Determination of Elastic Parameters of Full-Size Wood Composite Boards

Samples of five commonly used sheathing materials were tested to determine their in-plane elastic parameters. A total of 219 pieces of 4-foot by 8-foot panels of 3/4-inch and 1/2-inch Douglas-fir plywood, Engelmann spruce plywood, and 1/2-inch Douglas fir particleboard (Underlayment grade) were selected. In-plane-moduli of elasticity were determined along both major axes of the panels by two newly developed testing techniques, One technique utilized the deflection of the panel as a simply supported beam, with a concentrated load applied to the overhang to obtain the static modulus of elasticity, The other method used transverse vibration of the panel to obtain the dynamic modulus of elasticity. A test for the in-plane modulus of rigidity, based on a variation of the ASTM test for shear modulus of plywood, was devised and evaluated. Regression analyses between static and dynamic MOE were found significant, as shown by the correlation coefficients ranging from 0.877 to 0.986. Significant differences were found between the elastic moduli tested along the two major panel axes. Analyses of covariance showed that none of the regression lines could be combined. The average dynamic MOE was 15-20 percent higher than the static counterpart in all cases. Additional stresses, other than those in bending, appeared to interfere with the measurement of the plate modulus of rigidity which was shown to be dependent on the width-to-depth, ratio of the specimen.

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