Issue 48

F.A.L. Viana et alii, Frattura ed Integrità Strutturale, 48 (2019) 286-303; DOI: 10.3221/IGF-ESIS.48.29 289 21.70  4.24%. The experimental tests are done with three structural adhesives: the brittle epoxy Araldite ® AV138, the ductile epoxy Araldite ® 2015 and the ductile polyurethane Sikaforce ® 7752, to evaluate different behaviours and types of failure. These properties were defined in previous works [16-18]. The measurement of E ,  y ,  f and  f was done by bulk specimens with dogbone shape. The specimens were fabricated following the French Standard NF T 76-142 in a custom mould for simultaneous production of six specimens. Shear characterization was performed by Thick Adherend Shear Tests (TAST). The DCB test was used for G IC and the ENF test was used for G IIC . The manufacture of these specimens was similar to that described in the work of Fernandes and Campilho [19] and curing was done in one week at room temperature. The collected data of the adhesives is summarized in Tab. 1. 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 Ultimate tensile 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 Ultimate shear 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 reference [16] Table 1: Mechanical and fracture properties of the adhesives Araldite ® AV138, Araldite ® 2015 and Sikaforce ® 7752 [16-18]. Experimental details The geometry and dimensions of the DCB and ENF specimens are depicted in Fig. 1. Figure 1 : Geometry and dimensions of the DCB (a) and ENF specimens (b). The main parameters are the total length L =140 mm (DCB) or mid-span length L =100 mm (ENF), initial crack length a 0 ≈40 mm (DCB) or ≈60 mm (ENF), adherends thickness h =3 mm, width B =25 mm and t A =0.2 mm [20, 21]. The geometry and dimensions of the SLJ and DLJ are described in Fig. 2. The parameters are the following: joint length between grips L =180 mm, h =3 mm, B =25 mm, t A =0.2 mm and overlap length L O =12.5, 25, 37.5 and 50 mm. The fabrication details presented here are divided into fracture and lap tests, due to the different procedures undertaken. Nonetheless, all specimens were fabricated at room temperature and with approximately 75% of relative humidity, and the respective bonding surfaces were abraded by grit blasting with corundum sand, degreased with acetone, and introduced in a steel mould for bonding. For the specific case of the DCB and ENF specimens, six specimens were fabricated for each joint configuration. For these specimens, calibrated steel spacers were placed between the lower and upper adherends to have the correct value of t A . To promote an easy extraction after curing the adhesive, these spacers were coated with demoulding agent. The spacers at the crack tip were composed of a sharp razor blade with a thickness of 0.1 mm in-between