Research on the metal magnetic memory effect of a steel box girder under four-point bending

Abstract

It is valuable to conduct non-destructive testing of steel box girders in order to evaluate their working status. The metal magnetic memory inspection method can effectively identify early damage and the stress state of ferromagnetic materials. However, applying this technique in the inspection of steel components is difficult due to insufficient research on magnetic memory signals under complex stress states. This study analyses the magnetic memory effect for a steel box girder under four-point bending. It is shown that the normal component Hp(y) of the magnetic signal can effectively locate the stress concentration area. The average absolute value Hm of Hp(y) can identify the yielding state and predict the occurrence of failure. Hm changes roughly quadratically with the average strain ɛm in the elastic stage of the specimen, which is consistent with the theoretical result. The ratio D of Hm to the equivalent stress σeqv changes continuously with the applied load, which can be used to estimate the stress state of the steel box girder.