A new phenomenological fatigue crack growth formulation for the modeling and the prediction of the Model fatigue behavior of adhesively-bonded pultruded glass fiber-reinforced polymer double cantilever beam joints under different R-ratios is introduced. The established formulation is based on the total fatigue life concept, considering however the model parameters as functions of the R-ratio by fitting the existing experimental data under two to three different R-ratios. This model can subsequently be used for the derivation of fatigue crack growth curves under any different R-ratio, thus assisting the development of methodologies for the fatigue life prediction of a joint comprising adherends with the same material under realistic loading conditions. An extensive fatigue/fracture database has been derived, containing results of 28 Model fatigue experiments, to assist the model development and to validate its predictions. Comparison of the model predictions and experimental results proved the model's validity. (C) 2012 Elsevier Ltd. All rights reserved.