Non-Destructive Еvaluation Of The Stress State In The Rim Of The Railway Wheels Yonka P. IVANOVA 1 , T. A.PARTALIN 2 1 Sofia University, Faculty of Physics ;Sofia, Bulgaria e-mail: yonivan@phys.uni-sofia.bg, 2 1 Sofia University, Faculty of Physics ;Sofia, Bulgaria Phone: +359 28161 562; E-mail: topart@fmi.uni-sofia.bg Abstract Residual stress can significantly influence and particularly reduce engineering properties and fatigue life of materials such as railway components. The paper presents results of stress state investigation of rail wheels new and in service by using different NDT methods. The combined use of ultrasonic, electro-magnetic Barkhausen noise and magnetic acoustic emission provide better reliability than any of separately used methods. The study will give possibility to check the state of the materials in situ, but not only in factory condition. The aim of the work is to find dependence between stress state and eventually microstructure parameters and non-destructive parameters (velocity of ultrasonic waves, Barkhausen noise and magnetic acoustic emission intensities). Keywords: non-destructive еvaluation, stress state, railway wheels, ultrasonic and magnetonoise methods 1. Introduction The production of railway wheel includes a heat treatment to obtain a fine grained ferrite- pearlite microstructure, compressive stresses close to the rolling surface and the tensile stresses - inside the wheel [1-4]. This heat treatment creates conditions for suppressing the appearance and development of cracks. Nevertheless during service the wheel is loaded with cyclic forces that cause fatigue and possibly fatigue cracks. For this reason the control of the residual stress level is included in the regulations as a requirement in the maintenance repair (in-service) [7-8]. The wheels are usually subjected to preventive control by non-destructive testing methods after approximately 224,000 km mileage [2] General non-destructive method for residual stress determination is the ultrasonic method based on the acousto-elasticity effect [9-15]. The technique is founded on the measurements of the difference between times-of-flights of ultrasonic shear waves polarized along the radial and the circumferential direction. Different ultrasonic set-ups for stress state evaluation in the rims of wheels are in use in the railway repair industry [9,10,11,15]. The apparatuses are specialized and usually are stationary systems that work in factory conditions. The aim of this study is to compare the results of several NDT methods for residual stress evaluation of railroad wheel. The combined use of ultrasonic, electro-magnetic Barkhausen noise and magnetic acoustic emission enables the evaluation of stress and microstructure states of all volume and in the surface layers in wheels and can be used as a current control with portable and convenient device. 2. Experimental methodology. Material characterization 2.1.Materials Railroad monoblock wheels were used as the test specimens. The type of wheels is R7 407 [5,15]. The carbon content of the steel is 0.55%, yield stress is of 550 N/mm 2 , a tensile strength 820-940 N/mm 2 [5]. 2.2. Experimental procedure 11th European Conference on Non-Destructive Testing (ECNDT 2014), October 6-10, 2014, Prague, Czech Republic More Info at Open Access Database www.ndt.net/?id=16541