PSI - Issue 47

J.E.S.M. Silva et al. / Procedia Structural Integrity 47 (2023) 70–79 Silva et al. / Structural Integrity Procedia 00 (2019) 000 – 000

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diameter ( d SE )=22.40 mm. In terms of the overlap length ( L O ) two values were analysed, 20 and 40 mm. The length of the adherends’ ( L S ) is variable and is dependent of L O , which will result in a total length to the test machine gripping devices ( L T ) equal to 80 mm. Five test specimens were manufactured for each L O accounting for a total of ten specimens. In Fig. 1 b) the dimensions for the TSJ are: t A =0.20 mm, tube thickness ( t S )=2 mm, external tube diameter ( d S )=20 mm, and L T =80 mm. The value of  took the values of 45°, 30°, 20°, 15°,10° and 3.43°.

a)

b)

Fig. 1. Schematic representation of: a) TLJ and b) TSJ.

2.2. Adherend and adhesives The material selected for the adherends was the aluminium alloy AW6082-T651. This alloy was previously characterised in reference (Campilho et al. 2013). The ASTM-E8M-04 standard was adopted to obtain the experimental stress-strain curves (  -  ) of the aluminium alloy AW6082-T651. Three adhesives with different characteristics were chosen, including the Araldite ® AV138, which is considered a brittle adhesive, and the Araldite ® 2015, a moderately ductile adhesive (both epoxy-based adhesives). The Sikaforce ® 7752 is a ductile polyurethane based adhesive. The mechanical and fracture properties of the three adhesives are listed in Table 1 and were previously determined (Neto et al. 2012, Campilho et al. 2013, Faneco et al. 2017). Bulk specimens were tested experimentally, to determine their tensile mechanical properties. Thick-adherend shear tests (TAST) composed by steel adherends were considered for the shear properties. The double-cantilever beam (DCB) and the end-notched flexure (ENF) tests were used for the fracture energy in pure mode I ( G IC ), and fracture energy in pure mode II ( G IIC ), respectively.

Table 1. Mechanical and fracture properties of the adhesives (Neto et al. 2012, Campilho et al. 2013, Faneco et al. 2017).

Property

Araldite ® AV138

Araldite ® 2015 1.85 ± 0.21 12.63 ± 0.61 21.63 ± 1.61 4.77 ± 0.15 0.56 ± 0.21 14.60 ± 1.30 17.90 ± 1.80 43.90 ± 3.40 0.43 ± 0.02 4.70 ± 0.34 0.33 a

Sikaforce ® 7752 0.494 ± 0.089 3.24 ± 0.50 11.49 ± 0.30 19.18 ± 1.40 0.188 ± 0.016 5.16 ± 1.10 10.17 ± 0.60 54.82 ± 6.4 2.36 ± 0.20 5.41 ± 0.50 0.33 a

Young’s Modulus, E (GPa)

4.89 ± 0.81

Poisson’s ratio, ν

0.35 a

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 (%) Toughness in tension, G IC (N/mm) Toughness in shear, G IIC (N/mm) a manufacturer’s data b estimated from (Neto et al. 2012)

36.49 ±2.47 39.45 ± 3.18 1.21 ± 0.10 1.56 ± 0.01 25.10 ± 0.33 30.20 ± 0.40 7.80 ± 0.70

0.20 0.38

b b

2.3. Fabrication and testing The aluminium tubes were machined from rods with diameters close to d SE and d SI . The exterior diameters were shaped with a carbide insert and the interior tube holes were drilled with a carbide drill attached to the tail of the lathe. Surface preparation began with the roughening of the surfaces by sand blasting with corundum particles, and afterwards the surfaces were cleaned with a degreaser to remove contaminants like oil or dust. The concentricity of the tubes and t A =0.2 mm was achieved by placing three nylon threads with diameter equal to 0.2 mm and equally spaced along the outer tube inner perimeter. Subsequently, the adhesive was poured over the bonding surfaces of both