基于图像处理的木材断裂面分形分析

Fractional analysis of wood fracture surface based on image processing

利用分形理论对水曲柳木材三点弯曲断裂和冲击断裂的断面进行定量研究,探索木材断裂的分形特性以及定量地分析木材断裂机制。试验中,利用计算机图像处理技术从微观和宏观的角度提取断裂面图像信息,并通过小岛法计算分形维数,分析分形维数与弹性模量、抗弯强度和冲击韧性的关系。结果显示,木材断面微观和宏观形态在一定的尺度范围内存在自相似性,具有分形特征;材料裂纹试样的分形维数2.601 2高于无裂纹试样的分形维数2.566 3,而裂纹试样的弹性模量6.17 MPa和抗弯强度105.17 MPa均小于无裂纹试样的弹性模量7.08 MPa和抗弯强度109.18 MPa;抗弯强度与断裂面分形维数之间的线性关系明显,弹性模量与分形维数之间线性关系不明显。木材冲击断裂面的分形维数2.607 8要高于弯曲断裂面分形维数2.566 3,但是与裂纹试样弯曲断裂面的分形维数值2.601 2接近;而且,水曲柳的冲击韧性和断裂韧性与分形维数之间呈明显的线性关系。

Quantitative studies on the fracture surfaces of three-point bending fracture and impact fracture for the com- mon timber ashtree were launched using the fractal theory, the fraetal feature of wood fracture was explored and the fracture mechanism of wood fracture was analyzed quantitively. In the study, computer image processing technology is employed to extract the image information of fracture surface both in macro and micro views;and the fraetal dimension of fracture surface is calculated with Slit Island Analysis. Moreover, the relationships between fractal dimensions and MOE, bending strength as well as impact toughness are analyzed. The results show that the wood fracture surface within a limited dimension has remarkable self-similarity and fractal feature. The fractal dimension of the SE （B） samples is 2. 601 2 and is higher than that of the WL samples,which is 2.566 3 ,but the MOE and bending strength of the SE （B） samples are 6.17 MPa and 105.17 Mpa,respeetively,and are lower than those of the WL samples,which are 7.08 MPa and 109.18 MPa,respectively. There exists significant linear correlation between fractal dimension and bending strength, but the linear correlation between fractal dimension and MOE is not obvious. The fractal dimension of wood impact fracture surface is 2.607 8 and is higher than that of bending fracture surface ,which is 2.566 3 ,but is close to the fraetal dimension of three-point bending fracture surface of SE （B） samples,which is 2.601 2. Moreover, for the timber ashtree, there exists significant linear correlation between fraetal dimension and impact toughness as well as fracture toughness.