Comparison of the TL-shear strength of normal and compression wood of European larch

The strength of larch compression wood specimens in longitudinal shear in the radial plane was determined and compared to normal wood. Fracture surfaces were examined with a scanning electron microscope. Compression wood showed higher shear strength than normal wood. The difference persisted after correction of the strength values for density. Scanning electron microscopy revealed clear differences in the pattern of failure in normal wood compared to compression wood. While transwall and intrawall fracture predominate in normal wood, intercell fracture at the middle lamella occurs in compression wood. An explanation of this change in fracture behaviour is proposed in terms of microfibril angle and lignification of the cell wall.