Analysis of microcrack growth in a 1015 SAE steel subjected to uniaxial and multiaxial loading

The influence of different types of cyclic loading on the microstructural damage of a case-hardening steel is investigated in strain-controlled fatigue tests within the LCF (low cycle fatigue) range. For the investigations, fine polished tubular specimens were applied which were analysed for microcracks on the specimen's surface after a defined number of cycles. The development of microcrack density and length was evaluated with respect to the applied load level and the number of cycles. Connecting these results with frequency distributions of the grain size it was concluded that the growth of microcracks stagnates at the grain boundaries. At the same time the number of newly developed short cracks rises.