• Composite materials
• Damage mechanics
• Invariants
• Laminates
• Thermodynamic potential

The purpose of this work is to define a ply damage onset and evolution criterion, thermodynamically consistent, based on the energy equivalence principle; the model accounts for multiple independent and interactive damage mechanisms required by multi-phase materials.
The proposed model can cope with unidirectional long fibers plies that, when in pristine conditions, are treated as a transversally isotropic material whose stiffness matrix is obtained from a stress invariant formulation of the thermodynamic potential. The damage activation functions are based on stress invariants as well and the damage evolution equations are derived enforcing the principle of maximum energy dissipation.