During heat treatment, the unalloyed C45E was austenitized at T = 850°C and then cooled to RT in a controlled manner, resulting in a predominantly ferritic-pearlitic microstructure with a Vickers hardness of HV10 = 216 [4,5]. In the tensile test, the material reached a maximum strength of Rm = 710 MPa and exhibited a yield strength of Rp0.2
The specimens used in SteBLife are characterized by a stepped geometry with different test section diameters, which leads to different local stress amplitudes along the specimen axis under cyclic loading (Fig. 2, bottom left).
The fatigue tests are carried out at a constant force amplitude Fa or stress amplitude σa and the material response (MR) is recorded using various measuring methods. Due to the geometry of the specimen, 5 alternating deformation curves can be recorded simultaneously. The alternating deformation curves form the basis for the σa-MR correlations
Following the SteBLifemsb approach, the results of the 5 tests carried out are analyzed with respect to the number of cycles NB and the sa-NB relationship (Fig. 4). Both NB and the σa-NB relationship show scatter, which can be attributed to material inhomogeneities, among other things.
According to the Gaussian distribution, NB can be determined
Based on the calculated NB and bM values, the Wöhler curves are then calculated with scatter bands for Pf = 5%, 50% and 95%. The results are shown in Fig. 5 together with the fracture load cycles of 11 ESV performed with conventional Hourglass specimens.
Fig. 5 illustrates that the conventionally determined service lives can be reliably described by the scatter bands calculated on the basis of SteBLifemsb. The fatigue strength coefficients and exponents of the calculated and conventionally determined Wöhler data are in the same value range.
