Fiber reinforced composite materials have been widely used in many structural applications. In this class of materials, if the underlying matrix is polymeric, then the material usually exhibits significant time-dependent mechanical behavior even at room temperature. When the long-term durability is of concern, good understanding of time-dependent behavior is needed.
The time-dependent mechanical behavior studied here comes from the composite material’s intrinsic viscoelastic properties. Damage due to loading, and physical and chemical aging may also be significant, but these were not addressed in our experimental research. It is very important to understand these time-dependent phenomena through testing and analysis before the materials can be confidently employed in long-term, primary structural applications. Of all the durability concerns about the material, the linear viscoelastic properties play a fundamental role, as may be seen in a paper on damage growth  that was prepared as part of the research on this project. It was the purpose of this experimental study to obtain the linear viscoelastic properties of two materials that may be used in the offshore applications.