1 Bogie frame design in consideration of fatigue strength and weight reduction B H Parkand K Y Lee

School of Mechanical Engineering,Yonsei University,Seoul,Republic of Korea The manuscript was received on 8 April 2005 and was accepted after revision for publication on 25 November 2005. DOI: 10.1243/09544097F01405

Abstract: In the development of a bogie, the fatigue strength of a bogie frame is an important design criterion. In addition, weight reduction is required in order to save energy and material .In this study, the fatigue analysis of a bogie frame by using the finite-element method is performed for various loading conditions according to the UIC standards and it is attempted to minimize the weight of the bogie frame by artificial neural network and genetic algorithm. Keywords: bogie, strength, fatigue analysis, neural network, optimization. 1 INTRODUCTION

A bogie in a train is a very important structural component loaded by various forces in the rail way vehicle motion. The motion of a railway vehicle is affect by the geometry of the track, the interaction between wheels and rails, the suspension, and the inertias of component part s. In the meantime, the weight of a bogie structure should be as light as possible at higher running speed. Therefore, the strength of the bogie should be carefully calculated and analysed by the international standards such as UIC [1] and JIS [2], in order to obtain a reasonable design scheme. In the past design process, the steps of many experiments, field tests, and prototypes to improve and obtain a reasonable design required much time and high costs. In the computer-aided engineering (CAE) product design step, however,the practical use of finite- element (FE) analysis can reduce the costs and time. The FE analysis of the bogie frame was studied several times [3,4]. In addition, the bogie has a large proportion of the total weight of a vehicle. Savings of energy and material are currently design drivers towards lightweight vehicle constructions. In 2

CAE product design step, optimization for weight reduction and application of the optimal algorithm can make the light weight and the constraint conditions for the fatigue strength satisfy. It is a typical structural optimization problem to minimize the weight of the bogie under the fatigue constraint, but the problem cannot be solved by simply applying the existing numerical optimization algorithms. In the problem, the fatigue constraint is not expressed as an analytical function in terms of the design variables.

In this article, the FE model of the bogie frame is constructed to simulate the fatigue test. The bogie that is used in this study is composed of welded frame, bolster, self-steering mechanism, primary suspension, secondary suspension, and disc brake system. The fatigue strength of the bogie frame is estimated by the international standard UIC615-4 ‘Motive Power Units Bogies and Running Gear Bogie Frame Structure Strength Test’. The 3

optimization problem is composed of an object function for the weight reduction of the bogie and the constraint conditions for the fatigue design criteria. The artificial neural network (ANN) to approximate a function for the fatigue constraint and the micro genetic algorithm (MGA) are used to solve this optimization problem. 2 STRESS ANALYSIS OF THE BOGIE FRAME 2.1 FE model of the bogie frame In this study, the analysed bogie frame is a bolster type bogie (Fig. 1(a)). The numerical analysis by the FE method is performed to evaluate the fatigue strength of the bogie frame except the bolster. The bogie is modelled using shell and solid elements and the FE model is shown in Fig.1(b ).The trailer bogie frame is meshed to have 28, 251 nodes, 23,870 rectangular shell elements, and 2710 hexagonal solid elements. Considering the boundary conditions of the trailer bogie frame for the primary suspension, the spring boundary elements are established and the stiffness of the elements is the same as the primary suspension. There are 12 spring elements for the primary suspension in the trailer bogie frame. The software programs used are Altair Hyper Mesh and ABAQUS . The material used in the bogie frame is SWS490A defined in reference [ 2 ] and the material properties are shown in Table 1.

2.2 Load conditions and the evaluation of fatigue strength of the bogie frame The fatigue analysis is based on the UIC standard. The main in- service load case is designed to verify the absence of any risk of fatigue cracks occurring under the combined