Issue 43

F.Z. Seriari et alii, Frattura ed Integrità Strutturale, 43 (2018) 43-56; DOI: 10.3221/IGF-ESIS.43.03 52 The results of predicted fatigue life and crack growth rates of repaired plate are presented respectively in Figs. 10 and 11 at ORL=2.4. It has shown clearly that applied spectrum causes noticeable crack growth delay for “q” equal or less then 100 cycles after constant amplitude compared to constant amplitude loading. Figure 10: Influence of band overloading parameter “q” on fatigue life for patched crack repair at ORL=2.4. Figure 11. Influence of band overloading parameter “q” on delay ratio N D /N CAL in repaired plate. Delay in fatigue life decrease with increasing band overloading parameter “q” from 1 to 100. No effect of band overloading at “q=10” is noticed comparatively to the single overload on fatigue life, expected in delayed crack length “a D ”. At “q=1 cycle”, the total delayed crack length “a D ” is about of 26.82 mm; but for “q=10 cycles”, total delayed crack length is about of 31.51 mm witch presents approximately 4.69 mm in difference. The delay cycles after application of specified spectrum with the presence of patch repair for band overloading cycles “q=100 cycles” is about 1.37  10 5 cycles compared to constant amplitude loading. These delays cycles increases for single overload “q=1” and band overload “q=10” and are respectively, 2.22  10 5 and 2.19  10 5 cycles. Also, these delays is attributed to the crack closure effect [44-46] under application of multiple variable spectrums with band overload from “q=1” to “q=100” cycles. The relationship between the retard ratio N D /N CLA and band overload “q” is plotted in Fig. 12. The developed equation has exponential form and is given below:      1.925 0.005 D CAL N Exp q N (13)