Assessing wood quality by spatial variation of elastic properties within the stem: Case study of Pinus pinaster in the transverse plane

Abstract

The wood quality of maritime pine (Pinus pinaster Ait.) is discussed in view of spatial variability of density, annual growth ring characteristics, and transverse elastic properties within and among five basal logs. X-ray microdensitometry measurements are carried out to assess both average (Dmean) and local (DEW, DLW) densities of annual growth rings, as well as the respective dimensions (EWW, LWW) and fractions of earlywood (EW) and latewood (LW) layers. Mechanical tensile tests on a set of specimens with different ring orientation are proposed. Transverse elastic properties are determined by coupling an inverse identification strategy with full-field deformation measurements provided by digital image correlation. For a suitable range of off-axis angles, this method allows the simultaneous characterisation of the four orthotropic elastic properties in the RT plane: ER, ET, νRT, and GRT. These results are found in agreement with reference values. From the sampled specimens among logs, ER and GRT are robustly identified in all cases and therefore are selected for further analysis of structure-properties relationships. Correlations between Dmean and ER and GRT are positive and statistically significant. Furthermore, other parameters also show significant correlations with the elastic constants, especially Dmin, LWW, and DEW.