Multifractal Parametrization of Welded Joints Structure as an Instrument of Diagnostics and Detection of Defects

Abstract

In each particular material the hierarchical peculiarities of defects indicate the corresponding hierarchical peculiarities of mechanisms of damage and limit states accumulation. In accordance with the points of view of V.S. Ivanova, V.V. Bolotin, A.A. Shanyavsky, L.I. Tushinsky, O.B. Naymark, V.V. Lepov, A.A. Bataev, the occurrence of the limiting state on a particular structural level is possible in case of accumulation on it of the ultimate concentration of defects of a certain kind. In such case the “established system” gets a new, additional degree of freedom, which promotes change of the prevailing mechanism of damage accumulation. The acceptability of this concept has been previously determined for a limited range of materials, which usually don’t have evident structural and mechanical heterogeneity. Thus, the extension of available results to the structurally heterogeneous materials and especially to the welded joints of such materials turned out to be a very difficult task. However, the concept of maximum (critical) level of damage accumulation on a particular scale level was introduced not so long ago. When assessing structural and mechanical heterogeneities of the structural material, an important role is played by concepts of similarity of mechanical phenomena, self-similarity of deformation and destruction processes and by the scale factor of reliability, which are considered in their historical development as a part of application of fractal concepts in the materials science. The application of complex synthesized approach (consisting of a set of diagnostic methods in the form of scanning electron microscopy and multifractal parametrization of materials microstructures) for detection of potentially hazardous zones of welded joints with the highest level of structural and mechanical heterogeneity was the main ideology of our study. In order to establish the cause-and-effect relationships of appearance of “macro-corrugations” on the surface of the material, the analysis of the structure of heterogeneous welded joints represented as a hierarchically organized system was performed.