Researcher:
Yalçınkaya, Mehmet Akif

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PhD Student

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Mehmet Akif

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Yalçınkaya

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Yalçınkaya, Mehmet Akif

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2014 - 20196

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Now showing 1 - 6 of 6
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    A novel mold design for one-continuous permeability measurement of fiber preforms
    (Sage Publications Ltd, 2015) N/A; N/A; Department of Mechanical Engineering; Yalçınkaya, Mehmet Akif; Sarıoğlu, Ayşen; Sözer, Murat; PhD Student; Master Student; Faculty Member; Department of Mechanical Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Engineering; N/A; N/A; 110357
    One-continuous permeability measurement experiments allow measuring permeability of a fiber preform within a range of fiber volume fractions by conducting a single unsaturated (a.k.a. transient) flow experiment on a dry specimen at an initial thickness, and a set of saturated flow experiments on the wetted specimen by varying the thickness of the mold cavity. This approach allows quicker database construction and reduces the effect of inherent variation of fabric structure caused by inconsistent labor on permeability. In this study, the drawbacks of previous mold designs are eliminated by using appropriate sealing, gap thickness adjustment mechanism and features that allow straightforward and reliable manual operation. Experiments for three different fabric types are conducted and the results are discussed. It is mainly observed that the unsaturated permeability is higher than the saturated permeability.
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    Dynamic pressure control in vartm: rapid fabrication of laminates with high fiber volume fraction and improved dimensional uniformity
    (Wiley, 2019) Altan, M. Cengiz; Department of Mechanical Engineering; Department of Mechanical Engineering; Yalçınkaya, Mehmet Akif; Sözer, Murat; Master Student; Faculty Member; Department of Mechanical Engineering; College of Engineering; College of Engineering; N/A; 110357
    The compaction pressure on the fibrous preform is one of the most critical parameters in vacuum assisted resin transfer molding (VARTM), which significantly affects the preform permeability, mold filling time, and final thickness of the fabricated composite. In this study, the compaction pressure on the vacuum bag was controlled during and after the mold filling to achieve rapid impregnation and improve the fiber volume fraction of the laminate. It was shown that the dynamic pressure control (1) enabled the manipulation of the fabric permeability and faster distribution of the resin to decrease the mold filling time, (2) improved the dimensional uniformity of the laminate by reducing the thickness variation, and (3) increased the fiber volume fraction by further consolidating the preform and removing the excess resin. One of the most essential and prominent features of the process was shown to be the resin removal from the inlet by applying external pressure, which reduced the thickness variation in laminates from 15 to 1%. The mold filling time was reduced by 48% compared with conventional VARTM, while achieving a high fiber volume fraction up to 64% and a low void content of below 1%. POLYM. COMPOS., 40:2482-2494, 2019.
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    Fabrication of high quality composite laminates by pressurized and heated-VARTM
    (Elsevier Sci Ltd, 2017) Altan, M. Cengiz; N/A; Department of Mechanical Engineering; Yalçınkaya, Mehmet Akif; Sözer, Murat; PhD Student; Faculty Member; Department of Mechanical Engineering; Graduate School of Sciences and Engineering; College of Engineering; N/A; 110357
    Although vacuum-assisted transfer molding (VARTM) is preferred for manufacturing medium to large composite parts due to its simple tooling and low cost, part quality dictated by dimensional tolerances, void content and mechanical properties is usually low due to inherent limitations of the process. In this study, the conventional VARTM process was modified by external pressurization of a heated mold to increase fiber volume fraction and improve mechanical properties of laminates. During post-filling, various levels of external pressure were applied in a pressure chamber mounted on top of the mold. It was observed that pressurized VARTM led to laminates with less than 1% void content. In addition, fiber volume fraction and flexural strength were increased 25% and 13% with respect to non-pressurized VARTM, respectively which demonstrates the potential for manufacturing considerably higher quality composites by pressurized VARTM.
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    Effect of permeability characterization at different boundary and flow conditions on vacuum infusion process modeling
    (Sage Publications Ltd, 2017) N/A; N/A; Department of Mechanical Engineering; Yalçınkaya, Mehmet Akif; Çağlar, Barış; Sözer, Murat; PhD Student; PhD Student; Faculty Member; Department of Mechanical Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Engineering; N/A; N/A; 110357
    Permeability characterization of a fabric preform is a key factor that affects the accuracy of process modeling of vacuum infusion. There are various flow types and boundary conditions (such as one-dimensional or radial flow under constant injection pressure or constant injection flow rate during unsaturated or saturated flow regimes) used in permeability measurement experiments in the literature. This study investigates the effect of using different flow and injection boundary conditions in permeability characterization on the results of coupled one-dimensional mold-filling and compaction model. The results of the model are compared with vacuum infusion mold-filling experiments. It is shown that using the permeability measured at constant injection pressure and unsaturated flow results in the closest fill time compared to the experiments for all three types of fabrics investigated in this study.
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    Effect of external pressure and resin flushing on reduction of process-induced voids and enhancement of laminate quality in heated-VARTM
    (Elsevier Sci Ltd, 2019) Altan, M. Cengiz; N/A; Department of Mechanical Engineering; Yalçınkaya, Mehmet Akif; Sözer, Murat; PhD Student; Faculty Member; Department of Mechanical Engineering; Graduate School of Sciences and Engineering; College of Engineering; N/A; 110357
    Applying external pressure on the vacuum bag in heated-Vacuum Assisted Resin Transfer Molding (heated-VARTM) is a new approach for manufacturing high quality composite laminates with minimal voids. The present study focuses on the effects of external pressure and resin flushing on the microstructural features of the laminates, including spatial variation and size distribution of the voids as well as the compaction of fiber tows. The microstructural analysis performed on glass/epoxy composites reveal that external pressure reduces void content and average void size, and leads to more uniform spatial distribution of voids. Significant increase in fiber volume fraction from similar to 50% up to similar to 62% and a low void content of less than 1% are achieved by applying modest gauge pressure levels up to 138 kPa on laminates with various thicknesses. The increase in fiber volume fraction coupled with low void content improves the flexural properties as much as 20%, while the short-beam shear strength of the laminates remains unchanged due to low void content in all laminates.
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    Effect of part thickness variation on the mold filling time in vacuum infusion process
    (Sage Publications Ltd, 2014) N/A; Department of Mechanical Engineering; Yalçınkaya, Mehmet Akif; Sözer, Murat; PhD Student; Faculty Member; Department of Mechanical Engineering; Graduate School of Sciences and Engineering; College of Engineering; N/A; 110357
    An experimental setup was used to fairly compare mold filling times in vacuum infusion and resin transfer molding, and a 9.5% shorter mold filling time in vacuum infusion was observed than in resin transfer molding. The setup was also used to conduct compaction and permeability characterization experiments, and the results were used in a simplified vacuum infusion model, which is more straightforward to solve than the conventional full and coupled models in the literature. Simulated filling time in vacuum infusion was 31% shorter than in resin transfer molding. The faster resin flow in vacuum infusion is explained by the fact that the thickness in the wetted upstream region increases with time, and thus the effective permeability in that region increases.