PSI - Issue 47

Christoph Bleicher et al. / Procedia Structural Integrity 47 (2023) 478–487 Author name / Structural Integrity Procedia 00 (2019) 000–000

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specimens) under constant amplitude loading and at load ratios R σ = -1 and 0 to assess the influence of mean loads on fatigue strength. The statistical evaluation to derive the parameter of the SN curve followed the maximum likelihood method according to Spindel and Haibach (1979) and Stoerzel (2021) for a probability of survival of P S = 10 %, 50 % and 90 %. Furthermore, the scatter band T σ and the slope of the SN curve k was determined. The slope after the knee point N k k* was assumed to be 44.9, which corresponds to a decrease in fatigue strength of 5 % per decade according to Sonsino (2007) which is in agood agreement with investigation of Bleicher (2015) on other nodular cast iron materials. Fig. 5 shows the test rig for the bending specimens under 2-point bending and a bending specimen after failure with the fatigue crack.

Fig. 5 Electric test rig for fatigue tests on bending specimens

5. Discussion Exemplarily the determined fatigue results are given in Fig. 6 and Fig. 7 in form to the SN curves for the axial fatigue specimens removed from the base material and for the integral material state for the pearlitic EN-GJS-700-2. For this material it was not possible to determine fatigue results for the welded bending specimens since after manufacturing the specimens from the blocks large cracks were present in in one side of each bending specimen in the fusion line making a fatigue investigation senseless. Those defects did not occur on all other specimens, so it seems that for this specific cast block the welding procedure was not conducted properly.

Fig. 6 Summary of the fatigue strength determined on the round axial samples for the three materials