Mixed-mode I+II continuum damage model applied to fracture characterization of bonded joints

A continuum mixed-mode I+II damage model allowing simulation of damage initiation and propagation in adhesive bonded joints is presented. The model is based on a stress criterion to identify damage onset and a fracture mechanics criterion to simulate gradual degradation of stiffness during loading. It is implemented in two-dimensional solid elements thus allowing identifying the volumetric shape of damaged regions in the vicinity of the crack tip. Additionally, the model is able to predict crack kinking which occurs as a function of the used criteria. The application of the proposed methodology in the context of pure modes (I and II) fracture characterization tests of bonded joints provide the evaluation of the influence of asymmetric propagation on the measured fracture energies. This phenomenon becomes more relevant with the increase of adhesive thickness.