Almudena Majano-Majano

The fracture toughness and properties of thermally modified beech and ash at different moisture contents

The fracture toughness of thermally modified beech (Fagus sylvatica L) and ash (Fraxinus excelsior L) wood under Mode I loading was quantified using Compact Tension (CT) specimens, loaded under steady-state crack propagation conditions. The influence of three heat-treatment levels and three moisture contents, as well as two crack propagation systems (RL and TL) was studied. Complete load–displacement records were analysed, and the initial slope, kinit, critical stress intensity factor, KIc, and specific fracture energy, Gf, evaluated. In the case of both species, thermal modification was found to be significantly affect the material behaviour; the more severe the thermal treatment, the lower the values of KIc and Gf, with less difference being observed between the most severe treatments. Moisture content was also found to influence fracture toughness, but had a much less significant effect than the heat treatment.

On the identifiability of stiffness components of clear wood from a 3D off-axes prismatic specimen: angle orientation and friction effects

The robustness of the test method based on a single 3D off-axis prismatic specimen for the simultaneous identification of the orthotropic stiffness components of clear wood is addressed. In this method, the specimen is consecutively submitted to uniaxial compression tests along its three orthogonal axes. A data reduction based on anisotropic elasticity is applied to extract active material parameters from 3D full-field deformation measurements provided by stereo-correlation over adjacent faces. Two major limitations of this test method, directly affecting the parameter identification, are analysed and discussed: (1) off-axes angle orientation; (2) friction effects. A numerical study pointed out that radial and tangential rotations of about 29° and 9°, respectively, balances out the strain components in the specimen response. Moreover, friction can be reduced by using mass lubricant or soft material in the contact interface, realising transverse shear deformation.