American Institute of Aeronautics and Astronautics 1 Strength Prediction in Open Hole Composite Laminates by Using Discrete Damage Modeling Michael J. Swindeman 1 , Endel V. Iarve 2 , Robert A. Brockman 3 , University of Dayton Research Institute, Dayton, OH, 45469 David H. Mollenhauer 4 Air Force Research Laboratory, Wright Patterson AFB, OH, 45433-7750, USA and Stephen Hallett 5 University of Bristol, Bristol, BS8 1TR, United Kingdom The present paper addresses the issue of direct simulation of complex local failure patterns in laminated composites. A model capable of discrete modeling of matrix cracking, delamination, and the interaction of these two damage modes is proposed. The analytical technique uses the eXtended Finite Element Method (X-FEM) for the simulation of matrix crack initiation and propagation at initially unknown locations, as well as a cohesive interface model for delamination. The model is capable of representing the complex kinematics of crack networks in composite laminates without previous knowledge of the crack locations or user intervention. An important feature of the technique is that it uses independently measured standard ply-level mechanical properties of the unidirectional composite (stiffness, strength, fracture toughness). Failure simulations of composites containing open holes are presented. Although the process of crack initiation is impossible to capture precisely due to local material variations, the proposed method exhibits excellent agreement with experimental data for matrix crack growth in unidirectional graphite-epoxy composites. I. Introduction trength prediction in laminated composite materials is a formidable challenge, even more than three decades after publication of pioneering works by Rosen 1 and Tsai and Wu 2 . Detailed modeling of damage initiation and propagation is particularly difficult in the regime where various damage modes, such as delamination and matrix cracking, interact. Strength prediction in unidirectional composites and composite laminates under uniform in-plane loading was the subject of a recently concluded first round of the World Wide Exercise 3 . This exercise has demonstrated that even failure prediction in unidirectional composites represents a formidable challenge. A significant body of research has been devoted to the development of comprehensive damage mechanics (CDM) models 4-5 to account for all modes of in-plane failure in composite laminates. These approaches are generally successful in predicting the softening behavior in laminates due to matrix crack accumulation under uniform loading conditions. The drawback of these models is their inability to accurately describe the local effects of interactions between various damage modes and local effects of stress redistribution in the damaged area. This issue was investigated in detail by Iarve 6 , where a property degradation CDM model was applied to modeling longitudinal splits in the plies with 0° fiber orientation, which also coincided with the tensile loading direction. Experimental 1 Research Engineer, 300 College Park Avenue, Dayton OH 45469, Non-Member. 2 Distinguished Research Engineer, 300 College Park Avenue, Dayton OH 45469, Member 3 Distinguished Research Engineer, 300 College Park Avenue, Dayton OH 45469, Non-Member. 4 Senior Research Engineer, Composites & Hybrids Branch, 2941 Hobson Way/AFRL/RXBC, Non-Member. 5 Senior Lecturer, Aerospace Structures, University Walk, Non-Member. S 52nd AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics and Materials Conference<BR> 19th 4 - 7 April 2011, Denver, Colorado AIAA 2011-1793 This material is declared a work of the U.S. Government and is not subject to copyright protection in the United States.