DETERMINATION OF THE FATIGUE LIFE OF AN ELECTRIC VEHICLE CHASSIS

Transcription

1 DETERMINATION OF THE FATIGUE LIFE OF AN ELECTRIC VEHICLE CHASSIS Yunus MARAL 1, Yusuf ALTUN 2, Fikret POLAT 3 1 Bursa Technical University, Mechanical Engineering, Bursa, Turkey. 2 Duzce University, Engineering Faculty, Computer Engineering, Duzce, Turkey. 3 Duzce University, Engineering Faculty, Mechanical Engineering, Duzce, Turkey. Abstract: In recent years, electric vehicles have tremendous potential due to their low maintenance costs and environmental friendliness. The purpose of this study is to provide fatigue analyses on the vehicle chassis to determine the parts to be fatigued and to find the critical life of these parts. Within the scope of this plan, first of all static analysis was carried out with 600 kg load on the chassis model. According to the results of the static analysis, it was observed that the system was within the safety limits, and then fatigue analysis was started. Fatigue analysis were carried out with 5 different road data collected during road tests. As a result of the analysis, the fatigue lives of the parts on the model were determined and It has been seen that the vehicle chassis is far below critical values in terms of fatigue life. Keywords: Fatigue analysis, electrical vehicle chassis, finite element analysis. 1. Introduction Our current technology is largely dependent on fossil fuels as essential energy source for almost all activities needed to sustain daily life. It is envisaged that the use of fossil-based fuels will pose two threats to humanity in the long run. The first threat is the increased costs associated with reduced reserves, particularly the reduction of fuels such as oil and natural gas, and hence the size of the social and economic impacts. The second threat is the harmful emissions resulting from the burning of fossil fuels and the environmental impacts of greenhouse gases [1-3]. In recent years, advances in electric vehicle technology, along with advances in electric machines, batteries and power electronics technologies, promise promising solutions in the near-term to prevent these threats. And also in the long run promises solutions that will completely eliminate it [2-4]. The first electric vehicle model was made in the Netherlands in 1835 by Professor Stratingh. It was reported by Thomas Davenport between 1834 and 1836 that an electric road vehicle was developed and put into practice in the United States. This vehicle is driven by non-rechargeable batteries with three wheels. Four years later, Robert Davidson developed an electric locomotive driven by a non-rechargeable battery. After 1859, lead-acid batteries were developed and started to be used. In 1882, Professor William Ayrton and John Perry in England implemented the application of three electric vehicles. There are 10 lead-acid batteries in each of these vehicles. The range of vehicles is km depending on the conditions of the land and the maximum speed is 14 km / h. Three years later, Carl Benz developed three-wheeled vehicles with internal combustion engines. Towards the end of the 19th century, many companies in America, England and France started to produce electric vehicles. The most important of these producers is Morris and Salomon who owns Electric Carriage and Wagon Company [3-6]. One of the most important points to consider when designing a vehicle is that the elements of the vehicle must be safe in terms of strength. Therefore, the strength analysis of the vehicle chassis needs to be done very well [7-9]. Using the solution of the balance equations under the forces and moments acting is not so easy. In this case it is necessary to use different methods. Finite element analysis of these methods is due to be integrated with computer-aided design system especially easy to use and is very heavily used in the automotive industry [10-13]. 207

2 With using the finite element methods in fatigue analysis, fatigue behaviours of elements can be examined without being subjected to test. Therefore, the fatigue behavior of many parts of the machine is determined before production. There are three important steps in fatigue analysis: Selection of Fatigue Method, Selection of Loading Method, Selection of Fatigue Curve. In this study we will use Variable Amplitude Loading Conditions Methods cause of collected data in different road conditions [14-16]. 2. Materials and Methods 2.1 Static Analysis The prepared solid model has been transferred to the Ansys Static Structural Programmer in.stp format for finite element models with some arangements. Static analysis will be done by applying the necessary boundary conditions. The mesh structure is created to chassis as shown in Fig.1. Mesh structure consists of a total of hekzahedron and tetrahedron elements and nodes. Fig. 1. Mesh structure of chassis model The mechanical properties of St 37 steel were used for material information in the chassis model. The mechanical properties of St 37 steel are as follows. Modulus of Elasticity : 210 GPa Density : 7850 kg/m 3 Yield Stress: 250 MPa Tensile Stress: 460 MPa Poisson's Ratio: 0.3 When the loads acting on the cab area and the rear cab area were measured with the 600-kg load on the car, it was seen that the load of the cab area is 650 kg and the load of the rear cab area is 730 kg. These load values found were applied to the contact areas on the chassis from the centre of gravity calculated on the cabinet and the rear cab as shown in Fig

