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PDF : 05020045.pdf
title(En) :Studies on the Elasticity of Plywood. I. The Effect of Grain Direction on the Elastic Constants of 3-Plywood in Tension or Bending.
author(En) :Minoru Sawada, Kenichi Hata
information :Mokuzai Gakkaishi 5(2), 45-49 (1959)
assort :Original Article
summary(En) :   If, as is usual, the plywood is made from a single species, and the grain directions in alternate veneers are at right angles, then the elastic constant E at an angle to the grain are given theoretically by the equations, (2.5) in tension and (2.8) or (2.9) in bending, in terms of the basic constants of all the veneers in the plywood (i.e. the Young's modulus parallel to the grain EL = E0 ; the Young's modulus perpendicular to the grain ET = E90 ; the rigidity modulus GLT ; the Poisson's ratio μLT).
   The basic constants (EL, ET and GLT) and their ratios (κ = EL/GLT and Ω = EL/ET) of the veneers in the plywood were determined by the tensile tests of the strips, as shown in Fig. 3, and lie at the angle Θ with the grain in the outer plies of the sheet, for the values of Θ: 0°, 45° and 90°.
   The specimens were conditioned in the room at 20°C and 75 per cent humidity and the measurements were carried out in the conditioning room in the Forest Experiment Station. The construction of test plywood is shown in Fig. 1, and the moisture contents u, specific gravities Ru and the thickness values in Table 1. The method of cutting the specimens is shown in Fig. 2.
   The Young's moduli determined by the tensile tests are as follows (see Table 2):
   solid wood (Japanese basswood; Tilia japonica SIMK.)
   at  0° EL = 67.8 × 103kg/cm2
      45° E45 = 11.8 × 103kg/cm2
      90° ET = 17.2 × 103kg/cm2
           κ = EL/GLT = 19.1
           Ω = EL/ET = 3.94
 where     μLT ≈ 0.5
            GL ≈ E45/(4 - E45/ET)
   The calculated curve in Fig. 4 was obtained from the equation (2.2) using these basic constants. In the case of Young's modulus in tension at grain angles up to 90°, the experimental results agree well with calculated curve from the equation (2.3) as shown in Fig. 5.
   In the case of Young's modulus in bending, the agreement with the calculated curve from the equation (2.9) is also approximately close as in Fig. 7.