PSI - Issue 61

G.J.C. Pinheiro et al. / Procedia Structural Integrity 61 (2024) 71–78 Pinheiro et al. / Structural Integrity Procedia 00 (2019) 000 – 000

73 3

Table 1. Scarf joint dimensions.

Total length ( L T ) [mm] Adherent thickness ( t P ) [mm] Adherent width ( w ) [mm]

170

3

25

3.43/10/15/20/30/45

Scarf angle (  ) [º]

Adhesive thickness ( t A ) [mm]

0.2

Fabrication of testing samples started by removing any oils and contaminants from the adherent s’ material surface prior to a milling process. The machining procedure gave origin to the bonding surfaces, according to the angle required for each test specimen. All samples were then deburred on a bench grinder. To promote adhesion, bonding surfaces of each specimen were sanded, which resulted in a rougher surface, while eliminating any oxide layers. Once again, every unit was degreased and cleaned to remove any surface contaminants. Bonding adherents in a scarf geometry was conducted with the placement of a 0.2 mm diameter wire as a method of controlling t A at the overlap region. Alignment between adherents was assured using clamps that pressed the joints against flat surfaces. This technique also provides an even pressure distribution on the adhesive layer area. The curing process occurred at room temperature for seven days. As a last step before testing, adhesive overflow was removed on a bench grinder. Testing was accomplished using a Shimadzu AG-X 100 tester with a 100 kN load cell at 1 mm /min. 2.2. Materials An artificially aged aluminum alloy, AW6082-T651, was selected as a single material for all adherents under testing. This alloy was chosen due to its widespread application in structural applications. The adherents were modelled as isotropic elasto-plastic solids, with the stress-strain behavior experimentally obtained in a previous work (Campilho et al. 2011b) according to the ASTM E8/E8M standard. A range of adhesives, from brittle to ductile, were used for this study with the objective of comparing the bonded joints’ behavior according to the different properties displayed in Table 2. The Araldite ® AV138 is a high strength epoxy adhesive, characterized by its brittle behavior. It’s a two -part adhesive, which results from combining AV138M-1 resin with HV988 hardener. With good properties when subjected to either traction or shear stresses, the Araldite ® 2015 has increased ductility when compared to the previous adhesive. This characteristic results in an improved stress distribution in the adhesive layer, especially in its outer boundaries. However, superior ductility results at the expense of lower strength. As the AV138, it is also a two-part epoxy adhesive. Contrasting with the previous adhesives, the SikaForce ® 7752 is polyurethane-based. Once again, it is a bi-component adhesive. Trading strength for ductility, this adhesive allows for high strain applied to the adhesive layer avoiding rupture of the outer limits of the bonding region. This behavior results in enhanced stress distributions in the adhesive, which improves the joints’ strength.

Table 2. Adhesive properties.

Araldite ® 2015 (Campilho et al. 2012, Campilho et al. 2013)

SikaForce ® 7752 L60 (Faneco et al. 2017) 0.493±0.0896

Araldite ® AV138 (Neto et al. 2012)

Property

Young’s modulus, E (GPa) Poisson’s coefficient Tensile yield stress, σ y (MPa) Tensile strength, σ f (MPa) Tensile failure strain, ε f (%) Shear modulus, G (GPa) Shear yield stress, τ y (MPa) Shear strength, τ f (MPa) Shear failure strain, γ f (%)

4.89±0.81

1.85±0.81

0.35 a

0.33 a

0.33 a

36.49±2.47 39.45±3.18 1.21±0.10 1.56±0.01 25.1±0.33 30.2±0.40

12.3±0.61 21.63±1.61 4.77±0.15 0.56±0.21 14.6±1.3 17.9±1.8 43.9±3.4 0.43±0.02 4.7±0.34

3.24±0.5 11.49±0.3 19.18±1.4 5.16±1.1 10.17±0.6 58.42±6.4 2.36±0.2 5.41±0.5 0.187±0.0164

7.8±0.7

Mode I fracture energy, G IC (N/mm) Mode II fracture energy, G IIC (N/mm)

0.2 0.38 b

b

a manufacturer’s data ; b from reference (Campilho et al. 2011b).