Issue 48

F.A.L. Viana et alii, Frattura ed Integrità Strutturale, 48 (2019) 286-303; DOI: 10.3221/IGF-ESIS.48.29 299 Araldite ® 2015 accomplishes higher performance for L O =25 mm (≈9.5 kN), attaining an increase of 79.3% comparing with the lowest L O . Indeed, at this L O , the Araldite ® 2015 P m exceeds the other two adhesives by 28.9% (Araldite ® AV138) and 24.3% (Sikaforce ® 7752). For L O =37.5 mm, the Araldite ® 2015 still has the highest P m (≈12.2 kN), while the Sikaforce ® 7752 is lower by 13.5%, and the Araldite ® AV138 by 52.6%. Regarding L O =50 mm, P m for the Araldite ® 2015 and Sikaforce ® 7752 attained ≈15.2 and ≈14.4 kN, respectively. P m for the Araldite ® AV138 is lower by 62.5 and 53.9% compared to the Araldite ® 2015 and Sikaforce ® 7752, respectively. The maximum values of percentile standard deviation were 8.1% for Araldite ® AV138, 4.4% for Araldite ® 2015 and 6.2% for Sikaforce ® 7752. a) b) Figure 15 : Experimental P m for the SLJ (a) and DLJ (b) bonded with the three adhesives. The P m evaluation for the DLJ (Fig. 15 (b)) showed that, for L O =12.5 mm, the Araldite ® AV138 and Araldite ® 2015 provide the best results, of ≈12 kN, with slight advantage for the Araldite ® AV138. The relative deviation of the Sikaforce ® 7752, when compared with the other two adhesives, was -66.9 and -56.7% for the Araldite ® AV138 and Araldite ® 2015, respectively. For L O =25 mm, the Araldite ® 2015 outperforms the other adhesives with P m of ≈22.7 kN, attaining a difference of 29.1 and 35.6% for the Araldite ® AV138 and the Sikaforce ® 7752, respectively. For L O ≥25 mm, the P m evolution for the adhesive Araldite ® AV138 is practically nil, and it remains close to 16 kN. For L O =37.5 mm, P m for the Araldite ® 2015 and the Sikaforce ® 7752 tends to become similar, at ≈24 and ≈22 kN, respectively, while the Araldite ® AV138 presents only 16.6 kN. The percentile difference between this adhesive with respect to the Sikaforce ® 7752 and Araldite ® 2015 was -31.2 and -46.1%, respectively. Regarding L O =50 mm, both Araldite ® 2015 and the Sikaforce ® 7752 behaved similarly ( P m ≈24 kN), while the Araldite ® AV138 showed an average of 16.9 kN. Thus, the difference of the Araldite ® 2015 is 0.5% to the Sikaforce ® 7752 and 42.0% to the Araldite ® AV138. It should be noted that the strength of the DLJ tested with the Araldite ® 2015 adhesive ( L O =25, 37.5 mm and 50 mm) and Sikaforce ® 7752 ( L O =37.5 and 50 mm) is limited by the adherends’ yielding. Due to the adherends’ plasticization, none of the adhesives presents a total proportionality of P m as a function of L O . Actually, while the Araldite ® AV138 does not have proportionality at all, the Araldite ® 2015 has it up to L O =25 mm, while Sikaforce ® 7752 records proportionality up to L O =37.5 mm. The maximum values of percentile standard deviation were 6.1% for Araldite ® AV138, 3.6% for Araldite ® 2015 and 5.5% for Sikaforce ® 7752. Similar to the SLJ, the highest P m variation between L O limit values also occur in the joints tested with the Sikaforce ® 7752, given its high ductility. On the other hand, the lower P m variation is again attributed to the Araldite ® AV138. This is due to its inherent reduced plasticization capacity of the adhesive, due to its brittleness, which implies the joint failure as soon as the limiting stresses are reached at the overlap ends. Comparing the SLJ and DLJ bonded with the Araldite ® AV138, a more than two times P m improvement was found, except for L O =50 mm. Indeed, P m increases by 123.9, 139.2 and 107.9% for L O =12.5, 25 and 37.5 mm, respectively. For the larger L O the P m increase was by 81.7%, due to the adherend plasticization effects. Comparing SLJ with DLJ bonded with the Araldite ® 2015, P m increases by 115.7, 139.8, 99.0 and 58.7% with L O =12.5, 25, 37.5 and 50 mm, in the same order. Comparing the SLJ and DLJ for the Sikaforce ® 7752, P m increases by 100.7, 103.8, 103.0 and 66.7%, for L O =12.5, 25, 37.5 and 50 mm, respectively. CZM law validation This Section provides a comparative evaluation between the experimental and numerical results for the three adhesives with both SLJ and DLJ geometries. The numerical analyses were performed as described, whilst the work methodology and inverse CZM law estimation, which are on the basis of this analysis, were also previously described. Initially, Fig. 16 and Fig. 17 present the stiffness degradation (SDEG variable), attained at P m , of the CZM elements representing the adhesive layer for the SLJ and DLJ, respectively. In these figures, the Araldite ® AV138 (a) and Sikaforce ® 7752 (b) were considered 0 5 10 15 20 25 30 0 12.5 25 37.5 50 P m [kN] L O [mm] AV138 2015 7752 0 5 10 15 20 25 30 0 12.5 25 37.5 50 P m [kN] L O [mm] AV138 2015 7752