Characterization of Wood Strands From Young, Small-Diameter Douglas-Fir and Western Hemlock Trees

Abstract

Tensile properties of strands processed from small-diameter Douglas-fir and western hemlock trees grown on the Washington coast were analyzed and effects of location within the tree on properties was examined. Reduction factors for strand properties relative to small, clear solid wood specimen properties were determined by correlating strand properties to previously examined small, clear solid wood specimen properties from the same set of trees. These reductions can be assumed to be damage reduction factors that could help in understanding the expected reduction in tensile or flexure property values from testing solid wood specimens to estimate strand tensile properties. The reduction factors ranged between 0.62 and 0.70 for Douglas-fir and 0.79 and 0.82 for western hemlock for the modulus and were approximately 0.46 for both Douglas-fir and western hemlock for strand tensile strength properties. Measured and calculated strand properties, based on transformation equations, will provide needed values for constructing constitutive relationships when modeling strand-based composites. These properties can also be estimated based on solid wood test specimens if necessary