Study On Interface Elements Used In Delamination Simulation Of Laminates

Composite laminated structures have been more and more used in various industries because of their very outstanding mechanical properties. However, the transverse strength of laminated plates is very weak, especially at the adhesive layers which are the resin rich zones at the interlaminar interface. As a result, laminated plates would suffer damages, such as matrix cracking, debonding and inter-ply delaminations especially under the action of low-velocity transverse impact Among these different damages, the delamination at the interlaminar interfaces with different fiber orientations is the most dangerous and could be one main source that the mechanical capability of the structures is seriously degenerated. Therefore, it is very desireable and important to study the mechanical behavior of the interlaminar interfaces in order to obtain realistic failure prediction.This thesis is composed of the followings three major parts.1. A simple and natural model to evaluate the stiffness of the spring interface elements, which is based on the physics and the geometry of the adhesive layers, is proposed. The proposed model is applied to the nonlinear spring element COMBIN39 and COMBIN14 in ANSYS to simulate the delamination propagations of the standard DCB and ENF tests. The resulting delamination predictions agree well with the experimental results, and the numerical examples demonstrated that the proposed model is not only simple but also an accurate and robust way to evaluate the stiffness of the spring interface elements used for the delamination simulations of laminated plates.2. The influence of the material modeling of the solid-shell interface element on the delaminations simulations of laminated plates is studied. The predicted results agree well with experimental results. It is shown that the solid-shell interface element is an efficient model for the adhesive layers of laminated plates.3. Based on the assumed element strain fields of the Quasi-Conforming Element Techniques, a 3-D solid-shell finite element, designed for the 3-D analysis of plates is developed. The element stiffness matrix of the present solid-shell element is would be free of shear locking as well as numerical ill-conditioning. The presented solid-shell element is applied to the analysis of mechanical behavior of plates in the paper. The numerical results show that the element processes high accuracy as well as high computational efficiency. Therefore, the solid-shell element presented in this thesis provides a brand new element for the delaminations simulation of laminated plates.The model of the stiffness evaluation of spring interface element and the material modeling approach for the solid-shell interface element presented in the thesis would be of great help in the delaminations simulating of composite laminated plates.