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.
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
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
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).
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
A normalized unalloyed steel of grade C45E was used as the test material. The specimens were machined from round material with a length of 5,000 mm and a diameter of 20 mm and subsequently polished to a roughness value of Rz < 6 µm. The chemical composition according to the manufacturer's specifications corresponds to the specified limit value
Experimental setup and material
The stress-controlled single-stage tests were carried out on a Shimadzu type EHF-U servo-hydraulic test system with a maximum load of 50 kN, a frequency of f = 5 Hz, a sinusoidal load-time function, and a load ratio of R = -1 at room temperature with RT = 25°C.
The specimens were stressed to failure or to reach th
