Dynamic Response and Identification of Critical Points in the Superstructure of a Vehicle Using a Combination of Numerical and Experimental Methods

In this work, a systematic methodology is applied, leading to an accurate prediction of the dynamic response of a complex vehicle, carrying a superstructure. This methodology helps in locating areas of the superstructure exhibiting a large stress concentration, for given loading conditions, without requiring any knowledge of the dynamic characteristics of the vehicle suspension subsystem. The basic idea is to first measure the acceleration time histories at the connection points of the vehicle superstructure with its suspension system and use them subsequently as a base excitation in a finite element model of the superstructure. More specifically, the vehicle superstructure is first discretized by appropriate finite elements. The resulting model is linear and is then updated through an experimental measurement of its dynamic response, yielding all the elements of the corresponding frequency response matrix of the superstructure. Then, a series of experimental trials is performed in real operating conditions, aimed at recording the acceleration time histories at the connection points of the superstructure with the chassis. These time histories are subsequently used as a ground excitation for the finite element model of the superstructure and the stresses developed under the specific loading conditions are evaluated. In this way, the critical points of the superstructure can be identified by numerical means. Finally, the reliability of the methodology applied was tested by two numerical examples as well as by placing strain gauges at the critical points of the superstructure and performing a new set of measurements for the vehicle under similar loading conditions. Direct comparison of the numerical and experimental data obtained in this manner verified the reliability and accuracy of the hybrid methodology applied.