In the modal tests used to verify the finite element model, free boundary conditions are usually simulated. It is generally known that any kind of boundary conditions affect the measured modal parameters. The modal damping rather than the modal frequency is affected more significantly. Due to this, the use of coil springs for fixturing the measured parts seems to be optimal in terms of damping. Coil springs themselves have very little damping. However, during a series of experiments, coil springs have been shown to negatively affect the vibration of the test piece and hence its modal parameters. The content of this paper is a description of this phenomenon and how to avoid it.
