A New Method for Internal Force Detection of Steel Bars Covered by Concrete Based on the Metal Magnetic Memory Effect

Abstract

In this paper, the specimens of steel bars covered by concrete (SBCC) are taken as research objects, and a new method for steel bar internal force detection based on the metal magnetic memory effect is proposed. The variation law of the self-magnetic flux leakage (SMFL) signals on the surfaces of SBCC specimens with loading tension and the variation of the SMFL signals along the axial positions of specimens under different tensile forces are studied. The results show that when the loading tension is about 90% of the yield tension, the tangential component of the SMFL signal has a maximum extreme point. The distribution of the SMFL signals along the axial position shows a smooth curve, where the values at both ends are small while the intermediate values are large. This paper also proposes the use of the "area ratio deviation parameter" to quantitatively calculate the internal forces of the steel bars. This parameter shows a significant linear relationship with the loading tension during the strengthening stage of the specimens. This method can supplement the existing steel bar stress detection methods and has prospective research value. damage detection (destruction, semi-destruction) and non-destructive detection [5,6]. Compared with damage detection, non-destructive detection has the advantages of high precision, small error, and no destruction to the structure, so it is used more now [7]. The traditional non-destructive stress detection methods, such as ultrasonic testing [8,9], eddy current testing [10,11], and X-ray testing [12,13], cannot detect early damage of steel bars [14]. In order to accurately detect the early damage of metal materials by means of non-destructive detection, some effective and new methods based on the physics have come into being [15][16][17]. Metal magnetic memory (MMM) detection technology is one of them [18,19], which was first proposed by Russian scholar Dubov [20]. The basic principle of MMM detection can be summarized as follows: Ferromagnetics indicate that magnetism is a basic property of matter, and that any substance is magnetic. When putting any substance in a magnetic field, under the action of a magnetic field, the substance will be magnetized. The reason why a substance is magnetic is because there is a phenomenon in which electrons rotate and spin around the nucleus, and the magnetic properties of the substance can be quantified by magnetic moments [21,22]. The steel bars in reinforced concrete structures are typical metal materials, and their interior structure can be regarded as being composed of many magnetic domains. The interface between the magnetic domains is called the magnetic domain wall [23]. When subjected to the geomagnetic field, the steel bars are magnetized to excite the magnetic fields around themselves, which form the initial magnetic fields under the action of the geomagnetic field. When the steel bars are subjected to the external tension, under the action of the tensile forces and the geomagnetic field, the magnetic domain structures orient and irre...

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