Makine Mühendisliği Bölümü

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Citation - WoS: 43
Citation - Scopus: 54
A normally closed electrostatic parylene microvalve for micro total analysis systems
(Elsevier Science Sa, 2012) Yildirim, Ender; Yıldırım, Ender; Arikan, M. A. Sahir; Kulah, Haluk; 120121; Makine Mühendisliği
This paper presents an electrostatically actuated, normally closed microvalve for parylene microfluidics. The proposed valve structure isolates the fluid from the electric field, and hence results in relatively low actuation potentials (<60 V) irrespective of the working fluid. Hereby, the microvalve solves electrolysis or electrode shielding problems observed in electrostatic actuation in micro total analysis systems. To investigate leakage properties, microvalves were tested under pressurized flow with de-ionized (DI) water. No detectable leakage ratio was observed up to 20 kPa inlet pressure, due to the unique semicircular valve seat design. It was shown that the valve seat could be reconfigured to enable sealing at various pressure levels for different applications. (C) 2012 Elsevier B.V. All rights reserved.
Citation - WoS: 12
Citation - Scopus: 14
Bioglass-polymer composite scaffolds for bone tissue regeneration: a review of current trends
(Taylor & Francis Ltd, 2024) Motameni, Ali; Cardakli, Ismail Seckin; Gurbuz, Riza; Alshemary, Ammar Z. Z.; Razavi, Mehdi; Farukoglu, Omer Can
Biocompatible and bioactive composite scaffolds are essential in bone tissue regeneration because of their bioactivity and multilevel porous assemblies. There is a high demand for three-dimensional (3D) scaffolds to treat bone regeneration defects, trauma, and congenital skeletal abnormalities in the current scenario. The main objective of this review is to collect all the possible information concerning synthetic and natural polymer-Bioglass (BG)-based scaffold materials and systematically present them to summarize the importance and need for these materials. The importance of the bone tissue engineering field has been highlighted. Given the current challenges, a comprehensive description of materials fabrication and patterns in scaffold structures is required. This review also includes the most crucial aspect of this study: why are polymeric materials mixed with BG materials? Individually, both BG and polymeric materials lack specific essential characteristics to enhance the scope of these materials. However, preparing the composites of both ensures the researchers that composites of polymers and BG have improved properties that make them versatile materials for bone tissue engineering applications. This study deals with the individual drawbacks of the inorganic BGs, synthetic polymers, and the deficiencies of natural polymers. This study has also included a brief description of various scaffold fabricating techniques. Finally, this study revealed that by manufacturing and developing novel composite materials-scaffolds bearing the capability to repair, heal, and regenerate accidentally damaged or badly injured bones, many occasional problems can be solved in vivo and in vitro. Moreover, this review demonstrated that natural polymeric materials present many advantages over synthetic bone grafts. Yet, synthetic biomaterials have one additional attractive feature, as they have the flexibility to be designed according to the desired demands. These features make them the best choice for a wide range of bone tissue engineering projects for orthopedic surgeons.
Citation - Scopus: 9
Effect of constitutive material model on the finite element simulation of shear localization onset
(Elsevier B.V., 2020) Yılmaz, O.D.; Nadimi Bavil Oliaei, S.
One of the most challenging problems in the field of machining is to determine the onset of shear localization. The consequences of the emergence of shear localized chips are fluctuations in the machining forces, tool wear, deterioration of the surface quality and out-of-tolerance machined components. Several constitutive material models are developed for the simulation of shear localization during machining, especially for Ti6Al4V. However, the accuracy and capability of the proposed models for the prediction of shear localization onset have not been investigated yet. In this study, the effect of different constitutive material models in the prediction of shear localization onset has been investigated. Different material models are studied including the Johnson-Cook (J-C) material model with Cockcroft-Latham damage model, J-C material model with a J-C damage model, models based on modified J-C material models (MJ-C) with strain softening terms, and material model with power-law type strain hardening and strain rate sensitivity, with polynomial thermal softening and polynomial temperature-dependent damage. The results of the finite element models are verified using orthogonal cutting experiments in terms of chip morphology and machining forces. Metallography techniques are used along with SEM observations to elucidate the distinction between continuous and shear localized chips. The results of this study indicate that three models are capable of predicting shear localization onset. However, when compared to the experiments, where a critical cutting speed of 2.8 m/min is obtained for shear localization onset, the results revealed that the model proposed by Sima and Ozel (2016) which is a model based on MJ-C model with temperature-dependent overarching modifier and temperature-dependent material model parameters is more accurate for the prediction of shear localization onset during machining Ti6Al4V. This model is shown to reveal a good prediction for the machining forces as well. © 2020 Elsevier B.V.
