PSI - Issue 13

Author name / Structural Integrity Procedia 00 (2018) 000–000

David Lenz et al. / Procedia Structural Integrity 13 (2018) 2239–2244

2243

Figure 1. Experimental and simulative results of the Charpy impact test (S355)

Figure 2. Force deflection curves for different temperatures.

Also the curves of the Charpy simulations at -40°C in the diagram on the right show that the MBW and the GTN model show the same result. Both the part of the plastic deformation and the failure due to cleavage fracture are represented almost identically. However, in comparison with the experimental result, it is noticeable that the fracture occurs much too early in the simulations. Already after a deflection of approx. 1.8 mm, abrupt failure occurs due to the cleavage fracture criterion and thus a drop in force. The simulated sample already fails 6 mm before the experiment. The two models do not differ in terms of the quality of the results. Looking at the computing time of the GTN and MBW models, it can be seen that the MBW model is approx. 85-95% faster, depend on the temperature. This speed advantage is due to the purely explicit calculation method of the modified Bai and Wierzbicki model. However, since both models deliver almost the same results, it can be said that the MBW model works more efficiently. 5. Conclusions and Outlook  The implementation of the stress based cleavage fracture criterion in the micromechanical Gurson- Tvergaard Needleman model was successful  Both models can very well simulate the behavior in the lower shelf of the Charpy-V-notch test and do not  differ with regard to their quality  For the transition area, both simulation models cannot adequately depict the material behavior. The stress based cleave fracture criterion leads to premature failure  A big difference can be seen in the simulation times. This shows that the MBW model is 85-95% faster and  therefore works much more efficiently The results shown in this study lead to the conclusion that a purely stress-based criterion for the image of the cleavage fracture is not sufficient. In order to counteract this inadequate description of the phenomenon, it is necessary to extend the cleavage fracture criterion by a strain-based fraction. The stress triaxiality and lode angle have an influence on this critical strain part.