3 Fig. 2. Effective loads to cabinet and rear cab area After all the data required for static analysis has been entered, the model of finite element created was runned. As a result of static analysis, the equivalent stress distribution is obtained as shown in Fig.3. Fig. 3. Equivalent stress distribution And as a result of static analysis, the elastic deformation on model is obtained as shown in Fig.4. The maximum stress on the model here is 97.9 MPa, and it occurs in the connection area of the suspension system. As can be understood from this stress value on the model, there is no problem in terms of static loading on the chassis and the safety coefficient is approximately 2.5. Fig. 4. Elastic deformation on the model 209

4 Fatigue analyzes were followed after observing that no permanent damage would occur on the model in the static analysis performed on the chassis. 2.2 Fatigue Analysis After the selection criteria and the method steps, fatigue analysis solution diagram was formed in ncode DesignLife programme as shown in Fig.5. Fig. 5. Design life fatigue analysis flowchart 3. Results By entering 3 basic parameters required for fatigue analysis, the analysis models prepared for each of the 5 different path data were solved. As a result of analysis, the life and damage values on the chassis model were obtained for four different tracks as shown in Table 1. Table 1: Fatigue life and damage results for five different test tracks Asphalt Road Downgrade Rugged Road Parker road Unpaved Road Life 1,082x10 3 1,155x10 5 3,303 4,081x10 3 8,686 Damage 4,607x10-4 7,022x10-6 8,571x10-2 1,420x10-4 1,135x

5 As can be seen from Table 1, the most critical result for fatigue life and damage was found in the analysis with test data from rugged area. As a result of the analysis in the rough road data, the life distribution on the chassis model is as shown in Fig.6. The connection profiles of the suspension system are locally shown because this is the part that gives the minimum value in terms of life on the vehicle. 4. Conclusions Fig. 6. Lifetime distribution on chassis with rugged road The length of the data used in the analysis; 200,000 km * 3,303 = 660,600 km. The meaning of the damage value obtained as a result of the analysis is how many percent damage is caused by the fatigue analysis on the part. In the analysis made from rugged road data, life and damage amounts were obtained at the most critical values according to fatigue results from the other test tracks. However, when these values are examined, the minimum lifetime of the chassis is around 600,000 km. This value does not mean risk. As a result of these analyzes, it has been seen that the critical value of the existing vehicle chassis is far below the fatigue life. 5. Acknowledgement This work was supported by Duzce University Scientific Research Project, No We thank Duzce University Scientific Research Project Coordinatorship for their support. References [1] D.C. Han, Ekim, 2002, Electric Vehicle Symposium 19 proceedings, EVAAP, Busan, Korea. [2] M.H. Westbrook, 2001, The electric and Hybrid Electric Car., SAE, London [3] I. Husain, 2003, Electric and Hybrid Vehicles Design Fundamentals, CRC Presss, New York. [4] C.M. Jefferson, R.H. Barnard, 2002, Hybrid Vehicle Propulsion, WIT Press, Boston. [5] C. C. Chan, K. T. Chau, 2001, Modern Electric Vehicle Technology, Oxford University Press, New York. [6] C.C. Chan, The State of the Art of Electric and Hybrid Vehicles, Proceedings of the IEEE, 90, [7] R. Talreja, Fatigue of Composite Materials: Damage Mechanisms and Fatigue-Life Diagrams, Proc. R. Soc. A Math. Phys. Eng. Sci., vol. 378, pp , [8] C. Wang, H. Zhang, C. Castorena, J. Zhang, Y. R. Kim, Identifying fatigue failure in asphalt binder time sweep tests, Constr. Build. Mater., vol. 121, pp , [9] W. Wang, L. Deng, X. Shao, Number of stress cycles for fatigue design of simply-supported steel I- girder bridges considering the dynamic effect of vehicle loading, Eng. Struct., vol. 110, pp , 211

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