Issue 48

F.A.L. Viana et alii, Frattura ed Integrità Strutturale, 48 (2019) 286-303; DOI: 10.3221/IGF-ESIS.48.29 301 the Araldite ® AV138, and to a higher extent for the DLJ with L O =37.5 and 50 mm. Also in these joints, the models managed to capture the experimental failure. a) b) Figure 19 : Experimental and CZM P m comparison for the SLJ (a) and DLJ (b) bonded with the Araldite ® 2015. The Sikaforce ® 7752 results can be found in Fig. 20. For these conditions, large deviations exist between the two data sets, for both SLJ and DLJ, with the numerical results showing higher P m than the experimental average P m . Through a detailed analysis of the numerical simulations, it was concluded that this difference was due to the excess estimation of t s 0 for this adhesive in particular. In fact, due to the use of a triangular cohesive law to model a high ductility adhesive, it was necessary to increase t s 0 in the inverse adjustment process of the ENF results, respectively. Thus, the subsequent application of these values for the strength prediction of adhesive joints leads to the excess estimation of P m . For the SLJ, the lowest deviation was 38.71% ( L O =12.5 mm). For L O =25, 37.5 and 50 mm, the relative deviations were 46.43, 48.17 and 50.78%, in this order. The DLJ also showed high deviations between numerical and experimental data. The minimum relative deviation was 49.7%, found for L O =12.5 mm. On the other hand, deviations of 57.9, 14.1 and 4.1% were found for L O =25, 37.5 and 50 mm, respectively. a) b) Figure 20 : Experimental and CZM P m comparison for the SLJ (a) and DLJ (b) bonded with the Sikaforce ® 7752. C ONCLUSIONS his work aimed at estimating the tensile and shear CZM laws of three structural adhesives by an inverse technique applied to DCB and ENF fracture tests, respectively, to enable their further use in the strength prediction of bonded joints with arbitrary geometry and loading. With this purpose, validation was undertaken with experimental SLJ and DLJ results. Application of the inverse technique initiated by the experimental estimation of G IC and G IIC by the fracture tests, whose P -  curves showed a good agreement for each test type/adhesive set. Few unstable crack growth phenomena were observed for the Araldite ® AV138, due to its brittleness. The resulting R -curves showed crack growth with a steady value of G I or G II , which enabled calculation of G IC and G IIC . The fitting process for the DCB specimens showed that t n 0 has a negligible influence on the outcome of the P -  curves and, as a result, the initial values provided a good response. On the other hand, this did not occur for the ENF specimens, in which the adjustment of t s 0 was clearly a necessity to adjust the curves. Validation of the CZM laws followed with SLJ and DLJ bonded with the same adhesives. The experimental 0 5 10 15 20 25 30 0 12.5 25 37.5 50 P m [kN] L O [mm] 2015 Experimental 2015 Numerical 0 5 10 15 20 25 30 0 12.5 25 37.5 50 P m [kN] L O [mm] 2015 Experimental 2015 Numerical 0 5 10 15 20 25 30 0 12.5 25 37.5 50 P m [kN] L O [mm] 7752 Experimental 7752 Numerical 0 5 10 15 20 25 30 0 12.5 25 37.5 50 P m [kN] L O [mm] 7752 Experimental 7752 Numerical T