Researcher:
Çağlar, Barış

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PhD Student

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Barış

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Çağlar

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Çağlar, Barış

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2011 - 201982020 - 20223

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Researcher Of Publications: search.filters.isAuthorOfPublication.86a3b4e2-d394-4b61-9b7f-b5950775f417

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Now showing 1 - 10 of 11
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    Minimizing thickness variation in the vacuum infusion (VI) process
    (Adcotec Ltd., 2011) N/A; Department of Mechanical Engineering; N/A; N/A; Yenilmez, Bekir; Sözer, Murat; Akyol, Talha; Çağlar, Barış; PhD Student; Faculty Member; Master Student; PhD Student; Department of Mechanical Engineering; Graduate School of Sciences and Engineering; College of Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; N/A; 110357; N/A; N/A
    In the Vacuum Infusion (VI) process, the thickness of a composite part changes as the compaction pressure on the vacuum bag and reinforcing fibre preform changes. Pressure and thickness were monitored along a 1D resin fl ow using pressure transducers and non-contact laser displacement sensors. To decrease the thickness variation, control actions were taken by adjusting the injection conditions, such as opening/closing gates/vents, changing pressure of them in the post-mold filling stage and bleeding out the excess resin. The control actions were taken based on an available compaction/decompaction database for the fabric type used. Compared to the case study with no control action other than bleeding, a better job was done in the controlled case study by decreasing the maximum thickness variation from 5.44% to 0.39%. A coupled fl ow and compaction model qualitatively verified the pressure and thickness distributions for both filling and post-filling stages.
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    Pressure-controlled compaction characterization of fiber preforms suitable for viscoelastic modeling in the vacuum infusion process
    (Sage Publications Ltd, 2017) N/A; N/A; Department of Mechanical Engineering; Yenilmez, Bekir; 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
    A woven fabric's compaction in the vacuum infusion process is characterized by applying an initial settling under a minor load, compaction, settling under a major load, decompaction and relaxation. The effects of compaction rate, relaxation pressure, wetting and debulking cycles are all investigated. Although wetting helps by increasing fiber volume fraction insignificantly, its contribution is more significant during debulking cycles by increasing the fiber volume fraction to 57.4% as compared to 55.4% for the debulked dry specimens. Recovery during decompaction is much less than the deformation during compaction, and thinning/thickening of the specimens with time under constant pressure, so called settling/relaxation pressures, indicates that fabric specimens are not elastic materials, but viscoelastic. The experimental data of this study will be valuable to compare different viscoelastic and elastic compaction models in our next study.
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    In-plane permeability characterization using an inverse method based on flow front visualization
    (Applied Mechanics Laboratory, 2020) Salvatori, Damiano, Michaud, Véronique; Department of Mechanical Engineering; N/A; Sözer, Murat; Çağlar, Barış; Faculty Member; PhD Student; Department of Mechanical Engineering; College of Engineering; Graduate School of Sciences and Engineering; 110357; N/A
    In this study, we propose a method to reduce the total number of required one-dimensional resin flow experiments for in-plane permeability (K) characterization of isotropic fabrics by achieving either: (i) a characterization and further statistical analysis of spatially varying permeability in the presence of fabric irregularity and possible race-tracking along the fabric - mold wall interface, or (ii) permeability characterization at more than a single fiber volume fraction (vf) in an experiment. The method is based on accurately detecting the flow front location in the flow propagation video frames and minimizing the deviation between experimental fill times and numerical fill times in Control Volume Finite Element based flow simulations through use of the Levenberg-Marquardt method. The permeability of an isotropic random mat was characterized through reference experiments. K-vf relationship was well represented by a power law. In cases with intentionally introduced race-tracking and with three sections of different vf, permeability results were in agreement with the results of the reference experiments (a set of experiments in which fabric irregularity and race-tracking were eliminated as much as possible). The results indicate that the number of experiments, thus the material and time invested, can be significantly reduced using the proposed method with an additional benefit of obtaining valuable insights on the statistics of the spatial permeability distribution.
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    Experimental investigation of textile permeability in the presence of spherical inclusions
    (European Conference on Composite Materials, ECCM, 2016) Michaud, V.; N/A; Department of Mechanical Engineering; Çağlar, Barış; Sözer, Murat; PhD Student; Faculty Member; Department of Mechanical Engineering; Graduate School of Sciences and Engineering; College of Engineering; N/A; 110357
    Addition of a third material phase to a resin and reinforcement system is a favored approach to tailor properties and features of composite materials, including but not limited to the ease of stacking and preforming, or healing ability. This addition changes the structure of the empty spaces between the reinforcing fibers and thus the overall permeability is affected. In this study, the effect of model rigid spherical inclusions on the permeability of woven textiles is investigated. Several diameter ranges of glass beads (40.0-70.0, 70.0-100, 100-200, 200-300, 300-400, and 400-800 μm) with a volume fraction of 5.0% are manually sieved between the layers of a plain weave glass textile, which has a bundle-interstice gap in 150-200 μm range. Experiments are repeated for 2.5 and 10% volume fractions for three diameter ranges (40.0-70.0, 100-200, and 400-800 μm) to investigate the influence of the concentration of inclusions on permeability. Experimental results show that an increase in the diameter or an increase in the volume fraction of the rigid inclusions causes a non-monotonic change in permeability. For all diameter ranges, the ratio between saturated and unsaturated permeability decreases as the volume fraction of beads increases, indicating that capillarity effects may decrease due to blocked flow channels between the fabric layers. © 2016, European Conference on Composite Materials, ECCM.
