Dokuma ve çapraz-katlı bükümlü kompozit yapılardakı hasarın deneysel yöntemlerle incelenmesi

Laminated curved-shape composite parts which are used in the spar and ribs in aircraft and wind turbine blades are subjected to high interlaminar tensile and shear stresses. These stresses cause delamination and subsequent reduction in load-carrying capacity. In this study, failure mechanism of cross-ply and fabric curved composite laminates under pure transverse loading are examined experimentally using an in-house designed test fixture. Stress field over the curved beam is obtained with finite element analyses (FEA) and analytic solution where multilayered theory is used. Dynamic delamination of the cross-ply and fabric curved specimens is recorded with a high-speed camera where the failure sequence is captured and the crack tip speeds are calculated. For the cross-ply laminates, von Mises strain field is obtained with digital image correlation (DIC) method where the strain fields are found to agree well with elastic FEA up to a specific loading at which a population of matrix cracks nucleate. Detailed fractography of the tested specimens is carried out with digital microscope. Finite element analysis with 2D Hashin Failure criteria is also successfully predict the radial cracks observed in the micrographs of cross-ply curved composite laminates. However, the meandering crack path could not be properly predicted with 2D Hashin Failure Criteria. In fabric curved composite laminates, the failure is observed to occur due to inter-ply and intra-ply crack growth. In fabric laminates, the crack tip travels in a fluctuating manner at speeds reaching intersonic speeds whereas in cross-ply laminates the crack tip speed reaches about Rayleigh wave speed.