INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING Int. J. Numer. Meth. Engng 2003; 00:1–44 Prepared using nmeauth.cls [Version: 2000/01/19 v2.0] Partition of Unity Enrichment for Bimaterial Interface Cracks N. Sukumar 1, ∗ , Z. .Y. Huang 2 , J.-H. Pr´evost 3 , Z. Suo 2 1 Department of Civil and Environmental Engineering, University of California, Davis, CA 95616. 2 Department of Mechanical and Aerospace Engineering, Princeton University, NJ 08544. 3 Department of Civil and Environmental Engineering, Princeton University, NJ 08544. SUMMARY Partition of unity enrichment techniques are developed for bimaterial interface cracks. A discontinuous function and the two-dimensional near-tip asymptotic displacement functions are added to the finite element approximation using the framework of partition of unity. This enables the domain to be modeled by finite elements without explicitly meshing the crack surfaces. The crack-tip enrichment functions are chosen as those that span the asymptotic displacement fields for an interfacial crack. The concept of partition of unity facilitates the incorporation of the oscillatory nature of the singularity within a conforming finite element approximation. The mixed mode (complex) stress intensity factors for bimaterial interfacial cracks are numerically evaluated using the domain form of the interaction integral. Good agreement between the numerical results and the reference solutions for benchmark interfacial crack problems is realized. Copyright c  2003 John Wiley & Sons, Ltd. key words: extended finite element method, interface crack, oscillatory singularity, stress intensity factor, four-point bending specimen, steady-state energy release rate * Correspondence to: N. Sukumar, Department of Civil and Environmental Engineering, University of California, One Shields Avenue, Davis, CA 95616. E-mail: nsukumar@ucdavis.edu Contract/grant sponsor: National Science Foundation; contract/grant number: CMS-9820713, CMS-9988788 Copyright c  2003 John Wiley & Sons, Ltd.