13th International Conference on Fracture June 16–21, 2013, Beijing, China -1- A New Interface Element for Shell Structures Delamination Analysis Biao Li1,*, Yazhi Li1, Jie Su1 1 School of Aeronautics, Northwestern Polytechnical University, Xi’an 710072, China * Corresponding author: libiao@mail.nwpu.edu.cn Abstract A combined interface element consists of eight rigid beams and a zero thickness cohesive element is presented. The type of elements are used in conjunction with shell elements to constitute the three dimensional model. In the FE model, intralaminar damage takes place within the shell elements and interlaminar damage is restricted to occur at the interface elements. The eight-node interface elements are of finite thickness, with each node possessing six DOFs. No additional DOFs are required in the FE model except those of shell elements. The translational and rotational movements of the shell nodes contribute to the deformation of the interface elements. The interfacial damage accumulation and final delamination are characterized by progressive stiffness degradation of the internal cohesive element. The crack growth in double cantilever beam (DCB) was simulated with the proposed elements and corresponding finite element model. The simulation results agree well with the experimental ones and analytical solutions. Keywords composite laminate, cohesive zone model, interface element, delamination 1. Introduction Fiber reinforced composites are mostly used in the form of laminates, which are susceptible to interfacial delamination due to the weak interfacial bonding strength. Several numerical tools such as fracture mechanics based virtual crack closure technique (VCCT) [1, 2] and damage mechanics based cohesive zone model (CZM) method [3, 4] have been proposed to simulate the interfacial fracture process. CZM is superior to other methods in that the initiation and growth of delamination are considered within the same analysis without previous knowledge of crack position. The conventional way of applying CZM is to embed the cohesive elements among the layers of three dimensional solid elements (Fig. 1a). A softening constitutive law described by traction-displacement jump curve is introduced for the cohesive elements. The irreversible softening process is initiated when the traction attains the maximum interfacial strength and delamination is fully developed when the local energy release rates approach their critical values. However, it has been shown that highly refined mesh is required within cohesive zone which is a softening region ahead of crack tip [5]. The length of cohesive zone is usually on the order of 1 mm for typical polymeric matrix composite, which requires that much smaller elements is unacceptable for large scale application of delamination analysis using solid elements. On the other hand, more computational efficient shell elements are suitable for modeling thin walled structures than solid elements [6]. In this paper, we present a new interface element being used in conjunction with shell elements to constitute three dimensional models for laminated structures. Double cantilever beam (DCB) test are simulated using the proposed interface elements and corresponding finite element model. The simulated results are compared with experimental results and analytical solutions. 2. Finite element model 2.1. Model description In the finite element model, laminated structures are divided into several sublaminates through the thickness. A sublaminate is a set of adjacent physical layers among which debonding is unlikely to occur. All sublaminates are modeled with four node quadrilateral shell elements on mid-planes of
RkJQdWJsaXNoZXIy MjM0NDE=