A damage model for a finite thickness composite interface accounting for in-plane deformation

The present paper deals with the formulation of an innovative interface model characterized by nonlinear response. The interface is assumed to be composed of several thin layers, one of which is characterized by nonlinear response. In this layer, denoted throughout the paper as detachment layer, the nonlinearity is modeled adopting a damage law and the decohesion process occurs. The kinematics of the interface is enriched accounting for the in-plane strain component; in such a way, the presence of the stress component arising in the plane of the interface can be computed and taken into account for the evaluation of the nonlinear response of the detachment layer. In fact, when in-plane compressive stresses are present a confinement effect occurs, slowing down the damage growth. On the contrary, when tensile in-plane stress is present in the detachment layer, the damage evolves more rapidly. The interface model is implemented in a finite element computer code and a numerical procedure is proposed. Two numerical applications are presented to assess the ability of the proposed interface model and of the implemented numerical procedure to reproduce specific decohesion problems. The first application deals with the debonding of a FRP reinforcement from a concrete support; comparison of the numerical results with available experimental evidences are given. The second application concerns the mixed mode decohesion in an edge-notch four-point bending specimen.