PSI - Issue 18

Christoph Bleicher et al. / Procedia Structural Integrity 18 (2019) 46–62 Author name / Structural Integrity Procedia 00 (2019) 000–000

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life curves. In the case of nodular cast iron materials and also for this investigation, a further slope k* of 44.9 is assumed after the knee point in the strain-life curve, according to Sonsino (2007). �� � (6) �� � � �� � � � � � (7) The results of this tri-linear approach for the cyclic stress–strain and the strain–life curves are shown in Fig. 11 and Fig. 12, now displaying a much better fit of the cyclic stress-strain curve and the strain-life curve to the fatigue results. The equations describing the course of the tri-linear strain-life curve in all three regimes are given in Equation (8), Equation (9) and Equation (10). � � � � �� ∙ �2 ∙ � � � � � � � ∙ �2 ∙ � � � (8) � � �� ∙ �2 ∙ � � � � � � � �� ∙ �2 ∙ � � � � (9) � � �� ∙ �2 ∙ � � � � � � � �� ∙ �2 ∙ � � � � (10) 3.2. Dross condition During the fatigue tests on the specimens with Dross, the rupture of the specimens started either in the test volume, in the transition area (22.5 mm radius) or in the specimen clamping area, due to the inhomogeneous distribution of Dross in the specimens, Fig. 13.

Fig. 13. Specimens with fractures in the test volume, in the transition area and in the clamping Thus, for the evaluation of the strain-controlled fatigue tests, as a first step, all fatigue results determined on specimens with a fracture in the test volume were evaluated with a common value for the Young’s modulus of 150 GPa and plotted in the strain-life and the stress-strain diagram of the sound material condition, Fig. 14 and Fig. 15. The results show a large scatter in the direction of lifetime and, additionally, a large loss in fatigue strength. In some cases, the specimens did not even reach one or two cycles to rupture, leading to the conclusion that this is the worst Dross configuration possible. Those specimens showed, for that much critical Dross, that a simple fatigue estimation is not enough for a sufficient lifetime assessment of the material or a component. Moreover, in these cases, failure can