Fractal dimension and multifractal analysis of the welds of metal structure

Abstract

In the paper, the results of the investigation of the connection between the content of non-metallic inclusions in the metal structure and the fractal dimension on the example of welds of high-strength, low-alloy steels.

The work expediency is justified by the fact that, although the quality of the metal is determined by its structure, currently the relationship between such parameters of the microstructure as the grain composition, the microstructure of the interphase boundaries (for welded joints) and the performance of the structure/object under load conditions during exploitation seems too complex and ambiguous for theoretical and phenomenological description. There is no comprehensive understanding of the mechanisms and factors that control the formation of microstructures during phase transformations, especially in the conditions of electric arc welding, which are far from equilibrium characteristicsat the present time.

Traditional concepts based on the principles of equilibrium thermodynamics and it doesn’t allow, in particular, to answer questions about the reasons for the appearance of one or another morphology of the isolated phases, as well as to adequately assess the determining role of kinetic factors in the problem of the formation of the structural state.The most difficult part of the problem isthe dependence on the cooling trajectory, which even in simpler cases, closer to equilibrium conditions compared to welding processes.

Management of the structure formation of welds and determination of the location of failure in existing structures are connected with the need for a correct description of the structure. The complexity of the structure of real metals or welds is the main obstacle to the synthesis of adequate models for computer-aided design of the structure and prediction of their properties.

Fractal formalism, in particular, fractal and multifractal parameterization of structures, can in principle become the basis for choosing adequate numerical models of structures of real welds, necessary for computer design of structures and prediction of their properties.

The influence of non-metallic inclusions can have a negative character and even pose a serious danger, since the stress concentration can exceed the limit values ​​for the material and the inclusion, therefore, can become a focus of destruction.