PSI - Issue 13

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

62

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

P

NP 1/-1s+1

NP 1/0s+1

20 µm

20 µm

20 µm

Figure 8. Fracture surfaces by scanning electron microscopy for the final load ratio F 1 = F 2 = 1 / + 1

specimen is firstly deformed by the shear which is then continuously replaced by tension loading. During shear loading formation of micro-shear cracks occurs which is then, after the change in the loading path (see Fig. 4), superimposed by tension leading to additional growth of voids. Compared to the proportional loading path, the voids in the fracture surface are remarkably smaller in size and number. Therefore, the SEM analysis clearly demonstrates that the loading path remarkably a ff ects the damage and fracture processes on the micro-scale and the mechanisms occurring firstly are the predominate ones in the final fracture process.

5. Conclusions

In this paper a series of experiments with the biaxially loaded X0-specimen has been presented. The experiments have shown the e ff ect of the loading path on damage and fracture mechanisms of ductile metals. These mechanisms are considered in the presented phenomenological continuum model, which is based on di ff erent branches of ductile damage and fracture criteria corresponding to various stress-state-dependent mechanisms. In the notched parts of the specimens shear and tension behavior occurs during loading leading to di ff erent localized deformations. The SEM analyses revealed various stress-state-dependent damage and fracture mechanisms in the specimen during the defor mation path. In addition, proportional and di ff erent non-proportional loading paths lead to di ff erent failure processes on the micro- and the macro-scale demonstrating the remarkable e ff ect of loading histories on evolution of damage leading to final fracture. The results will be used to validate the proposed continuum damage model.

Acknowledgements

The project has been funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) - project number 322157331, this financial support is greatfully acknowledged. The SEM images of the fracture surfaces presented in this paper were performed at the Institut fu¨r Werksto ff e im Bauwesen, Bundeswehr University Munich and the support of Wolfgang Saur greatfully acknowledged.

References

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