New shear assay for the simultaneous determination of shear strength and shear modulus in solid wood:: Finite element modeling and experimental results

Using a new modified shear test set-up, the longitudinal shear strength and the shear modulus of solid wood were determined, and the resulting shear strength was compared to the widely used block shear test. The two studied wood species-Norway spruce and European larch-showed a clear increase of shear properties with increasing density. Regarding shear strength, the values determined with the ASTM D 143 block shear test were consistently, by a factor of 1.7, above those obtained with the new modified test setup. Finite element analysis revealed the cause for this difference. At a load situation leading to a theoretical shear stress of 6 N/mm(2) obtained by dividing the applied load by the area of the shear plane, the distribution of shear stress in the ASTM block shear specimen is inhomogeneous. A high stress concentration near the loading edge (stress concentration factor = 2.3) is indicated, accompanied by low shear stress towards the opposite end of the shear plane. By contrast, shear stress is consistently high (5.8 N/mm(2)) across the larger part of the new modified shear test specimen, leading to fracture at a lower applied external load than is the case for the ASTM block shear specimen. The distribution and intensity of shear stress in the new test set-up are fairly close to the stress state required for the determination of shear strength and shear modulus, and the new method therefore appears very suitable for the determination of the shear properties of solid wood.