Primary Exploration Of Fractal Dimension Of Fracture Surface Of Deposited Metal And Its Mechanical Properties

The fractal theory developed in the middle of 1970s is a new mathematical branch, and is a useful tool for the nonlinear and non-equilibrium systems. From that time, the fractal theory has been widely applied to different fields of material science. In this paper the application of fractal theory in the physics, chemistry, computer science, especially in material science, have been reviewed. The following results are the basis of our topic:(1) The fracture surfaces of metals have fractal characteristic.(2) As a geometrical parameter, the fractal dimension D, which has the meaning of a entropy, is a result of material meso-structure. Both GIC and KIC are starting fracture parameters and are related with the morphology of material meso-structure. Therefore, it is introducing D into the express formula of GIC and/or KIC that definitely reflects the effect of mesostructure on the toughness. So there is no confliction between D and GIC, KIC.There mainly introduced the fractured surfaces' fractal dimensions of metal and its mechanical properties. Based on the summary, the plans of our research are putted forward. The relationship between fractal dimension of metal fracture surface and mechanical properties of metals are researched and analyzed. Following experimental methods and measure means, such as coated electrodes fusion welding, V-type groove butt joint, tension test, Charpy impact test, Rockwell hardness test, scanning electron microscope, optical metallography, computer image processing, etc. are used to measure the mechanical properties of deposited metal of the coated electrodes, to analyze the content of alloying elements, microstructure and grain size of the deposited metal and to calculate the fractal dimensions of deposited metal fractured surfaces, and to construct the relationships between fractured surfaces' fractal dimensions of deposited metal and its mechanical properties.Based on above-mentioned experiments, the conclusions are listed as follows:(1) The fractal dimensions, which is measured byvertical section method, of the fractured surfaces is about 1-1.25.(2) The fractal dimensions of fracture surfaces of tensile specimens are decreased from the center to the edgy of fractured specimens. For the fractal dimension of fracture surface of impact specimens are increased when the surfaces are parallel to fracture surface, but are decreased when the surface is perpendicular to fractured surface.(3) For the deposited metals specimens of low carbon or low alloying high strength coated electrodes, there is a upwards parabolic dependence of D on the tensile and yield strengths of specimens. And there is a downwards dependence of D on the area ratio and elongation of specimens. As for the dependence of D on the impact absorb energy, it is a proportional relationship. So it is concluded that there is no quantitative but qualitative dependence of D of the fractured surface on the mechanical properties, such as tensile and yield strengths, area ratio and elongation, while D is qualitatively related with the impact toughness. The relationships betweenfractal dimensions of fractured surfaces of deposited metals of coated electrodes and its mechanical properties still need further to explore and research.