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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In Figure 1, a comparison of the cyclic stress-strain curve estimated with the adapted method for ultra-high strength steels (full line) to the experimental results (points) for all four materials is shown. To visualize the improvement of the adapted estimation method, the dashed line represents the corresponding curve using the material group "Steel". Although this group is not approved for such high tensile strengths, the guideline provides no alternative methods either, whereby the approximation method based on Brinell hardness by Roessle and Fatemi (2000) is noteworthy. As can be seen, the cyclic stress-strain curve of the material X3CrNiMoAl13-8-2 is estimated almost perfectly, whereby the nearly elastic ideal-plastic behaviour is remarkable. Likewise, the experimental test points of both conditions of X40CrMoV5-1 can be accurately described by the estimated curve. For these three materials, the new material group "Ultra-high strength steel" provides a significantly improved estimation in direct comparison to the existing group "Steel". For the material 100Cr6, as can be seen in Figure 1, there is a greater difference between the test points and the estimated cyclic stress-strain curve. This mismatch is due to a discrepancy between the static and cyclic maximum load resistance of this material, since the tensile tests resulted in an ultimate tensile strength of 2286 MPa and total elongation at break of 3.5 %, while the strain-controlled cyclic tests caused several instant failures at strain amplitudes higher than 1.2 %, resulting in a maximum stress of 2166 MPa. Nevertheless, this new estimation method for the cyclic stress-strain curve is the best compromise for the examined materials and could also be successfully applied to other ultra-high strength steels (e.g. X50CrMoV5-3-1, ultimate tensile strength of 2245 MPa, see Fällgren et al. (2021)) that were not investigated in this research project.

Fig. 2. Comparison of the estimated cyclic stress-strain curve to the experimental results for all four materials.