Mechanical Properties of Rotary Veneers Recovered from Early to Midrotation Subtropical-Hardwood Plantation Logs for Veneer-Based Composite Applications

Abstract

This paper experimentally investigates the mechanical properties of rotary veneers peeled from small-diameter hardwood plantation logs, recovered from early to midrotation subtropical hardwood plantations. The study aims at providing essential probabilistic data needed to ultimately predict the capacity and reliability of veneer-based composites structural products [such as laminated veneer lumber (LVL) and plywood] from characteristics that can be measured in line during manufacturing. Two species planted for solid timber end-products (Gympie messmate, Eucalyptus cloeziana, and spotted gum, Corymbia citriodora) and one species traditionally grown for pulpwood (southern blue gum, Eucalyptus globulus) were studied. The compressive and tensile modulus of rupture (MOR) of the veneers, parallel to the grain and for veneer-based composite applications, were experimentally investigated. Results show that the compressive MOR for all species typically ranges from 30 to 50 MPa [for modulus of elasticity (MOE)<12,000  MPa (MOE)<12,000  MPa to 60 to 90 MPa (for MOE>22,000  MPa MOE>22,000  MPa ). The tensile MOR is typically lower than or in the range of the compressive MOR for MOE less than 12,000 MPa, while for larger MOE (MOE>22,000  MPa MOE>22,000  MPa ) tensile MOR greater than 140 MPa were observed. The total knot area ratio (tKAR) of the veneers is also analyzed and Weibull distributions were found to provide a good characterization of the statistical repartition of the tKAR value along the length of a veneer sheet. For each species, equations to best predict a veneer MOR from its measured MOE and tKAR value are derived and fit the experimental results with a coefficient of determination between 0.63 and 0.74. The variability of the MOR of each species was accurately modeled by Weibull distributions, with the distribution parameters determined based on the experimental data. Results shown that southern blue gum and Gympie messmate are the most and least sensitive species to size effects, respectively.