Evaluating effect of magnetic flux leakage signals on fatigue crack growth of mild steel

In engineering applications, analysis of crack growth life is useful in situations where an unexpected crack has been found in a component of a machine, vehicle, or structure. The objectives of this research are to investigate the correlation curve of magnetic flux leakage, Hp(y) signals by evaluating their critical value point with respect to step size. Moreover, the relation of the fatigue crack growth rate, da/dN with the stress intensity range, Delta K and Hp(y) in metal components is also discussed in this paper. The tension-tension fatigue test was conducted with the metal magnetic memory (MMM) scanning device and crack opening displacement (COD) gauges at 10 Hz (testing frequency) by applying a load of 3.0-5.0 kN. As a result, the correlation curve of Hp(y) was built with the R-squared values in the range of 0.99 and a mathematical model was developed for estimation analysis. The sigmoidal shape curve was plotted on the graph of da/dN versus Delta K and also with Hp(y). Thus, for validation, the linear relation is represented between Delta K and Hp(y) and presents a good approach for magnetic parameters to be developed for fatigue crack growth analysis. Therefore, the magnetic method has a greater capability to analyse the fatigue crack propagation life in a real application.