Anomalous roughening of wood fractured surfaces

Scaling properties of wood fractured surfaces are obtained from samples of three different sizes. Two different woods are studied: Norway spruce and Maritime pine. Fracture surfaces are shown to display an anomalous dynamic scaling of the crack roughness. This anomalous scaling behavior involves the existence of two different and independent roughness exponents. We determine the local roughness exponents ${\ensuremath{\zeta}}_{\mathrm{loc}}$ to be 0.87 for spruce and 0.88 for pine. These results are consistent with the conjecture of a universal local roughness exponent. The global roughness exponent is different for both woods, $\ensuremath{\zeta}=1.60$ for spruce and $\ensuremath{\zeta}=1.35$ for pine. We argue that the global roughness exponent $\ensuremath{\zeta}$ is a good index for material characterization.