Citation - WoS: 5
Citation - Scopus: 5
Experimental investigation into the effect of magnetorheological fluid damper on vibration and chatter in straight turning process
(Elsevier Sci Ltd, 2023) Emami, Mohsen; Akar, Samet; Nasab, Vahid Hasan; Akar, Samet; Batako, Andre; 315516; Makine Mühendisliği
Magneto-Rheological (MR) dampers have received a great deal of attention in recent years due to the potential of offering semi-active control. MR dampers have been successfully applied in the vibration control of several machining processes. However, the effect of the material of the damper's fluid chamber on its magnetic prop-erties has not been studied much. In this study, an MR damper has been designed to control the chatter vibration of the straight turning operation. The magnetic properties of the MR damper are simulated in the FEM software COMSOL Multiphysics with two types of steel AISI 410 and AISI 1018, and the material with the best perfor-mance for constructing the fluid chamber is determined. Then, the MR damper with an assembly to hold the cutting tool was fabricated and experimentally tested during straight turning operation and its effect on the tool vibration, and work surface roughness was analyzed. From the result, it was observed that the MR damper reduced tool vibration and chatter effectively. The results obtained in this research confirm that the application of the MR damper in the straight-turning process can either suppress the chatter or greatly reduce the frequency amplitude of the chatter. The reduction of the tool's acceleration amplitude with the MR damper was more intense in the condition of chatter suppression and reached up to 89.42 %. Moreover, the MR damper reduced the roughness of the machining surface. This reduction was higher in cases where the chatter was suppressed and it was observed up to 29 %.
Citation - WoS: 43
Exploring the relationship between software process adaptive capability and organizational performance
(Ieee Computer Soc, 2015) Clarke, Paul; Yılmaz, Murat; O'Connor, Rory V.; Leavy, Brian; Yilmaz, Murat; Yazılım Mühendisliği
Software development is a complex socio-technical activity, with the result that software development organisations need to establish and maintain robust software development processes. While much debate exists regarding the effectiveness of various software development approaches, no single approach is perfectly suited to all settings and no setting is unchanging. The capability to adapt the software process is therefore essential to sustaining an optimal software process. We designed an exploratory study to concurrently examine software process adaptive capability and organisational performance in 15 software development organisations, finding that companies with greater software process adaptive capability are shown to also experience greater business success. While our exploratory study of the complex relationship between these phenomena is limited in some respects, the findings indicate that software process adaptive capability may be worthy of further integration into software process engineering techniques. Software process adaptive capability may be an important organisational strength when deriving competitive advantage, and those responsible for the creation and evolution of software process models and methodologies may want to focus some of their future efforts in this area.
Citation - WoS: 6
Citation - Scopus: 10
Implementation and characterization of an absorption filter for on-chip fluorescent imaging
(Elsevier Science Sa, 2017) Yildirim, Ender; Yıldırım, Ender; Arpali, Caglar; Arpali, Serap Altay; 31835; 20809; 51304; Makine Mühendisliği
Here we present fabrication and characterization of an absorption filter with superior roll-on properties and precisely tunable cut-off wavelengths for fluorescent imaging applications in lab-on-a-chip systems. The filters were fabricated by spinning dye doped photopolymer (Orasol Yellow in Norland Optical Adhesive 60) on glass substrates. The fabrication technique allowed us to precisely tune the cut-off wavelength of the filters. We showed that filters with different cut-off in the range of 386 nm-504 nm could be obtained simply by controlling the settling time before spinning. The filters exhibited a steep roll-on from stopband to passband at the cut-off. Transmission in the stopband was observed to be maximum 3% while it was almost constant at 100% in the passband within the range of 220 nm-620 nm. On-chip use of the filters was also demonstrated for imaging particular fluorescent beads. (C) 2016 Elsevier B.V. All rights reserved.
Citation - WoS: 16
Citation - Scopus: 19
Investigation of surface integrity in laser-assisted turning of AISI 4340 hardened steel: Finite element simulation with experimental verification
(Elsevier Sci Ltd, 2022) Khatir, Farzad Ahmadi; Akar, Samet; Sadeghi, Mohammad Hossein; Akar, Samet; 315516; Makine Mühendisliği
This study investigates the laser-assisted turning (LAT) of AISI 4340 hardened steel (similar to 52 HRC). Despite the various advantages of this process for machining hard materials, the issues related to the machined surface integrity remain the most important challenge. The laser heating used in this process substantially affects the surface integrity characteristics of the workpiece and its mechanical properties. Therefore, it is important to understand, predict, and optimize the workpiece's heat effects at various regions. Due to the complexity of the process, experimental investigations alone cannot reveal thorough information of various phenomena involved. Therefore, a reliable finite element model has been developed to predict the effect of various process input parameters on the metallurgical changes of the machined workpieces. Since general-purpose finite element codes cannot predict the phenomena of interest, three user-defined subroutines have been developed to capture surface integrity parameters such as heat-affected zone, hardness variations of the machined surface, and white layer formation. The developed FE model consists of three parts: mechanical model, thermal model, and coupled thermo-mechanical model. The results of the FE models are verified with experimental data, and a good agreement has been observed. The effect of various process parameters on the surface integrity characteristics of the workpiece has been studied in detail. It has been observed that the laser scanning speed, laser power, and undeformed chip thickness have the most significant influence on the metallurgical effects on the workpiece, respectively.
