Linear shear properties of spruce softwood

The shear test described by Arcan was used to investigate orthotropic shear properties of clear softwood from Norway spruce. The test was chosen on the basis of a thorough literature study, although the experimental setup was somewhat modified compared to the original. A total number of 85 specimens were tested for loading and unloading in 6 different configurations. Manufacturing and mounting of specimens as well as testing worked well. Video extensometry was used to measure strain in the critical specimen section, and the determined moduli were evaluated by means of FEM calculations. The average shear moduli were found to equal G (LR) = 640 MPa, G (LT) = 580 MPa and G (RT) = 30 MPa, which correspond well with values reported in literature for various spruce species. No significant differences in shear moduli could be found for configurations comprising the same material plane. Moduli determined from unloading generally showed higher values than those obtained in loading, but only the rolling shear RT demonstrated a significant difference. Each of the three shear moduli was found to be significantly different from each other, with G (LR) about 10% higher than G (LT) , and approximately 20 times higher than G (RT) . The coefficient of variation equalled 0.24, 0.37 and 0.28, respectively. The correlation with density was in general low. It was found that the 3-parameter Weibull distribution is most appropriate for a probabilistic description of the three orthotropic shear moduli of wood.