The thin‑walled heat exchange tubes operating at high temperature and pressure also occur in the steam generators of pressurized water reactors. These components ensure the hermetic separation of the primary and secondary circuits, cool the reactor core, and produce the steam required for power generation. In operating plants—and likewise in Gen III+, Gen IV, and SMR designs currently under construction—there are typically 1–4 steam generators, each of which may contain tens of thousands of such tubes. Because these tubes will be under high loads over the service lives, various tube failure modes must be anticipated, as decades of operation experience have shown. The isolation of defective tubes from service to preserve circuit hermeticity can reduce the heat‑transfer capability on the primary side and the energy available for steam generation; in critical cases, this process may even necessitate steam‑generator replacement. We aim to develop the groundwork—through numerical simulations—for an evaluation method that meets FFS requirements, which can assess the combined effects of volumetric (pitting) and planar (crack) defects that form and act on the outer or inner tube surfaces. The procedure is designed to jointly assess the structural‑integrity impact of combined volumetric and planar flaws on the basis of non‑destructive examination (NDE) data, and to reliably forecast when these degradation mechanisms become critical, thereby supporting FFS‑based decision‑making. As part of this foundation, we investigated equivalent crack geometries suitable for representing the effects of volumetric and planar defects. While different forms of FFS evaluations are widely used in industry, reducing combined failure mechanisms to a 2D formulation enables the criticality of these degradation modes to be checked against established assessment methods. To achieve this, we applied four industry‑used approaches. First, we examined the combined depth of the volumetric and planar defects and approximated their effect with a semi‑elliptical surface crack. Secondly, we compared the difference in stress intensity factors (SIFs) using a semi‑ellipse equivalent to the projected area of the volumetric defect. Third, we compared the stress concentration factor (SCF) of a corrosion pit and a stress‑corrosion‑cracking flaw with that of a semi‑elliptical surface crack producing the same SCF. Fourth and finally, we determined a semi‑elliptical crack by fitting to the SIF values computed from the actual geometry of the combined volumetric and planar defect. The structural‑integrity effect of the resulting equivalent cracks are then evaluated by burst‑pressure analyses and crack‑growth simulations in a simplified FEM, in ANSYS environment.

The railway systems used today are developing rapidly, overcoming the challenges of the age and meeting its demands. Initially powered by animals and then by steam engines, these vehicles have become an integral part of our lives and our economy. In the short and medium term, it has become the most economic form of transport and freight delivery. The system's high load capacity and speed have induced new failures on the track side. The composition of the rails has changed, and stiffer, harder materials are used to withstand heavy loads. Under normal operating conditions, the increased load and the highly rigid wheel-rail contact on a small surface area create high stress peaks. These stress peaks pass cyclically through each cross-section, causing significant fatigue and resulting in the phenomenon known as head-check caused by rolling contact fatigue (RFC). Detection and monitoring of this phenomenon is not sufficiently accurate using current systems. The assessment of faults and damage is of paramount importance from an economic, track maintenance and operational safety perspective. Accurate measurements and data collection are necessary to better understand cracks and how they work. The correct construction of simulation models is extremely important in order to make accurate lifetime estimates. In addition to the model, its results must also be validated. Scheduled control measurements enable the continuous refinement of the model.

In most engineering applications the structural elements are exposed to multiaxial loading, in which case fatigue life estimations are based on critical plane search. The main drawback of these calculations is the huge computational cost, which can only be reduced by the sacrifice of accuracy. In this paper, an optimized algorithm is presented, by which the computational cost can be reduced significantly without the loss of accuracy.

The rail industry has made great improvements since its inception. The load and speed are greatly increased to the initial state. Comfort-enhancing electronic systems have also become commonplace and are used by all vehicles. As a result of these modifications, the operating conditions are deviating from those experienced so far and new failure modes have emerged. New calculation procedures and methods need to be developed due to the differences in lifetime and failure behaviour. With calculations and simulation models, we are able to give a more accurate estimate of lifetime. The estimates make operation easier and more economical, and also improve the safety of operation.

This paper presents the analytical validation methods of contact analysis conducted in finite element environment. A railway wheel-rail contact phenomenon including slip is modelled, but the main focus is on the wheel, so the effect of the rail was considered only by the pressure and traction loads on the wheel surface. The finite element model was validated by analytical methods from the point of view of stress distribution, and the effect of simplifications were evaluated.