Citation - WoS: 22
Citation - Scopus: 25
Investigation of surface integrity in the laser-assisted turning of AISI 4340 hardened steel
(Elsevier Sci Ltd, 2021) Khatir, Farzad Ahmadi; Akar, Samet; Sadeghi, Mohammad Hossein; Akar, Samet; 315516; Makine Mühendisliği
The use of laser-assisted turning (LAT) can improve different aspects of the machinability of high hardness/strength materials. The heat applied in this process reduces the strength of the material and upon a proper selection of laser heat source and machining process parameters, a significant improvement in the machining process can be achieved. This research studies the effect of machining and laser heat source parameters on the surface integrity of the LAT process of AISI 4340 hardened steel with a hardness of 560 HV using Response Surface Methodology (RSM). The effect of machining process parameters (feed rate, depth of cut and cutting speed) and laser power on the surface integrity characteristics of the machined surfaces (white layer thickness, microhardness, surface roughness, and surface chemical composition) are investigated. A detailed finite element simulation of the process has been performed to better understand the physics of the process and to interpret the experimental results. Laser power and feed rate are shown to be the most significant parameters affecting the surface integrity of the machined surfaces. It has been shown that a proper selection of machining and laser heat source parameters makes it possible to minimize the adverse effect of laser heating in the LAT process. This can pave the way for the widespread application of the LAT process by eliminating one of the most important obstacles of this process by controlling the laser heat diffusion into the workpiece.
Citation - WoS: 27
Citation - Scopus: 30
Investigation on replication of microfluidic channels by hot embossing
(Taylor & Francis inc, 2017) Çoğun, Ferah; Cogun, Ferah; Yildirim, Ender; Yıldırım, Ender; Arikan, M. A. Sahir; 31835; Makine Mühendisliği
In this study, effects of embossing temperature, time, and force on production of a microfluidic device were investigated. Polymethyl methacrylate (PMMA) substrates were hot embossed by using a micromilled aluminum mold. The process parameters were altered to observe the variation of replication rate in width and depth as well as symmetry of the replicated microfluidic channels. Analysis of variance (ANOVA) on the experimental results indicated that embossing temperature was the most important process parameter, whereas embossing time and force have less impact. One distinguishing aspect of this study is that, the channels were observed to be skewed to either side of the channel depending on the location of the protrusions on the mold. The mechanism of the skewness was investigated by finite element analysis and discussed in detail. Results showed that the skewness depends on the flow characteristics of the material and could be reduced by increasing the embossing temperature. The best replication rates were obtained at parameter settings of 115 degrees C, 10kN, and 8min for the molds with minimum 56 mu m wide features of 120 mu m depth. We also showed that the fabricated channels could be successfully sealed by solvent-assisted thermo-compressive bonding at 85 degrees C under 5.5kN force.
Citation - WoS: 1
Citation - Scopus: 1
Motion Control of a Spatial Elastic Manipulator in the Presence of Measurement Noises
(Springer Heidelberg, 2021) Kilicaslan, Sinan; Ider, S. Kemal; Ozgoren, M. Kemal; 108608
This paper presents a method for the end effector motion control of a spatial three-link robot having elastic second and third links including measurement noises. In the derivation of equations of motion, not to face with complex equations of motion, each link is modeled as though the links are not connected and the restrictions on the links due to connecting them by joints are written as constraint equations. After that the Lagrange multipliers are eliminated and the constraint equations at the acceleration level are substituted into the equations of motion to reduce the number of equations. To handle the non-minimum phase property, the equations of motion of the elastic manipulator are divided as the equations corresponding to a pseudostatic equilibrium and the equations of the deviations from them. Definition of the pseudostatic equilibrium used in this study can be given as a hypothetical state in which the end effector velocity and the end effector acceleration possess their reference values while the elastic deflections are instantly constant. The advantages of this control method are that the elastic deflections and the control inputs required for the pseudostatic equilibrium are obtained by an algebraic method and the feedback stabilization control inputs for the deviation equations are determined without linearizing the dynamic equations. The required measurements are obtained from the strain gauges on the links, the encoders placed on the joints and the position sensors attached to the end effector. For each sensor, a low pass filter is used. Simulations are made with low and high values of crossover frequencies to show the positive and negative effects of filtering on the responses of the system.
