Fatigue behavior of nitrided and shot peened steel with artificial small surface defects

In this paper the effect of small defects on fatigue threshold of different series of nitrided and nitride-shot peened low alloy steel specimens is investigated by means of experimen- tal rotating bending tests on sandglass specimens. Micro-holes acting as pre-cracks are introduce dby means of different methods (electro-erosionand indentation)in order to evaluate the effect of defect size as well as the influenceof the process to generate them on the fatigue threshold.The results,inter preted in terms of DKth, show good agreement with estimated ones, calculated by aformula that considers the experimen tally measured residual stresses, FWHM parameter,micro-hardness values and SEM observation of broken and run-out specimens. Acritical discussion of the obtained results highlights the influence of the defect size and of the method used to generate the micro-holes on the fatigue threshold.