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Vibration-damping behavior of unidirectional and symmetric angle-ply carbon fiber-epoxy laminates as well as their interleaved counterparts with a layer of poly(ethylene-co-acrylic acid) (PEAA) at the mid-plane was examined. The introduction of the PEAA layer significantly improved the damping capability. The effectiveness of interleaving increased with the flexural modulus of the outer layers. In the case of unidirectional laminates, calculations based on a sandwich structure of isotropic layers quantitatively reproduced this trend. In the case of angle-ply laminates, however, the model predicted only part of the improvement experimentally observed. This was explained in terms of the bending of the angle-ply laminates in the transverse direction which would induce additional deformations in the interleaf layer and was not accounted for by the present model.

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SYNOPSISThe vibration damping properties of the polymer-laminated steel sheet have been investigated theoretically and experimentally. The laminate consisted of a polymer layer, which was sandwiched between two steel sheets. Two polymers, a polyvinyl butyral and a copolymer of ethylene and acrylic acid, were used. The theoretical analysis was based on a model proposed by Ungar. A frequency analyzer was used to measure the loss factor of the laminate. The model required rheological data, such as storage modulus G' and loss tangent of the polymer at high frequency, which could not be obtained from commercially available dynamic rheometers. The time-temperature superposition principle was applied to the laminated polymer to construct the master curves of G' and loss tangent vs. frequency. These master curves provided rheological data a t high frequency, which were superposed from data measured at low temperature. The results showed that a discrepancy existed between the loss factors predicted with superposed and without superposed data and the reasons for this discrepancy were discussed. The measured loss factors of the laminates at high frequency followed the predictions using superposed data, but not for those measured at low frequency. Factors accounting for this deviation were analyzed. The results also indicated that, in general, the transition temperature of the polymer-laminated steel sheet was 15"C-3OoC higher than the corresponding glass transition temperature of the laminated polymer. I NTRO D UCTlO NIn recent years, there has been increasing interest in the development and utilization of polymer-laminated steel sheet for vibration damping purposes.192 The laminate usually consists of a viscoelastic polymer layer, which is sandwiched between two steel sheets. The constrained polymer layer provides the laminate with satisfactory vibration and noise attenuation over a specific range of temperature. It is believed that the shear deformation of the constrained layer dominates the laminate damping and the loss tangent of the polymer used is of greatest importance in this type of Thus, noise is substantially reduced, mainly by the shear defor- To whom correspondence should be addressed.CCC 002 1-8995/92/050893-08$04.00 mation of the polymer laminated. Ungar et a1.6-8 proposed a theoretical approach to calculate the damping efficiency of a sandwich panel. Detailed derivations can be found in the literature. According to this approach, the loss factor 7 of the laminate used in this study can be represented bywhere Y is the stiffness parameter, X is the shear parameter of the laminate, and p2 is the shear loss tangent of the viscoelastic layer. In general, the stiffness parameter is a function of the elastic modulus, the thickness, and the density of the steel sheet. The shear parameter is a function of the elastic modulus and the thickness of the steel, the storage modulus and the thickness of the polymer, the applied frequency, and the density of the laminate (mass per unit area). The loss factor, defined above 893

SYNOPSISThis study sought to develop a sandwich-type vibration damping laminate suitable for room-temperature applications. The laminate consisted of a polymeric interlayer that was sandwiched between two steel sheets. The study was initiated to promote the relatively low-damping capability of a maleic anhydride-grafted polypropylene (mPP ) -based laminate, which failed to meet the requirement that the loss factor of the laminate should be greater than 0.05 for effective damping. Modifications of mPP by incorporation of a dynamically vulcanized PP/butyl rubber blend were then followed. The modifications were based on the theoretical analysis proposed by Rose, Ungar, and Kenvin (RUK) for a general polymerbased laminate. The design criteria for the polymeric interlayer, i.e., the preferred range of storage modulus G' for a set of reasonable values of loss tangent (tan 6 ) , were first established from calculations by use of the RUK theory. The theoretical calculations revealed that the low damping of the mPP-based laminate resulted primarily from the high G' and low tan 6 of the interlayer. Incorporation of butyl rubber into the polymeric interlayer led to a strong decrease in G' and a moderate increase in tan 6. These modifications resulted in significantly improved damping capability of the laminate, as predicted by the RUK theory.