Improvement of damping at the micromechanical level in polymer composite materials under transverse normal loading by the use of special fiber coatings

This paper describes preliminary results from a systematic analytical study of the improvement of damping in polymer composites at the micromechanical level under transverse normal loading by the use of special fiber coatings. Since shear deformations are important in damping of viscoelastic polymers, and large shear strains are generated in the region of the fiber/matrix interface, one idea for improving damping is to put a fiber coating made from a highly dissipative material in this region. A finite element model based on a "representative volume element" or repeating element of a continuously reinforced coated fiber composite is used to study damping under transverse normal loading. The micromechanical composite model investigated is a unidirectional graphite/epoxy with an acrylic polymer as the fiber coating material. Both two and three dimensional finite element models are analyzed in order to compare the influence of plane stress and plane strain conditions on the damping and stiffness properties of the composite micromechanical model. Parametric studies are conducted by using a two dimensional plane strain finite element model in order to illustrate how the coating applied to the fiber influences dynamic properties of the composite structure. The parametric studies are done with particular emphasis on the effects of frequency temperature, and fiber coating thickness on the damping of the composite structure.