Uniaxial fatigue tests for 17-4PH stainless steel with various types of small defects

What is it about?

The fatigue tests results in the VHCF regime, up to 10^10 cycles to failure are reported. Tests were performed at three different R-ratios with ultrasonic fatigue testing and rotating bending testing. The results are evaluated using the square-root-area parameter model to predict the fatigue strength of 17-4PH stainless steel for different stress ratios with a focus on addressing failure from non-metallic inclusions. Furthermore, the lower bound of the scatter in the fatigue limit is determined using the statistics of extremes by analysing the defect size at crack initiation sites.

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Photo by Inspirationfeed on Unsplash

Photo by Inspirationfeed on Unsplash

Why is it important?

1) The fatigue strength can be estimated according to the square-root-area parameter model . 2) The stress ratio dependency of the fatigue limit can be deduced with the fractographic investigations on the specimens failed from non-metallic inclusions. 3) Optically dark areas (ODA) are formed during failure from internal inclusions. The stress intensity factor range at the border of ODA, ΔK_ODA is correlated with the size-dependent threshold value for propagation of small cracks, ΔKth. However, the values of ΔK_KODA are approximately 40% higher than the calculated value of ΔKth. 4) The lower bound of the fatigue limit can be predicted by usinge of the inclusion rating and the extreme value theory.