Magnetic evaluation of fatigue damage in train axles without artificial excitation

The metal magnetic memory (MMM) method, based on the magnetomechanical effect, provides an effective and simple approach for fatigue evaluation of train axles in laboratory tests as well as in service on railway systems. In lab tests carried out to analyse the fatigue process, the distribution of the surface magnetic field on axle model specimens under different cycle numbers (N) was investigated. Good correlation between resulting fatigue level and MMM signals has been demonstrated. In the M (magnetic)-N (cycle) curve derived from the experimental data, three stages corresponding to the fatigue process can be clearly distinguished. A similar situation was found in the practical inspections of train axles in service. This technique could be further studied for fatigue evaluation.