Mixed Mode Delamination Analysis by a Thermodynamically Consistent Cohesive Interface Model with Independent Mode i and Mode II Fracture Energies

In the present paper a new thermodynamically consistent cohesive interface model is proposed; it based on a predefined Helmhotz free energy with a single scalar damage variable and produces two independent fracture energies, in pure mode I and pure mode II debonding conditions. The proposed model can also take in to account the frictional effects with a smooth transition of the mechanical behaviour, from the initial cohesive one of the sound material, to the frictional one of the fully debonded interface. The cohesive-frictional behaviour is based on the mesoscale geometric interpretation of the scalar damage variable, which distinguish sound and debonded fractions of a representative surface element of the interface. The proposed formulation is defined by a damage activation function, which depends on the separation displacement. Traction components, damage evolution and the relevant constitutive equations are derived by following the classical Noll and Coleman procedure, and the model implicitly verify the second thermodynamic law by proving that dissipation is non-negative for any loading path. The numerical simulations of mixed mode delamination tests are performed and compared to the experimental results, for different mixed mode ratio.