American Institute of Aeronautics and Astronautics 1 Single Edge Notch Tension Test on Cross-Ply Laminated Composites for Intralaminar Fracture Properties Stewat Boyd 1 Ashith P. K. Joseph 2 and Anthony M. Waas 3 University of Michigan, Ann Arbor, MI, 48109 Wooseok Ji 4 Ulsan National Institute of Science and Technology, Ulsan, S. Korea A systematic yet simple way to measure the fracture toughness value for a Mode I crack that occurs perpendicular to the fiber direction in a unidirectional composite is presented. Cross-ply single edge notch tension (SENT) tests combined with finite element analysis areutilized to obtain the in-plane fracture toughness value under tension in the direction of fibers. The notch length of the SENT specimen is used as a parameter to back out the fracture toughness value in a consistent manner. I. Introduction Interlaminar fracture in polymer matrix composite (PMC) laminates, often called delamination, is defined as an out-of-plane discontinuity between two adjacent plies of a laminate. Delamination behavior has been studied by many researchers and now can be characterized in a standardized manner. Fracture properties of Mode I, Mode II, and mixed-mode (between Mode I and Mode II) delamination can be obtained from standard tests in conjunction with finite element analysis (FEA). However, a systematic approach to quantify and measure intralaminar fracture properties is not available in the literature. This presentation pertains to the development of a suitable test-analysis protocol to obtain such toughness values that can be used in virtual tests. Intralaminar cracks are defined as in-plane discontinuities that advance through the entire laminate thickness in the direction parallel to the fiber direction. Intralaminar fracture modes are typically characterized as three major intralaminar failure mechanisms, which are distinct from the microdamage mode. They are transverse (Mode I) matrix cracking, shear (Mode II) matrix cracking, and axial (Mode I) fiber fracture as shown in Figure 1. These fracture modes are consistent with the in-plane failure typically observed in PMC laminates. The interlaminar cracks, once initiated, can trigger other failure mechanisms such as delamination and/or act as delamination migration pathways between adjacent interfaces, leading to the further growth of the delamination. Presence of such damage can cause significant reduction of the overall performance of structural components and thus, an accurate measurement and quantification of the fracture modes are fundamental to the understanding of the onset, growth, and interaction of interlaminar and intralaminar cracks. However, this activity cannot occur in isolation of the subsequent modeling effort and use of finite-element based structural analysis. This presentation will describe a combined experimental and numerical study to provide a systematic and reliable way for measuring the intralaminar fracture properties. Especially, the fracture toughness value for the Mode I fiber failure will be obtained from single edge notch tension (SENT) tests combined with FEA simulation. It is assumed that the fracture toughness value for Mode I trasverse cracking is the same as the value for the interlaminar Mode I fracture and the vaue for shear Mode II matrix cracking is the same as the vaue for the interlaminar Mode II fracture. SENT specimens are designed to have different notch lengths with the same dimensions elsewhere in order to control the main in-plane fracture mode. The measured experimental force-displacement data, converted to a suitable stress- strain response will be compared to corresponding FEA simulations to back out the individual intralaminar fracture properties. 1 Graduate Student Research Assistant, Department of Aerospace Engineering, 2038 FXB 2 Graduate Student Research Assistant, Department of Aerospace Engineering, 2038 FXB 3 Felix Pawlowski Collegiate Professor, Department of Aerospace Engineering, 3044 FXB, Fellow of AIAA. 4 Assistant Professor, School of Mechanical and Advanced Materials Engineering, 301-7 Engineering Building #1, Member of AIAA. Downloaded by University of Michigan - Duderstadt Center on December 13, 2017 | http://arc.aiaa.org | DOI: 10.2514/6.2014-0852 55th AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference 13-17 January 2014, National Harbor, Maryland 10.2514/6.2014-0852 Copyright © 2014 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved. AIAA SciTech Forum