PSI - Issue 54

D.F.T. Carvalho et al. / Procedia Structural Integrity 54 (2024) 398–405 Carvalho et al. / Structural Integrity Procedia 00 (2019) 000 – 000

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2. Materials and methods 2.1. Material characterisation

The material selected for the adherends was the high strength aluminium alloy AW6082 T651. The material stress strain (  -  ) curves were obtained accordingly to the specifications of the ASTM-E8M-04 standard (2004) and will be subsequently used as inputs int the numerical models. The mechanical properties of the AW6082 T651 alloy are Young’s modulus, ( E ) 70.07±0.83 GPa, Poisson’s ratio, (  ) 0.3, Tensile yield stress, (  e ) 261.67±7.65 MPa, Tensile strength (  f ) 324±0.16 MPa and Tensile failure strain, (  f ) 21.70±4.24 %. Three adhesives with different behaviour were analysed in this work. The Araldite ® AV138 that is considered brittle, Araldite ® 2015 that is considered a moderate ductile and Sikaforce ® 7752 that presents a ductile behaviour. In Table 1 is listed the mechanical and fracture properties of the adhesives (Campilho et al. 2011, Campilho et al. 2013, Faneco et al. 2017). The tensile mechanical properties of the adhesive, such as E ,  e ,  f and  f , were determined by means of experimental testing with bulk dogbone specimens. The shear properties were determined by means of Thick Adherend Shear Tests (TAST) and the shear modulus ( G ) was obtained by the Youngs’ modulus ( E ) and Poisson’s coefficient (  ). The assessment of tensile yield strength (  e ) and shear yield strength (  e ) consisted of drawing a parallel line in the elastic region and displacing the strain by 0.2%, the intersection of which supplied their respective values. The pure mode I fracture energy or tensile toughness ( G IC ) was determined using the double cantilever beam test, while the pure mode II fracture energy or shear toughness ( G IIC ) was obtained using the end-notched flexural test. Table 1. Mechanical and fracture properties of the Araldite ® AV138, Araldite ® 2015 and Sikaforce ® 7752 (Campilho et al. 2011, Campilho et al. 2013, Faneco et al. 2017). Property AV138 2015 7752 Young’s modulus, E [GPa] 4.89±0.81 1.85±0.21 0.49±0.09 Poisson’s ratio,  0.35 a 0.33 a 0.30 a Tensile yield stress,  e [MPa] 36.49±2.47 12.63±0.61 3.24±0.48 Tensile strength,  f [MPa] 39.45±3.18 21.63±1.61 11.48±0.25 Tensile failure strain,  f [%] 1.21±0.10 4.77±0.15 19.18±1.40 Shear modulus, G [GPa] 1.81 b 0.70 b 0.19 b Shear yield stress,  e [MPa] 25.1±0.33 14.6±1.3 5.16±1.14 Shear strength,  f [MPa] 30.2±0.40 17.9±1.8 10.17±0.64 Shear failure strain,  f [%] 7.8±0.7 43.9±3.4 54.82±6.38 Toughness in tension, G IC [N/mm] 0.20 c 0.43±0.02 2.36±0.17 a manufacturer’s data 2.2. Geometry and experimental details In Fig. 1 a) is presented the stepped-lap joint geometry, the boundary and loading conditions, and is identified the key geometrical parameters. Regarding the boundary and loading conditions, the specimens were clamped at one end, and at the other end a horizontal tensile displacement was applied together with a vertical restriction of movement. The adhesive joint under consideration, as already mentioned, has a step geometry and in combination with this geometry, the concept of a dual-adhesive joint is also employed. In the present work, three different adhesive ratios were considered, each applied to the four L O under analysis. Experimentally, only single-adhesive joints composed of Araldite ® 2015 and Sikaforce ® 7752 were tested, and the dual-adhesive concept was tested in two different combinations, the Sikaforce ® 7752-Araldite ® 2015-Sikaforce ® 7752 and the Sikaforce ® 7752-Araldite ® AV138 Sikaforce ® 7752 configurations. The adhesive ratio of 25%-50%-25% was kept constant in all the dual-adhesive cases b estimated from the Hooke’s law using E and  c estimated in reference (Campilho et al. 2011)