Identification of structural loss factor from spatially distributed measurements on beams with viscoelastic layer

The problem of estimation of a structural loss factor for a beam covered with a viscoelastic layer is addressed in the paper. Two estimation methods based on analytical models for wave propagation in viscoelastic homogenous beams are tested. The methods use different theoretical solutions for spatial distribution of a wave field in the beam. The solutions depend on a complex wave number and frequency. At each frequency within an investigated range the wave number, for which model predictions best approximate experimental response, is found. Structural loss factor is calculated based on the identified value of wave number. Experimental data are measured in a cantilever beam test. For verification purposes the obtained values of loss factor are compared with the results of Oberst test. The presented methods enable determination of loss factor for arbitrary discrete frequencies. They provide an alternative to modal techniques which estimate only values of the parameter corresponding to resonant frequencies.