13th International Conference on Fracture June 16–21, 2013, Beijing, China -6- Gologanu model, this criterion can by written as 0 1 2 = + − = b R w CEmbury . (11) The model has been implemented by Andrieux [17] into the finite element code ABAQUS/Explicit. 3.2. Identification of model parameters of the different weld zones The parameters of the Gologanu model and the fracture criteria were identified by inverse simulations of smooth and notched tensile specimens as well as double notched shear specimen, which were cut from the base materials, the weld nugget itself and heat treated sheets with microstructures corresponding to the heat affected zones. In case of the specimens cut from the weld nugget reduced dimensions have had to be used, due to the geometry of the weld nuggets. All specimens have been modeled using detailed finite element models meshed with 3-dimensional brick elements with edge lengths of 0.1 mm in the regions of interest. Using the symmetry of the specimens only one eighth of the smooth and notched tensile specimen and half of the double notched shear specimen has been modeled. The finite element models are shown in Fig. (6). (a) (b) (c) Figure 6.Finite element models of smooth (a) and notched tensile (b) and double notched shear (c) specimens Up to uniform elongation the true stress-strain curves of the base material, heat affected zones and the weld metal were measured in smooth tensile tests. Subsequently the true stress vs. true strain curves are determined in simulations of the smooth tensile tests. The damage and failure parameters for the different material zones of the weld were identified by simulating the smooth and notched tensile tests and the shear tests on double notched shear specimens and adjusting the parameters to match the numerical results with the experimental ones. The parameters identified are given in Table (1). Table 1. Parameters of the material model and the failure criteria f0 εN fN SN q S0 H0/R0 α β 22MnB5 BM 0.002 0.20 0.02 0.1 1.5 0.0001 1.2 0.1 1.2 22MnB5 SHAZ 0.002 0.30 0.008 0.1 1.5 0.0001 1.2 0.1 1.2 HC340LAD BM 0.002 0.85 0.003 0.1 1.5 0.0001 0.5 0.1 1.2 HC340LAD HAZ 0.002 0.15 0.005 0.1 1.5 0.0001 0.5 0.1 1.2 WM 0.002 0.15 0.02 0.1 1.5 0.0001 1.8 0.1 1.2
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