Issue 48

J.P.S.M.B. Ribeiro et alii, Frattura ed Integrità Strutturale, 48 (2019) 332-347; DOI: 10.3221/IGF-ESIS.48.32 341 presented a reduction of the constant G I and G II extent because of the inherent ductility of this adhesive. On the other hand, the Sikaforce ® 7752 R -curves showed a minor increasing trend of G I and G II with a in line for the large dimensions of the FPZ. Figure 7: P -  curves obtained for the SLB specimens with the adhesive Araldite ® AV138. Fig. 8: Example of tensile (a) and shear (b) experimental R -curves for an SLB specimen with the adhesive Araldite ® AV138. Fracture envelope The fracture envelopes of the three tested adhesives depicted in Fig. 9 were constructed from the mixed-mode results of the SLB tests and also the pure-mode G IC and G IIC values. In all cases, the CBBM data reduction method was used. Four theoretical fracture envelopes are presented, by applying an energetic crack propagation criterion of the type of Eqn. (6) with the exponents  =1/2, 1, 3/2 and 2. This will enable framing the behaviour of each adhesive in the most appropriate criterion. Regarding the Araldite ® AV138, a small relative standard deviation of the experimental data was attained, i.e., 5.2 and 5.9% for G I and G II , respectively. Oppositely, the other two adhesives presented a higher scatter in the experimental outcomes, even though this was still satisfactory. Actually, the deviation found for G I and G II was by 9.4% and 9.2%, respectively, for the Araldite ® 2015, and 3.7% and 3.6% for the Sikaforce ® 7752, in the same order. The energetic propagation criterion with  =1/2 provides a good agreement to the behaviour of the Araldite ® AV138. The same exponent is also the best solution for the Araldite ® 2015, even though the correlation is not as obvious as for the Araldite ® AV138. On the other hand, the Sikaforce ® 7752 presents a noticeably different mixed-mode behaviour compared to that of the other adhesives, in such a way that the mixed-mode energies during propagation largely exceed the linearity between the corresponding pure-mode values. In fact, for this adhesive, the best propagation criterion exponent to be used in mixed- mode simulations is  =2. Validation with lap geometries This Section aims at validating the estimated mixed-mode crack propagation criteria defined for each adhesive. With this purpose, initially the experimental P m results for the SLJ and DLJ are presented and discussed. Following, P m prediction takes place for all tested conditions, and the relevant conclusions are taken. 0 20 40 60 80 100 0 1 2 3 4 P [N] δ [mm] 0 0.02 0.04 0.06 0.08 0.1 120 130 140 150 160 170 180 G I or G II [N/mm] a eq [mm] GI GII