Issue 43

F. Berto et alii, Frattura ed Integrità Strutturale, 43 (2018) 1-32; DOI: 10.3221/IGF-ESIS.43.01 12 The Kitagawa diagram was extended to blunt notches in 2001 [104] and then applied to summarize a number of experimental data taken from the literature [105]. The diagram was obtained by imposing the constancy of the notch acuity, a/ ρ , where a and ρ are the notch semi-depth and the notch root radius, respectively. The constancy of that ratio results in the constancy of the theoretical stress concentration factor K t . With respect to the crack case, there exists now a second plateau on the right hand side of the diagram. When the notch acuity is infinite, the diagram degenerates into the Kitagawa diagram, which appears to be a particular case of the diagram in [104]. Since it is valid the expression  2 0 * t a K a , K t and a 0 determine the position of point P , which is the ideal breaking point between LEFM and Linear Notch Mechanics. It is worth noting that the real behavior shown in Fig. 12 differs from the full a * ; the “sensitivity to defects” present in correspondence of a 0 . Consider again the elementary volume of material shown in Fig. 1-c. R 0 is measured along the notch bisector while the origin of the arc delimitating the volume is at a distance ρ /2 from the notch tip. A number of FE analyses allowed us to determine the mean value of the strain energy over the volume. The results are plotted in Fig. 13, where the inverse of 1 W is plotted against the notch depth a (or the notch root ρ ). It is evident that the constancy of R 0 is able to assure the presence of a double plateau and a natural transition between the three regions of the diagram. Figure 13: Influence of the notch depth on the finite-volume-energy (plane strain, infinite plate). Figure 14: Influence of notch depth on finite-volume-energy (plane strain, infinite plate).