The angle of the growth rings in relation to the direction of the applied load and the absorbed energy in impact bending(toughness) were measured for 10 species. Specimen size was 2 cm square by 28 cm long. The orientation of the annual rings resulting in the load being applied to the tangential face(radialdirection) is defined as β = 0°, and β = 90°indcates that the load is applied to the radial face(tangential direction) as shown in Figs 1 and 2. The data were analyzed statistically and the results are as follows :
1) Statistically siginficant correlation between the absorbed energy of impact bending, U and β was found for 6 of 8 species of softwoods and for 2 of 4 species of hardwoods. Multiple regression analyses for U as the dependent and β, the specific gravity Ru, and in some oases moisture content M.C. as independent variables were siginficant for all species of this study as shown in Table 2.
2) The relationship between β and U is sb own in Fig.1 and 2. In those species where there was significant correlation, the slop of the linear regression equations had the same tendency from species to species. Types of failure in impact bending test are shown also in Figs. 1 and 2.
2) Using a quadratic regression equation, statistically siginficant curvilinearity was found in Scot Pine(Ohoshu Akamatsu), when β ranged from 0°to 180°, with a minimum at β = 90°(Fig. 3).