Fatigue Crack Growth in a Solid Circular Shaft Under Fully Reversed Rotating Bending
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TECHNICAL ARTICLE—PEER-REVIEWED
Fatigue Crack Growth in a Solid Circular Shaft Under Fully Reversed Rotating Bending A. R. Torabi • M. Heidary Khavas
Submitted: 12 November 2011 / in revised form: 21 April 2012 / Published online: 22 May 2012 Ó ASM International 2012
Abstract The axle of a load train failed after 5.37 9 106 cycles from its service. Macro-fractography showed clearly the fatigue fracture. The stress distribution in the shaft revealed that the maximum alternating stress was considerably less than the material modified fatigue limit obtained at 107 cycles from the S–N diagram. Micro-fractography reported from the metallurgical laboratory proved the existence of a surface flaw. Ultimately, fatigue crack growth simulation was performed based on the simple Paris–Erdogan model for estimating the fatigue life of the defective axle. The results showed that the actual life of the axle could be satisfactorily predicted by means of the Paris–Erdogan model. Keywords Fatigue crack growth Railway axle Finite element method Flaw Rotating bending Nomenclature 3D Three dimensional FE Finite element KI Mode I stress intensity factor KII Mode II stress intensity factor KIII Mode III stress intensity factor KIc Plane-strain fracture toughness
A. R. Torabi (&) Fracture Research Laboratory, Department of Aerospace Engineering, Faculty of New Science and Technologies, University of Tehran, P.O. Box 13741-4395, Tehran, Iran e-mail: [email protected] M. Heidary Khavas Fatigue and Fracture Research Laboratory, School of Mechanical Engineering, Iran University of Science and Technology, Narmak, 16846 Tehran, Iran
Se Su SIF DKth
Material endurance limit Ultimate tensile strength Stress intensity factor Fatigue crack propagation threshold
Introduction Railway axle is one of the most important components in the train mechanical system that it is usually designed to be in service for a long time (up to 30 years) as a safety critical component. This element transmits the vehicle’s weight to the wheels, and due to its rotation; it is subjected to fatigue loading conditions. The alternating stresses applied to the axle (which is in fact, a solid shaft) result in fatigue crack nucleation from the surface and then in the crack propagation till final sudden fracture. After manufacturing processes, different types of stress concentrations such as non-metallic inclusions, voids, flaws, and scratches are occasionally experienced in the axle; some of these discontinuities may be dangerous. The criticality of such pre-existing flaws can be determined thanks to the fracture mechanics which is an advanced engineering tool in the context of damage tolerant design. Since cracks having sizes larger than permitted would grow and result in axle premature fatigue failure, it is essential to check the axle before its service to see if the size of likely flaws is in allowable range. The fatigue failure of railway axles has been extensively investigated by the researchers, being a common cause of derailment, both theoretically and experime
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