The effect of volume percent and morphology of phases on the damping behavior of epoxy/aluminum composites
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I.
INTRODUCTION
T H E damping capacity of a material is the ability of the material to dissipate vibrations by converting the vibrational energy into other forms of energy. In metallic systems, this energy dissipation occurs by the release of heat, which is caused by internal friction across the specimen. Polymeric materials have high damping capacity, usually more than an order of magnitude greater than structural metallic materials, but in general, they have low stiffness. Composites are a class of materials whose properties can be tailored according to specific requirements by varying the component phases. For many applications, the goal is to obtain high damping with reasonable stiffness. In composite materials, there are numerous methods of energy dissipation, such as by viscoelastic response of the material constituents in polymer systems, thermoelastic conversion of mechanical energy into heat, friction at the fiber-matrix or particulate-matrix interface, and from the absorption of vibrational energy during microplastic deformation of the particle itself. The nonhomogeneous characteristics of the composite give rise to damping due to the resulting stress variations across the interfaces. The problem of low stiffness can be overcome by reinforcing polymers with rigid particulates or fibers resulting in optimal damping and stiffness. The present study involves the damping behavior of fiber and particulate epoxy/A1 composites. The damping behavior of such a composite depends on complex interplay between the properties of the individual constituent phases: the resin, the filler, and the interfacial phase. The loss factor
of a composite is affected by a number of parameters, such as size, shape, aspect ratio, distribution, adhesion between phases, and continuity of the phases. Most of the analytical solutions available are concerned with specific geometries and are not suitable to predict the damping behavior of composites as a function of these morphological factors. In this study, the finite element method (FEM) has been employed to study the damping behavior of the epoxy/Al composites as a function of particle size, morphology, and volume percent of the phases.
II.
TECHNICAL BACKGROUND
Damping capacity of a material can be measured/characterized in a number of ways. Damping is measured either during free decay or during continuous driving force, at a given frequency and strain amplitude. The simplest experiment to measure damping involves a cantilever beam which is excited or loaded into its fundamental mode of vibration by an external force. The damping capacity can be measured in a number of ways, one of which is loss factor. This is described subsequently. The modulus of a viscoelastic material is expressed as a complex quantity. When a harmonic stress is applied to a material in steady state, the corresponding strain lags behind the applied stress by an angle 05. The loss factor is given by the tangent of the phase angle, 05, between stress and strain. The stress-strain relationship can be expressed
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