Relationship between applied force and magnetic field in a pseudo-static test of a portal frame

Abstract

Metal magnetic memory (MMM) testing is a nondestructive approach for evaluating the stress concentration and early damage of ferromagnetic components. However, research on the MMM testing of large steel structures has been limited. Thus, this study investigates the suitability of MMM technology for monitoring the damage in steel structures exposed to complex stresses. The normal components of magnetic signals H _p (y) on the beams and columns of a portal frame are obtained through pseudo-static testing. The signal increment ΔH _p (y) and its absolute value |ΔH _p (y)| under different loads are analyzed. The relationship between the equivalent stress and magnetic signal is investigated through numerical simulation. The results show that the ΔH _p (y) curves are similar during the elastic stage but change abruptly during the plastic phase. Moreover, the differences in the magnetic signal directions caused by the varying detection directions cannot be ignored. In the elastic stage, with the increase in the load, |ΔH _p (y)| curves initially increase and then decrease. The formation of the ΔH _p (y) curve is similar to the distribution of the equivalent stress. The mutation of ΔH _p (y) can determine whether a specimen is entering the plastic phase, and can warn against structural failure. The magnetic signal distribution qualitatively reflects the stress distribution.