  Citation: Chmelko, V.; Harakal’, M.; Žlábek, P.; Margetin, M.; ˇ Durka, R. Simulation of Stress Concentrations in Notches. Metals 2022, 12, 43. https://doi.org/10.3390/met12010043 Academic Editors: Roberto Citarella, Abílio M.P. De Jesus and José César de Sá Received: 20 November 2021 Accepted: 23 December 2021 Published: 25 December 2021 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). metals Article Simulation of Stress Concentrations in Notches Vladimír Chmelko 1, * , Michal Harakal’ 1 , Pavel Žlábek 2 , Matúš Margetin 1 and Róbert ˇ Durka 1 1 Institute of Applied Mechanics and Mechatronics, Slovak University of Technology in Bratislava, Námestie Slobody 17, 81231 Bratislava, Slovakia; michal.harakal86@gmail.com (M.H.); matus.margetin@stuba.sk (M.M.); durka@vakuumtechnik.sk (R. ˇ D.) 2 Regional Technological Institute, University of West Bohemia, Universitní 8, 306 14 Pilsen, Czech Republic; zlabek@rti.zcu.cz * Correspondence: vladimir.chmelko@stuba.sk Abstract: The fatigue life curves of materials are very sensitive to the magnitude of the stress amplitude. A small change or inaccuracy in the determination of the stress value causes large changes or inaccuracies in the calculated fatigue life estimate. Therefore, the use of computer simulations for fatigue life estimation requires a proper model development methodology. The paper is devoted to the problem of the modeling of components in notches using FEM. The modeling parameters significantly influencing the obtained stress results have been defined. Exact analytical solutions served as a benchmark for comparing the accuracy of the stress values obtained using FEM models. For the selected 2D and 3D notched components, diagrams were created for sensitivity analysis of the influence of the mesh element density at the root of the notch in correlation with the exact analytical solution. The findings from model building were applied to model the stress concentration at the root of a V-weld joint in a gas pipeline. Keywords: notch; FEM simulation; stress concentration; analytical solution 1. Introduction For a reliable assessment of the fatigue life of a structure, it is necessary to define two types of input parameters: load parameters and material parameters. The accuracy and validity with which these parameters are obtained directly affect the results of the fatigue life assessment. For both groups of parameters, it is best to obtain them by direct measurement. To define a loading of structures in service generally means to define a representative stress in time history at a critical cross-section or point of the structure (the critical cross- section or point of the structure as the cross-section or location with the highest stress variability). The best practice is to directly measure the strain history at the critical point during operation of the structure. Critical locations are most often of a complicated shape because of the stress concentrations, and their overall notching effect determines the fatigue life of that location, and hence, of the entire structure. The possibilities for direct measurement of strain in notches are still limited [1,2]. Measurement with FBG sensors in the notch is not practically feasible. Measurements using optical methods (ESPI, DIC, Photo-Stress, etc.) are applicable on the limited geometry at the measured location and practically excluded in direct operation. Measurement by strain gauges is most commonly used in praxis, but its application in the notch also has limitations. An acceptable approach for obtaining an accurate and valid stress history at a critical location in a structure may be a combination of direct measurement and computer simula- tion: direct measurement at the nominal stress (strain) location and accurate simulation of the notching effect at the critical location. Knowledge of the nominal stress (strain) history and the stress concentration factor, as a result of the shape of the notch at the critical location of the structure, allows the nominal stress history to be recalculated in the notch. Several procedures can be found in References [3–5]. Metals 2022, 12, 43. https://doi.org/10.3390/met12010043 https://www.mdpi.com/journal/metals