Effect of periodic overloads and spectrum loading on fatigue life and microstructure in a Grade 900A rail steel

Fatigue life and crack growth retardation due to spectrum loading, which are superposed on constant amplitude cycles, have been investigated in this paper. For this purpose, numerical and experimental methods are used to investigate the behavior of fatigue crack growth in the rail specimens. A 3D nonlinear boundary element model has been applied to estimate the fatigue life of the rail specimens. Then, the effect of several parameters on the fatigue life in rail specimens is investigated using the suggested 3-D boundary element model and experimental tests. In the numerical analysis, the modified Paris model has been used. The analysis and experimental tests have been performed on C(T) specimens made of a pearlitic Grade 900A steel. In the experimental tests and numerical analysis, the periodic overloads have remained constant and the effect of overload ratio (OLR) and occurrence ratios (OCR) on the fatigue life has been investigated. Finally, microstructure analysis on microstructure morphology of the region where cracks grow for specimens was performed. Comparison between experimental results and numerical data indicates that the modified Paris model and the Forman_Newman_De Koning (FNK) model is actually accurate.