Issue 49

F.J.P. Moreira et alii, Frattura ed Integrità Strutturale, 49 (2019) 435-449; DOI: 10.3221/IGF-ESIS.49.42 442 Figure 4: Fracture surfaces for the five sets of T-joints bonded with the Araldite ® AV138 and with t P2 =2 mm (for each set the L -parts are at the left and the base adherend to the right). Stresses in the elastic domain This Section briefly evaluates  y and  xy stresses along the adhesive during the initial stages of the elastic loading, such that the differences between adhesives and t P2 are properly accounted for. The graphics are represented as follows:  The x -axis represents the normalized distance along the adhesive length ( x / L O ), in which x is the horizontal coordinate beginning at the leftmost edge of the adhesive layer, i.e. the edge closest to the central portion of the joint;  The y -axis represents the normalized  y and  xy stresses (  y /  avg and  xy /  avg , respectively).  avg is the average  xy stress along the adhesive mid-thickness for the respective t P2 . Between the three adhesives, stresses in the elastic loading stage are identical, with the sole difference residing in the normalized peak values, since these increase in proportion with the adhesive stiffness ( E values compared in Tab. 1) [31]. Thus, graphically, only the results for one adhesive are presented, in this case for the Aradite ® 2015 (Fig. 5), which has the middle stiffness. It can be first observed that  y stresses are prevalent over  xy stresses, which was expected due to the expected peel loading, although  xy of non-negligible magnitude also develop due to the sliding of the L-part over the base adherend. Independently of t P2 , peak stresses or at least stress perturbations exist at the vicinity of x/L O =0 and 1 mm, which consist of the stress singularity regions. a) b) Figure 5 : Normalized  y (a) and  xy (b) stresses along the adhesive mid-thickness for the T-joints bonded with the Araldite® 2015.  y stresses were identical between the three adhesives, although with the aforementioned differences in magnitude of peak stresses. The curves depicted in Fig. 5 (a), relating to the Araldite ® 2015, showed intermediate peak values between the other two adhesives. For the joints with t P2 =1 mm, the critical region was undoubtedly x/L O =0, due to the small stiffness of the L-part, arising from its low thickness. For the other t P2 ,  y stresses are either close to zero or compressive at this location. The increase of t P2 gradually reduces the harmful effect of  y peak stresses at x/L O =0, but gradually loads the other edge ( x/L O =1), which is deemed to occur because of the growing thickness and stiffness of the L-part. Actually, this change in deformation pattern of the L-part, namely the significant reduction of its bending, works against the natural curvature -50 0 50 100 150 200 0 0.2 0.4 0.6 0.8 1  y /  avg x / L O 1 mm 2 mm 3 mm 4 mm -100 -50 0 50 100 0 0.2 0.4 0.6 0.8 1  xy /  avg x / L O 1 mm 2 mm 3 mm 4 mm