Analytically Driven Experimental Characterisation of Damping in Viscoelastic Materials

The damping assessment of highly dissipative materials is a challenging task that has been addressed by several researchers; in particular Oberst defined a standard method to address the issue. Experimental tests are often hindered by the poor mechanical properties of most viscoelastic materials; these characteristics make experimental activities using pure viscoelastic specimens prone to nonlinear phenomena. In this paper, a mixed predictive/experimental methodology is developed to determine the frequency behaviour of the complex modulus of such materials. The loss factor of hybrid sandwich specimens, composed of two aluminium layers separated by the damping material, is determined by experimental modal identification. Finite element models and a reversed application of the modal strain energy technique are then used to recover the searched storage modulus and loss factor curves of rubber. In particular, the experimental setup was studied by comparing the solutions adopted with the guidelines given in ASTM-E756-05. An exhaustive validation of the values obtained is then reported.