The use of strain sensors in an experimental modal analysis of small and light structures with free–free boundary conditions

Abstract

Small and light structures have distinctive features, which cause difficulties in the measurement of their modal parameters. The major issues are the mass, which is added to the measured structure by sensors, and the very high resonant frequencies. Those difficulties occur with a measurement of the excitation force. An innovative procedure for the experimental modal analysis of small and light structures was developed in this study. This procedure involves a measurement of the excitation force, which was performed by a piezo strain gauge that enables an analysis of the aforementioned structures with free–free support. The main advantage of this sensor in comparison with other devices used for force measurements is that it adds a very small mass to the measured structure (≈0.4 g) but at the same time enables an accurate measurement of the modal parameters in a wide frequency range (up to 20 kHz). This makes it suitable for a measurement of the frequency-response functions of light structures that have high resonant frequencies. Consequently, an experimental modal analysis can be performed. The presented approach was experimentally tested on a sample with small dimensions and mass. The results of the experiment (modal parameters) were compared with the results of the numerical model. The good agreement between the results indicates that this procedure can be used on other similar structures.