Effects of grain angles of face veneer on surface wave velocities and dynamic shear moduli of wood-based composites

The effects of grain angle of face veneer on surface wave velocity and dynamic shear modulus of three types of wood-based composites were examined using a surface wave propagation method. It was found that grain-angle dependence of surface wave velocity and dynamic shear modulus indeed exists for wood-based composites. Grain angles of face veneer were found to have substantial effects on the surface wave velocities and dynamic shear moduli of wood-plastic composite (WP), wood-fiberboard composite (WF), and wood-metal composite (WM). The orthotropic properties of the three composites were defined as the ratio of surface wave velocities at 0° and 90° grain angles (V₀/V₉₀), which were 3.7, 2.2, and 2.0 for WP, WF, and WM, respectively. For WP, WF, and WM, the dynamic shear moduli in the 90° grain angle of face veneer were approximately 7%, 19%, and 25% of that in the 0° grain angle, respectively. The relationships between grain angles of face veneer and the shear moduli of the three types of wood-based composites could be represented by Hankinson's equation, and their optimal n values were 2.1, 1.2, and 1.3 for WP, WF, and WM, respectively.