PSI - Issue 38

9

Alexander Erbe et al. / Procedia Structural Integrity 38 (2022) 192–201 Author name / Structural Integrity Procedia 00 (2021) 000 – 000

200

In Figure 11, left side, the curve shift factors for the results obtained at for 400 °C, shown in Figure 6, right are evaluated and sorted in terms of axis ratio to illustrate the general trend in the order of axis ratios. Figure 9: Curve-shift factors: left shift factor related to uniaxial LCF curve at T = 400 °C (regarded to HS); right: shift factor related to uniaxial LCF curve at T = 500 °C (regarded to HS)

Since all values are referred to the uniaxial reference line, the axis ratio of = 0 can be, in that case, perfectly described by the uniaxial reference line without any required shift, indicated by the curve shift factor of 0. However, for the axis ratio of = -1 for instance the uniaxial reference line need to be shifted by a factor of 2.33 in order to mimic the biaxial performed experiments for this case. In addition to this already known experimental result for 400 °C the same evaluation principle is utilized but for the experiments performed at 500 °C, Figure 9, right. It can be seen, that for the case without hold time but at 500 °C the same order of axis ratio is reproduced than at 400 °C. The axis ratios of = 0 and -0.5 are very well represented by the uniaxial line, indicated by comparably low shift factors of -0.2 and 0.0. Nevertheless, the order of = 0 and - 0.5 seem to be flipped. Again a clear trend to higher load cycles are found for the axis ratio = 1 and - 1. The identified shift factors are even higher than the corresponding factors at 400 °C. The order is identical. Beside this, Figure 9, right indicates as well the results performed by inserting a hold time of 3 minutes in tension and compression. Interestingly, the reduction of life provoked by the hold time is a function of the axis ratio, too. Furthermore, the order of axis ratio seems to be also identical. The lowest hold time debit or negative shift factor is represented by the axis ratio of = -0.5 followed by the axis ratio of = 0. The largest hold time debits can be concluded for the axis ratios of = 1 and -1.