Numerical analysis of the ENF test for mode II wood fracture

A numerical study was performed on the End Notched Flexure (ENF) test to obtain the critical strain energy release rate (GIIc) of a clear Pinus pinaster wood, in the orthotropic directions TL and RL. Two-dimensional numerical analysis, including interface finite elements and a progressive damage model based on indirect use of Fracture Mechanics, was performed to simulate the ENF test. The numerical results were used as input data in the Corrected Beam Theory (CBT) and Compliance Calibration Method (CCM) to obtain GIIc. The influence of geometrical parameters and friction effects between the crack surfaces were evaluated. Moreover, some conclusions were drawn about the influence of cohesive shear strength on the load–displacement relationship and on measured GIIc. The main objective is to define adequate specimens for the ENF test in wood. Finally, on the basis of a two-dimensional approach, it was concluded that the used geometry allows obtaining rigorous values of GIIc, not only at initiation but also during a stable crack propagation. The CBT using an equivalent crack length approach proved to be accurate for the selected geometry.