Issue 49

R. Suresh Kumar et alii, Frattura ed Integrità Strutturale, 49 (2019) 526-535; DOI: 10.3221/IGF-ESIS.49.49 532 As already indicated, the crack growth rate depends upon the SIF at the crack front. The numerically obtained K I along the crack front indicates that K I B (SIF at location B in Fig.7) is higher than K I A (SIF at location A in Fig.7). This is due to the high crack size aspect ratio (c/a). Subsequently, the critical location SIF (K I B ) variation during the advancement of the crack is presented in Fig.8. It shows that K I increases with an increase in ‘a/t’ ratio up to 0.6, and then it decreases, which is attributed to the influence of neighbouring compressive stress zone, as shown in Fig.5. The predicted FCG behaviour of the plate specimen is compared with the experimental data [4] in Fig.9. It shows that the numerically estimated crack growth is in good agreement with the experimental results. Figure 9: Comparison of ‘a’ Vs ‘N’ for a plate specimen Figure 10: FE sub-model of the cracked pipe bend geometry FCG on Pipe Bend The FCG analysis for the pipe bend geometry is carried out with an initial elliptical surface crack length (2c 0 ) of 87 mm and depth (a 0 ) of 2 mm. The locations A and B in Fig.10 represent the crack surface location (crack length ‘c’ direction) and the crack deepest location (crack depth ‘a’ direction). Cyclic bending stress is applied with a load ratio of 0.1. The large shallow surface crack is introduced in the hoop tensile stress region (outer surface at the crown location from Fig. 6) of the pipe bend. Simulation of a crack along the axial direction on the outer surface, as shown in Fig.3, will enhance the mode-1 crack propagation. The sub-model concept is adopted in this case and the respective FE mesh given in Fig.10. The difference between the full model and the sub-model will be clear with the comparison of Figs. 6 and 10, respectively. The sub model contains a combination of the 3D tetrahedron, hexahedron and wedge elements. In total, there are 167969 elements against