Detection of mechanical fatigue in structural steelusing SQUID and flux-gate sensors

In this work we present a non-destructive technique to detect the magnetization changes due to mechanical stress produced in steel notched plates under tensile loads. The measurements have been carried out using, separately, a magnetic field probe based on HTS dc SQUID and a fluxgate gradiometer probe. The aim of this work is to demonstrate that it is possible to localize the dislocation density change in the samples and to correlate it with the change of magnetization using a contact-less and non-invasive technique.