13th International Conference on Fracture June 16–21, 2013, Beijing, China In order to verify the presented model the simulation results are compared to the experimental data of Sorem, Dodds und Rolfe [11] in the following. These authors investigated the fracture behavior of an A36 steel in the ductile-brittle transition region. They focused on the effect of the crack-tip constraint which is why specimens of different crack depth were employed having all a width of W=34 mm. Since the predictive capabilities of the presented model shall be checked the model parameters are determined only from the deep-cracked standard specimen with a/W=0.50. Finally, the behavior of the shallow-cracked specimen with a/W=0.15 is simulated. According to the procedure proposed in [10] the intrinsic length of the non-local GTN-model is determined to be lnl=0.34 mm corresponding to a size ratio of W/lnl = 93.5. The yield stress is given in [11] for the complete temperature range. The work of separation corresponds to the lower-bound fracture toughness as discussed above and is assumed to be temperature-independent for simplicity leading to a value Γ0=0.028 MPam. The cohesive strength is now determined via the ductile-brittle transition temperature which gives σc=780 MPa. The fracture toughness values extracted from the simulations of the shallow-cracked specimens (a/W=0.15) are compared to the corresponding experimental data in Fig. 10. It has to be noted that the simulation results from above with W/lnl = 100 are used for convenience. Fig. 10 shows that the shift of the ductile-brittle transition temperature is predicted adequately. Furthermore, it is predicted correctly that even at a high level of fracture toughness of about Jc=0.15 MPam there is pure cleavage. This high fracture toughness is attributed to the initially stable crack propagation by cleavage as found above. Fig. 10: Fracture toughness of an A36-steel [11] in comparison to simulation results The employed model is deterministic. Thus, in the current state only mean properties can be considered. It remains open to investigate whether information about the scatter of the fracture toughness values can be gained if local imperfections are considered in the model. -7-
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