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 M aritime pine. Fracture surfaces are shown to display an anomalous dynamic s caling of the crack roughness. This anomalous scaling behavior involves the existence of two different and independent roughness exponents. We determi ne the local roughness exponents zeta(loc) to be 0.87 for spruce and 0.88 f or pine. These results are consistent with the conjecture of a universal lo cal roughness exponent. The global roughness exponent is different for both woods, zeta=1.60 for spruce and zeta=1.35 for pine. We argue that the glob al roughness exponent zeta is a good index for material characterization. [ S1063-651X(98)00512-1].