Static and dynamic stiffness: One test, both results

All car companies, as part of their vehicle design strategy, perform a variety of static as well as dynamic tests. Dynamic test procedures are fairly well defined and their results are relatively stable; changes in the test and analysis methods have a minimal effect on the test data. In contrast, static test procedures are poorly defined and their results are unstable; differences in the test procedure quite often significantly effect the test data. This paper presents a practical method to obtain static stiffness values from a dynamic (modal) test. This eliminates any dependencies of the static results on the test and fixturing methods while providing the economy of a single test. These methods are in a state of development. In this paper, they have been successfully applied to a truck frame. Work on a car body-in-prime is in progress. In the future, these methods will be expanded to include trimmed bodies and body-on-frame vehicles.