FATIGUE LIFE ESTIMATION OF VEHICLE MOUNTED COMPONENTS USING FULL CAR SUSPENSION BOND GRAPH MODEL

Abstract

Fatigue life of vehicle mounted components is dependent on a number of factors like mounting location, suspension parameters, component design, and anti-vibration mount properties. A study of influence of these parameters on component fatigue life will greatly help in establishing the most suitable values of these parameters for a given mounting problem. The existing techniques to determine the fatigue life of vehicle mounted components are not used to study fatigue life variation by changing the above mentioned parameters as the practice is time consuming and costly with these techniques. This calls for the development of an efficient framework by which such a study can be carried out. In the present research work such a framework is developed by using the bond graph method of modeling and simulation. With the help of this framework, a rough estimation of fatigue life of vehicle mounted components can be made, for various parameter values, in considerably less time as compared to existing techniques of fatigue life determination. Thus the variation occurring in the component fatigue life by varying parameter values can be known, which allows determination of most appropriate values of these parameters to get maximum fatigue life of vehicle mounted components. Once the suitable parameter values have been established, the detailed fatigue life of component can be determined using existing techniques. A full car suspension model is generated using bond graph method, and after validation of the model it is augmented to include a component mounted on vehicle body at four points. To simulate actual travel conditions, a road profile is generated and is provided as input to the model, which provides the load values acting at the component mounting points. The dynamic stresses generated in component are known by performing finite element analysis of the component with known load values. From these dynamic stresses a preliminary fatigue life of component is calculated using Rainflow counting algorithm and Palmgren-Miner’s rule. The whole process is repeated at four mounting locations on vehicle body and the variation occurring in component fatigue life by varying mounting location is established. Finally, modal analysis of the full car suspension is carried out and the variation in fatigue life is related to the variation of modal displacements of various points on vehicle body.