Issue 42

I. Milošević et alii, Frattura ed Integrità Strutturale, 42 (2017) 1-8; DOI: 10.3221/IGF-ESIS.42.01 1 Focused on Mechanical Fatigue of Metals Influence of the stress gradient on the fatigue life calculation of a martensitic high strength steel Igor Milošević, Gerhard Winter, Florian Grün Montanuniversität Leoben, Franz-Josef-Strasse 18, 8700 Leoben, Austria igor.milosevic@unileoben.ac.at, gerhard.winter@unileoben.ac.at , Florian.gruen@unileoben.ac.at Martin Kober LEC GmbH, Inffeldgasse 19/11, 8010 Graz, Austria Martin.kober@lec.tugraz.at A BSTRACT . Nowadays lifetime calculation in the high cycle fatigue region is commonly based on S/N curves which are modified by different influences to ensure accurate results. Especially the application of these models is important when small components with complex stress distributions are used. The influence of the stress distribution was considered by the stress gradient approach which is implemented in the lifetime tool FEMFAT. Specimens with diameters of D4mm and D7.5mm were used to examine the effect of the calculation modified by the stress gradient. On the one hand regarding different types of this approach it can be shown that the results fit very well compared to the testing results but on the other hand a big difference was observed when the gradient increases by smaller specimen sizes. K EYWORDS . High cycle fatigue; stress gradient approach; lifetime calculation; stress based approaches; martensitic high strength steel. Citation: Milošević, I., Winter, G., Gruen, F., Kober, M., Influence of the stress gradient on the fatigue life calculation of a martensitic high strength steel, 42 (2017) 1-8. Received: 31.05.2017 Accepted: 07.06.2017 Published: 01.10.2017 Copyright: © 2017 This is an open access article under the terms of the CC-BY 4.0, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. I NTRODUCTION resent technical applications regarding weight reduction and higher loads lead to increasingly complex component geometries. These complex shapes require high demands on the lifetime and therefore the lifetime calculation based on different models. Since the finite element analysis (FEA) is capable of determining different load situations and the resulting stress and strain distributions the influence of the stress distribution is implemented into commonly used simulation tools like FEMFAT known as the stress gradient approach. In the actual case, the focus is mainly set on the lifetime calculation under the stress gradient influence. Material testing is always affected by other additional influences as size effect, temperatures, residual stresses and the stress distribution itself through different types of loads, which could cause an impact on the material properties. This has to be considered within the lifetime calculation of complex components. P