To perform an evaluation of the abilities of a bonded structure to endure repetitive loadings, characterizations of structural adhesive joints mechanical behavior are key objectives. The aim of this study is to describe the phenomena occurring in the bonded joint until the appearance of a macroscopic crack. Using lap-shear type specimens, associated with stress concentrations, crack initiation generally appears early at the edge of the adhesive joint, which makes it difficult to identify the crack initiation phase. To characterize more properly the crack initiation phase, bonded joints designed to limit stress concentrations allowed the accurate characterization of the mechanical phenomena occurring in a polyurethane structural ductile adhesive. Then, based on the experimental response of the bonded assembly to creep recovery tests, a visco-elastic visco-plastic behavior law is defined for the adhesive joint mechanical behavior. In the following, details of such a model able to take into account the hydrostatic sensitivity with a non-associated formalism are given. The numerical work performed here relies on the identification of the material parameters of the behavior law using creep-recovery tests to model the cyclic behavior of bonded structures. Then, experimental results under fatigue loading are presented and compared to numerical simulations. Finally, using a strain-based criterion for the definition of crack initiations, predictions of fatigue lifetime are performed for specimens under shear loadings. The quality of the results obtained underlines that an accurate description of viscous mechanisms in the adhesive layer allows describing efficiently the mechanical behavior of bonded joints under cyclic loading.