Orthotropic Strains in Compression Parallel to Grain Tests

Strains were measured in the radial; tangential, and longitudinal directions during the loading of small wood columns in compression parallel to the grain. Eight wood species were included in the testing. Strain per unit stress in the radial direction and that in the tangential direction could be plotted as linear functions of strain per unit stress in the longitudinal direction. These linear functions apply to both hardwoods and softwoods. Since these functions are all equivalent to terms in the compliance matrix relating strains to stresses, a good estimate of the compliance terms can be obtained from the derived equations. Estimates of Poisson’s ratios for wood at approximately 12 percent moisture content having Young’s moduli parallel to the grain of 1 x 106, 2 x 106, and 3 x 106 psi are 0.38, 0.36, and 0.34 for vLR, respectively, and 0.48, 0.46, and 0.44 for vLT, respectively. One of the objectives for future research of this type should be to improve strain measurement perpendicular to the load axis in column testing.

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