PSI - Issue 54

I.R.S. Araújo et al. / Procedia Structural Integrity 54 (2024) 406–413 Araújo et al. / Structural Integrity Procedia 00 (2019) 000 – 000

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3

2. Materials and methods 2.1. Joint geometry

Fig. 1 illustrates the geometry of the scarf joint. Its dimensional specifications are as follows (in mm): length L t =170, adherend thickness t P =3 and adhesive thickness t A =0.2. These parameters remain constant, with only the scarf angle  (3.43 o , 10 o , 15 o , 20 o , 30 o and 45 o ) varying, to study its influence on the joint’s strength.

Fig. 1. Scarf joint geometry.

2.2. Materials The material used as adherend was the aluminum alloy AW 6082-T651. This aluminum alloy was characterized in previous works (Campilho et al. 2011), where the following properties were defined: tensile strength ( f ) of 324.00±0.16 MPa, Young's modulus ( E ) of 70.07±0.83 GPa, tensile yield stress ( y ) of 261.67±7.65 MPa, and tensile fracture strain ( ε f ) of 21.70%±4.24%. The stress-strain curves ( σ - ε ) of the aluminum adherends were obtained experimentally, in accordance with ASTM standard E8/E8M, to be introduced in the numerical models. The adhesives considered for this work are the Araldite ® AV138, a brittle epoxy adhesive, the Araldite ® 2015, a ductile epoxy adhesive, and the Sikaforce ® 7752, a highly ductile polyurethane adhesive (Table 1).

Table 1. Properties of the Araldite ® AV138, Araldite ® 2015, and Sikaforce ® 7752 (Neto et al. 2012, Campilho et al. 2013, Faneco et al. 2017).

Property

AV138

2015

7752

Young’s modulus, E [GPa] Tensile yield stress, y [MPa] Tensile failure strength, f [MPa] Tensile failure strain, ε f [%] Shear modulus, G 13 [GPa] Poisson’s ratio, v Shear yield stress, τ y [MPa] Shear failure strength, τ f [MPa] Shear failure strain, γ f [%] Toughness in tension, G Ic [N/mm] Toughness in shear, G IIc [N/mm]

4.89±0.81

1.85±0.81

0.493±0.0896

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

0.2

b

0.38

b

a Manufactu rer’s data; b Estimated in reference (Campilho 2012)

2.3. Numerical modelling The numerical analysis of the scarf joint was carried out using the FEM software Abaqus ® , since it allows the use of the integrated XFEM module for predicting the strength of the scarf joint. The joints were configured in a two dimensional format, employing solid plane strain elements (specifically CPE4 and CPE3 in ABAQUS ® ) to model the adherends. The triangular CPE3 elements were used in the scarf edge to enable the respective slope without inducing distortions in the mesh. Fig. 2 illustrates a detail of mesh refinement for a model with  =45º. In the longitudinal direction of the adherends, a selective mesh refinement was employed using the bias ratio. The mesh has a higher level of refinement near the adhesive layer. The number of elements and the refinement ratio for each