Uniaxial compression of rotationally symmetric Norway spruce samples: surface deformation and size effect

The influence of size on strength is well known for various materials and testing methods, but not enough data and knowledge of the effect on wood under compressive strength can be found. Therefore, the deformation and compressive strength of hyperboloid Norway spruce samples were tested for different dimensions. To determine the influence of size on the strength, three different approaches were used: “weakest link theory”, “size effect law” and “multifractal scaling law”. Of the three scaling theories, the “size effect law” and the “weakest link theory” predicted the effect well. Additionally, to determine the surface deformation of various samples, DIC3D was used on the largest sample geometry. The experiments show the existence of a possible size effect during compression, while digital image correlation illustrates the expected differences in deformation due to the shape and dependence of the strain distribution on the structure of wood. Additional experiments are proposed to further verify the observed effects and expand the knowledge of the size effect.