Numerical Simulation Of Delamination Damage For Composite Laminates

With the extensive use of composites, the research of failure modes is gradually perfected. From the microscopic damage mechanics point of view, the failure of composite laminates is attribute to intralaminar and interlaminar damages, such as fiber breakage in plane, delamination, and sub-laminate buckling. According to the statistics. Delamination contributes to 60% in all failure modes. Either for monotonic static loading or cyclic fatigue one, delamination and delamination propagation can significantly reduce the loading capacity of composite structures, and even make catastrophic damage, leading to serious safety problems. Delamination is the most dangerous failure mode in composite structures. Therefore, it is very important to study delamination of composite laminates.There are two major models for the numerical simulation of laminates delamination, one based on damage mechanics and the other on fracture mechanics. The damage mechanics model introduces interface elements between composite layers. The behavior of the interface elements is determined by the relationship between the gap opening and the traction across the interface. The area covered by the stress and relative displacement curve equals to the critical energy release rate. This method can provide an energy dissipation mechanism due to the development of micro-cracks and micro-voids within the composite. Mesh size in the crack tip can be relatively coarse, and no re-meshing is necessary, and also it is easy to generate finite element models without pre-defined crack.The damage mechanics model is used in this paper. Boundary element is used to model interfacial layer and shell element for laminates. In older to prevent penetration between sub-laminates, contact constraints are imposed in the region where initial crack exists. This article focuses on the damage behavior of composite laminates with initial crack under tension land compressive loadings. In the case of tension loading, the influence of interface stiffness, the length of the initial crack, non-symmetric debonding and interfacial fiber ply angle on the delamination damage of laminates is investigated. According to the analysis, it is inferred that the interface stiffness has little effect on delamination; the length of the initial crack acts on the loading procession before delamination initiation and doesn't affect the delamination propagation; in the instance of non-symmetric debonding, a theoretical formula is proposed to predict the maximum load, and its reliability is verified by its good agreements with numerical results. For compression loading, the influence of delamination area, stacking sequence, and non-symmetric debonding on the delamination behavior is studied. For the case of symmetric debonding, the laminate undergoes global buckling initially and changes to local buckling as the delamination area increases. However, the critical buckling and failure loads are independent on the delamination area. Equivalent elastic modulus in the compression loading direction has great influence on the critical buckling and failure loads. If the initial delamination is close to the surface of the laminate, the laminate undergoes initial globle buckling and changes to a mixed-mode buckling, with the critical buckling load decreases rapidly and the failure one slowly.