Fractal Dimension for Ceramic Fracture Surface
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0904-BB04-05.1
Fractal Dimension for Ceramic Fracture Surface Jerzy Bielecki1 and Piotr Kotowski Institute of Materials Science and Applied Mechanics Wroclaw University of Technology Smoluchowskiego Str. 25, 50370 Wroclaw, Poland 1 Institute of Power Energy Mory Str. 8, 01-330 Warszawa, Poland ABSTRACT An investigation of an influence of loading parameters on fractal dimension of electrotechnical ceramics fracture has been presented. Objects examined were samples made of C110 and C130 ceramics. Specimens were breaking under cyclic and static loading conditions. To estimate fractal characteristics a method used for metals fracture had been adapted. Fractal dimensions were estimated for profiles obtained by the vertical cross section method. Obtained results show that fractal dimension does not characterises the material. That dimension does not characterises loading conditions, as well. INTRODUCTION Ceramic is still the most common material in the world used for insulators. High-voltage power lines during operation are exposed to different types of loads. They are operating among other things in changing mechanical loading conditions caused by wind blows that may lead to fatigue failures of insulators ceramic parts. Therefore many works concerning metods of prediction of ceramic materials lifetime appear. Ceramic belongs to the group of brittle materials for which small strains measurement is a very difficult methrological problem. Therefore some try to use other investigation methods enabling to learn more about fracture process in ceramics. One of the latest tool used for real systems modeling is fractal geometry [1]. Research results from that field unequivocally show that most of real objects have fractal features [2-4]. It convince to use fractal models that, in many cases, give better approximation than models using smooth manifolds. It is very important to know fractal characteristics among which fractal dimension is a fundamental one. It is well established that the fracture properties of materials depend on the microstructure and on the damage process. Both these parameters may have a strong influence on the local deviations of the main crack and thus on the shape of fracture surface. Many experiments on materials as different as ductile aluminum alloys or brittle materials like rock have shown that the topography of fracture surfaces is self-affine. However, the fractal dimension characterising the surface D is ~2.2 (or Hurst exponent H ~0.8) has been reported in many cases. These results seem to support the idea that the fractal dimension of fracture might have a universal value, i.e., independent of the material. Majority of experiments in this field concern the fracture surfaces obtained under static torn condition. In this paper, we present experiments for fracture obtained under conditions of cyclic loading as well.
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EXPERIMENTAL DETAILS The object of investigation was C110 and C130 electrotechnics ceramic (fig. 1). Cylindrical, not glazed specimens were manufactured using throwing f
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