Analysis Method For Composite Delamination Based On Shape Simplification And Stiffness Degradation

Composite materials have higher strength ratio, higher stiffness ratio, and better corrosion resistance than classical metallic materials. Its mechanical property can be designed to meet different requirements. Components made from composite materials have already become the main load-carrying structures in aviation and aerospace fields. However, composite components are usually somewhat damaged due to manufacturing technique and environmental effects. Delamination whose occurrence and initiation could cause substantially loss of load carrying capacity is one of the most common damage types of composite components. Therefore, it is very important to find a simple and effective method to study delamination damage of composite components.In the present paper, buckling and postbuckling behavior of composite laminates with initial delamination damage under compressive load is studied. The equivalent models of delamination are compared through numerical examples to utilize simple shapes instead of irregular shapes for analysis of mechanical behavior of plates with delamination.The geometry-equivalent models commonly used in engineering, such as the envelope ellipse, circle and rectangle are considered to simplify irregular shapes of delamination damage area. Delamination initiation loads of composite laminates are calculated by finite element analysis with delamination damage for equivalent simplified shapes and original irregular shapes of delamination area. Comparison among these three equivalent simplified shapes is completed, based on buckling modes and load-displacement curves. It is found that results from the equivalent elliptic shapes of delaminations is better than the envelope circle and rectangle, and can be used instead of the original irregular shapes for common analysis of delamination damage of composite components.Through comparison of results from the previous study on equivalent simplified shapes of delamination damage area, it is concluded that significant effect of delamination damage on structure is changing critical load of structure buckling, without affecting stiffness of structure. Thus, a stiffness reduction model, whose reduction factor is derived based on variation of critical load of structure buckling, is proposed with two approaches of stiffness reduction of whole structure and of delamination damage area only. Then, load-displacement curves of stiffness reduction model and original model with delamination damage are compared under same loading condition. It is found that the stiffness reduction model with simplified procedure for analysis and delamination damage modeling, is not only able to simulate buckling and postbuckling behavior of composite laminates with initial delamination damage under compression load, but also able to reduce the analysis time considerably.