A penalty-based interface technology for connecting independently modeled substructures and for simulating growth of delamination in composite structures

An effective and robust interface element technology able to connect independently modeled finite element subdomains is presented. This method has been developed using penalty constraints and allows coupling of finite element models whose nodes do not coincide along their common interface. Additionally, the present formulation leads to a computational approach that is very efficient and completely compatible with existing commercial software. A significant effort has been directed toward identifying those model characteristics (element geometric properties, material properties and loads) that most strongly affect the required penalty parameter, and subsequently to developing simple “formulae” for automatically calculating the proper penalty parameter for each interface constraint. This task is especially critical in composite materials and structures, where adjacent sub-regions may be composed of significantly different materials or laminates. The present interface element has been implemented in the commercial finite element code ABAQUS as a User Element Subroutine (UEL), making it easy to test the approach for a wide range of problems.; Once the reliability and the effectiveness of the interface element were established, new capabilities were implemented in the FE code in order to simulate delamination growth in composite laminates. Thanks to its special features, the interface element approach has several advantages over the conventional FE ones. An analysis of the literature on delamination techniques shows that generally delamination growth is simulated in a discretized form by releasing nodes of the FEM. The presented interface element allows this limitation to be overcome. It is possible to release portions of the interface surface whose length is smaller than that of the finite elements. In addition, for each portion the value of the penalty parameter can be changed at will, allowing the damage model to be applied to a desired fraction of the interface between the two meshes. The approach implemented in the interface element is one of the most commonly adopted. It mixes features of the strength of materials approach and fracture mechanics. Results for double cantilever beam DCB, end-loaded split (ELS) and Fixed-Ratio Mixed Mode (FRMM) specimens are presented.