A coupled damage-plasticity model for the cyclic behavior of shear-loaded interfaces

• A model to study the fatigue behavior of interfaces under mode-II loads is proposed.
• The model is thermodynamically consistent and couples damage and plasticity.
• A bilinear interface law is assumed under monotonic conditions.
• Four parameters are needed, three for the monotonic and one for the cyclic behavior.
• Comparison with experimental tests on FRP bonded joints shows excellent agreement.

The present work proposes a novel thermodynamically consistent model for the behavior of interfaces under shear (i.e. mode-II) cyclic loading conditions. The interface behavior is defined coupling damage and plasticity. The admissible states’ domain is formulated restricting the tangential interface stress to non-negative values, which makes the model suitable e.g. for interfaces with thin adherends. Linear softening is assumed so as to reproduce, under monotonic conditions, a bilinear mode-II interface law. Two damage variables govern respectively the loss of strength and of stiffness of the interface. The proposed model needs the evaluation of only four independent parameters, i.e. three defining the monotonic mode-II interface law, and one ruling the fatigue behavior. This limited number of parameters and their clear physical meaning facilitate experimental calibration. Model predictions are compared with experimental results on fiber reinforced polymer sheets externally bonded to concrete involving different load histories, and an excellent agreement is obtained.