Interaction between static fatigue and zero-stress aging in E-glass fiber composites

Interaction between static fatigue and zero stress aging of E-glass fiber composites is investigated. A comprehensive gathering of available experimental data for E-glass fibers and unidirectional composites is presented. A methodology is proposed that allows us to utilize seemingly ill-assorted data developed under noncomparable environmental exposure conditions. This is made possible by using the concept of inert aged strength, which allows us to homogenize all aging data regardless of the conditions of exposure by shifting it to the inert condition. Such inert aged data is then used to generalize the static fatigue model. Models for the two phenomena, static fatigue and zero-stress aging, acting separately and jointly are presented. Conditions are established for proper determination of the static fatigue susceptibility. Available experimental data of fibers and unidirectional composites is used to support the arguments made for an interacting model. The conditions for which aging becomes significant are outlined.