PSI - Issue 37

Patrick Yadegari et al. / Procedia Structural Integrity 37 (2022) 500–507 P. Yadegari et al. / Structural Integrity Procedia 00 (2019) 000 – 000

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The comparison of the damage parameter life curve estimated with the new method for ultra-high strength steels to the test results is shown in Figure 2 for all four materials. The dashed line again represents the estimation with material group "Steel" already defined in the guideline. As can be seen in the diagrams, the damage parameter life curve, which is estimated on the basis of the corresponding tensile strength, matches the test results very accurately. For the range of low-cycle fatigue, the fixed slopes d 1 and d 2 are almost identical for all materials and fit almost perfectly. Especially for cycles to failure N < 10³, the new estimation method provides a much better agreement with the experimental results. Although a slight discrepancy can be noticed for the blind-hardened X40CrMoV5-1, this lies nevertheless on the conservative, safer side. In addition, the endurance limit can be estimated much better, too. In conclusion, the new estimation method for ultra-high-strength steels can be successfully applied to estimate the damage parameter life curve of the four investigated materials, without the calculated cycles to failure being significantly higher than the experimental ones – in the case of a failure probability of 50 %,

Fig. 3. Comparison of the estimated damage parameter life curve to the experimental results for all four materials.

The second damage parameter P RAJ , based on P J by Vormwald (1991, 1992, 1994), provides, besides the consideration of the material-dependent mean-stress sensitivity, the possibility to take into account the crack closing and opening as well as sequence effects. The estimation of the corresponding damage parameter life curve is analogous to the described procedure with P RAM and not explained in more detail in this paper.