Orthotropic Strength and Elasticity of Hardwoods in Relation to Composite Manufacture Part III: Orthotropic Elasticity of Structural Veneers

Abstract

Structural veneers approximately 3.2 mm (1/8 in.) in thickness are widely used as basic constituents in structural composites such as plywood, laminated veneer lumber (LVL), and parallel strand lumber (PSL). The veneer processing operation (peeling) may adversely alter the mechanical properties of the wood substance by introducing compression-set, cracks, and splits, etc. The modulus of elasticity (MOE) in tension of five hardwood species, which are potential raw materials for composite manufacture, was investigated in veneer form. The experimental work included dynamic MOE determination using ultrasound stress wave timing and static MOE measurements for comparison purposes. The orthotropy of MOE in the longitudinal-tangential (LT) plane was also a target of the investigation. Theoretical models were fitted to experimental data that may predict the MOE of the constituents according to their position within the consolidated composites. Experimental and analytical results indicated that a combined model including the Hankinson's formula and an orthotropic tensorial approach is the best estimator for MOE of veneers having inclined grain orientation. Furthermore, the relationship between static and dynamic MOE values may be obtained by second-order polynomial models.