A phenomenological model of active constrained layers

Active constrained layer (ACL) treatments consist of a layer of viscoelastic material bonded to the host structure and constrained by an actuator. These treatments control vibrations by means of several mechanisms: the actuator increases the dissipation of energy by increasing the shearing in the viscoelastic layer, and simultaneously it controls the vibrations by applying forces to the host structure through the viscoelastic layer. To optimise ACL treatments, it is necessary to understand their physics. While several models in the literature successfully predict the response of structures treated with ACL, the complexity of these models is not well suited for investigating the mechanisms underlying the behaviour of ACL treatments. aper describes a simple model of beams treated with ACL, which allows analytical investigations of the damping and control mechanisms of ACL treatment. The model is based on a modal approach in which each mode of the structure is represented by a mass–spring system. The two layers of the ACL patch are represented by two springs in series, the control voltage in effect driving one of these springs. A numerical validation indicates that the model accuracy is good for ACL patches whose length is smaller than the wavelength of the beam and located at appropriate positions on the host structure. er to demonstrate the usefulness of the lumped parameter model to get insight into the behaviour of ACL treatments, the various ACL damping mechanisms are briefly discussed. Results indicate that proportional feedback control is associated with an increase of shearing in the viscoelastic layer, while the action of active forces dominates when derivative feedback is used.