Twelve Elastic Constants of Betula platyphylla Suk.

Wood elastic constants are needed to describe the elastic behaviors of wood and be taken as an important design parameter for wood-based composite materials and structural materials. This paper clarified the relationships between compliance coefficients and engineering elastic constants combined with orthotropic properties of wood, and twelve elastic constants of Betula platyphylla Suk. were measured by electrical strain gauges. Spreading the adhesive quantity cannot be excessive or too little when the strain flakes were glued. If excessive, the glue layer was too thick which would influence the strain flakes' performance, and if too little, glues plastered were not firm, which could not accurately transmit the strain. Wood as an orthotropic material, its modulus of elasticity and poisson's ratios are related by two formulas: μ_ij/E_i=μ_ji/E_j and μ_ij < (E_i/E_j)1/2. The results showed that the elastic constants of Betula platyphylla Suk. measured by electrical strain gauges were accurate and reliable. The results of shear elastic modulus G_TL and G_LR show a high linear regression correlation coefficient (>0.95) between the reciprocal of elastic modulus MOE-1 and the square of the ratio of depth to length (h/l)², which indicate that shear modulus values measured were reliable by three point bending experiment.