Fracture-based interface formulation for FRP-to-concrete debonding mechanisms in mixed cracking mode

The present work proposes a fracture-based model for analysing the cracking processes possibly arising at the interface between FRP strips loaded in tension and glued to concrete or other brittle substrates. Particularly, it aims at simulating the “mixed” nature of such cracking processes actually characterised by both axial and transverse relative displacement components. The model is formulated within the general framework of the Finite Element Method. Thus, four-node plane stress elastic elements simulate the two adherents, which are connected to each other via a layer of zero-thickness interface elements where all mechanical nonlinearities, induced by the cracking process, are actually embedded. A hyperbolic maximum strength criterion, in the normal/shear stress space, is considered for such interface elements and post-peak behaviour is controlled by the fracture work spent under I, II and/or mixed failure modes. Finally, numerical simulations of pull-out tests are presented to highlight the predictive capabilities of the proposed formulation.