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Publication Metadata only 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; 110357One-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.Publication Metadata only 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; 110357The 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.Publication Metadata only 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; 110357An 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.Publication Metadata only 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; 110357Permeability 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.Publication Metadata only Electro-conductive silica nanoparticles-incorporated hydrogel based on alginate as a biomimetic scaffold for bone tissue engineering application(Taylor and Francis Ltd., 2023) Derakhshankhah, Hossein; Eskandani, Morteza; Vandghanooni, Somayeh; Jaymand, Mehdi; Department of Mechanical Engineering; N/A; Taşoğlu, Savaş; Nakhjavani, Sattar Akbar; Faculty Member; Researcher; Department of Mechanical Engineering; Koç University Research Center for Translational Medicine (KUTTAM) / Koç Üniversitesi Translasyonel Tıp Araştırma Merkezi (KUTTAM); College of Engineering; N/A; 291971; N/AAn innovative electrically conductive hydrogel was fabricated through the incorporation of silica nanoparticles (SiO2 NPs) and poly(aniline-co-dopamine) (PANI-co-PDA) into oxidized alginate (OAlg) as a biomimetic scaffold for bone tissue engineering application. The developed self-healing chemical hydrogel was characterized by FTIR, SEM, TEM, XRD, and TGA. The electrical conductivity and swelling ratio of the hydrogel were obtained as 1.7 × 10−3 S cm−1 and 130%, respectively. Cytocompatibility and cell proliferation potential of the developed scaffold were approved by MTT assay using MG-63 cells. FE-SEM imaging approved the potential of the fabricated scaffold for hydroxyapatite (HA) formation and bioactivity induction through immersing in SBF solution.Publication Metadata only Electroadhesion with application to touchscreens(Royal Soc Chemistry, 2019) Ayyıldız, Mehmet; Persson, Bo N. J.; N/A; Department of Mechanical Engineering; Şirin, Ömer; Başdoğan, Çağatay; PhD Student; Faculty Member; Department of Mechanical Engineering; Graduate School of Sciences and Engineering; College of Engineering; N/A; 125489There is growing interest in touchscreens displaying tactile feedback due to their tremendous potential in consumer electronics. In these systems, the friction between the user's fingerpad and the surface of the touchscreen is modulated to display tactile effects. One of the promising techniques used in this regard is electrostatic actuation. If, for example, an alternating voltage is applied to the conductive layer of a surface capacitive touchscreen, an attractive electrostatic force is generated between the finger and the surface, which results in an increase in frictional forces acting on the finger moving on the surface. By altering the amplitude, frequency, and waveform of this signal, a rich set of tactile effects can be generated on the touchscreen. Despite the ease of implementation and its powerful effect on our tactile sensation, the contact mechanics leading to an increase in friction due to electroadhesion has not been fully understood yet. In this paper, we present experimental results for how the friction between a finger and a touchscreen depends on the electrostatic attraction and the applied normal pressure. The dependency of the finger-touchscreen interaction on the applied voltage and on several other parameters is also investigated using a mean field theory based on multiscale contact mechanics. We present detailed theoretical analysis of how the area of real contact and the friction force depend on contact parameters, and show that it is possible to further augment the friction force, and hence the tactile feedback displayed to the user by carefully choosing those parameters.Publication Metadata only Resin transfer molding (RTM) in polymer matrix composites(Woodhead Publ Ltd, 2012) Simacek, P.; Advani, Suresh G.; Department of Mechanical Engineering; Sözer, Murat; Faculty Member; Department of Mechanical Engineering; College of Engineering; 110357The resin transfer molding (RTM) process was adopted for composite manufacturing for high volume production net shape structural parts using low viscosity thermoset resins and continuous fibers. This chapter discusses how to overcome the challenges of RTM, which has led to many variations that have sprung over the last two decades to fill a niche need. The part quality manufactured using RTM varies due to the effects of inherent variations in the materials and process parameters. The following important issues that manifest themselves either during fiber preforming or mold filling stages of RTM have been identified and discussed: racetracking channels, deformation of fiber structure during draping, macrovoid formation, microvoid formation, transverse flow in the thickness direction and dual scale fiber structure in a preform. One can address and overcome them with process modeling, control and automation as discussed in this chapter.Publication Metadata only Stability of hydrophobically modified poly(p-phenylenesulfonate) bundles as observed by molecular dynamics simulation(Amer Chemical Soc, 2007) Holm, Christian; Hess, Berk; Department of Mechanical Engineering; Sayar, Mehmet; Faculty Member; Department of Mechanical Engineering; College of Engineering; 109820The bundle formation in solution of hydrophobically modified sulfonated poly(p-phenylene) oligomers (PPP) is studied by molecular dynamics simulations. These oligomers form cylindrical micelles in water. Light scattering experiments suggest that the number of PPP oligomers in the cross section is around 10-19 when monovalent Na+ is used as counterion. On the other hand, if divalent Ca2+ counterions are used, this number dramatically increases to 60 oligomers. Here, we show that the basic packing of the PPP oligomers does not change upon increase of the counterion valency. However, the interaction among bundles goes from repulsive to attractive as the counterions are changed from Na+ to Ca2+. We propose that the observed aggregate size of 60 oligomers could be explained by aggregation of several bundles (i.e., bundle of bundles).