Issue 30

R. Louks et alii, Frattura ed Integrità Strutturale, 30 (20YY) 23-30; DOI: 10.3221/IGF-ESIS.30.04 26 assuming that that the investigated materials were linear-elastic, isotropic and homogeneous. The mesh density in the vicinity of stress concentration features apex was refined until convergence occurred at the critical distance (i.e., at L E /2). The typical mesh spacing for convergence was between 1-10μm. The local effective stress calculated according to the PM was extracted from along the focus path, the focus path being coincident with the notch bisector under Mode I loading. The required S-D curves were calculated by FEA in terms of maximum principle stress. It is worth observing here that, under Mode I loading, the first principal stress is coincident with the maximum opening stress. Further, for the quasi- brittle and ductile materials, the S-D curves were calculated and post-processed also in terms of Von Mises equivalent stress. The S-D curves for each investigated geometrical feature were post-processed according to the PM. Finally, the failure prediction was compared with the experimental results, the error being calculated according to definition (3),  %  100 Validation UTS UTS Error       (3) where Validation  is either the maximum principal stress or the Von Mises stress obtained, at a distance from the notch tip equal to L E /2, from the finite element results calculated for the failure stress of the data. The error calculation for each data will show if the proposed method predicts the failure conservatively or non-conservatively by assigning either positive or negative results, respectively. R ESULTS hown in Figs 3 and 4 are the error predictions against changes in the material characteristic behaviour (i.e., from brittle to ductile) using the maximum principal stress and Von Mises equivalent stress, respectively. Material class Reference Material Notch Type Test Type σ UTS (MPa) K IC (MPa.M 0.5 ) L E (mm) ρ Range (mm) B1 [8] Soda-Lime Glass V BD 14 0.6 0.585 1 - 4 B2 [9] Alumina- 7%Zirconia V FPB 290 5.5 0.114 0.031- 0.1 B3 [10] Isostatic Graphite Key U Tension 46 1.06 0.169 0.25 - 4 B4 [11] Polycrystalline Graphite V TPB & BD 46 1.06 0.169 1 - 4 B5 [12] Isostatic Graphite Internal Bean Tension 46 1.06 0.169 0.25 - 4 B6 [13] PMMA -60°C U Tension 128.4 1.7 0.056 0.04- 7.07 QB1 [14] PMMA 20°C V TPB 111.8 1.12 0.032 0.03- 0.25 QB2 [15] PMMA 20°C U TPB 71.95 2.03 0.253 0.01- 2.5 QB3 [16] PMMA 20°C CVT Tension 67 2.2 0.343 0.2 - 4 QB4 [17] PMMA 20°C V TPB 75 1 0.057 0.08- 0.08 QB5 [18] PMMA 20°C U TPB 75 1 0.057 0.11 – 4 D1 [19] High Strength Steel U TPB 1285 33 0.210 0.1 – 1 D2 [7] En3B U-V TPB 638.5 97.4 7.407 0.1 - 5 Table 1 : Summary of experimental data (B=Brittle, QB=Quasi-Brittle and D=Ductile, BD=Brazilian Disk, TPB=Three Point Bending, FPB=Four-Point Bending) S