Analytical modeling of damping at micromechanical level in polymer composites reinforced with coated fibers

Theoretical models using theory of elasticity, finite-element, and mechanics-of-materials formulations for characterizing the damping loss factor of composites with coated fiber reinforcement are described. The theoretical models are validated through comparison with experimental damping results conducted on composites having coated fibers as reinforcement. Explicit micromechanics equations are presented in order to define the damping and stiffness of unidirectional coated fiber composites under longitudinal normal (LN), transverse normal (TN), transverse shear (TS) and longitudinal shear (LS) loading conditions. Since shear deformation is essential for viscoelastic damping in polymers, and large shear strains are generated near the fiber/matrix interface in composites, it is shown that the use of a viscoelastic polymer coating on the fibers is an effective way of improving damping in such composites. A strain-energy approach was implemented with both a closed-form theory-of-elasticity solution and finite-element numerical simulations in order to carry out the analysis.