This paper presents a possible modelling technique for the propagation of the so-called head check cracks. The term head check (HC) refers to a kind of multiple hairline cracking in the railhead caused by rolling contact fatigue (RCF). This phenomenon has become widespread in recent decades and is still a major problem for the rail industry. The aim of this study is to create a specific finite element modell to examine head checks numerically in order to gain a better understanding of the behaviour of these cracks. The paper summarises the most important aspects of the phenomenon under study and outlines the methods used. Regarding the fatigue-based crack growth simulation the Extended Finite Element Method was applied. The finite element analysis examines the development of the already-initiated cracks in the cross-section of the rail. The finite element modell also takes into account the effect of fluid forced between cracks using a certain technique. The study aims to explore the possibilities of the modelling technique and to estimate the level at which the head check phenomenon can be examined from this approach. Consequently, the exact numerical value of the results might be less relevant, but the characteristics of the results may become rather more interesting. Results achieved in the study have shown that the developed method can be used to examine the head check phenomenon, even if it needs further improvements. Overall, the modelling technique has potential and is a direction for further research in the future.

In this research, a rolling contact fatigue (RCF) caused crack the so-called head check (HC) was studied by the extended finite element method (X-FEM). The formation and treatment of these cracks is a major problem in the railway industry worldwide. The study aimed to explore the capabilities of the X-FEM concerning examinations of crack propagation in rolling contact conditions. The paper introduces the X-FEM from a practical point of view, with an emphasis on the application of the method, rather than focusing on the exact values. Results showed that the method can be used adequately for such complex issues as examination of crack propagation. However, the possibilities of this technique are quite limited in practice yet due to technical reasons.

In this research, the strength increasing effect of nitriding was investigated on a small series of spur gears with a module of 1 mm. The nitriding process was simulated in ANSYS FEM software with DANTE heat treatment external add-on. Only a simplified transient heat treatment model was created to study the basics and the effects of nitriding on spur gears. As a result, the nitrogen distributions, the hardness of the gear tooth flanks, the residual stresses and deformations were calculated with DANTE. Approximate surface endurance limit could be calculated analytically for the analysed spur gears according to the local endurance limit formula of Kloos and Velten. As the surface endurance limit value increased because of the nitriding process, the calculated allowable torque of the driving gear also increased. Even though the higher allowable torque and the initial residual stress increased the contact stress of the gear pairs, the calculated contact stress remains acceptable.

Research significance: In the clinical practice, surgeons sometimes must deal with extended bone defects. Among others, bone grafts are used for filling the large absence. After implantation, the structure of the graft can change, and the graft's load-bearing effect can be significant. This leads to the idea, that during the design of an implant this effect should be taken into account in the finite element simulations. In this paper, the authors show the implementation of the bone graft adaptation. Methodology: This programming task was done by using Python, Tcl and the HyperMesh interface. The bone remodeling algorithm and the related parameters were from the literature research. The results are shown with a finite element model prepared for the Optistruct solver, where the geometry models were based on a patient's CT data. Results: Viewing the bone graft's elemental apparent density, the most loaded areas could be detected. Conclusion: The model can predict qualitatively the bone graft's change, which can provide additional information for the implant design. Further analyses are required to investigate the sensitivity of the results.

The main goal of this research was to study the influence of involute spur gear tip relief on the contact stress at the engagement meshing point (the begining point of the line of contact A). Different predefined involute spur gears and modification parameters (amount and length of modification) were already available from previous studies (Schmidt 2019). In this study, both the drive and the driven gear has tip relief. The modification of the gear profile was achieved through the modification of the gear rack cutter’s profile. This way the profil modification of the gear profiles are generated during the gear generation (gear planning) process. The gears have been nitrided, so after the gear manufacturing process, the heat treatment did not defrom the modified gear profile. The gear modifications were generated in a CAD system, and the calculations were made with FEM. The results show that the tip relief influences the magnitude of the gear contact stress at the first meshig point. With the use of tip relief modification, the contact stress of the meshing gears can be reduced at the beginning of the meshing line.