Constrained-layer damping with gradient polymers for effectiveness over broad temperature ranges

The effectiveness of a constrained-layer damping treatment in dissipating energy and thereby augmenting the system damping is contingent on the viscoelastic polymer having a fairly significant value of material loss factor. A monolithic viscoelastic polymer tends to be lossy over a fairly narrow temperature range, corresponding to the material being in the transition state. At temperatures below this range, the viscoelastic polymer displays glassy behavior, whereas for higher temperatures, it displays rubbery behavior. In either case, the material loss factor reduces sharply and the effectiveness of the damping treatment is severely degraded. A gradient viscoelastic polymer layer, for which the properties vary through the thickness of the layer, can increase the temperature range of effectiveness of the damping treatment. This is because different regions through the thickness enter transition at different temperatures, and so the gradient polymer as a whole provides damping augmentation over a broader temperature range. Classical constrained-layer damping treatments with monolithic polymeric damping layers routinely assume a uniform shear strain through the thickness of the damping layer. However, because the shear modulus of the gradient viscoelastic polymer can vary by up to two-three orders of magnitude through the thickness, the shear strain can also be expected to vary substantially through the thickness. Consequently, a new analysis is developed with the gradient viscoelastic polymer modeled as comprising N discrete sublayers, each with its distinct properties and each assigned an independent shear degree of freedom. Simulation results are presented for a gradient polymer comprising N = 2 discrete sublayers. The results of the study are used to understand the underlying physics. It is seen that ideally, the glassy temperature of the two sublayers should be approximately similar. Further, the treatment is most effective if the sublayer that goes into glass transition at higher temperatures has a lower rubbery modulus than the sublayer going into glass transition at lower temperatures.