Organizational Unit: Department of Mechanical Engineering
Loading...
Date established
City
Country
ID
Is Parent Of
Is Child Of
ROR Identifier
Description
841 results
Publication Search Results
Now showing 1 - 10 of 841
Publication Metadata only An inverse synthesis method for the determination of effective mechanical properties for additively manufactured aperiodic structures with finite thickness(IEEE, 2023) Acar, Eren; Şimşek, Uğur; Şendur, Güllü Kızıltaş; Department of Mechanical Engineering; Gökçay, Barış; Department of Mechanical Engineering; College of EngineeringThe production of thin-walled structures via Additive Manufacturing is common for thermo-mechanical applications such as heat exchanger cores. However, accurate and efficient models predicting the effective material response of complex geometries with periodic inclusions where the finite size effect or aperiodicity is considered are limited. To address this challenge, here an inverse synthesis approach to calculate the effective material properties of periodic structures with finite thickness or aperiodicity is studied based on the Hill-Mandel equivalence principle under specific loading conditions using ANSYS optimization solver. The method is demonstrated on periodic microstructures with finite thickness/aperiodicity and square unit cells with circular inclusions. Results show that boundary conditions need to be revised to capture the finite size effect, but the framework has the potential of incorporating metrics and loadings for a variety of geometries with aperiodicity.Publication Metadata only Evolution of transformation plasticity in austenite-to-bainite phase transformation: a multi parameter problem(Elsevier Science Sa, 2012) Lambers, Hans -Gerd; Maier, Hans Jürgen; Department of Mechanical Engineering; Canadinç, Demircan; Faculty Member; Department of Mechanical Engineering; College of Engineering; 23433The current paper presents a thorough experimental analysis of the austenite-to-bainite phase transformation, and provides insight into microstructural changes associated with the observed transformation plasticity (TP). Specifically, the evolution of TP was studied in the presence of several parameters, namely pre-deformation, temperature and superimposed constant stresses, and the observed phenomena were linked to microstructural changes under these circumstances based on experimental data. One major finding is that the evolution of TP strains is governed both by the superimposed external stresses and the temperature dependence of internal stresses introduced by pre-deformation.Publication Metadata only Sculpture surface machining: a generalized model of ball-end milling force system(Elsevier Sci Ltd, 2003) N/A; Department of Mechanical Engineering; Lazoğlu, İsmail; Faculty Member; Department of Mechanical Engineering; College of Engineering; 179391A new mechanistic model is presented for the prediction of a cutting force system in ball-end milling of sculpture surfaces. The model has the ability to calculate the workpiece/cutter intersection domain automatically for a given cutter location (CL) file, cutter and workpiece geometries. Furthermore, an analytical approach is used to determine the instantaneous chip load (with and without runout) and cutting forces. In addition to predicting the cutting forces, the model also employs a Boolean approach for a given cutter, workpiece geometries, and CL file to determine the surface topography and scallop height variations alone, the workpiece surface which can be visualized in 3-D. The results of model validation experiments on machining Ti-6A1-4V are also reported. Comparisons of the predicted and measured forces as well as surface topography show good agreement.Publication Metadata only Biomedical optical fibers(Royal Soc Chemistry, 2021) Jiang, Nan; Yetişen, Ali K.; N/A; N/A; Department of Mechanical Engineering; Sarabi, Misagh Rezapour; Öztürk, Ece; Taşoğlu, Savaş; PhD Student; Faculty Member; Faculty Member; Department of Mechanical Engineering; Koç University Research Center for Translational Medicine (KUTTAM) / Koç Üniversitesi Translasyonel Tıp Araştırma Merkezi (KUTTAM); KU Arçelik Research Center for Creative Industries (KUAR) / KU Arçelik Yaratıcı Endüstriler Uygulama ve Araştırma Merkezi (KUAR); Graduate School of Sciences and Engineering; School of Medicine; College of Engineering; N/A; 326940; 291971Optical fibers with the ability to propagate and transfer data via optical signals have been used for decades in medicine. Biomaterials featuring the properties of softness, biocompatibility, and biodegradability enable the introduction of optical fibers' uses in biomedical engineering applications such as medical implants and health monitoring systems. Here, we review the emerging medical and