Issue 49

F.J.P. Moreira et alii, Frattura ed Integrità Strutturale, 49 (2019) 435-449; DOI: 10.3221/IGF-ESIS.49.42 443 developing in the straight adherend due to the tensile pulling. This gives rise to tensile  y peak stresses near x/L O =1, while the other edge tends to become lightly loaded. This effect can even be responsible by an alteration of the failure path if t P2 reaches a given limit. On the other hand,  y stresses tend to span for a bigger region of the bonding length with the increase of t P2 , which can be responsible for a P m improvement. Identically to that found for  y stresses, the behaviour of  xy stresses has large similarities between adhesives, although with peak magnitude variation between adhesives due to their stiffness differences. The T-joints bonded with the Araldite ® 2015, whose curves are shown in Fig. 5 (b), presented a middle behaviour between the three tested adhesives. The smallest  xy peak stresses are those of the joints with t P2 =1 mm and, for this joint,  xy stresses peak close to x / L O =0, while being negligible for the remainder of the bonding portion. On the other hand, the increase of t P2 lightly increases  xy peak stresses near x / L O =0, concurrently with a progressive increase of  xy peak stresses near x / L O =1. This modification in the  xy stress plots is related to the aforementioned behaviour of  y stresses, i.e., due to the stiffening effect of the L-part, which is not accompanied by the transverse deformation of the base adherend, which subsequently leads to large adhesive strains near x / L O =1. Moreover, the variation of  xy stress plots can also influence the failure onset and growth, identically for that discussed for  y stresses. Study of the SDEG (damage) variable The stiffness degradation (SDEG variable) of the XFEM damage laws along the bonded length is addressed in this Section, with the objective of describing the extent of damage along the adhesive at the P m of the joints. The SDEG variable ranges from 0 to 1, in which 0 represents the absence of damage, i.e., the respective set of nodes are within the elastic loading phase, and 1 corresponds to full separation. SDEG values in-between indicate that the set of nodes is in the stress softening phase. Fig. 6 shows the SDEG plots at P m along x / L O for the T-joints bonded with the Araldite ® AV138 (a), Araldite ® 2015 (b) and Sikaforce ® 7752 (c). For each adhesive, the four joint geometries are analysed ( t P2 =1, 2, 3 and 4 mm). a) b) c) Figure 6: SDEG variable at the P m instant for the T-joints bonded with the Araldite ® AV138 (a), Araldite ® 2015 (b) and Sikaforce ® 7752 (c). The comparison between the three adhesives clearly shows different behaviours. The brittleness of the Araldite ® AV138 reflects on a much localised portion of the adhesive layer under damage at the time P m is reached in the T-joints. This is visible by the steepness of the SDEG plot between SDEG=1 and 0. Moreover, at P m some portion of the adhesive layer is already fully damaged, especially for bigger t P2 . This could be indicative of brittle failure and a lesser performance of this 0 0.2 0.4 0.6 0.8 1 0 0.2 0.4 0.6 0.8 1 SDEG x / L O 1 mm 2 mm 3 mm 4 mm 0 0.2 0.4 0.6 0.8 1 0 0.2 0.4 0.6 0.8 1 SDEG x / L O 1 mm 2 mm 3 mm 4 mm 0 0.2 0.4 0.6 0.8 1 0 0.2 0.4 0.6 0.8 1 SDEG x / L O 1 mm 2 mm 3 mm 4 mm