Issue 30

A. Fernández-Canteli et al., Frattura ed Integrità Strutturale, 30 (2014) 383-393; DOI: 10.3221/IGF-ESIS.30.46 390 The results for this model, however, approaches the load-displacement curves of models 3 and 4 (see Figs. 8 and 9), especially in the initial ascending part of the curve. The maximum load is about the same, and the same applies for the initial region of the softening curve. Then, a new rise in the load happens, due to the difficulty of continuing crack opening. a) b) c) Figure 10 : Schematic representation of the opening mechanism of the notch: a) parallel opening, b) angular opening and c) transversal displacement of the specimen during testing by parallel opening. Models 1 and 2 correspond to a parallel opening, whilst models 3 and 4 generate an angular opening.  Correction of the Load-Displacement Curves Some problems appear in describing the softening part of the Load-COD curves in both experimental and simulation results. In most cases, the last part of the softening curve has an asymptotic behavior tending to a certain value of the load different from zero, instead of approaching gradually to null load, as it would be expected in a real case. Accordingly, a correction in the ordinate is introduced using the following equations, see Fig. 11:   tan y x x    (3)       corrected y x y x y x    (4) where: θ = Angle between abscissa axis and the slope line y’ . Line y’ is formed by connecting the origin of the θ coordinate system with a far point, or eventually, the last point of the curve y . tan θ = Slope of the line y’. Figure 11 : Scheme for the correction of the y axis.