Finite element simulation of delamination growth in composite materials using LS-DYNA

Abstract

In this paper, a modified adaptive cohesive element is presented. The new elements are developed and implemented in LS-DYNA, as a user defined material subroutine (UMAT), to stabilize the finite element simulations of delamination propagation in composite laminates under transverse loads. 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 dependent on the opening velocity of the displacement jump. The traction based model includes a cohesive zone viscosity parameter (g) to vary the degree of rate dependence and to adjust the maximum traction. 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, overcoming the numerical instability and can be widely used in quasi-static, dynamic and impact problems.

Mode I fracture in adhesively-bonded joints: A mesh-size independent modelling approach using cohesive elements

“…However, the higher the value of the maximum cohesive stress, the more refined the mesh needs to be to avoid spurious oscillations in the overall response of the FEA model. Information on several techniques to address the numerical instability can be found elsewhere in the literature [21,[49][50][51][52]. Turón et al [20] proposed a simple strategy to increase artificially the cohesive zone length by reducing the value of the maximum cohesive stress.…”

Cohesive zone models and impact damage predictions for composite structures

“…Further developments of this approach can be found in [249][250][251]. Other approaches have been presented including one in which, ahead of the delamination, the initial stiffness and strength are lowered while keeping the same onset displacement and the same fracture toughness which will increase the final displacement in the cohesive law [169,252].…”

“…In addition to the Corigliano's method discussed above [141,142], rate dependent cohesive laws have been proposed in [168][169][170][171][172][173][174][175] and the effect of friction between delaminated interfaces was introduced in cohesive laws Alfano and Sacco [176], Yang and Cox [177]. The mechanical behavior of polymer matrix materials and adhesives is usually affected by moisture absorption.…”

The interfacial fracture behavior of foam core composite sandwich structures by a viscoelastic cohesive model

“…Recently, combined with finite element methods, more complicated cohesive laws were developed to simulate interfacial delamination propagation [8]. Sridharan and Li [9] compared two types of CZMs: one with a finite thickness and the other with zero initial thickness.…”