The Application Of Fractal Theory To Wood Fracture Behavior

Fractal theory is employed to analyze the wood fracture. And the relationship between fractal dimension and mechanics property of wood is discussed in this study. Three parts are involved in this paper.One is the effect of LT crack of wood on wood transverse bending property. Birch, ash tree, walnut are studied, and it appears that under the bending loads the bending strength of the beam with crack will decrease, but not obviouslyThe second one is the relationship between mechanical properties and fractal characters of wood destroyed fracture. In the study of material science profile analysis and slit island analysis are employed generally to calculate the fractal dimension. But the error is large by profile analysis, moreover, which is not representative. In this study slit island analysis is used and after extracting the fractal curves of the cross section the fractal dimension is computed by the "area-perimeter" method. Consequently the fractal property of wood fracture is verified.As the correlation analysis of wood fracture fractal dimension and mechanical property, it is found that there is the positive correlation between the fractal dimension of wood fracture and fracture toughness. It is different from the traditional opinions of material researchers that the fractal dimension of fragile material is positive proportional to fracture toughness, and the fractal dimension of plastic material is negative proportional to fracture toughness. This is relative to the special structure of wood that is a kind of biomacromolecule material with the property of anisotropy. And this should be probed and researched further. In addition, there is positive correlation between fractal dimension and bending strength, bending elastic modulus.For the relationship of fractal dimension and impact toughness, lots of scholars consider that fractal dimension is positive proportional to the impact power whatever fragile material or ductile material. But it is found that there is negative correlation between them in this study. The reason is that wood is a kind of heterogeneous and isotropic material. And the fracture of wood must be much more complex than that of single-component material; moreover, there are much more the stress concentration and defects. The information about fractal dimension of single component material is limit very much. So fracture conditions of each fracture zones should be taken consideration when the fractal dimension is measured. It needs to be researched further.The third one is that fracture fractal of wood cells is analyzed by SEM. It is found that the fracture of some cells has fractal characteristics, and latter research can focus on studying quantitatively the micromechanics behaviors by fractal theory.