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Abebaw Abie Mekonnen,우경식,강민송,In-Gul Kim 대한기계학회 2020 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.34 No.3
Delamination occurred due to poor manufacturing process or in-service actions significantly affects the mechanical and failure behavior of laminated composite structures. In this study, the buckling and post-buckling delamination behavior of laminated composite with an embedded initial delamination under in-plane compression was studied experimentally and numerically. First, compression tests for laminated composite specimens with embeded initial delamination were performed and the buckling and delamination responses were obtained. Then the experimental test was numerically simulated using finite element methods with the progressive failure accounted for by using cohesive zone modeling. The load-displacement curve, strain behavior and delamination shapes of experimental specimens obtained from load cells, strain gages installed at different locations, and C scan images, respectively, were compared with the FEM results, and good agreements were attained. The effect of the buckling modes, laminate stacking sequence and shape of initial delamination on the buckling load and propagation behavior was studied by considering different ply stacking and shapes of initial delaminations. It was found that the buckling mode determined the growth direction of the delamination propagation, and the stacking sequence influenced the extent of the propagation area, while the orientation of the delamination affected the buckling loads.
Abebaw Abie Mekonnen,우경식,강민송,김인걸 한국항공우주학회 2020 International Journal of Aeronautical and Space Sc Vol.21 No.1
In this paper, buckling, post-buckling, and delamination behavior of composite laminates subjected to axial compression was studied. First, compression tests were performed for composite laminate specimens with through-width delamination and the history of buckling and delamination propagation was measured. Next, the tests were simulated using two-dimensional finite-element models. A geometrically non-linear post-buckling analysis was performed for the finite-element mesh seeded with small amount of geometric imperfection based on eigenmodes. The growth of delamination due to sub-laminates buckling was simulated using the cohesive zone modeling. The analysis results were compared with the test results for the verification of the numerical model. Then, the analysis results were examined to study the relation between geometric parameters of initial delamination and buckling loads and post-buckling delamination propagation behavior of the composite laminates. The effects of different sizes and locations of initial delamination on the delamination behavior were systematically investigated. It was found that the buckling loads, mode shapes, and the delamination growth behavior are affected by the geometry variation of pre-included delamination. The long and shallow initial delaminations prompt local buckling the deep delaminations induce global buckling mode.
Effects of Defects on Effective Material Properties of Triaxial Braided Textile Composite
Mekonnen Abebaw Abie,우경식 한국항공우주학회 2020 International Journal of Aeronautical and Space Sc Vol.21 No.3
In this study, the effects of defects in a triaxial braided textile composite was studied at unit cell level using three-dimensional finite element analysis. The manufacturing defects such as void defect and tow misalignments were considered in the model and the effect of their presence at different scale on the effective material properties were studied. The configuration of the finite element model was based on the geometric data extracted from an experimental test specimen. The representative unit cells (RUC) that repeat itself to build the whole braid were sliced out from the full interlaced geometry of axial and bias tows. Periodic boundary condition (PBC) was used to simulate the repeating nature of the unit cells. Then, numerical tests were performed to compute three-dimensional effective material properties for triaxial braided RUCs with predetermined void volume fractions and axial tow misalignment under uniaxial tension and shear loadings in different directions. It was observed that the void defects severely affected the out-of-plane properties of the material, while the tow misalignments influenced the axial modulus mostly.