Issue 42

D. Rozumek et alii, Frattura ed Integrità Strutturale, 42 (2017) 23-29; DOI: 10.3221/IGF-ESIS.42.03 23 Focused on Mechanical Fatigue of Metals Fatigue crack growth in 2017A-T4 alloy subjected to proportional bending with torsion D. Rozumek, S. Faszynka Opole University of Technology d.rozumek@po.opole.pl , sebastian.faszynka@op.pl A BSTRACT . The paper presents the results of tests on the fatigue crack growth for a constant moment amplitude under combined bending with torsion in the aluminium alloy AW-2017A-T4. The tests were performed under different values of the load ratio R. Plane specimens with stress concentrators in form of the external one-sided sharp notch were tested. A non-uniform fatigue cracks growth on both lateral surfaces of specimens was observed during experimental tests. Fatigue cracks were developing in the specimens in two stages; quarter-elliptic edge cracks were observed at the beginning, then evolving into through cracks. K EYWORDS . Fatigue crack growth; Load ratio; Notch; Bending with torsion. Citation: Rozumek, D., Faszynka, S., Fatigue crack growth in 2017A-T4 alloy subjected to proportional bending with torsion, Frattura ed Integrità Strutturale, 42 (2017) 23-29. 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 atigue of materials, especially formation of fatigue cracks and their growth belong to the most important problems of solid mechanics, and they have been intensely investigated for many years [1, 2]. These phenomena are extremely important, because they damage components of machines, and in many cases they cause disasters. Descriptions of fatigue crack growth under bending with torsion of elements with rectangular cross sections are rarely discussed in the literature. Reason behind this is that such elements are less widely used in the industry. In the literature can be found various problems of fatigue crack growth for simple load conditions, such as: tension, torsion or bending [3- 6], as well as for complex load conditions, including: tension with torsion [7], bending with torsion [8], and others [9-11]. The paper [12] the authors described propagation of short cracks and fatigue cracks within threshold range on specimens under three-point bending, during which the researchers initiated crack plane at a certain angle towards bending plane. That allowed obtaining combination of normal and shearing stresses in the crack tip. In Ref. [13] presented three-point cyclic bending of specimens with slits for mixed modes I and III in threshold cracking range. While the performed tests of steel specimens domination of mode I was expected. At the initial stage, changes of mode I were observed, next a fluent rotation of the crack front occurred up to the moment of its perpendicular positioning to the specimen side. The aim of the paper is to describe fatigue cracks growth in specimens with rectangular cross-section made of the AW- 2017A-T4 aluminium alloy under bending with torsion. F