1 Submitted to: International Journal for Numerical Methods in Engineering Revised paper: # NME-Jan-07-0035 New development in extended finite element modeling of large elasto-plastic deformations M. Anahid and A.R. Khoei * Center of Excellence in Structural and Earthquake Engineering, Department of Civil Engineering, Sharif University of Technology, P.O. Box. 11365-9313, Tehran, Iran Abstract. In this paper, new achievement is presented in the extended finite element modeling of large elasto-plastic deformation in solid problems. The computational technique is presented based on the extended finite element method coupled with the Lagrangian formulation in order to model arbitrary interfaces in large deformations. In X-FEM, the material interfaces are represented independently of element boundaries and the process is accomplished by partitioning the domain with some triangular sub-elements whose Gauss points are used for integration of the domain of elements. The large elasto-plastic deformation formulation is employed within the X-FEM framework to simulate the nonlinear behavior of materials. The interface between two bodies is modeled by using the X-FEM technique and applying the Heaviside and level set based enrichment functions. Finally, several numerical examples are analyzed, including arbitrary material interfaces, to demonstrate the efficiency of the X-FEM technique in large plasticity deformations. Keywords: Extended FEM, Partition of unity, large deformation, Lagrangian formulation, elasto- plasticity. 1. INTRODUCTION In large deformation problems with internal discontinuities or material interfaces, the note for mesh adaption in different stages of process is of great importance. The need for mesh conforming to the shape of the interface must be preserved at each stage of simulation. In numerical simulation, the requirement of mesh adaptation may consume high expenses of capacity and time. Thus, it is necessary to perform an innovative procedure to alleviate these difficulties by allowing the discontinuities to be mesh-independent. There are several new finite element techniques, which * Corresponding author. Tel. +98 (21) 6600 5818; Fax: +98 (21) 6601 4828. Email address: arkhoei@sharif.edu (A.R. Khoei)