Orthotropic strength and elasticity of hardwoods in relation to composite manufacture. Part I. Orthotropy of shear strength

The orthotropy of apparent shear strength of three Appalachian (aspen, red oak, and yellow-poplar) and two East European (true poplar and turkey oak) hardwood species was investigated. The experimental approach included shear force applications in planes parallel to the grain so that the annual ring orientation and the orientation of the grain relative to the applied force direction were systematically rotated. Statistical analyses of results dem onstrated significant effects of grain and ring orientation on the shear st rength for all species. Furthermore, interaction between these two factors was detected. Three models, developed to appraise the orthotropic nature of shear strength, were fitted to experimental data demonstrating acceptable to good agreement between predicted and experimental values. A combined mod el based on tensor theory and a modified version of Hankinson's formula pro vided the best fit by r(2) analysis. The information obtained and the model s developed might be used to explore the shear strength of structural compo sites in which the constituents are systematically or randomly aligned.