A novel method for characterizing the fatigue crack propagation of steel via the weak magnetic effect

Abstract Generally, the fatigue failure of reinforced concrete beams under the coupled action of fatigue and corrosion is mainly controlled by the brittle fracture of the steel bar, confirming the significance of the fatigue crack growth (FCG) behavior of the steel bar. In this regard, FCG tests of opening mode I were conducted based on standard compact specimens manufactured from HRB400E steel bar. Meanwhile, the weak magnetic field, including the piezomagnetic field throughout the FCG process and the residual magnetic field (RMF) at certain crack lengths were both recorded. Piezomagnetic hysteretic curves and RMF distribution were analyzed separately, and the characteristic parameters of them were both determined. The evolution mechanism of the weak magnetic field was then comprehensively explored. Finally, the quantitative relationships between the FCG parameters and the characteristic parameters of weak magnetic field were separately established. The proposed relationships were applied in a prediction model of crack length, FCG rate and the FCG life, which were validated through the experimental results. The results showed that the prediction accuracy of stress intensity factor using PE method, and the prediction accuracy of crack length using PE and MMM methods all reached 90%. The errors between the FCG life predicted by PE and MMM methods and the experimental results were both within 20%.