Methodology for evaluation the technical condition of welded elements of steel bridge structures based on the principles of thermodynamics

Abstract

The article presents a methodology for non-destructive testing of the appearance and development of fatigue cracks in the elements of steel bridges at all stages of their development using infrared thermography. Methods of thermal non-destructive testing based on energy balance (dissipative heating method and thermo elastic stress analysis method) are described, and the temperature gap method is introduced. The place of each method at each stage of the development of fatigue cracks is shown. The dissipative heating method is applicable at the stage of crack initiation and makes it possible to establish the cyclic durability according to the criterion of macro crack initiation based on the analysis of energy dissipation during inelastic deformation. The method of analysis of thermo elastic stresses makes it possible to identify areas in which there are stress concentrations caused by internal imperfections and fatigue micro cracks, to evaluate the stress intensity factor, to evaluate the change in the stress state after repair work on the structure, and to establish the exact position of the crack tip. The temperature gap method is based on the thermal insulation effect of the crack. Despite the fact that this method as a whole is of an auxiliary and approximate nature, however, it has the advantage that, unlike methods based on energy balance, it does not require mechanical action, which opens the way to its practical application. For this, as a rule, natural heating of the structure is sufficient, however, additional stimulation by an external heat source can be used. The results of applying the presented methods of thermal non-destructive testing for crack detection and structural integrity assessment both in laboratory conditions and on bridges in operation are presented.