health-field applications of optical fibers, illustrating the new wave for the fabrication of implantable devices, wearable sensors, and photodetection and therapy setups. A glimpse of fabrication methods is also provided, with the introduction of 3D printing as an emerging fabrication technology. The use of artificial intelligence for solving issues such as data analysis and outcome prediction is also discussed, paving the way for the new optical treatments for human health.Publication Metadata only A computational study of drop formation in an axisymmetric flow-focusing device(Amer Soc Mechanical Engineers, 2006) Department of Mechanical Engineering; Department of Mechanical Engineering; Filiz, İsmail; Muradoğlu, Metin; N/A; Faculty Member; Department of Mechanical Engineering; College of Engineering; College of Engineering; N/A; 46561We investigate the formation and dynamics of drops computationally in an axisymetric geometry using a Front-Tracking/Finite-Difference (FT/FD) method. The effects of viscosity ratio between inner and outer liquids on the drop creation process and drop size distribution are examined. It is found that the viscosity ratio critically influences the drop formation process and the final drop distribution. We found that, for small viscosity ratios, i.e., 0.1 < lambda < 0.5 drop size is about the size of the orifice and drop distribution is highly monodisperse. When viscosity ratio is increased, i.e., 0.5 < lambda < I a smaller drop is created just after the main drop. For even higher viscosity ratios, the drop distribution is usually monodisperse but a satellite drop is created in some cases. The effect of the flow rates in the inner jet and the co flowing annulus are also studied. It is found that the drop size gets smaller as Q(in) / Q(out) is reduced while keeping the outer flow rate constant.Publication Metadata only Contact mechanics between the human finger and a touchscreen under electroadhesion(Natl Acad Sciences, 2018) Scaraggi, Michele; Persson, Bo N. J.; N/A; N/A; Department of Mechanical Engineering; Ayyıldız, Mehmet; Şirin, Ömer; Başdoğan, Çağatay; Researcher; 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; 125489The understanding and control of human skin contact against technological substrates is the key aspect behind the design of several electromechanical devices. Among these, surface haptic displays that modulate the friction between the human finger and touch surface are emerging as user interfaces. One such modulation can be achieved by applying an alternating voltage to the conducting layer of a capacitive touchscreen to control electroadhesion between its surface and the finger pad. However, the nature of the contact interactions between the fingertip and the touchscreen under electroadhesion and the effects of confined material properties, such as layering and inelastic deformation of the stratum corneum, on the friction force are not completely understood yet. Here, we use a mean field theory based on multiscale contact mechanics to investigate the effect of electroadhesion on sliding friction and the dependency of the finger-touchscreen interaction on the applied voltage and other physical parameters. We present experimental results on how the friction between a finger and a touchscreen depends on the electrostatic attraction between them. The proposed model is successfully validated against full-scale (but computationally demanding) contact mechanics simulations and the experimental data. Our study shows that electroadhesion causes an increase in the real contact area at the microscopic level, leading to an increase in the electrovibrating tangential frictional force. We find that it should be possible to further augment the friction force, and thus the human tactile sensing, by using a thinner insulating film on the touchscreen than used in current devices.Publication Metadata only The effect of strut protrusion on local shear stress and neointimal hyperplasia(Oxford University Press (OUP), 2019) Tenekecioglu, E.; Katagiri, Y.; Torii, R.; Onuma, Y.; Serruys, P. W.; Department of Mechanical Engineering; Pekkan, Kerem; Faculty Member; Department of Mechanical Engineering; College of Engineering; 161845N/APublication Metadata only Silk as a biodegradable resist for field-emission scanning probe lithography(Institute of Physics (IOP) Publishing, 2020) Sadeghi, Sadra; Rangelow, Ivo W.; Department of Mechanical Engineering; Department of Electrical and Electronics Engineering; N/A; N/A; Department of Electrical and Electronics Engineering; Alaca, Burhanettin Erdem; Kumar, Baskaran Ganesh; Melikov, Rustamzhon; Doğru-Yüksel, Itır Bakış; Nizamoğlu, Sedat; Faculty Member; Other; PhD Student; PhD Student; Faculty Member; Department of Mechanical Engineering; Department of Electrical