Prediction of delamination initiation and growth from discontinuous plies using interface elements

Abstract

A special type of interface element was created to represent the resin-rich layers between plies in a finite element model of a composite structure. Yielding of the element depended on an interactive stress-based criterion and final failure depended on a mixed-mode fracture mechanics criterion. Both perfectly plastic and work softening types of damage behaviour were modelled. The interface elements were inserted into finite element models of two different straight specimens and two different curved specimens at all possible delamination sites. The specimens contained a group of discontinuous plies which produced a similar stress concentration to that at a ply-drop. Failure was due to multiple delaminations initiating at the cut. The interface elements successfully predicted the locations of the delaminations and were able to account for the changing mode ratio as damage progressed. The predicted failure loads using ‘perfectly plastic’ interface elements were very good for the straight specimens but unconservative for the curved specimens. On the other hand, the predictions using the ‘work softening’ interface elements were reasonable for all four types of specimen.