1971 Volume 20 Issue 218 Pages 1181-1187
The elastic constants of plywood can be mathematically calculated when those values of veneers and glue layers have previously been known. In the fact, however, that glued veneers in the plywood have plenty of minute cavities filled with adhesives, it is suggested that there must be variation from the single veneer to the glued veneer in their mechanical properties. It is necessary in the calculation of the constants that such variation will be taken into account. So in the first place the variation in the elastic constants of Japanese Oak was experimentally examined (under three different conditions); in solid wood, in the rotary-cut veneer and in the“veneer-laminated wood”, in which all the veneers were laid in parallel with their grain direction. Another investigation was carried out to calculate Young's moduli and the modulus of rigidity of plywood constructed of Red Lauan, Basswood and Japanese Oak using the elastic constants obtained from the veneer-laminated wood.
The results of the tests are summarized as follows:
(1) Of the longitudinal direction there has been but little difference made to Young's modulus (Figs. 4 and 6) by the lathe checks and gluing process.
(2) The veneers 3mm thick showed remarkable drop in Young's modulus tangential to about 15% as hard as solid wood, while with the veneers 1mm and 2mm thick, the drop was only to 50% and 30% as hard respectively (Fig. 5).
(3) When glued together the veneers 3mm thick recovered its stiffness to be 85% as hard as solid wood, while thinner veneers showed full recovery, or even showed excess stiffness (Fig. 7).
(4) Altogether 11 samples of plywoods were examined to calculate their elastic constants, and there has been good agreement of their calculated values with their observed values (Table VII).