A combined interface element to simulate interfacial fracture of laminated shell structures

A new combined 8-node interface element is developed to simulate the interfacial fracture of shell-like structures such as composite laminates or adhesively bonded joints. It is composed of eight rigid bars and an 8-node zero-thickness cohesive element, each node of which possesses six degrees of freedom (DOFs). Layers of the shell structures are discretized by shell elements and the interface elements are embedded among them. The rigid bars are used to transfer mid-plane nodal displacements of the shell elements to the internal cohesive elements on which the interfacial fracture is actually occurred. The interface element is appeared as a solid one with its 4 nodes at each side connected with the adjacent 4-node shell element. No additional degree of freedoms is introduced by the new element in finite element (FE) model except those of shell elements. A bilinear mix-mode constitutive law is used to characterize the interfacial damages and a viscous regularization method is employed to treat the difficulty on the convergence of implicit FE algorithm. Parametric studies were conducted on double cantilever beam (DCB) specimen to investigate the effect of viscous coefficient and mesh size on the simulation results. The results indicate that the viscous regularization method is effective and the proposed shelled model is less mesh size sensitive than 3D solid model. An adhesively bonded single lap joint (SLJ) and a mixed-mode bending (MMB) specimen with various loading mode ratios were simulated to demonstrate the capability of the element to deal with interfacial fracture problems. The results show that the interfacial element and the simulation results agree well with the experimental results and those obtained through 3D solid models as well as analytical solutions.