and Electronics Engineering; Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştirmalari Merkezi (KUYTAM); N/A; N/A; N/A; N/A; College of Engineering; College of Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Engineering; 115108; N/A; N/A; N/A; 130295The patterning of silk allows for manufacturing various structures with advanced functionalities for optical and tissue engineering and drug delivery applications. Here, we propose a high-resolution nanoscale patterning method based on field-emission scanning probe lithography (FE-SPL) that crosslinks the biomaterial silk on conductive indium tin oxide (ITO) promoting the use of a biodegradable material as resist and water as a developer. During the lithographic process, Fowler-Nordheim electron emission from a sharp tip was used to manipulate the structure of silk fibroin from random coil to beta sheet and the emission formed nanoscale latent patterns with a critical dimension (CD) of similar to 50 nm. To demonstrate the versatility of the method, we patterned standard and complex shapes. This method is particularly attractive due to its ease of operation without relying on a vacuum or a special gaseous environment and without any need for complex electronics or optics. Therefore, this study paves a practical and cost-effective way toward patterning biopolymers at ultra-high level resolution.Publication Metadata only Dimensional stability of 51CrV4 steel during bainitic phase transformation under tensile and compressive stresses(Elsevier, 2010) Lambers H.-G.; Maier H.J.; Department of Mechanical Engineering; Canadinç, Demircan; Faculty Member; Department of Mechanical Engineering; College of Engineering; 23433The effect of the prior austenitization treatment on the stress-strain response of a low alloy 51CrV4 steel in its supercooled austenitic state and its effect on the evolution of transformation plasticity strain during a subsequent isothermal bainitic transformation was investigated. One of the key findings is that the prior austenitization treatment strongly affects the evolution of transformation plasticity strains during the subsequent isothermal bainitic transformation under stress, such that higher transformation plasticity strains are present when the austenite grain size is increased. In addition, higher 0.2% offset yield strengths of the supercooled austenite are present following an incomplete austenitization treatment due to the existence of residual carbides. Overall, the current results clearly lay out the effect of the prior austenitization treatment on the stress-strain response of the supercooled austenite and the evolution of transformation plasticity during bainitic transformation.Publication Metadata only Infusion jet flow control in neonatal double lumen cannulae(Asme, 2020) Yıldız, Yahya; Department of Mechanical Engineering; Department of Mechanical Engineering; Department of Mechanical Engineering; Rasooli, Reza; Jamil, Muhammad; Pekkan, Kerem; Researcher; Researcher; Faculty Member; Department of Mechanical Engineering; College of Engineering; College of Engineering; College of Engineering; N/A; N/A; 161845Clinical success of extracorporeal membrane oxygenation (ECMO) depends on the proper venous cannulation. Venovenous (VV) ECMO is the preferred clinical intervention as it provides a single-site access by utilizing a VV double lumen cannula (VVDLC) with a higher level of mobilization and physical rehabilitation. Concurrent venous blood drainage and oxygenated blood infusion in the right atrium at the presence of the cannula makes the flow dynamics complex where potential mixing of venous and oxygenated blood can drastically decrease the overall performance of ECMO. There are no studies focusing on the neonatal and pediatric populations, in which the flow related effects are critical due to the small atrium size. In this study, fluid dynamics of infusion outflow jet for two commercially available neonatal VVDLC is analyzed using particle image velocimetry (PIV). Moreover, six new designs are proposed for the infusion channel geometry and compared. Important flow parameters such as flow turning angle (FTA), velocity decay, potential core, and turbulent intensity are investigated for the proposed models. The experiments showed that the outflow parameters of commercial cannulae such as FTA are strongly dependent on the operating Re number. This may result in a drastic efficiency reduction for cannula operating at off-design flow conditions. Moreover, the infusion outlet tip structure and jet internal guiding pathway (JIGP) was observed to greatly affect the outflow flow features. This is of paramount importance since the anatomical positioning of the cannula and the infusion outlet is strongly dependent on the outflow properties such as FTA.