PSI - Issue 25

R.M.D. Machado et al. / Procedia Structural Integrity 25 (2020) 71–78 Machado et al. / Structural Integrity Procedia 00 (2019) 000 – 000

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most relevant properties were defined as follows: tensile yield stress (  y ) of 261.67  MPa, Young’s modulus ( E ) of 70.07  0.83 GPa, tensile strength (  f ) of 324  0.16 MPa and tensile failure strain (  f ) of 21.70  4.24%. The adherends were bonded with a moderate ductile epoxy adhesive, the Araldite ® 2015. The mechanical properties of the adhesive were evaluated in previous works (Campilho et al. 2011, Campilho et al. 2013). Table 1 presents all the collected information about the Araldite ® 2015 properties.

Table 1 – Properties of the adhesive Araldite ® 2015 (Campilho et al. 2011, Campilho et al. 2013).

Property

2015

Young’s modulus, E [GPa]

1.85±0.21

Poisson’s ratio, 

0.33 a

12.63±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 4.70±0.34

Tensile yield stress,  y [MPa] Tensile strength,  f [MPa] Tensile failure strain,  f [%] Shear modulus, G [GPa] Shear yield stress,  y [MPa] Shear strength,  f [MPa] Shear failure strain,  f [%]

G IC [N/mm] G IIC [N/mm]

a manufacturer’s data

2.2. Geometry, fabrication and testing

The architecture of the stepped-lap joints is depicted in Fig. 1. Essentially, the bonded area consists of three steps of equal length. L O is the only geometric parameter with varying dimensions (12.5, 25, 37.5 and 50 mm). As for the other parameters, they were kept constant and considered as: adherends’ thickness ( t P ) of 3 mm, longitudinal adhesive thickness ( t A ) and step-end adhesive thickness ( t A1 ) of 0.2 mm, and joint total length between grips ( L T ) of 180 mm.

Fig. 1 – Geometry and dimensions of the stepped-lap joints.

Five specimens were produced and tested for each configuration. The manufacturing process begin by cutting the supplied aluminum sheet to the final specimens’ width (25 mm). Further, a milling operation was performed to create the steps design. With the aim of achieving a good adhesive wettability, the adherends were grit-blasted with corundum sand to remove the surface oxide layer and contaminants, and then they were cleaned with acetone. Furthermore, a steel apparatus was used during adhesive application and joint assembly, to ensure a correct adherends’ alignment and t A . The joints were left to c ure at room temperature in accordance with the adhesives’ curing cycle. Additionally, the adhesive excess that eventually appeared at the overlap ends and the joints’ lateral sides was removed either by manual or milling techniques. The tensile tests were performed at room temperature in a Shimadzu AG-X 100 (Shimadzu, Kyoto, Japan) testing machine with a 100 kN load cell, applying a velocity of 1 mm/min. A number of four valid results was always provided for each joint configuration.