Analysis of axial waves in viscoelastic complex structural-acoustic systems: Theory and experiment

An experimental and theoretical study of the spectral response of coupled viscoelastic bars subject to axial oscillations is performed. Novel closed formulas for the envelope function and its width are derived. These formulas explicitly show the role played by energy dissipation. They show that the internal friction does not affect the width of the envelope of the individual resonances. The formulation is based on the equations of classical mechanics combined with Voigt’s viscoelastic model. The systems studied consist of a sequence of one, two, or three coupled bars, with their central axes collinear. One of the bars is assumed to be much longer than the others. We discuss the connection between our results and the concept of the strength function phenomenon discovered for the first time in nuclear physics. Our formulation is an alternative and exact approach to the approximated studies based on the fuzzy structure theory that has been used by other authors to describe systems consisting of coupled bars. The analytical expressions describe the measurements in the laboratory very well.