified J–A model is consistent with the experimental results at the plastic stage.
Highlights
Because of the advantages of light weight, high strength, good plasticity, good toughness, excellent mechanical properties, and good processability performance, Q235 low-carbon steel is extensively applied in structural industry
According to the distribution of surface spontaneous magnetic signals, the macroscopic defect and the microscopic damage, such as the stress concentration area, can be detected, and efficient precaution can be taken to avoid the abrupt failure of the structure
According to above experimental analysis, the general guidelines of magnetic memory (MMM) technology can be summarized as follows: first, identify the steel grades of ferromagnetic materials; second, identify the area of stress concentration and other damages according to the characteristic of Hp(y) and K curves; third, identify whether the specimen enters the plastic stage according to the distribution of the Hp(y) curve in the area of stress concentration; and evaluate the degree of damage by calculating characteristic parameters Kmax, ζ, and η
Summary
Because of the advantages of light weight, high strength, good plasticity, good toughness, excellent mechanical properties, and good processability performance, Q235 low-carbon steel is extensively applied in structural industry. According to the distribution of surface spontaneous magnetic signals, the macroscopic defect and the microscopic damage, such as the stress concentration area, can be detected, and efficient precaution can be taken to avoid the abrupt failure of the structure.. According to the distribution of surface spontaneous magnetic signals, the macroscopic defect and the microscopic damage, such as the stress concentration area, can be detected, and efficient precaution can be taken to avoid the abrupt failure of the structure.1–3 This method is green and simple to operate and utilizes the geomagnetic field as the exciting field without other magnetization equipment. The authors of Ref. 13 carried out research on the variation law of magnetic signals of the Q345C steel box girder with a corrugated web under bending loads and established the relation between magnetic signals and different stress states. The corresponding relation between the distribution of Hp(y) and stress (or strain) at the elastic stage and the plastic stage was obtained by the MMM signals analysis of the point of contraflexure and stress concentration
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