PSI - Issue 47

8

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

485

All fatigue results being determined are summarized in Table 2 in form of the parameters of the SN curves including the mean stress sensitivity M defined by Schuetz (1967). For all SN curves in a range of 10 to 18 fatigue specimens have been investigated until failure or N lim . Looking at the results for the base material not surprising and with good agreement to investigations of Bleicher (2015), Bleicher (2017) and Schoenborn (2020) EN-GJS-400-18LT shows the lowest fatigue strength followed by EN-GJS-450-18 and EN-GJS-700-2 both for axial and bending loading and for both load ratios with one exception: The investigated EN-GJS-700-2 shows a very high mean stress sensitivity of M = 0.75 due to a comparably low nominal stress amplitude for tensile loading, R σ = 0, σ a,n,Nlim = 110 MPa, what is 15 MPa lower than the corresponding value for EN-GJS-450-18. Generally, the determined mean stress sensitivities differ a lot and do not meet requirements given in DNV (2016) or FKM guideline (2020). The FKM guideline standardized the mean stress sensitivity to M = 0.4 for all nodular cast iron grades. In the present investigations the values for the mean stress sensitivity differ between 0.25 and 0.75 for the base material. The determined scatter bands for the base material T σ are comparable to results given in literature for sound thick-walled nodular cast iron and do not exceed a typical maximum value for those materials of T σ = 1:1.30 as reported in Bleicher (2015), Bleicher (2017) and Schoenborn (2020). For the welded condition it was not possible to determine a knee point during the statistical evaluation in all cases. For EN-GJS-400-18LT (R σ = 0) and EN-GJS-450-18 (R σ = -1 and R σ = 0), the bending specimens in welded condition showed no knee point until N lim and thus a behavior as under corrosive media. Nevertheless, the mean stress sensitivity seems to be quite unaffected by the welding so that the integral axial and welded bending specimens reached comparable values as for the base material. In comparison to the base material the scatter band increases for all welded material states and reached values of T σ = 1:1.62 for the bending specimens of EN-GJS-450-18 under tensile loading. Except the integral material specimens for EN-GJS-450-18 all other SN curves showed a scatter band far above T σ = 1:1.30. This leads to a higher safety factor for the lifetime assessment of the local welding and the wind energy component.

Fig. 8 Summary of the fatigue strength determined on the round axial samples for the three materials