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Application of fractal and wavelet theory in the bending fracture of Fraxinus mandshurica

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Tutor: WangFengHu
School: Northeast Forestry University
Course: Wood Science and Technology
Keywords: Wood,fracture,fractal,wavelet
CLC: TS61
Type: Master's thesis
Year:  2012
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Abstract:
This paper will use the fractal and wavelet to study the mechanics properties of wood. Research work consists of three parts.Firstly the wavelet theory is used to study the properties of diameter cut material and the string cut material separately.In particular,is to study the wavelet energy rate of different crack length、different moisture content of specimens and the wavelet energy rate of specimens of combining the two factors.By researching the changing of wavelet energy rate of different crack length、different moisture content and double factors under the condition of the specimens,the relationship of the energy rate of different level is obtained by wavelet analyse to forecast the defect and the moisture content of the specimen.Secondly is to qualitative the outward appearance of specimens which are fractured by bending,and find that as the reduction of crack length and the decrease of the moisture content,the fracture present a trend of complexity,and the outward appearance of the specimen under double factors is more complex, then use the "island law" to study the fracture of the specimens which is based on "perimeter-area" method to calculate the fractal dimension of the fracture, in the calculation of fractal dimension the computer software is used.the inclusion is o that with the length of the fracture increasing, the fractal dimension of the fracture decreased, with the moisture content increasing, the fractal dimension of the fracture decreased.Finally, the tend of the fracture fractal dimension and flexural strength,bending fracture toughness,elastic mechanics properties of the specimens as the crack length and the moisture content change is researched,the study finds that the fractal dimension of specimens don’t present a significantly linear relationship with the crack length and moisture content,so the research uses the wavelet theory to extract eight wavelet parameters of the signals, and proceeds the linear regression analysis of the wavelet parameters and the fractal dimension, linear regression equation is concluded,and this will play an important role to understand the nature of the wood.In wood science,wavelet theory is mainly used in the fields of woodiness material nondestructive testing,and fractal theory is used to characterize the complexity of the fracture. Combining the two will make us to understand its mechanical properties with little damage to the wood,and understand wood internal structure and the moisture content of the situation.
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