A simple model to predict the time- and environment-dependent degradation of tensile strength of unidirectional E-glass fiber composites is presented. The model is phenomenological; that is, based on curve-fits of data for the individual time- and environment-dependent behavior, for which data is available in the literature. These include stress corrosion, zero-stress aging, interphase aging, and moisture-dependent matrix stiffness. The ineffective length at fiber break sites is corrected for debonding length. The average strength of the fiber is reduced to account for zero-stress aging. The concept of inert aged strength is proposed to be able to use data developed under different environmental exposure and load-testing conditions. The conditions for which exposure and aging affect the composite significantly are discussed. Different exposure and loading times are accounted for in the model. Model predictions are compared with available experimental data.
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