Experimental investigation of stress and damage characterization of steel beam buckling using magnetic memory signals

Metal magnetic memory is a new passive nondestructive method for assessing stress conditions that can be used in the detection of early damage in ferromagnetic materials. To obtain the signal characteristics of steel beams, the normal components of the surface‐spontaneous magnetic signals of a flange and web of Q235B I‐steel beams were measured using four‐point flexural tests under different loads. The variation in the normal component and its gradient were analyzed. The results show that the normal component can reflect the stress distribution of the flange, a significant decrease in the normal component of the flange, and a reversal of the normal component of the web can predict the instability of a beam. The location of a concentrated load on a steel beam can be determined by the highest value of the magnetic signal and the peak–peak value of the magnetic gradient. Finite element software was employed to calculate the von Mises stress, and a qualitative relationship between the distribution of the normal component and the distribution of the von Mises stress was obtained. A quantitative correlation between the applied stress and the average value of the normal component of the flange was developed. Quantitative analyses of the applied stress should consider the dimensional effect of different specimens. A new method is proposed to estimate the location of the stress concentration and to evaluate the degree of damage using a gradient curve, and several parameters are defined to characterize the metal magnetic memory signal. These characteristic parameters may reflect the degree of damage and the range of loads. Copyright © 2015 John Wiley & Sons, Ltd.