Issue 41

K. Slámečka et alii, Frattura ed Integrità Strutturale, 41 (2017) 123-128; DOI: 10.3221/IGF-ESIS.47.17 123 Focused on Multiaxial Fatigue Simple criterion for predicting fatigue life under combined bending and torsion loading K. Slámečka, J. Pokluda Brno University of Technology, Central European Institute of Technology, Purkyňova 123, 612 00 Brno, Czech Republic karel.slamecka@ceitec.vutbr.cz , http://orcid.org/0000-0001-8847-075X jaroslav.pokluda@ceitec.vutbr.cz, http://orcid.org/0000-0002-8449-1200 A BSTRACT . Multiaxial fatigue is a challenging problem and, consequently, a number of methods has been developed to aid in design of components and assemblies. Following the complexity of the problem, these approaches are often elaborate and it is difficult to use them for simple loading cases. In this paper, an empirical approach for constant amplitude, proportional axial and torsion loading is introduced to serve as a basic engineering tool for estimating fatigue life of rotational structural parts. The criterion relies on a quadratic equivalent-stress formula and requires one constant parameter to be determined from experiments. The comparison with similar classical stress- based approaches using data on diverse materials (several steels, aluminium alloy, and nickel base superalloy) reveals very good agreement with experimental data. K EYWORDS . Multiaxial fatigue; Life prediction; Equivalent stress. Citation: Slámečka, K., Pokluda, J., Simple criterion for predicting fatigue life under combined bending and torsion loading, Frattura ed Integrità Strutturale, 41 (2017) 123-128. Received: 28.02.2017 Accepted: 15.04.2017 Published: 01.07.2017 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 atigue failure under multiaxial cyclic loading is undoubtedly one of the most common concerns among engineers. The multiaxial fatigue process itself is rather complex and a tremendous effort has been invested in developing methods capable of capturing some of its most relevant aspects, such as the importance of shear stresses for the fatigue crack initiation stage, the short crack problem, crack closure, or non-proportional hardening observed in some materials [1, 2]. Consequently, these methods are often quite elaborate and their employment may require a skilled person using a specialized software. On the other hand, the first-approximation estimation of multiaxial fatigue failure is frequently based on the von Mises stress, the Tresca criterion, or some other static hypothesis, e.g. [3, 4], which apparently are among a few simple formulas qualified for a widespread usage. As these simple methods are known to be generally not acceptable, the purpose of this work was to introduce a similarly simple empirical approach which is intended to serve as a basic engineering tool for initial estimation of fatigue life under combine proportional axial and torsion loading, being of a special interest for rotational structural parts operating under such conditions. The method relies on fitting the F