PSI - Issue 13

Marco Schmidt et al. / Procedia Structural Integrity 13 (2018) 91–96 M. Schmidt et al. / Structural Integrity Procedia 00 (2018) 000–000

96

6

5. Conclusion

The main objective of this paper was to evaluate the influence of negative stress triaxialities on the damage and fracture behavior of ductile metals. For this purpose, a biaxial test specimen made of an aluminum alloy was tested experimentally and analyzed numerically under various shear-compression loading conditions. The numerical simu lations are based on the presented anisotropic damage model with stress-state-dependent criteria. In addition to the evaluation of the force-displacement curves, the strain fields were visualized with the help of a digital image correla tion system and compared with results of corresponding numerical simulations. To analyze the relationship between stress state and damage mechanisms, stress triaxialities and Lode parameters were evaluated numerically and com pared to the fracture surfaces of the failed specimens, which were recorded with a scanning electron microscope. Furthermore, a stress-state-dependent function of the cut-o ff value for negative stress triaxialities, below which no damage occurs, is discussed on the basis of the experimental and numerical results.

6. Acknowledgments

Financial support from the Deutsche Forschungsgemeinschaft DFG (German Research Foundation - project num ber 281419279) is gratefully acknowledged. The SEM pictures have been performed at the Institut fu¨r Werksto ff e des Bauwesens at the Universita¨t der Bundeswehr Mu¨nchen and the special support of Wolfgang Saur is gratefully acknowledged.

References

Bao, Y., Wierzbicki, T., 2004. On the fracture locus in the equivalent strain and stress triaxiality space. International Journal of Mechanical Sciences 46, 81–98. Bru¨nig, M., 2003. An anisotropic ductile damage model based on irreversible thermodynamics. International Journal of Plasticity 19, 1679–1713. Bru¨nig, M., Chyra, O., Albrecht, D., Driemeier, L., Alves, M., 2008. A ductile damage criterion at various stress triaxialities. International Journal of Plasticity 24, 1731–1755. Bru¨nig, M., Gerke, S., Hagenbrock, V., 2013. Micro-mechanical studies on the e ff ect of stress triaxiality and Lode parameter on ductile damage. International Journal of Plasticity 50, 49–65. Bru¨nig, M., Gerke, S., Schmidt, M., 2016. Biaxial experiments and phenomenological modeling of stress-state-dependent ductile damage and fracture. International Journal of Fracture 200, 63–76. Bru¨nig, M., Gerke, S., Schmidt, M., 2018. Damage and failure at negative stress triaxialities: Experiments, modeling and numerical simulations. International Journal of Plasticity 102, 70–82. Driemeier, L., Bru¨nig, M., Micheli, G., Alves, M., 2010. Experiments on stress-triaxiality dependence of material behavior of aluminum alloys. Mechanics of Materials 42, 207–217. Dunand, M., Mohr, D., 2011. On the predictive capabilities of the shear modified Gurson and the modified Mohr-Coulomb fracture models over a wide range of stress triaxialities and Lode angles. Journal of the Mechanics and Physics of Solids 59, 1374–1394. Gao, X., Zhang, G., Roe, C., 2010. A study on the e ff ect of stress state on ductile fracture. International Journal of Damage Mechanics 19, 75–94. Gerke, S., Preawpan, A., Bru¨nig, M., 2017. New biaxially loaded specimens for the analysis of damage and fracture in sheet metals. International Journal of Solids and Structures 110-111, 209–218. Kuwabara, T., 2007. Advances in experiments on metal sheet and tubes in support of constitutive modeling and forming simulations. International Journal of Plasticity 23, 385–419. Makinde, A., Thibodeau, L., Neale, K., 1992. Development of an apparatus for biaxial testing using cruciform specimens. Experimental Mechanics 32, 138–144.