On the Interface Elements for Delamination Simulation of Laminated Plates Subject to Low-Velocity Impact

This paper review the interface elements for the cohesive layers of laminates used in the numerical predictions of delamination of laminated plated subjected to low velocity transverse impact. Laminated plates and shells made of fiber reinforced polymer composites possess high specific modulus and high specific strength in the reinforcement direction, and they are widely used in the industries of aerospace, automobile, ship building, construction etc. But laminated plates have very weak strength in the transverse strength, especially at the interfaces between the laminates. As a result, laminated plates will suffer delamination damage when laminates are under the action of the low-velocity transverse impact. Delamination can severely affect the strength and stability of the damaged laminates. Numerical simulation based on the finite element method is a powerful tool for the prediction of delaminations of laminated plates subjected to low velocity impact. In recently years, many interface elements were proposed for the modeling of the cohesive layers, or called cohesive zones of the laminates where the delaminations occur either for the 2-D shell element models or for the 3-D element models. These interface elements are based on the adhesive penalty contact approach, in which the stiffness of the virtual contact springs are used. However, the determination of spring stiffness is not based on the physics of the adhesive layers, but rather arbitrary which leads to some numerical difficulty and instability. In these models, the onset of the delaminations is controlled by the strength based criteria, and the delamination progress is governed by means of the indirect use of fracture mechanics, and the constitutive law of springs for the softening of the damaged springs is by the equivalency of spring energy dissipation with the strain energy release rate in fracture mechanics. These models are difficult to deal with the delaminations with the mixed modes of fractures. The issues of the influence of various constitutive laws of the virtual springs used in the interface elements on the degradation of the spring stiffness, which is caused by the progressive damages of the delaminations, are discussed in the paper, and a new interface element based on the damage mechanics and on the real geometry and material properties of the cohesive layers and is suggested.