Issue 30

A. Fernández-Canteli et al., Frattura ed Integrità Strutturale, 30 (2014) 383-393; DOI: 10.3221/IGF-ESIS.30.46 389 R ESULTS AND DISCUSSION he Load-COD curves for every model are generated. The following graphs, see Figs. 8-9, show the numerical results obtained for the different numerical models and those from the experimental test for comparison. 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4 2.6 2.8 3 0 1 2 3 4 5 6 COD (mm) Load (kN) Experimental 2D-Model 1. Atena 2D-Model 2. Rigid bars 3D-Model 3. Free bars EL 3D-Model 4. Intermediate 0 0.2 0.4 0.6 0.8 1 1.2 1.4 0 0.5 1 1.5 2 2.5 3 COD (mm) Load (kN) Experimental 3D-Model 3. Free bars EL 3D-Model 4. Intermediate a) b) Figure 8 : Load-COD curves for specimen 1: a) all modes including 2D model, and b) zoom detailing only 3D models and experimental results. 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 0 1 2 3 4 5 6 7 COD (mm) Load (kN) Experimental 2D-Model 1. Atena 2D-Model 2. Rigid bars 3D-Model 3. Free bars EL 3D-Model 4. Intermediate 0 0.2 0.4 0.6 0.8 1 1.2 1.4 0 0.5 1 1.5 2 2.5 3 3.5 4 COD (mm) Load (kN) Experimental 3D-Model 3. Free bars EL 3D-Model 4. Intermediate a) b) Figure 9 : Load-COD curves for specimen 2: a) all modes including 2D model, and b) zoom detailing only 3D models and experimental results. The theoretical difference between the cohesive model adopted in the ATENA code [16] and the smeared crack model used in ABAQUS [18] has not noticeable influence on the numerical results obtained.  Opening mechanisms There are two different forms in the evolution of the Load-COD curves obtained from models 1, 2, 3 and 4. These differences are related to the boundary conditions applied in the bars. Curves with higher maximum load emanate from models in which the transversal displacement is impeded along the total length of the bar. Otherwise, models with lower maximum load are only restricted at the ends of the bar. In consequence, models behavior is influenced by the enforced perpendicularity of the bars to the notch plane. As a result, two different notch opening mechanisms, parallel and angular ones, appear, see Fig. 10.  Influence of the transversal displacement in the fracture energy The first analysis of the model of MCT proposed by Holušová et al. [19], points out that the determinant factor explaining differences among the load-displacement curves is the restriction of the transversal Y-displacement of the model. That’s why model 4 has been developed, changing from 2D to 3D and from a restriction in the length of the bars to a restriction in the notch mouth. T