Issue 46

G. Deng et alii, Frattura ed Integrità Strutturale, 46 (2018) 45-53; DOI: 10.3221/IGF-ESIS.46.05 45 Developments in the fracture and fatigue assessment of materials and structures Bending fatigue strength design method for machine components with complex geometries Gang Deng, Tsutomu Nakanishi Department of Mechanical Design Systems Engineering, Faculty of Engineering, University of Miyazaki, 1-1 Gakuen Kibanadai-nishi, Miyazaki Shi, Miyazaki 889-2192, Japan t0d114u@cc.miyazaki-u.ac.jp , t0d115u@cc.miyazaki-u.ac.jp A BSTRACT . The purpose of this study is to devise a bending fatigue strength evaluation method that can be widely used for any machine component under the consideration that bending fatigue breakage depends on the initiation of a surface fatigue crack, namely, the conditions for the initiation of a fatigue crack can be used as the criteria for bending fatigue strength design. The specially designed and manufactured three-point bending specimens with crowned round notches are used in bending fatigue experiments. The obtained bending fatigue strengths are expressed as the maximum actual stress at the critical point, which increases with decreasing notch radius. Considering the effects of the stress distribution on the bending fatigue strength, we present a method for estimating the tension fatigue strength of a smooth specimen, which is shape-independent fatigue strength and can be applied to bending fatigue strength design for machine components with complex geometries. K EYWORDS . Bending fatigue strength; Fatigue crack initiation; Stress distribution; Shape-independent fatigue strength Citation: Deng, G., Nakanishi, T., Bending fatigue strength design method for the machine components with complex geometries, Frattura ed Integrità Strutturale, 46 (2018) 45-53. Received: 07.03.2018 Accepted: 15.04.2018 Published: 01.10.2018. Copyright: © 2018 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 lthough the bending fatigue strength design of machine elements such as gears and shafts can be performed in accordance with design documents, there are still no practical methods applicable to other machine elements with different shapes. Many accidents have occurred owing to the fatigue of machine component with a wide range of geometries, such as the fatigue breakage of the tire hub of heavy-duty truck. Since the bending fatigue strength is expressed as the nominal stress calculated on the basis of material mechanics with many simplifications of the shapes and loading conditions, it varies even among machine components with the same material qualities [1,2]. Consequently, the bending fatigue strength design of machine components with a wide range of geometries cannot be performed using the methods shown in the design documents. To avoid accidents owing to the bending fatigue breakage of machine components, a general bending fatigue strength evaluation method applicable to a wide range of geometries is required. Bending fatigue breakage is a result of surface crack initiation and propagation. Nisitani [3] and Ohba [4] indicated that a fatigue crack will not stop growing unless an extremely high stress concentration occurs at the critical point where the fatigue crack is initiated. Deng [5] and Hammouda [6] showed that the fatigue initiation life accounts for a large proportion of the A