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    The effect of lamina configuration on low-velocity impact behaviour for glass fiber/rubber curved composites
    (Sage Publications Ltd, 2023) Albayrak, Mustafa; Kaman, Mete Onur; Bozkurt, Ilyas
    The aim of this study is to produce curved sandwich composites with different arrays by adding Ethylene Propylene Diene Monomer (EPDM) rubber interlayers between glass fiber woven fabrics and to investigate their behaviours under low-velocity impact. For this purpose, sandwich plates were produced through the vacuum infusion method by using glass fiber and rubber layers on the steel mold manufactured in curved form. Impact tests were applied on the plates and the effect of the stacking sequence for glass fibers/rubber layer on the impact energy absorption was examined. The energy absorption property of the composites was improved by a maximum of 45% with a layer epdm used in the midplane of the composite. Also, when rubber layers were used on the outermost surface of the composites, the damage area reduced by 14%. In the numerical part, the tests were modelled using LS-DYNA finite element packaged programme and the Hashin failure criterion-based material model was used in order to view any damages on the composite structure after the tests. The agreement between numerical and experimental results was obtained with a maximum error of 19%
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    Experimental and numerical impact behavior of fully carbon fiber sandwiches for different core types
    (Springer Heidelberg, 2024) Bozkurt, Ilyas; Kaman, Mete Onur; Albayrak, Mustafa
    The aim of this study is to experimentally and numerically examine the impact strength and damage mechanisms of sandwich composites consisting entirely of fiber-reinforced composites for different core geometries. For this purpose, firstly, composite sandwich plates with egg box, lattice and square plate core structures were produced. Low-velocity impact tests were carried out by dropping impactors with hemispherical geometry onto the resulting sandwich structure with three different core geometries, and the effect of the core shape on impact strength was determined. For comparison, the cell width and height of these three different types of core were chosen to be similar. In addition, progressive damage analysis with the finite element method was applied. For this purpose, the MAT-162 material model, which provides three-dimensional progressive damage analysis in composite materials and applies the Hashin damage criterion, was preferred to be used in the LS-DYNA (R) program. When specific loads are compared using a square core specimen under the same conditions, it can be said that the contact force of the egg box structure is higher. While the striker rebounded from the square core at the same impact energy, it perforated the sandwich structure in the egg box and completely damaged the lattice core structure.
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    Experimental and Numerical Investigation of the Geometrical Effect on Low Velocity Impact Behavior for Curved Composites with a Rubber Interlayer
    (Springer, 2023) Albayrak, Mustafa; Kaman, Mete Onur; Bozkurt, Ilyas
    The present study aims to produce sandwich composites with curved surfaces with different surface geometries by adding rubber (EPDM) between glass fiber woven fabrics and to examine their behavior under the influence of low-velocity impact numerically and experimentally. For this purpose, glass fiber and rubber layers were added to steel molds manufactured in curved forms and sandwich plates were produced through the vacuum infusion method. Low-velocity impact tests were performed by lowering strikers with a hemispherical tip on the produced curved-surface plates, and the effect of the surface geometry on the impact energy absorption was determined. By using rubber intermediate layers, the energy absorption ability can be increased by a maximum of 21%. The curved surface geometry affects the absorbed energy. If the height of the curved surface composites is kept constant and the width is increased to 1.5 times, the impact energy absorption increases by 16 percent. If the width is kept constant and the height is increased to 2.3 times, the impact energy absorption has decreased by 13 percent. When the impact resistance of composites with triangular rectangular, R125 circular arc and flat geometries with the same height and width are compared, it is observed that the lowest impact absorption ability occurs in the plates with triangular geometry, while the impact damping feature increases as the surface geometry becomes flatter and accordingly the contact surface increases. The impact absorption energies of the specimens were determined to be 82% compared to the flat plates. When the impact absorption energies of the upper side lengths of the outer tangent quadrilaterals to the R125 circle arc are compared, a significant increase in the impact absorption capabilities was observed as the side lengths increased. In the numerical part, the tests performed were modeled using the LS-DYNA finite element package program and the Hashin damage criterion-based MAT162 material model was used in order to see the damage caused to the composite structure in three dimensions after the tests. The numerical results obtained were a minimum of 84% compatible to the experimental results.
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    Low-velocity impact behaviours of sandwiches manufactured from fully carbon fiber composite for different cell types and compression behaviours for different core types
    (Walter De Gruyter Gmbh, 2023) Bozkurt, Ilyas; Kaman, Mete Onur; Albayrak, Mustafa
    This study aims to manufacture sandwich composite structures consisting of fully fiber-reinforced composites and then to investigate experimentally and numerically the impact and compressive strength and damage mechanisms of these structures for different cell and core types. To achieve this, firstly, composite sandwich plates with triangular, square and rectangular cell structures were manufactured. Low-velocity impact tests were run on sandwich structures with these three different cell geometries and the effect of cell shape on impact strength was determined. Although the maximum contact force of the square structure under impact load was smaller than the maximum contact force of the triangular and rectangular specimens, the specific contact force was 15.52 % greater than the triangular specimen and 16.29 % greater than the rectangular specimen. Then, the specimens with square, egg box and lattice core types were manufactured and compression tests were performed. The specific peak load value for square specimens was 33.2 % greater than that of egg box specimens and 78.1 % greater than that of lattice specimens. In the numerical study, the experimental results were confirmed by applying the progressive failure analysis with the LS-DYNA finite element program.