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    In-plane permeability distribution mapping of isotropic mats using flow front detection
    (Elsevier Sci Ltd, 2018) Salvatori, Damiano; Michaud, Veronique; N/A; Department of Mechanical Engineering; Çağlar, Barış; Sözer, Murat; PhD Student; Faculty Member; Department of Mechanical Engineering; Graduate School of Sciences and Engineering; College of Engineering; N/A; 110357
    In-plane permeability of textile fabrics is often characterized by one-dimensional rectilinear flow experiments, displaying limitations related to potential race-tracking effects and the need to run experiments at several fiber volume fractions. We propose a practical approach to alleviate these drawbacks. Resin flow front location is detected by image processing of videos and coupled to a Control Volume Finite Element solver with an error minimization routine based on Levenberg-Marquardt method comparing numerical and experimental fill times of all control volumes. Permeability of an isotropic random mat was characterized through reference experiments: cases with intentionally introduced race-tracking and cases with varying permeability along the resin flow direction with three different sections and fiber volume fractions. The method led to an efficient permeability determination and provided valuable insights on the statistics of spatial permeability distribution while highlighting the benefits of a thresholding algorithm for interpretation of permeability experiments in the presence of race-tracking.
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    Monitoring and modeling of part thickness evolution in vacuum infusion process
    (Sage Publications Ltd, 2021) N/A; N/A; Department of Mechanical Engineering; Çağlar, Barış; Hancıoğlu, Mert; 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
    The main hurdles in Vacuum Infusion (VI) are the difficulty in achieving complete mold filling and uniform part thickness. This study integrates process monitoring by full field thickness measurements and resin flow modeling that accounts for compaction and permeability characterizations of fabric reinforcements to assess the evolution of part thickness during filling and post-filling stages of VI process. A Structured Light Scanning system is used for full field thickness monitoring in experiments and a Control Volume Finite Element Method solver is implemented to couple resin flow with fabric's compaction and permeability. Two cases are studied both experimentally and numerically. Evolutions of thickness and pressure validate the developed flow solver, its accuracy in terms of predicting fill times and fill patterns, suitability and limitations of the elastic compaction models for thickness modeling.
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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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    Viscoelastic modeling of fiber preform compaction in vacuum infusion process
    (Sage, 2017) Department of Mechanical Engineering; Department of Mechanical Engineering; Department of Mechanical Engineering; Yenilmez, Bekir; Çağlar, Barış; Sözer, Murat; PhD Student; PhD Student; Faculty Member; Department of Mechanical Engineering; College of Engineering; College of Engineering; College of Engineering; N/A; N/A; 110357
    A woven fabric's compaction was modeled by using five viscoelastic models - Maxwell, Kelvin-Voigt, Zener, Burgers, and Generalized Maxwell - to reveal the capabilities and limitations of the models. The model parameters were optimized by minimizing the deviation between the model results and experimental data collected in our previous material characterization study mimicking different compaction stages (loading, fiber settling, wetting, unloading, and fiber relaxation) that a fiber structure undergoes during vacuum infusion process. Although Burgers and Generalized Maxwell models have the highest performance due to their almost equal coefficient of determination values, they have diverse characteristics in terms of modeling different stages of compaction. Burgers model allowed modeling the permanent deformation in relaxation stage, but failed in modeling permanent deformation in settling stage. Generalized Maxwell model could do the opposite, i.e. failed in the former and could handle the latter. This study's major contribution is a holistic numerical approach and its conclusions by modeling all stages of the vacuum infusion process instead of one stage at a time, and thus optimizing only one set of model parameters (constants of springs and dampers) since they do not change with time. The numerical results of different models were fit to the results of a specially designed compaction characterization experiments conducted in our complementary study.
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    The relationship between functional status and fatigue after COVID-19 infection
    (European Respiratory Society (ERS), 2022) Candemir, I. Cayli; Ergun, P.; Kaymaz, D.; Ozmen, I; Yildirim, E.; Dilektasli, A. Gorek; Yigitler, B.; Kizilirmak, D.; Sari, S.; Korkmaz, C.; Tasci, C.; Arslan, Y.; Savci, S.; Kahraman, B.; Tanriverdi, A.; Sevinc, C.; Saglam, M.; Ince, D. Inal; Yagli, N. Vardar; Kutukcu, E.; Durmaz, D.; Duruturk, N.; Ulubay, G.; Moray, A.; Olcay, S. S.; N/A; Kılıç, Lütfiye; Çağlar, Barış; Doctor; Faculty Member; N/A; School of Medicine; Koç University Hospital; N/A; N/A; N/A
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    Modeling of post-filling stage in vacuum infusion using compaction characterization
    (Sage Publications Ltd, 2015) N/A; N/A; Department of Mechanical Engineering; Çağlar, Barış; Yenilmez, Bekir; 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
    Two-dimensional finite-element method solution of the post-filling stage of vacuum infusion was studied based on mass conservation in an infinitesimal control volume. First, resin pressure distribution at the instant of mold filling was calculated and then used as the initial condition for the transient post-filling stage. Explicit time-marching algorithm was used for the evolution of resin pressure and part thickness, and its stability was ensured by selecting the time step adaptively. Finite-element method solution was verified analytically for one-dimensional case and numerically for two-dimensional cases using global mass conservation. The time that it took for the settlement of pressure and thickness was investigated to compare the effectiveness of different resin-bleeding scenarios where different number and locations of gates were used. It was shown that the settlement time increased exponentially as the dimensions of the mold increased, which proved that process simulation fed with correctly designed material characterization can replace tedious trial-and-error search of control actions to reduce the settlement time and variation in part thickness.