Finite element analysis of interface cracks using multiple point constraints

A finite element technique to analyse closed-mode interface cracks is proposed in this study. Stress boundary conditions for a closed-tip model are transformed into multiple point constraints (MPCs) for nodal displacements. These constraints are imposed upon the finite element solutions to simulate closed-tip stress fields in crack-tip elements. This technique can deal with small as well as large crack-tip contact zones, and no special elements other than the standard quarter-point elements are needed. Since stresses approach infinity at the crack tip in a quarter-point element, dominant terms are used in deriving MPCs for nodal displacements. Fracture parameters are obtained by using the virtual crack extension method, and numerical results are in good agreement with analytical results.