A new rate-dependent cohesive model for simulating dynamic composite delamination

A new eight-node adaptive rate-dependent cohesive element is proposed in this paper. In this model, a pre-softening zone is proposed ahead of the existing softening zone. In this pre-softening zone, the initial stiffness and the interface strength are gradually decreased. The onset displacement corresponding to the onset damage is not changed in the proposed model. In addition, the critical energy release rate of the materials is kept constant. Moreover, the constitutive equation of the new cohesive model is developed to be depended on the opening velocity of the displacement jump. The traction based model includes a cohesive zone viscosity parameter (η) to vary the degree of rate dependence and to adjust the maximum traction. The new cohesive element is implemented in LS-DYNA as a user defined material subroutine (UMAT) designed for solid elements. The numerical simulation results of DCB in Mode-I is presented to illustrate the validity of the new model. It is shown that the proposed model brings stable simulations and can be widely used in quasi-static, dynamic and impact problems.