A survey on the variability of dynamic stiffness data of identical vehicles

The variation in material quality, production tolerances and joint conditions in nominally 'identical' vehicles means that the level of noise and vibration perceived in the cabin will vary from car to car. To assess the level of variability in the low and medium frequency range a series of measurement have been conducted on a small set of nominally identical sedan vehicles. Measurements are presented in the form of dynamic stiffness data for twenty three vehicle mounting and response points and for three different translational directions. In this paper, the methodology used to analyse the large data set is shown. The level of variability in the corresponding frequency response functions (FRFs) from all the vehicles are then presented and compared for different locations and the different loading measurement directions. The mean value is calculated for each data set and compared and the variability is also presented as a function of frequency for a selected set of the dynamic stiffness data. The intention is to demonstrate how the level of FRF variability changes depending upon the excitation/response location chosen and how this can be related to the frequency band characteristics.