PSI - Issue 13

Florian Fehringer et al. / Procedia Structural Integrity 13 (2018) 932–938 Fehringer, F., Schuler, X., Seidenfuß, M. / Structural Integrity Procedia 00 (2018) 000 – 000

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of notched tensile tests was carried out. The experiments were conducted for three different stress triaxialities, for each triaxiality three different sizes (see Fig. 4 (b)) were used. As an example, the experimental and numerical results for a stress triaxiality of approximately 0.9 are shown in Fig. 4 (c). From the results, a size effect could be observed, but only with a small impact (see also Krieg and Seidenfuß (2003)).

Fig. 4. (a) Torsion test (b) notched specimens to investigate size effects (c) experimental und numerical results – size effect.

Fig. 5 shows the results of a two-step pressure-tension test. During the first step, the specimen is pre-strained by a pressure load up to 2000 bar (see Fig. 5 (a)). The pressure load causes a local plastic pre-strain of up to 20 %.

Fig. 5. Experimental and numerical results of a pressure-tension test (a) pressure load (b) tensile load.

In the second step, a tensional load is applied (specimen depressurized). Fig. 5 (b) shows the corresponding load necking curve. The predicted moment of failure fits the experimental values quite good. At the point of failure, the calculated value deviates only by +0.12 mm from the experimental one.

5. Limit strain curve

As mentioned before, the main part of the proposed limit strain concept is the limit strain curve. Fig. 6 (a) shows the loading paths and limit strains for a tensile test, notched round tensile bars, C(T)25-specimens, plane strain specimens and a torsion test for the material 20MnMoNi5-5. The limit strains are plotted against the stress triaxiality. Furthermore, two limit strain curves are added. The curves were obtained from a semi-analytical solution of the shear enhanced Rousselier equations (Seidenfuß (2012)). As the void growth behavior depends on the Lode angle (see eq. (3)), two boundary curves were plotted. A first one for a Lode angle parameter of  = 1 (plane-strain specimens, C(T)25-specimens, torsion specimens) and the second one for a Lode angle parameter of  = 0 (notched round bars