Resistance-curves and wood variability: Application of glued-in-rod

The current study investigates the withdrawal strength of glued-in rods as part of linear elastic fracture mechanics. An experimental campaign was performed in order to observe the effect of the specie (spruce and oak) on the axial strength of glued-in rods for given geometrical configurations. Finite elements modelling was presented in order to consider the progressive damage and the crack propagation located at the wood-adhesive interface (failures obtained during experiments). The approach aims at separating the progressive failure due to mode I and mode II. For this, Resistance-Curves, regarded as material properties, were used to characterize the peeling and the shear effects at the ultimate state. The study reveals that the mode I initiates the damage in the glued interface. Using several finite element runs, the predicted pull-out strengths were estimated from the elastic properties of substrates (wood, adhesive and steel) and the fracture properties of wood. Numerical results show the dependence of the strength according to the stiffness of the materials. Moreover, the scattering of the results is also affected by the variability of the fracture energies of the wooden substrates. The investigation leads to propose a robust approach which is able to predict the axial strength of glued-in-rods, considering the variability of each material and combining damage and crack propagation of the wooden substrate. It reveals that the prediction of the ultimate load cannot be performed considering only the failure mode II.