Magnetic flux leakage signal response for determining the fatigue life of reinforced concrete beams under cyclic loading

Monitoring the behaviour of reinforcement in reinforced concrete (RC) is essential to ensure structural integrity, as cyclic loading over time can cause hidden damage that compromises safety. The aim of this study is to investigate the behaviour of RC beams under cyclic loading using the Metal Magnetic Memory (MMM) technique. RC beams measuring 150 mm × 200 mm × 1750 mm were prepared and subjected to cyclic loading at three points. During the fatigue test, maximum loads (Pmax) of 90%, 80%, 70% and 60% of the ultimate load (Pult) were applied, with a constant minimum load (Pmin) of 20% of Pult. Using the MMM technique, the soffit of the beams was scanned over a length of 1150 mm to detect magnetic anomalies indicating stress concentrations and damage. It was found that the fatigue life of the RC beam shows a strong correlation between the percentage of Pmax and fatigue cycles, with an R² of 0.871, providing a reliable representation of the relationship between load and fatigue life. The fatigue life correlation was identified using an ANN model trained with fatigue amplitude and magnetic signal parameters, achieving a correlation above 0.999. Crack development increased with higher cyclic loading and was visually monitored, while critical crack locations were confirmed using the MMM method through tangential gradient signal analysis. Combined, the MMM technique and ANN model enable accurate damage detection and fatigue life prediction, enhancing early assessment and structural safety.