The Influence of Quality of Adhesion on the Damping Characteristics of a Two-Layer Compound Beam

Abstract

A two-layer compound beam submitted to forced extensional vibrations was used to study the quality of adhesion between the phases and its influence on the overall mechanical behaviour of the compound. The one layer consisted of an unplasticized epoxy polymer, whereas the other layer of a 20 percent plasticized with Thiokol LP3 polysulfide. It was shown, by the theory of elasticity of vibrating bodies, that the influence of the dif ferences in moduli and Poisson's ratios of the phases at each position of loading along the viscoelastic spectrum was insignificant for the combination of phases studied, so that the simple theory of extensional forced vibrations of the compound was valid. Then, the eval uation of the storage- and loss-moduli for the independent phases and the compounds with good or bad adhesion at the length of their interface along the whole viscoelastic spectrum has shown that compound specimens with good adhesion behaved exactly as if they consisted of a unique material with the properties of the compound according to its law of mixtures, whereas in the case of bad adhesion, a further reduction in the values of loss moduli and the loss factors of the compound appeared, due to the high dissociation of the phases. The positions and the extents of these quantities may be adequately ex plained by the two-term unfolding model for the mesophase, valid for forced-vibrating bodies.