Issue 31

C.L. dos Santos et alii, Frattura ed Integrità Strutturale, 31 (2015) 23-37; DOI: 10.3221/IGF-ESIS.31.03 33 (elastic stiffness). In addition, the curve obtained with distinct plastic parameters calibrated for each direction (“Elastic- plastic (2)” series), showed better performance at the beginning of the yield region. The experimental analysis revealed that the T-connection exhibited two distinct failure modes: a dominant ductile failure mode, when it occurs at the centre member and a dominant brittle failure mode when it occurs at the side members. With respect to the stress distributions, it was observed (see Fig. 10) that the maximum shear stresses, in the RL plane, occurred at the centre member and the maximum direct stresses, along the radial direction, occurred in the side members, in both cases at the vicinity of holes. The centre member shows a shear (RL plane) stress concentration above the hole, at locations where cracks were observed to initiated and propagated (see Fig. 5). In the side member, significant radial tensile stresses was verified in the hole surface at the horizontal mid-plane. These tensile stresses can be related to the failure modes occurred in those members (see Fig. 5). Results illustrated in Fig.10 were obtained for the elasto-plastic analysis with similar plastic constants for each wood member. However the previous discussion is also valid if distinct plastic constants were used for each wood member. (a) (b) Figure 10 : Stress fields from elastic-plastic analysis, using constants from Tab. 3: (a) centre member; (b) side member (F=14kN). Figure 11 : Load-displacement curves: experimental vs. elastic-plastic and elastic with cohesive damage modelling. Fig. 11 presents the experimental data with the numerical load-displacement curves resulting from the exclusive application of plasticity models and also resulting from the use of a full elastic model with a cohesive damage interface on the side member. The later numerical result exhibits a near linear behaviour until failure and slightly higher elastic stiffness than resulted from the application of the plasticity models. The cohesive damage model with elastic simulation did not provide any load reduction before the crack propagation onset; therefore a typical brittle behaviour is modelled. The cohesive damage model was able to prevent the unbounded load growing. The simulation was performed until a crack initiated and propagated under unstable conditions. Thus, it is demonstrated the good performance of the cohesive model in predicting the ultimate load. In Fig. 12, the nodal relative opening displacements of crack faces are quantified, confirming a corner crack, with a maximum crack opening of about 0.19 mm, at the unstable crack propagation onset. Fig. 13b illustrates the resistance degradation (evolution of radial stresses) in the interface nodes located at the hole surface