The effect of board density on the modulus of elasticity and the modulus of rupture of Ra
board is shown in Fig. 3. As the board density increased, modulus of elasticity and modulus
of rupture of both Sugi and Douglas-fir strand board become larger. When the board density
was larger than 0.55 g/cm3, the modulus of elasticity and modulus of rupture of both boards
exceeded type 18 PB standard, and the modulus of rupture of both boards was larger than
type 24-10 PB standard. In the case of Sugi strand board with a density of 0.7 g/cm3, the
modulus of rupture had the same value as commercial plywood for construction.
The effect of strand orientation on modulus of elasticity and modulus of rupture of Sugi
strand board is shown in Fig. 4. The modulus of elasticity and modulus of rupture of parallel
specimens in R board were larger than those in the Ra specimen. However, that of the right
angle specimen in R board was smaller than that of the Ra specimen. This tendency was
remarkable for the specimens of P board. Therefore, it was considered that the strength of
the strand made the best use of the bending strength for the strand orientation.
The effect of resin content on modulus of rupture of a parallel specimen in R board is
shown in Fig. 5. When the resin content of the core layer was increased while keeping that of
the face layer constant, the modulus of rupture of both boards showed a tendency to increase.
On the other hand, when the resin content of the face layer was increased while keeping that
of the core layer constant, the modulus of rupture of Sugi strand board increased slightly.