Impact of Veneer Layouts on Plywood Tensile Strength

The aim of the research presented in this paper is to study the plywood tensile strength through a change of the position of layers in the panel structure around the central axis, without changing the number and thickness of veneers. So far, it has been known that the veneer layout in plywood structure has a significant impact on plywood bending properties. Besides these mechanical properties, the tensile strength of plywood is also a property that can define the use of plywood as a structural or non-structural panel. For studying the impact of veneer layout on plywood tensile strength, experimental models of nine-layer plywood were made. The models were made from peeled beech veneer with the thickness of 1.2, 1.5, 2.2 and 3.2 mm. The modelling was performed on the basis of changing the position of veneer, 3.2 mm thick, around the central axis. Pure water-soluble phenol-formaldehyde resin was used as plywood binder. The tensile strength of plywood panels was tested in five directions: parallel and perpendicular to the face grain, as well as at the angle of 22.5°, 45° and 67.5° to the face grain of the plywood panel. On the basis of the obtained data for tensile strength in different directions of plywood panel, the coefficient of equality of tensile strength of plywood models was calculated (Ket). The coefficient of mass quality (Kmq) was calculated, too. The research results showed that different veneer layouts in plywood structure have a significant impact on plywood tensile strength. All tested plywood models meet the defined values of tensile strength in accordance with the requirements of the national (МКС) standard for structural plywood for use in construction. Different layouts of veneer sheets in panel structure give opportunities for production of panels with different strength characteristics.