Abstract
A micromechanics formulation of composite properties in terms of the constitutent properties using Eshelby's inclusion principle and Mori-Tanaka's mean field method. A linear four-element Burger mechanical model has been employed for application to viscoelastic polymers. The influence of volume fractions of inclusions on the overall creep strain of a polyether-ether-ketone (PEEK)-matrix composite is investigated. The creep rate of the PEEK-matrix which depends linearly on the creep strain and the primary creep, resulting from the viscous flow of creep deformation, is also considered in addition to the usual steady state, or secondary creep. In order to examine the applicability of the model to pure PEEK resin and carbon/PEEK, a series of experiments on PEEK 150P and unidirectional carbon fiber-reinforced PEEK composites has been carried out, which included constant rate of tensile tests and constant load tensile creep tests. It is found that the pure PEEK resin and its composite satisfies the four element Burger model, and that the model agrees with the experimental results extremely well. Also, it is demonstrated that this simple, albeit micromechanic theory is capable of predicting the volume fraction dependence of the time dependent creep, with a characteristic consistent with the known elastic behavior.
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