A new energy based mixed-mode cohesive zone model

In this work a novel energy based mixed-mode I+II cohesive zone model is proposed. The model uses the incremental calculation of energy dissipated at each integration point in order to define the damage parameter that simulates gradual material softening as a function of loading. The new model was compared with classical mixed-mode cohesive zone models in which the damage parameter is determined from relative displacements. With this aim, simulations of the Mixed-Mode Bending test considering carbon-epoxy bonded joints were used to assess the differences between the two methods. It was shown that this test reveals a constant global mode ratio with important variations of local mode ratio. The mode I and II fracture energy components issuing from the results were compared with the energy based criterion used as input. It was verified that the relative displacement based method reveals inconsistent results when different pure mode cohesive properties are considered as a consequence of local mode ratio variation. In contrast, it was concluded that the proposed energy based method behaves well in several different circumstances, thus constituting a better solution to deal with general mixed-mode fracture problems.