AUTOMATIC STRESS DETECTION IN REINFORCED BAR BASED ON METAL MAGNETIC MEMORY

Accurate detection of the stress level of steel bars inside a reinforced concrete bridge plays a vital role in assessing the bearing capacity and safety of the bridge and is one of the urgent problems in the field of bridge non-destructive testing. Based on the magnetic memory effect of ferromagnetic materials, this paper experimentally studied the leakage magnetic field distribution on the surface of the reinforced bar in the bridge with axial tensile stress. A force-magnetic coupling parameter named A(F) was proposed, and it depends on the maximum fluctuation value of the axial leakage magnetic field scanning curve of the steel bar. Within the range of elastic deformation, A(F) varies linearly with the axial tension F. The influence of concrete strength, steel bar diameter, and lift-off height on the distribution characteristics of leakage magnetic field, especially the slope of the A(F)-F line in the elastic stage, is analyzed. After calibrating the slope of the A(F)-F line for a specific steel bar covered by concrete, an automatic stress non-destructive testing method is proposed to calculate the tensile stress level of the steel bar inside the bridge by using the leakage magnetic field.