Fatigue life assessment regarding different influences on the HCF/VHCF behavior of a martensitic steel

Abstract

Modern applications require a special treatment when the conventional specimen size is much larger than the component size. Additional to that, high sophisticated materials are used for highly loaded components. Often the conventional fatigue limit is exceeded and loads are applied in the VHCF regime. Focus was put on the lifetime calculation and the implementation of investigated fatigue data of a X5CrNiCuNb-16-4 type steel. Two specimen geometries with diameters D7.5=7.5 mm and D2.5=2.5 mm were tested at R=-1, at room temperature and up to 109 cycles to failure. The application of different software tools (FEMFAT, fe-safe) showed several issues based on the current results. Results showed a change of crack initiation mechanism to subsurface crack initiation at approx. 2x106 cycles to failure. The gradient based correction of the reference fatigue data showed a good applicability up to 2x106 cylces. The application of fe-safe allows the flexible modification of S/N parameters over the whole cycle range. The usage of the actual material configuration introduced several important questions regarding the fatigue data and the implementation into lifetime calculation tools.

Microstructural and Very High Cycle Fatigue (VHCF) Behavior of Ti6Al4V—A Comparative Study

“…As the life expectancy increases, the core components sustaining extremely high numbers of cycles of loads will face increasingly severe challenges in gigacycle regions and it is necessary to study the very high cycle fatigue (VHCF) or giga cycle fatigue (GCF) performance. Various studies [15,16] are available on VHCF (over 10 7 cycles) and GCF (above 10 9 cycles). The VHCF and GCF tests were carried out in the range from 10 7 to 10 10 on ultrasonic fatigue testing machine at the frequency of 20 kHz.…”