Creep and physical aging of composites

Abstract

It is well known that the viscoelastic properties of polymer glasses are significantly influenced by a physical aging process. Although one expects this phenomenon to be operative for polymer matrix composites, very little data at present exist in the literature on the subject. In this paper, the linear viscoelastic creep behaviors of a unidirectional fiber reinforced plastic and its corresponding resin are presented with special emphasis on elucidating the influence of physical aging. It is found that physical aging causes a significant reduction in the creep of these systems and that its influence is comparable in magnitude to that of the temperature. The temperature and aging dependencies of the viscoelastic shift rate, an important quantity needed for long term viscoelastic predictions, are discussed. Further, the time-temperature superposition principle is shown to be unsuitable when applied to long term creep results but is perfectly applicable to momentary creep results. Finally, theoretical predictions of long term creep from momentary creep master curves using an effective time theory are shown to be within 5% of experimental results.