V ECCOMAS Thematic Conference on the Mechanical Response of Composites COMPOSITES 2015 S.R. Hallett and J.J.C. Remmers (Editors) MIXED-MODE DELAMINATION ANALYSIS OF COMPOSITE LAMINATES WITH XFEM BASED ON A COHESIVE ZONE MODEL Saleh Yazdani * , Wilhelm J.H. Rust † , Peter Wriggers †† * Institute of Continuum Mechanics, Leibniz Universität Hannover Appelstraße 11, 30167 Hannover, Germany yazdani@ikm.uni-hannover.de † Hochschule Hannover - University of Applied Sciences and Arts Ricklinger Stadtweg 120, 30459 Hannover, Germany wilhelm.rust@hs-hannover.de †† Institute of Continuum Mechanics, Leibniz Universität Hannover Appelstraße 11, 30167 Hannover, Germany wriggers@ikm.uni-hannover.de Key words: Delamination, XFEM, Cohesive. Summary: A numerical model is developed to analyse the delamination propagation for a mixed-mode loading. A First order Shear Deformation Theory (FSDT) is utilized to model the multi-layered composite plates by four-node elements. To simulate the delaminated surface, the level set method in the context of the eXtended Finite Element Method (XFEM) is implemented in the shell elements. In order to investigate onset of the damage and its propagation in the mixed-mode loading, a traction-separation law with an exponential softening behaviour is developed. Several standard numerical tests for a double cantilever beam (mode I) and end notch flexure (mode II) are carried out to verify the accuracy of the model. The new formulation is able to model discontinuities with less computational effort. In order to solve the non-linear progressive damage an arc-length method with full Newton- Raphson iteration is chosen. The influence of different integration schemes of the interface formulation is studied with respect to the stability of the results. Furthermore, the effect of the exponential damage parameter is investigated with respect to the robustness of the results. 1 INTRODUCTION First order Shear Deformation Theories (FSDT) are widely used to model the relatively thick composite laminates [1]. Taking into account their lower order formulation and the lower order interpolation functions utilized in the FSDT theories, they have superiority over the three-dimensional formulation to analyse the multi-layered laminates, especially in case of non-linear analysis. The major attentions toward the failure analysis of multi-layered laminates are devoted to their delamination analysis [2]. In order to perform a progressive delamination analysis, one might consider both the delamination onset and its propagation. Taking into account the simplicity and low computational cost of the FSDT theory, one can