Issue 43

F.Z. Seriari et alii, Frattura ed Integrità Strutturale, 43 (2018) 43-56; DOI: 10.3221/IGF-ESIS.43.03 53 In term of crack growth rate, fatigue behavior under application of band overloading is characterized by differed delay for “q” greater than one cycle (single overloading) (Fig. 11). Crack growth rates are stabilisation at high value after application of band overloading in high stress intensity factor i.e. at high of crack length values with loss of patch rigidity. Figure 12: Influence of band overloading parameter “q” on crack growth rates of crack patch repair at ORL=2.4. C ONCLUSION atigue crack propagation predictions were carried out on patched and unpatched 2024 T351 Al-alloy plates. Performance of composite patch repair was evaluated under constant amplitude and variable amplitude loading conditions. Combination of retardation model (modified Willenborg model) and patch repair accounting of Ratwani model have given good prediction of composite patch repair performances. From the results of the present investigation, we can conclude that:  After application of overload, instantaneous delay is noticed in unrepaired specimens witch theirs levels depends upon the amount of overload.  Also, in composite patch repair, differed delays have affected the total fatigue life and crack growth rates  High efficiency is given in fatigue life for repaired specimens.  As the overload ratio (ORL) increases, the fatigue life increases for both repaired and unrepaired specimens  The fatigue life is found to be larger if the applied overload was important (ORL=2.4) compared to constant amplitude loading in unrepaired and repaired specimens.  The fatigue life increases in each periodic band of overload “q” as compared to constant amplitude loading. Also the fatigue life decreases in increasing of band of overload “q”.  Finally, experimental studies are needed in order to understanding of the key mechanisms that affect the efficiency of the patch repair under variable amplitude loading effects. R EFERENCES [1] Baker, A.A., Fatigue crack propagation studies on aluminium panels patched with Boron/Epoxy composites. In: Jones R, Miller NJ, International conference on aircraft damage assessment and repair, Melbourn, Australia, (1991) 209-215. [2] Baker, A.A., Fibre composite repair of cracked metallic aircraft components - practical and basic aspects. Composites, 18 (1987) 293-308. DOI: 10.1016/0010-4361(87)90293-X. [3] Baker, A.A., Rose, L.R.F., Jones, R., Advances in the bonded composite repair of metallic aircraft structures. Elsevier Publisher, Amsterdam (2002). F