Browsing by Author "Sayman, O"

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    The mechanical behaviour of adhesively bonded composite joints under repeated axial impacts at different temperatures
    Kemiklioglu, U; Sayman, O; Soykok, IF; Akderya, T; Dere, R
    In this study, the failure strength of single-lap adhesively bonded joints was investigated. The glass fibre epoxy composites used as adherends were manufactured by using a vacuum-assisted resin infusion method. These composites were bonded with a commercial material of epoxy-adhesive DP-460, which can be cured easily at room temperature. The specimens were built by bonding, and then repeated axial impact loads having various energy levels ( 0, 5, 10, 15, and 20 J) were implemented to the single-lap adhesively bonded composite joints at different temperatures (-20 degrees C, 0 degrees C, 20 degrees C, 40 degrees C, and 60 degrees C). Subsequently, the specimens were exposed to static tensile loading at the same temperatures as those applied during the primary impacts. The variation in failure loads due to the effects of repeated axial impact loadings at different temperatures were investigated. Generally, the increase of impact energy level from 0 to 20 J leads to a gradual decrease in failure loads at all temperature levels except for the specific value of 40 degrees C.
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    Effect of material nonlinearity on symmetric aluminum metal-matrix laminated composite beams under a bending moment
    Sayman, O; Çallioglu, H; Meriç, C; Can, N
    In this study, an elastic-plastic stress analysis is carried out on symmetric laminated composite beams subjected to a bending moment. The composite beam is to be strain hardening. The Tsai-Hill theory is used as a yield criterion in the solution. The Bernoulli and Euler hypotheses are assumed to be valid. The beam lay-up sequences are chosen as [90degrees/0degrees](s), [30degrees/-30degrees](s), [45degrees/-45degrees](s), and [60degrees/-60degrees](s). The bending moment starting plastic yielding is found to be highest for [30degrees/-30degrees](s) orientation. sigma(x) residual stress component is found to be highest at the upper and lower surfaces. However sigma(x), residual stress component becomes the highest at the elastic and plastic boundary for further expansion of the plastic region. The transverse displacement is obtained at the free end, numerically.
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    Elasto-plastic stress analysis of aluminum metal-matrix composite laminated plates under in-plane loading
    Sayman, O; Akbulut, H; Meriç, C
    The study presents an elasto-plastic stress analysis of symmetric and antisymmetric cross-ply, angle-ply laminated metal-matrix composite plates. Long stainless steel fiber reinforced aluminum metal-matrix composite layer is manufactured by using moulds under the action of 30 MPa pressure and heating up to 600 degrees C. A laminated plate consists of four metal-matrix layers bonded symmetrically or antisymmetrically. The first-order shear deformation theory and nine-node Lagrangian finite element is used. The in-plane load is increased gradually. (C) 2000 Elsevier Science Ltd. All rights reserved.
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    Elasto-plastic stress analysis of aluminum metal matrix laminated plates with a circular hole under transverse loading
    Sayman, O; Aykul, H
    Metal-matrix composites provide new materials with superior properties. They give high strength and stiffness and fatigue properties. In this study, a stainless steel fiber reinforced aluminum metal-matrix laminated simply supported plate with a circular hole is loaded transversely. Elastic, elasto-plastic and residual stresses are calculated in the symmetric and/or antisymmetric cross-ply and angle-ply laminated plate for small deformations by using finite elements method. Load steps are chosen 200, 400 and 600. Isoparametric quadrilateral element with nine node is developed for the elasto-plastic analysis. Metal-matrix composite laminated plate is manufactured by using moulds under the action of 30 MPa and heating up 600degreesC. The first-order shear deformation theory is used in the study.
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    A study on the mechanical and morphological behavior of polyurethane-encapsulated cholesteric liquid crystal composite films
    Kemiklioglu, E; Kemiklioglu, U; Sayman, O
    This study explores the preparation and mechanical behavior of free-standing polymer-dispersed liquid crystal (PDLC) film membranes. Polyurethane (PU) was used as a thermoplastic polymer matrix to form these free-standing film membranes. Cholesteryl oleyl carbonate (COC) and cholesteryl pelargonate were used as liquid crystals (LCs) with different molecular weights. PDLC membranes were produced by casting method after LCs and polymer were mixed in the tetrahydrofuran solvent at room temperature. These membranes were formed at different concentration ratios of polymer and LCs. The relationship among the phase separation, LCs and polymer contents as well as the LCs molecular weights was investigated. The morphological structures of these membranes were studied using scanning electron microscopy (SEM). SEM images exhibited that the shapes of LC droplets embedded in PU matrix were more uniform and smaller than those of the membranes which include LC with lower molecular weight. The mechanical properties of the PDLC membranes were determined by carrying out the tensile tests. It was found that the membranes which include COC LC were more flexible.
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    Effects of axial impacts at different temperatures on failure response of adhesively bonded woven fabric glass fiber/epoxy composite joints
    Sayman, O; Soykok, IF; Dogan, T; Dogan, A; Arikan, V
    Evaluating post-impact failure responses of single-lap adhesively bonded composite-to-composite joints in uniaxial static tensile loading was the main objective of the current experimental study. At first, axial tensile impacts having various energy levels (10, 15, 20, and 25J) were applied to the joints at different temperatures (-20, 0, room temperature, 50, and 80?). Afterward, the samples were secondarily subjected to static tensile loading at ambient temperature, so that reductions in joint strengths arising from the impacts performed under different loading conditions could be assessed. Consequently, it was definitely proved that each of the axial impacts performed in any loading case has a noticeable effect on ultimate joint strengths, proportionally to the acting condition. Besides, the combination of high energy and temperature sometimes appeared to be the reason of impact failure, which occurs instantly without being able to perform axial static tests. When applied energy and/or absolute difference from room temperature is increased, lower joint resistances could be measured during secondary tensile tests.
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    An elastic/plastic solution for a thermoplastic composite cantilever beam loading by bending moment
    Sayman, O; Aksoy, S; Aykul, H
    In this study, an elastic/plastic stress analysis is carried out for a thermoplastic composite cantilever beam loaded by a bending moment at the free end. The composite beam is reinforced by woven steel fibers, at 0, 15, 30 and 45 degrees orientation angles. An analytical solution is performed for satisfying both the governing differential equation in the plane stress case and boundary conditions for small plastic deformations. The solution is carried out under the assumption of the Bernoulli-Navier hypotheses. It is found that the intensity of the residual stress component of sigma (x) is a maximum at the upper and lower surfaces. The composite material is assumed to be as hardening linearly. The Tsai-Hill theory is used as a yield criterion. (C) 2000 Elsevier Science Ltd. All rights reserved.
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    Nonlinear stress analysis of unidirectionally reinforced symmetric aluminum metal-matrix laminated beams under a bending moment
    Sayman, O; Çallioglu, H; Atas, C; Köksal, NS
    This study deals with elastic-plastic behavior of aluminum metal-matrix laminated cantilever beam subjected to a bending moment at the free end. The Bernoulli-Euler theory is utilized in the solution and small plastic deformations are considered. The beam consists of four layers and its material is assumed to be linearly hardening. A few ply arrangements such as [90degrees/0degrees]s, [30degrees/-30degrees]s, [45degrees/-45degrees]s and [60degrees/-60degrees]s are taken into consideration for such an analysis. The moment values that initiate plastic flow at any point of the beam are carried out for diverse stacking sequences. The variation of the elastic, elastic-plastic and residual stress components versus increasing plastic zone spread are given in tables and figures.