Issue 49

B. El-Hadi et alii, Frattura ed Integrità Strutturale, 49 (2019) 547-556; DOI: 10.3221/IGF-ESIS.49.51 552 Figure 6 : Comparisons of finite element results with experimental data for the fatigue life of repaired panels. (a) t =2.29mm (b) t=6.35mm. R ESULTS AND DISCUSSION igs 7.a and 7.b present the distribution of von-mises stresses in thin and thick repaired aluminum plates respectively. The crack length is taken to be 2a=10 mm. From fig 7.a, a non uniform distribution along the crack front can be observed. In fact, the stress transfer between the repaired plate and the patches mainly occurs in the patched side of the plate. The stress at the crack tip in the patched side of the plate is much smaller than that in the unpatched side of the plate, which accounts for SIF variation in thickness direction of the aluminum plate. Moreover, comparing the crack tip stresses distribution between figs7.a and 7.b, one can also observe that with the help of the patches, the stress at the crack tip in thin repaired plate is much smaller than that in the thicker one. This accounts for the significant SIF's difference between thin and thick plates. Figure 7: Distribution of the Von-Mises stresses across the crack front for the repaired plate. (a) t=2.29mm; (b) t=6.35mm. Fig.8 shows that the change in maximum values of von-mises stresses (red zone in fig) is with growth of the crack where this value is shifted from the free side toward the patched side and this applies to all panels, whether thin or thick. Accordingly, this finding will be highlighted, hereinafter by the stress intensity factor results in fig 9.a and 9.b. Figures 9.a and 9.b shows the distribution of stress intensity factor along the crack front. It is noted through the curves trend that the maximum value of SIF is shifted from the free side of the plate towards the patched side. This suggests a cascade growth of the crack, obviously starting from the free surface going toward the patched surface. A differed of this behavior can be noted between the thin and the thick plates. Effectively, the maximum value in fig 8.a is resulted for the angle Ө =0° curve and the last point in crack front in the free side of the plate. This maximum value is in no case F