Experimental study on stress-magnetic effect of low-carbon steel bar during complete elastic-plastic process under tensile stress

Investigating the magnetization reversal phenomenon in the force-magnetic effect is of crucial importance for stress monitoring based on metal magnetic memory. The study of the stress-magnetic reversal phenomenon of steel bars during the complete elastic-plastic tensile process is still insufficient. Moreover, existing studies have been conducted under ambient magnetic fields, significantly compromising measurement accuracy. To address this issue, a weak magnetic testing system was developed using non-magnetic and weak magnetic materials to measure the magnetic field of steel bar under tensile load. The system analyzed the influence of ambient magnetic field and separated the magnetic flux density and magnetic gradient of steel bar itself. Experimental research was conducted to study the correlation between three steel bars’ own magnetic flux density, magnetic gradient, and stress during the complete elastic-plastic tensile process. The results show that when the stresses of the three steel bars reach 173.44MPa, 172.45MPa and 147.18MPa, respectively, the correlation between their magnetic flux density and magnetic gradient with stress are reversed. The stresses at magnetization reversal points, 173.44 MPa, 172.45 MPa and 147.18 MPa, are all lower than their respective yield strengths of 372.41 MPa, 375.38 MPa and 369.44 MPa. When the stress is less than the stress at magnetization reversal point, the absolute values of magnetic flux density and its gradient in steel bars increase with increasing stress. From the stress at magnetization reversal point to strain gauge failure, the absolute values of the magnetic flux density and magnetic gradient of the steel bars decrease with increasing stress.