The paper presents the results of the study concerning elastic properties of beech veneers assembled in plywood panels. There has been derived a complete set of elastic constants for veneers considered as orthotropic bodies. Young’s moduli in the grain direction and in the direction perpendicular to the grain were determined by bending plywood strips with their longitudinal axis parallel and perpendicular to the grain of the face plies. The other elastic moduli of the veneers were calculated through the Young’s modulus in the grain direction, with using the regression functions derived for hardwoods by Bodig and Goodman (1973). The effect of glue lines in plywood on the veneer elastic properties was evaluated.
The paper presents the results of a study concerning the elastic moduli of veneers assembled in pine and beech plywood panels. The elastic modulus of veneers in the direction of the grain and the elastic modulus of veneers in the direction perpendicular to the grain were determined by bending plywood strips with their longitudinal axis parallel and perpendicular to the grain of the face plies. The effects of a resin type and the number of veneer plies in the plywood were evaluated. Threeand five-ply plywood bonded with urea and phenol resins were tested. The effect of glue lines in the plywood on the veneer elastic moduli was also evaluated.
The thickness of glue lines in 3-layer beech plywood was investigated. The plywood was manufactured in a laboratory using the phenol- formaldehyde and urea-formaldehyde resin. The thickness of the real glue lines between surfaces of adjacent veneers was measured using microscopy, and the thickness of the apparent glue lines including the real glue lines and the glue which penetrated into the wood was determined by means of a method worked out by the authors. It was found that the urea glue lines were thicker than the phenol ones and that the depth of glue penetration into veneers was the same for both glues.
The method for determination of the thickness of glue lines in plywood is proposed. This thickness, named the apparent thickness of the glue line, includes the real glue line between surfaces of adjacent veneers and the glue which penetrated into the wood. Application of the method for calculation of the apparent thickness of glue lines in beech 5-ply plywood manufactured in a laboratory using the phenol-formaldehyde resin is presented. Moreover, the real thickness of glue lines in plywood was determined using an optical microscope. The results of the microscopic measurements confirmed the proposed method.