Predicting progressive delamination via interface elements

Publisher Summary This chapter reviews some of the background behind the development of interface elements with application to composites delamination. Interface elements are elements which model a thin or zero thickness layer between continua in a finite element analysis. The location of the interface elements are not themselves a prediction of the crack path but a plane of potential delamination which may or may not fail depending on the loading and the relevant failure criteria. For laminated composites this approach works well as the planes of possible delamination are generally well defined between the plies or at adhesive bond lines. The relative nodal displacements under an applied load can be separated out into normal and shearing components. The normal component represents a mode I type crack opening and the shearing a combination of mode II and III since these cannot be distinguished without knowledge of the direction of the crack front. The constitutive relation of the interface element is based on a traction-displacement law which is generally elastic up to a stress-based failure criterion (initiation) and then undergoes a softening behavior which describes an area under the curve equal to the critical fracture energy (GC) at complete failure (propagation).