The dissertation is devoted to the description of a possible additional method for the di-agnosis of materials, based on the concept of fractal dimension and multifractals.
Such a discipline as the diagnosis of metal structures has many different approaches to determining their technical condition. To a large extent, reliability depends on the structure and mechanical properties of the materials used. The mechanical properties, in turn, depend, first of all, on the method of obtaining and operating conditions. As you know, most of the methods and means of technical diagnostics are quite labor-intensive. Therefore, a very actual task is to search for correlation dependencies between the parameters of the fractal structure and indicators of mechanical properties, which does not require significant expenses.
Preparation of the dissertation material was carried out at the Institute of Electric Welding. E.O. Paton of the National Academy of Sciences of Ukraine during studing in postgraduate studies 2014-2018.
The analysis of the data obtained by the method of fractal analysis for the structure of the metal, the influence of inclusions and the dependence on the mechanical properties for steels Ds, 35G / 40, 20K, 70,80 and 85. The results suggest that the method of fractal analysis can be further used to diagnose and further expand the understanding of this approach for steels of other brands.
Fractal analysis in materials science is a mathematical algorithm for detecting a single numerical element to describe multilevel structures, which, in particular, are the structure of metals, fracture surfaces, fracture zones, structural boundaries of the viscous-brittle transition, and so on.
Due to the long service life of a number of existing structures in these industries, the problem of choosing the optimal method of assessing the technical condition for forecasting their residual life remains urgent. To solve this problem, such a discipline as technical diagnostics is designed, which has a variety of approaches, the reliability of which largely depends on the structure and mechanical properties of the materials used, which in turn depend primarily on the method of production and operating conditions. As you know, most of the methods and tools of technical diagnostics are quite time consuming. Therefore, the search for modern control methods that do not require significant costs is a very important task. In view of this, the paper presents data on existing approaches to assess the impact of structural condition of the material, including rolled anisotropy, the duration of its safe operation and - justification for choosing the fractal method as a modern, affordable, correct and inexpensive way to determine the necessary parameters. The essence of this approach is formulated, which consists in processing by scaling of fractal structure and descriptions of distribution of any structural characteristic at the given scaling. It is postulated that fractal geometry describes the structure more carefully than standard metallography, but on the condition that this structure is fractal.
Thus, the aim of the study is to identify and substantiate correlations between fractal parameters of structure D and physical and mechanical characteristics of a number of low-alloy structural steels, including yield strength, destructive pressure, toughness, coercive force, etc. The choice of the type of steel with ferrite-pearlitic structure, to which the investigated materials belong, is substantiated, namely: steel Ds for oxygen cylinders, steel 20K for pressure vessels, and high-strength steel for reinforcing ropes. Full-scale samples, as well as samples destroyed after mechanical tests, calculate the fractal dimension and search for the relationship between mechanical characteristics and fractal dimensions in order to predict performance using fractal sets.
Therefore, without conducting high-value special tests, but only using a fractal approach, there is a real opportunity to determine and predict the performance of materials, in particular in existing structures. In this regard, an algorithm was developed and software was created to assess the structural and textural state of the material based on its fractal characteristics and compared the results of the study of fragments of metal structures by the proposed method during experimental tests with the results of previously known methods of metal diagnostics.
