Modern computers have enabled engineers to perform large scale analyses of complex structures like entire aircrafts, automobiles, and ships. One issue that arises often is the need to perform a unified analysis of a structural assembly using sub-structural models created independently. These sub-structural models are frequently designed by different engineers, thus they are likely to be incompatible at their interfaces. Finite element interface technology has been developed to facilitate the joining of independently modeled substructures. Here an effective and robust interface element is presented. This method has been developed using penalty constraints and allows computationally efficient coupling of finite element models whose nodes do not necessarily coincide along their common interface. A significant effort has been directed toward developing an automatic calculation of the proper penalty parameter. Additionally, the interface formulation has been modified to simulate delamination growth in composite laminates. This work is aimed at research workers and students in mechanical engineer. It would also be of great interest to all scientists concerned with numerical simulations.