Issue 42

M. Peron et alii, Frattura ed Integrità Strutturale, 42 (2017) 196-204; DOI: 10.3221/IGF-ESIS.42.21 203 Coarse mesh (64 finite elements) Refined mesh (3395 finite elements) R 0 [mm] Method K 1 K 2 Δ K 1 (%) Δ K 2 (%) K 1 K 2 Δ K 1 (%) Δ K 2 (%) Gross and Mendelson 0.595 0.595 0.1 Treifi et al. 0.667 0.564 12.10 -5.21 0.703 0.547 18.15 -8.07 0.1 New method 0.649 0.572 9.08 -3.87 0.596 0.595 0.17 0.00 0.1 New modified method 0.598 0.594 0.50 -0.17 0.01 Treifi et al. 0.582 0.599 -2.18 0.67 0.603 0.592 1.34 -0.50 0.01 New method 0.649 0.571 9.08 -4.03 0.597 0.594 0.34 -0.17 0.01 New modified method 0.598 0.594 0.50 -0.17 0.001 Treifi et al. 0.575 0.602 -3.36 1.18 0.593 0.595 -0.34 0.00 0.001 New method 0.649 0.571 9.08 -4.03 0.612 0.588 2.86 -1.18 0.001 New modified method 0.598 0.594 0.50 -0.17 Table 5 : Comparison between approximate methods for NSIFs evaluation of central tilted crack (2 α = 0°) in a plate of infinite extension. The described methods have been applied to plates subjected to mixed mode I+II loading and weakened by different V- notch geometries. The values of the NSIFs derived according to Gross and Mendelson have been compared with those obtained by means of the approximate methods taking into consideration three different values of the control radius R 0 (0.1, 0.01 and 0.001 mm) and by using coarse and refined FE meshes. The comparison of the results shown that the new proposed method provides the best combination between the degree of approximation and the level of applicability, so it could be useful for rapid calculation of the NSIFs. Central tilted cracks in a plate of finite (Fig. 4c) or infinite (Fig. 4d) extension are characterized by a projected crack length 2 a = 2 mm and a crack inclination angle φ = 45 o . The obtained results and the comparison between the different approaches are reported in Tables 4, 5. It is worth noting that the case of the infinite plate has been modelled as a finite plate characterized by width and height two orders of magnitude greater than the crack length. R EFERENCES [1] Lazzarin, P., Comportamento a fatica dei giunti saldati in funzione della densità di energia di deformazione locale: influenza dei campi di tensione singolari e non singolari, Frattura ed Integrita Strutturale, 9 (2009) 13-26. [2] Maragoni, L., Carraro, P. A., Peron, M., Quaresimin, M., Fatigue behaviour of glass/epoxy laminates in the presence of voids, Int. J. Fatigue, 95 (2017) 18–28. [3] Brotzu, A., Felli, F., Pilone, D., Effects of the manufacturing process on fracture behaviour of cast TiAl intermetallic alloys, Frattura ed Integrita Strutturale, 27 (2013) 66-73. [4] Askes, H., Susmel, L., Gradient enriched linear-elastic crack tip stresses to estimate the static strength of cracked engineering ceramics, Frattura ed Integrita Strutturale, 25 (2013) 87-93. [5] Susmel, L., On the overall accuracy of the Modified Wöhler Curve Method in estimating high-cycle multiaxial fatigue strength, Frattura ed Integrita Strutturale, 16 (2011) 5-17, [6] Seweryn, A., Brittle fracture criterion for structures with sharp notches, Eng. Fract. Mech., 47 (1994) 673–681. [7] Boukharouba, T., Tamine, T., Niu, L., Chehimi, C., Pluvinage, G., The use of notch stress intensity factor as a fatigue crack initiation parameter, Eng. Fract. Mech., 52 (1995) 503–512. [8] Lazzarin, P., Tovo, R., A notch intensity factor approach to the stress analysis of welds, Fatigue Fract. Eng. Mater. Struct., 21 (1998) 1089–1103. [9] Atzori, B., Meneghetti, G., Fatigue strength of fillet welded structural steels: Finite elements, strain gauges and reality, Int. J. Fatigue, 23 (2001) 713–721.