Roughness of Two-Dimensional Cracks in Wood

Fractures in wood that are parallel to the fibers will be quasi-two-dimensional in the orthogonal directions. We have measured the roughness of fractures in Malaysian nemesu and Norwegian spruce wood. Tangential and radial fracture surfaces have very different morphologies due to the strong anisotropy of wood, but the scaling properties seem to be the same. We determine the roughness exponent $\zeta$ to be 0.68 ± 0.04, where the average is taken over different woods, fracture modes, and analyses. These results support the conjecture of a universal roughness exponent of brittle fracture surfaces.