13th International Conference on Fracture June 16–21, 2013, Beijing, China -7- ABAQUS/Explicit. Therefore, it is essential to develop a complete damage model with the ability of simulating the whole process from void nucleation to the final damage. Finite element predictions both using the developed damage models and porous metal material provided by ABAQUS, and experimental results given by Oh et al. (2007) [15] are presented in Fig. 3. Since the axial displacement is monitored with the length of 25mm in experiments, the nominal strain and nominal stress of FEM results are derived from the mean nodal displacements and total nodal force at the section which is 12.5mm from the middle section, respectively. It can be seen from Fig. 3 that the extended damage models with two different coalescence criteria can give almost identical predictions that are very close to the experimental results for all the specimens, irrespective of geometry. Simulations without the coalescence model can still predict the experimental curve very well before void coalescence. The FEM predictions without the coalescence response definition, however, cannot predict the sharp reduction in the slope of the nominal stress versus nominal strain curve after instability. 0.00 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.10 0.11 0 100 200 300 400 500 600 700 Nominal stress Nominal strain Experiment [15] Criterion 1 Criterion 2 Porous metal material in ABAQUS 0.00 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0 100 200 300 400 500 600 700 800 Nominal stress Nominal strain Experiment [15] Criterion 1 Criterion 2 Porous metal material in ABAQUS 0.00 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0 100 200 300 400 500 600 700 800 900 Nominal stress Nominal Strain Experiment [15] Criterion 1 Criterion 2 Porous metal material in ABAQUS (a) (b) (c) Figure 3. Comparison of FEM results with notched tensile tests: (a) R6; (b) R3; (c) R1.5 3.3. Crack formation in the notched bars One of advantages of the developed model is that both the crack initiation site and propagation path can be simulated. Fig. 4 (a) shows the crack initiation location of the R6 notched tensile bar, the center site in the minimum section, which is in accordance with results observed from experiments.
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