Investigation of viscoelastic structures with extreme damping and high stiffness using negative stiffness layered composites

Materials that exhibit high damping are often used in structures to reduce noise and vibrations; however, most materials display an inverse relationship between stiffness and damping. Therefore, materials that display both high damping and stiffness are of great interest in many structural applications. Earlier analysis using linearized viscoelastic theory has demonstrated that high damping and high stiffness can be simultaneously achieved using viscoelastic layered composites consisting of a lossy polymer and a stiff constituent. In this research we use finite element simulations to analyze the finite deformation response of these viscoelastic layered composites in cyclic compression. We demonstrate using nonlinear finite element analysis that geometric nonlinearities affect the response of these composites at finite but moderate macroscopic strain amplitudes. In addition to the softening, the composite exhibits negative stiffness above a certain amplitude threshold, i.e., the value of the stress decreases when the strain is increased. By combining the layered composites with another constituent material, these geometric nonlinearities and the negative stiffness are exploited to obtain viscoelastic composites with higher damping than the constituents. Both analytical formulae based on composite theory and finite element simulations are used to guide the optimal choice of the geometrical parameters of the composite topology and of the material constituents to achieve extreme damping and high stiffness

Nonlinear mechanics of composite materials

Composite materials have been an area of active research in recent years due to the possibility of obtaining multifunctional structures. Viscoelastic layered composites with parallel plane layers consisting of a stiff constituent and a soft viscoelastic constituent are of particular interest as they have been shown to exhibit simultaneous high stiffness and high damping. Such materials would be useful in structural applications and in high vibration environments such as in a vehicle or machinery. They would provide the rigidity required while simultaneously dissipating mechanical energy. The finite deformation mechanics of parallel plane viscoelastic layered composites has not been extensively studied. Under compressive loads they are very susceptible to instabilities. Buckling, for example is an elastic instability seen in load bearing materials. Since viscoelastic materials are rate and time dependent, the buckling modes for these composites not only depend on these factors, but also on the volume fraction of the stiff constituent. Three different cases are identified in the buckling and post-buckling response of these composites: non-dilute (high volume fraction), transition (intermediate volume fraction) and dilute (small volume fraction) cases. Due to buckling from the application of prestrain, the stiffness and damping of these composites can be tuned by orders of magnitude. Adaptive and multifunctional materials can be designed taking advantage of this idea and the rate dependence of the modes of deformation.M.S