PSI - Issue 18

Kim Bergner et al. / Procedia Structural Integrity 18 (2019) 792–801 Author name / Structural Integrity Procedia 00 (2019) 000–000

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Fig. 2. Bending specimen geometry (left), bending specimen with machined surface (top right) and with casting skin (bottom right)

Fig. 3. Fatigue test setup (left) and FE-simulation (right) of the bending tests under two-point bending

3. Results The results of the load-controlled fatigue tests under tensile loading R σ = 0 are shown in Fig. 4 for EN-GJS-400-15, as a comparison between the specimens with and without roughness. The test results are evaluated for the determination of the slope k of the low cycle fatigue regime by means of a regression calculation based on the maximum likelihood method, which uses the least squares approach. With this approach, the curve parameters are determined so that the sum of the square deviations of the curve is minimized. The measure of variation is assumed to be constant in the low cycle fatigue regime and will be adapted for the high cycle fatigue regime until the limit number of cycles N G = 1 ∙ 10 7 . For this, the slope k* in the high cycle fatigue regime has to be specified [Spindel (1979)]. The mathematically determined scatter of the S-N curves for the bulk specimens is T σ = 1 : 1.10 and, for the specimens with surface roughness, it is T σ = 1 : 1.13. Nevertheless, a scatter band of 1:1.30 is recommended for the