Quantitative measurement of stress in steel bars under repetitive tensile load based on force-magnetic coupling effect

For the ambiguous status of force-magnetic effect on bridges under repeated loading, different repetitive loads were applied to HRB400 steel bars. The magnetic leakage intensities of steel bars were detected and the ‘magnetic leakage ratio parameter’ BN was introduced. The results indicate that the fluctuation of tangential magnetic leakage intensity BσY is consistent with the variation of tensile load. The variation ΔBσY is positively correlated with steel bar tensile displacement v and repetitive tensile load amplitude 2fi. At various loading phases, the proportional change of 2fi is equal to the proportional change of ΔBσYi. That makes a linear relationship between 2fi and BN, which derives the expression of fi. Tensile loads are effectively calculated, enabling quantitative measurement of fluctuating stresses in steel bars. The measured deviation rate is within 10.0%. The theoretical model verifies the correctness of experimental results. This study provides new ideas for the nondestructive testing of stress.