Issue 30

M. Da Fonte et alii, Frattura ed Integrità Strutturale, 30 (2014) 360-368; DOI: 10.3221/IGF-ESIS.30.43 360 Focussed on: Fracture and Structural Integrity related Issues The effect of steady torsion on fatigue crack growth under rotating bending loading on aluminium alloy 7075-T6 M. da Fonte IDMEC & ICEMS, Department of Mechanical Engineering, Nautical School fonte@enautica.pt L. Reis, M. de Freitas IDMEC & ICEMS, Instituto Superior Técnico, Universidade de Lisboa luis.g.reis@ist.utl.pt , mfreitas@dem.ist.utl.pt A BSTRACT . Axles and shafts are of prime importance concerning safety in the transportation industry and railway in particular. Design rules for axles and shafts are mainly based on endurance curves for the material used according to the established standards and procedures. Recently, the knowledge of fatigue crack growth under typical loading conditions of axles and shafts with rotating bending and steady torsion is being object of research and industrial studies in order to apply damage tolerance concepts, mainly for maintenance purposes. The effect of a steady torsion on fatigue crack growth under rotating bending is focused in this paper. While axles and shafts in the transportation industry are traditionally designed on steels, the need for weight reduction due to fuel economy and eco-design constraints, lightweight materials must be considered for these applications. In this study, fatigue crack growth on rotating bending axles and shafts with or without an applied steady torsion is presented. Fracture mechanics approaches are used to analyze the results based on Stress Intensity Factors developed for bending and torsion in shafts and show fatigue crack growth retardation when steady torsion is applied. Fractographic observations using SEM are presented and helped to explain the fatigue crack growth retardation observed when steady torsion is applied to rotating bending. Results are compared for the same loading conditions on steels and relevant differences on fatigue crack growth are commented. K EYWORDS . Multiaxial fatigue; Mixed-mode fatigue crack growth; Axles; Shafts. I NTRODUCTION ailure of railway axles has been a matter of concern since the development of railway industry and some dramatic failures have been reported from the early decades of the XIX century. Since the Wöhler studies on fatigue failure of railway axles in the middle of the nineteen century, endurance curves determined under rotating bending tests constitute the most important data when designing against fatigue failure and avoid crack initiation. With the development of modern high speed trains, railway axles are submitted to more severe loading conditions and it is still a challenge for the test and design engineers to accurately determine the fatigue lifetime of railway components [1]. Nowadays, due to the F