Modeling the Initiation and Growth of Delaminations in Composite Structures

A method for modeling the initiation and growth of discrete delaminations in shell-like composite structures is presented. The laminate is divided into two or more sublaminates, with each sublaminate modeled with four-noded quadrilateral shell elements. A special, eight-noded hex constraint element connects opposing sublaminate shell elements, and makes the two opposing shell elements act as a single shell element until a prescribed failure criterion is satisfied. Once the failure criterion is met, the connection is broken, and a discrete delamination initiates or grows. This approach has been implemented in a three-dimensional finite element code. This code uses explicit time integration, and can analyze shell-like structures subjected to large deformations and complex contact conditions. Tensile, compressive, and shear laminate failures are also modeled. This paper describes the eight-noded hex constraint element used to model the initiation and growth of a delamination, and discusses associated implementation issues. In addition, calculated results for double cantilever beam and end notched flexure specimens are presented and compared to measure data to assess the ability of the present approach to model a growing delamination. Results are also presented for a diametrally compressed ring to demonstrate the capability for analyzing progressive failure in a highly deformed composite structure.