PSI - Issue 13

Moritz Zistl et al. / Procedia Structural Integrity 13 (2018) 57–62

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M. Zistl et al. / Structural Integrity Procedia 00 (2018) 000–000

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Figure 1. Biaxial testing machine without DIC system

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Figure 2. Detailed sketch of XO-specimen: (a) complete specimen, (b) central part, (c) notched part and (d) cross section of notched part, all measures in mm

In the present paper, an additional path is presented with special focus on non-proportional loading scenarios and the experimental results will be compared with those based on previously presented loading histories. During the proportional experiments, the load ratio is kept constant during the entire tests. The non-proportional ones start with respective successive loadings and end after an axis-switch with the final proportional path up to final fracture guaranteeing the same final load ratios F 1 / F 2 to obtain comparable results. The non-proportional scenario (NP 1 / 0 s + 1 ) investigated by Gerke et al. (2018) is first loading by only F 1 (black arrows, loading ratio 1 / 0 ) followed by F 2 (green arrow, 1 / + 1 ) whereas in the new, second scenario (NP 1 / − 1 s + 1 ) in the first step both axes are simultaneous loaded by F 1 and F 2 = − F 1 (black arrows, 1 / -1 ) followed by a switch in axis 2 with only loading by F 2 up to F 2 = F 1 (green arrows, 1 / + 1 ) whereas F 1 is kept constant, followed by the final proportional loading path up to final fracture, see Fig. 4. During the biaxial experiments, the displacement of the specimens’ surface are analyzed by digital image corre lation (DIC) technique. The displacements in 1-direction u 1 . 1 and u 1 . 2 are shown in Fig. 3. The relative movement of these points is given by ∆ u ref.1 = u 1 . 1 − u 1 . 2 and for the 2-direction accordingly. After the experiments scanning electron microscopy (SEM) of fracture surfaces is conducted to reveal the stress-state-dependent ductile damage and fracture processes on the micro-level.