New test method reveals how wood creeps and warps under pressure over decades
Researchers have developed a practical way to measure how wood deforms slowly under sustained stress—a critical property for designing buildings and wind turbines that must remain stable for 30+ years. The findings fill a gap in material data that engineers have lacked, potentially enabling more efficient and cost-effective structural designs.
Originaltitel: Evaluating the viscoelastic shear properties of clear wood via off-axis compression testing and digital-image correlation
<p>Highly anisotropic materials like wood and unidirectional polymer composite structures are sensitive to shear deformations, in particular close to fixed joints. Large wooden structures in buildings and, e.g. wind-turbine blades, are designed to last for decades, and hence are susceptible to unwanted creep deformations. For improved structural design, the shear-creep properties of the material are needed. These are rarely available in the literature, possibly because of technical difficulties to achieve a well-defined shear-stress state in test specimens. For cost-efficient testing, this goal of a pure stress state necessarily needs to be compromised. In the present study, we propose a simple test method based on uniaxial compression on wooden cubes, but is equally applicable for fibre composites. The viscoelastic shear properties of Norway spruce (Picea abies) under off-axis creep compression tests have been characterised in all three directions. The tests are performed in a controlled climate chamber and the creep strains are captured using digital-image correlation.</p>