PSI - Issue 33

A.F.M.V. Silva et al. / Procedia Structural Integrity 33 (2021) 138–148 Silva et al. / Structural Integrity Procedia 00 (2019) 000–000

141

4

( G ) do not vary with the testing velocity (Karac et al. 2011) and, thus, the properties at 1 mm/min were used for all simulations (Table 1).

Table 1. Properties of the adhesive Araldite ® AV138 (Campilho et al. 2011).

Shear yield stress,  y [MPa] Shear failure strength,  Shear failure strain,  f [%]

25.1±0.33 30.2±0.40

Young’s modulus, E [GPa]

4.89±0.81

Poisson’s ratio, 

0.35 a

f [MPa]

Tensile yield stress,  y [MPa] Tensile failure strength,  f [MPa] Tensile failure strain,  f [%]

36.49±2.47 39.45±3.18 1.21±0.10

7.8±0.7

Toughness in tension, G IC [N/mm] Toughness in shear, G IIC [N/mm]

0.20 0.38

Shear modulus, G [GPa]

1.81 b

a manufacturer’s data b estimated from the Hooke’s law using E and v

Table 2. Mechanical and fracture properties of the Araldite® AV138 as a function of the test velocity.

t n 0 [MPa]

t s 0 [MPa]

G IC [N/mm]

G IIC [N/mm]

Test velocity

1

41.0 49.1 70.2

30.2 36.2 51.7

0.35

0.6

100

-

-

105000

0.35

0.6

2.2. Adherend and adhesive materials To validate the numerical model used in this work, the authors used experimental data from a previous work (Valente et al. 2019). The SLJ dimensions depicted in Fig. 1 include a total length between the testing machine’s grips ( L T ) of 200 mm, adherend thickness ( t P ) of 2 mm, joint width ( b ) of 25 mm, t A =0.2 mm and L O =25 mm.

Fig. 1. SLJ geometry and boundary conditions.

The manufacturing activities started by sandblasting the adherend surfaces to be bonded with corundum sand, to improve the adhesive wettability and, therefore, the bonding process. Subsequently, the adherends were cleaned with acetone to remove oil residues and solid particles. To assist the joint assembly, a steel jig with guiding pins through the specimens’ length was used, assuring the adherends’ alignment. Spacers were included to achieve the desired t A . Initially, the lower adherend was inserted in the jig and the adhesive poured into the overlap region. Next, the top adherend was lowered to position and compressed against the lower adherend, removing the extra adhesive. Specimens were left to cure at room temperature according to the manufacturer specifications. After the curing process, the entire adhesive in excess was trimmed by milling. The joints were impact tested in an Instrumented Falling Weight Impact Tester, type 5HV from Rosand ® (Stourbridge, West Midlands, United Kingdom). The impact test consists of dropping a weight on the vertically-mounted specimen from a pre-established height. One of the specimens’ end is fixed by a claw system, while the other is stroked by the weight with a given kinetic energy ( U c ), easily defined by the law of conservation of energy U c =½ mv 2 , where m is the mass and v is the velocity. The setup included dropping the weight (26 kg) from 157 mm height, therefore providing an impact energy of 40 J. With a load cell, the load from the impact is measured by the reaction in the fixed end of the specimen, whereas an accelerometer measures the displacement. After the numerical model validation, the tubular joint design depicted in Fig. 2 was used to evaluate the geometry effect on the tubular joints’ strength. The base dimensions are L T =100 mm, t A =0.2 mm, inner tube thickness t SI =2 mm,