Modulus of elasticity and tensile strength of Douglas-fir roots

The modulus of elasticity and the tensile strength were determined for a sample of live Douglas-fir (Pseudotsugamenziesii (Mirb.) Franco) roots collected in the Oregon Coast Range. Most of the roots displayed both a "form" modulus of elasticity and a "material" modulus of elasticity. The form modulus occurred as a tortuous root straightened out, whereas the material modulus developed following this initial straightening as the wood fibers within the root directly resisted elongation. The average form and material moduli of elasticity were, respectively, 185 and 503 MPa, whereas the average tensile strength was 17 MPa.