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Research on Wood Chip Shear and Impact of the Fracture Characteristics Based on Fractal Theory

Author: XuWei
Tutor: ZhangShaoQun
School: Northeast Forestry University
Course: Mechanical Manufacturing and Automation
Keywords: wood fractal theory shear strength impact toughness fractal dimension
CLC: TS62
Type: Master's thesis
Year: 2012
Downloads: 49
Quote: 0
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Abstract


This article will analyze wood material in the process of grinding that happening continuous shearing and impact fracture, into a single pieces of wood. Through analyzing the experiment of the wood specimen transverse longitudinal shear and impact to develop the disintegrate mechanism of raw material. Due to the wood are of different hierarchy, porosity, anisotropic properties, the process of fracture not only the characteristics of ordinary materials fracture, but also a process that be non-equilibrium and nonlinear. The traditional study methods of fracture cannot be found the law of breaking wood. But the fractal theory is a powerful tool to the nonlinear system. So this text researches the shearing characteristic to the wood specimen based on the fractal theory of fracture characteristics of them.This paper through the fracture tests of the white pine, linden, birch, poplar and mongolian pine specimens of transverse shearing (softening and not softened) fracture tests, analyzing the heat-water softening to the physical and mechanical influence of the wood. Then the results show that there is a strong influences that the hot water softening to the physical mechanism. But not all of the wood can achieve the desired softening effect.This article through the experiment to the transverse, longitudinal specimens of the impact of shear of the white pine, linden, birch, poplar and mongolian pine, researching the differences between mechanical properties on the different directions. The results show that there is a bigger strength difference between wood transverse and longitudinal shear. The white, linden, birch, poplar and mongolian pine longitudinal shear strength is till the transverse shear strength of2～4times, but it is a little differences of impact toughness between wood transverse and longitudinal. Through the analysis of variance can be found that the white pine, linden, poplar and mongolian pine transverse and longitudinal differences are not obvious except birch.This paper makes the correlation analysis to the main features of the fracture, existing certain the linear positive correlation among the shear strength, impact toughness and fracture fractal dimension. But there are big differences to the significant correlation through the different ways whether softening. Wood of transverse shear strength, impact toughness and fracture fractal dimension of the relevance of significant is higher than vertical. The linear correlation of the specimen of shear strength and fracture fractal dimension after softening in the transverse shear of the white pine, birch, poplar and mongolian pine is higher than other specimens without softening.The research shows that:the choice of wood material softening conditions should change with different species of wood material to achieve best softening effect in the actual fiber separation process. Thus reduce plate wear and the energy consumption that from the grinding process of the heat grinding machine. If wood materials mainly happened shear fracture along the transverse, would greatly reduce the energy consumption of the grinding process. It provides the theory basis of mechanics for the optimization design of structure of the refining plate.

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CLC: > Industrial Technology > Light industry,handicrafts > Wood processing industry,furniture manufacturing industry > Raw materials and accessories
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