Metal magnetic memory testing (MMMT) has demonstrated considerable potential for the identification and quantitative evaluation of hidden fatigue damage; however, the applicability of current damage evaluation indicators in actual structural inspections remains insufficiently explored. In this study, this issue was examined by designing two types of plate specimens to model the fatigue damage characteristics of orthotropic steel bridge decks. Prefabricated gaps were incorporated to simulate hidden fatigue damage in actual components, and the initial magnetic fields of the specimens were retained. The specimens were subjected to tensile‒tensile fatigue testing, and their surface magnetic fields were monitored online via a three-dimensional probe along predefined scanning paths. Digital image correlation was concurrently utilized on the opposite side of the specimens to verify the capability of the MMMT for fatigue damage detection and to evaluate the reliability of the fatigue life predictions. Analysis of the measured data revealed the limitations within the existing damage evaluation indicators, and new indicators of Mc, Div, and Curl were proposed. To minimize missed and false detections in the MMMT, a joint analysis of local contour maps for these indicators was conducted. By extracting the first-order longitudinal difference characteristic values of the proposed indicators and applying Bayes' theorem, a characteristic value database was established to assess the fatigue life of the specimens. The field detection from three fatigue designs in the orthotropic steel bridge deck of an in-service cable-stayed bridge indicated that the proposed MMMT-based scheme is highly efficacious for detecting the fatigue damage in the steel structures.
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