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Investigation of Cross-ply Curved Composite Laminates under Pure Transverse Loading

A. Cevik 1 , ∗ , D. Yavas 2 , D. Coker 1 , 3

1 Department of Aerospace Engineering, Middle East Technical University, Ankara 06800, Turkey 2 Mechanical Engineering, Lamar University, Beaumont, Texas 77710, USA 3 METU Center for Wind Energy, Middle East Technical University, Ankara 06800, Turkey

∗ cevik.ahmet@metu.edu.tr

Keywords: curved composite laminates, matrix crack-induced delamination, fractography

Curved composite laminates have been utilized in the primary structures such as ribs and spars of airplane wings and wind turbine blades. These structures are exposed to high loads which creates high interlaminar stresses in the curved area leading to the delamination failure mode. Delamination results in a significant loss in the load-carrying capacity of these structures and eventually catastrophic failures [1,2]. This study presents an experimental and numerical inves tigation of cross-ply curved composite laminates, having a stacking sequence of [(90/0) 4 , 90 ] s subjected to pure transverse loading. The experiments are conducted with an electromechanical testing machine. The load-displacement data of specimens are recorded, which reveals that the specimens lose their load-carrying capacity with single or multiple load drops accompanied by 4-5 delaminations in total. In the experiments, a high-speed camera is utilized to observe the failure sequence of specimens and the digital image correlation method is used to obtain in-situ strain field over the curved region. High-speed camera observations show that specimens have the same failure sequence though having different load drop schemes; first delamination initiates at the in ner side of the curved region and subsequent failure occurs at the next neighboring interfaces. In-situ strain field reveals the strain concentration regions occur at the inner side of the curved region where the first failure is observed Post-mortem specimens are investigated with a digital microscope, and in the micrographs, radial & transverse matrix cracks, delamination migration and meandering crack path are observed. Explicit finite element analyses are conducted using interlaminar and intralaminar damage models to simulate the delamination and matrix failure modes, respectively. LaRC04 failure criterion is implemented to ABAQUS via user subroutine. The effect of matrix crack on the failure load are investigated by using LaRC04 failure criterion. The results of analysis reveal that matrix cracks induce delamination at lower loads, which leads to a better agreement with experimental data. The matrix damage pattern observed in the finite element analyses are matched with the experimental one well. References [1] F. Chang, G.-S. Springer. The Strengths of Fiber Reinforced Composite Bends. The Journal of Composite Materials, 20:30-45, 1986 [2] C.-T. Sun, S.-R. Kelly. Failure in Composite Angle Structures Part I: Initial Failure. The Journal of Reinforced Plastics and Composites, 7:220-232, 1988

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