Issue 49

F.J.P. Moreira et alii, Frattura ed Integrità Strutturale, 49 (2019) 435-449; DOI: 10.3221/IGF-ESIS.49.42 438 be used in this work for input in the numerical simulations. To be noted that the values of yield stress were defined considering a plastic strain of 0.2%. Property AV138 2015 7752 Young’s modulus, E [GPa] 4.89±0.81 1.85±0.21 0.49±0.09 Poisson’s ratio,  0.35 a 0.33 a 0.30 a Tensile yield stress,  y [MPa] 36.49±2.47 12.63±0.61 3.24±0.48 Tensile failure strength,  f [MPa] 39.45±3.18 21.63±1.61 11.48±0.25 Tensile failure strain,  f [%] 1.21±0.10 4.77±0.15 19.18±1.40 Shear modulus, G [GPa] 1.81 b 0.70 b 0.19 b Shear yield stress,  y [MPa] 25.1±0.33 14.6±1.3 5.16±1.14 Shear failure strength,  f [MPa] 30.2±0.40 17.9±1.8 10.17±0.64 Shear failure strain,  f [%] 7.8±0.7 43.9±3.4 54.82±6.38 Toughness in tension, G IC [N/mm] 0.20 c 0.43±0.02 2.36±0.17 Toughness in shear, G IIC [N/mm] 0.38 c 4.70±0.34 5.41±0.47 a manufacturer’s data b Estimated from the Hooke’s law using E and  c estimated in Campilho et al. [23] Table 1: Properties of the adhesives Araldite ® AV138, Araldite ® 2015 and Sikaforce ® 7752 [23-25]. Experimental details Fig. 2 represents the geometry and dimensions of the T - joints. The relevant dimensions are the following: L O =25 mm, B =25 mm, base length L T =80 mm, base thickness t P1 =3 mm, t P2 =1, 2, 3 and 4 mm, L-part length L A =60 mm, L-part radius R =5 mm and t A =0.2 mm. Specimen fabrication was initiated by cutting/bending the adherends to the respective shapes. The straight adherend, used as the specimen base, is obtained by cutting, in an automated cutter, a bar to the final dimensions. The L-parts were subjected to an identical procedure, but then they were manually bent in a press, such that the end surfaces were at an angle of 90º, and applying a tool with the chosen R , to produce the geometry depicted in Fig. 2. The surface preparation before bonding consisted of manually increasing the roughness by sanding using emery paper with coarse grain (60 grit), followed by wiping with cleaning agent (acetone) to eliminate dust and oxides, thus achieving a strong bond. Joining of the different parts was accomplished in a jig that positioned the three adherends in the layout of Fig. 2 and enabled keeping this position throughout the entire adhesive hardening process. To assure the specified t A , steel spacers with identical thickness to t A were inserted at the edges of the bonded parts are removed after adhesive curing. Before placing the spacers, they were initially coated with Loctite ® Frekote 770NC demoulding agent, to guarantee easy removal after the adhesive has cured, which is essential to prevent damage to the cured adhesive layers. With the specimens in position after depositing the adhesive, and with the spacers providing the correct offset between adherends, grips were used to apply pressure to the set and enable curing to take place. This process was accomplished during a one-week period. The final step consisted of trimming the excess cured adhesive by milling. As a result of this set of operations, it was possible to obtain a good representation of the theoretical geometry of Fig. 2, with emphasis to the bondline end geometry positioned at x / L O =0 ( x is the horizontal coordinate initiating at the bondline end). The specimens were tested as depicted in Fig. 2, i.e. by clamping the edges of the straight adherend and pulling in peel while transversely restraining the upper joint edge. This was done in a Shimadzu AG-X 100 testing machine, equipped with a 100 kN load cell, at an approximate temperature of 20ºC and testing speed of 1 mm/min. Five specimens were fabricated and tested for each joint type. A minimum of 4 valid tests was always assured for each joint type.