Issue 43

F.Z. Seriari et alii, Frattura ed Integrità Strutturale, 43 (2018) 43-56; DOI: 10.3221/IGF-ESIS.43.03 47 where “a” is crack length, “aol” crack length at overload,  Kth threshold value of stress intensity factor at R=0. In patch repair stress intensity factor K IP , given by equation 5, is integrated in equation 8. S PECIMEN , MATERIAL & PATCH REPAIR he geometry and dimensions of the single edge through crack specimen aluminium specimens investigated in cyclic loading are presented in Fig. 1. The nominal thickness of the aluminium alloy plate, t p , is 3 mm. Specimen have length L p =320 mm and width W p =160 mm. At the edge of each specimen there is a through thickness initial crack, having length “a=3 mm”. A composite patch was laminated on one of the sides of the specimen, having thickness t r =2 mm, effective length L r =80 mm and width W r =80 mm. The material, used in this study, was 2024-T351 sheet aluminium alloy. The mechanical properties of are presented in Table 1. The composite patch used for repair is boron/epoxy. The mechanical properties of this composite patch (Boron/Epoxy) are presented in Table 2 and adhesive film used for patching is FM-73 where shear’s modulus is Gxy= 413.68 MPa and thickness t=0.15 mm. The composite patch was composed by four symmetric ply oriented to the direction (±45.02). The maximal applied remote stress on edge-cracked plate with adhesively bonded composite patch for constant amplitude loading is  aMax =100 MPa. The spectrum forms of applied cyclic stress for variable amplitude loading are given in Fig. 2 for single overload and band overload. The main parameters of fatigue crack growth Nasgro equation for investigated material at R=0 are given in Table 3. Figure 1: Edge-cracked plate with adhesively bonded composite patch  0.2 E (GPa) UTS K IC (MPa.m 1/2 ) K C (MPa.m 1/2 )  372.31 73.08 469 37.36 74.72 0.33 Table 1: Mechanical properties of 2024 T351 Al-alloy. E L (GPa) E T (GPa) G LT  206.84 193.05 5171 0.33 Table 2: Mechanical properties of Boron/Epoxy. T