Cyclic behaviour and fatigue of stainless steels

The cyclic stress-strain curve is used for describing a stabilized (averaged) stress-strain response in strain concentrations. Importantly, it describes the extremes of the stabilized hysteresis loop. This data is needed for estimating fatigue life based on the strain-life method for components subjected to cyclic loading. A typical application for this calculation method is the design of exhaust manifolds and cylinder heads experiencing severe temperature cycles and thermal straining. Cyclic tests with variable and constant strain amplitude, as well as tensile tests have been carried out for three materials: 1.4307, 1.4404 and 1.4541 -type commercial stainless steels in order to study the material response. The formation of martensite was measured in the tests. Secondary hardening was observed with all strain amplitudes in 1.4307 and 1.4541 whereas in 1.4404, secondary hardening occurred only with the smallest test amplitude. Also, the fatigue life of 1.4404 tended to be shorter than that of 1.4307 and 1.4501 in the high cycle fatigue (HCF) regime