The research represents the ongoing investigation of the welded joints behavior made of low-carbon low-alloyed steel in the presence of different multiple defects. Following the initial experimental and numerical analyses performed on low-grade steel, a set of experiments were performed with specimens made of steel EN 1.0044 (commercial designation S275JR), along with development of new numerical models. Four combinations were made, including defects like undercuts, excess weld metal, misalignment, weld face sagging and incomplete root penetration, considering that these defects are often encountered in practice, and can appear simultaneously. The finite element method (FEM) was used to simulate the experiments. Tensile properties of the HAZ and weld metal were calculated using strain measurements by the digital image correlation (DIC) method. The finite element method (FEM) results were in good agreement with the experimental ones.

Digital image correlation represents a useful, efficient, and widely applied method of non-contact strain and displacement measuring in various types of structures. It is often combined with other means of integrity assessment, such as the finite element method and the use of fracture mechanics parameters. This paper presents a short overview of digital image correlation in various fields including mechanical and civil engineering, biomedicine, and some other, more ‘exotic’ examples. Additionally, some of the examples shown here perfectly illustrate the applicability of this method to cases where high levels of detail and accuracy are necessary in order to measure strain.

Welded joints are widely recognized as the most critical point in structures made of armour steels due to pronounced thermal effects, microstructural heterogeneity, and the degradation of mechanical and fatigue properties. This study investigates the mechanical properties and fatigue crack growth resistance of a welded joint produced on SA 500 armour steel, with the aim of preserving the properties of the base material as much as possible. To achieve this, a welding procedure incorporating a high-strength filler wire and optimized welding parameters was applied. Hardness and tensile testing was conducted to evaluate the extent of property degradation caused by welding. The results demonstrate that the applied welding process effectively limited the reduction in hardness and tensile strength, achieving values reasonably close to those of the base material. In addition, fatigue crack growth behaviour was investigated in accordance with ASTM E647, using both the Paris law and the McEvily law. The obtained fatigue crack growth curves and threshold stress intensity factor (ΔK_th) values indicate the nearly identical fatigue behaviour of the base material and the heat-affected zone, confirming the successful preservation of base material fatigue behaviour in the thermally affected zone. Moreover, the weld metal exhibited superior resistance to fatigue crack initiation and growth. Overall, the results confirm that the proposed welding approach provides favourable mechanical and fatigue performance for welded joints in armour steel applications.

Belgrade fair hall 1 is well known for its dome, which is still the world largest self-supported construction made of pre-stressed concrete, with its diameter of 106 m. In this paper the Finite Element Method (FEM) was performed to analyze different loading and supporting conditions. At the same time, crack growth in a support column was simulated by the extended FEM (XFEM). Results of numerical calculations indicate ingenious design of such a complex structure which was based on “hand” calculation decades ago, without computers. In addition to classical engineering and more advanced numerical calculations, risk based analysis was performed taking into account artificially introduced crack and Failure Analysis Diagram, obtained using stress intensity factor and net stress, as well as fracture toughness and critical stress. This analysis, made for the first time for Belgrade fair hall 1, proved that its structural integrity is jeopardized only when a crack reaches half the thickness of a steel bar.

Due to exploitation conditions, pressure equipment is vulnerable to various damage mechanisms, including corrosion, fatigue, creep, etc. Therefore, it is of great importance to monitor and maintain such equipment regularly, in order to ensure its safe and reliable exploitation. In this paper, the focus is on repair welding activities for flue pipes in a steam boiler. In addition, research shown here also includes the techno-economical analysis of the repair procedure, outlining its numerous benefits in terms of structural integrity and sustainability.

Presence of defects in welded joints is inevitable, and more often than not, presence of a specific defect is accompanied by other types. This research represents the development of a combined method for analysing the structural integrity of welded joints with multiple defects - relying on experimental testing, deformation monitoring using digital image correlation, and numerical simulations via finite element method. It all started a long time ago, with simple 2D models, and continued over time, introducing new improvements to the existing models, taking into account various factors, such as welded joint material heterogeneity, the presence of cracks initiated from the most critical defects, and stresses which act in directions outside of the model specimen’s main axis.