Citation - WoS: 44
Citation - Scopus: 51
Numerical investigation on the performance of a small scale solar chimney power plant for different geometrical parameters
(Elsevier Sci Ltd, 2020) Yapici, Ekin Ozgirgin; Ayli, Ece; Nsaif, Osama; 31329; 265836
In recent decades, demand for energy has been significantly increased, and considering environmental impacts and the degrading nature of fossil fuels, clean and emission-free renewable energy production has attracted a great deal of attention. One of the most promising renewable energy sources is solar energy due to low cost and low harmful emissions, and from the 1980s, one of the most beneficial applications of solar energy is the utilization of solar chimney power plants (SCPP). A SCPP is a simple and reliable system that consists of three main components; a solar collector, a chimney (tower) and a turbine to utilize electrical energy. Recently, by the advancement in computer technology, the use of CFD methodology for studying SCPP has become an extensive, robust and powerful technique. In light of the above, in this study, numerical simulations of a SCPP through three-dimensional axisymmetric modeling is performed. A numerical model is created using CFD software, and the results are verified with an experimental study from the literature. After ensuring good agreement with the experiments, chimney's and collector's geometric parameters effects and different configurations effects on SCPP performance, simultaneously and additively is investigated. The study introduces an insight to the performance enhancement methods and finding the best configuration of a SCPP model, which will be the basis of a detailed prototyping process. Based on the numerical results, the best configuration of the SCPP has been found as the diverging chimney which enhances the generated power. The results of the study showed that the chimney height and collector radius increase has a positive effect on the power output and efficiency of the system, but when construction and material costs are also considered, each has an optimal value. The maximum impact on the performance is found to be by the chimney tower radius and the collector height and inclination are found to have optimum values considering performance. According to the obtained results, the best performance for the SCPP was obtained with 3.5 m chimney height, 30 cm tower diameter, 400 cm of collector diameter with 6 cm height and zero inclination angle. By the correct selection of the dominant performance parameter which can be done by correctly interpreting the results of this study, "the best" design of a SCPP real scale prototype considering maximum power requirement can be done. (C) 2020 Elsevier Ltd. All rights reserved.
Citation - WoS: 22
Citation - Scopus: 21
Phaseguide assisted liquid lamination for magnetic particle-based assays
(Royal Soc Chemistry, 2014) Phurimsak, Chayakom; Yıldırım, Ender; Yildirim, Ender; Tarn, Mark D.; Trietsch, Sebastiaan J.; Hankemeier, Thomas; Pamme, Nicole; Vulto, Paul; 31835; Makine Mühendisliği
We have developed a magnetic particle-based assay platform in which functionalised magnetic particles are transferred sequentially through laminated volumes of reagents and washing buffers. Lamination of aqueous liquids is achieved via the use of phaseguide technology; microstructures that control the advancing air-liquid interface of solutions as they enter a microfluidic chamber. This allows manual filling of the device, eliminating the need for external pumping systems, and preparation of the system requires only a few minutes. Here, we apply the platform to two on-chip strategies: (i) a one-step streptavidin-biotin binding assay, and (ii) a two-step C-reactive protein immunoassay. With these, we demonstrate how condensing multiple reaction and washing processes into a single step significantly reduces procedural times, with both assay procedures requiring less than 8 seconds.
Citation - WoS: 26
Citation - Scopus: 30
Phaseguides as tunable passive microvalves for liquid routing in complex microfluidic networks
(Royal Soc Chemistry, 2014) Yildirim, Ender; Yıldırım, Ender; Trietsch, Sebastiaan J.; Joore, Jos; van den Berg, Albert; Hankemeier, Thomas; Vulto, Paul; 31835; Makine Mühendisliği
A microfluidic passive valving platform is introduced that has full control over the stability of each valve. The concept is based on phaseguides, which are small ridges at the bottom of a channel acting as pinning barriers. It is shown that the angle between the phaseguide and the channel sidewall is a measure of the stability of the phaseguide. The relationship between the phaseguide-wall angle and the stability is characterized numerically, analytically and experimentally. Liquid routing is enabled by using multiple phaseguide with different stability values. This is demonstrated by filling complex chamber matrices. As an ultimate demonstration of control, a 400-chamber network is used as a pixel array. It is the first time that differential stability is demonstrated in the realm of passive valving. It ultimately enables microfluidic devices for massive data generation in a low-cost disposable format.

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