Mechanical Engineering / Makina Mühendisliği
Permanent URI for this collectionhttps://hdl.handle.net/11147/4129
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Article Citation - WoS: 1Citation - Scopus: 1Analysis and Comparison of the Projectile Impact Response of an Electron Beam Melt-Ti64 Body Centered Cubic Lattice-Cored Sandwich Plate(Springer, 2025) Erten, H.İ.; Çimen, G.; Yıldıztekin, F.M.; Güden, M.Background: One potential application of additively fabricated lattice structures is in the blade containment rings of gas turbine engines. The blade containment rings are expected to be able to absorb the kinetic energy of a released blade (broken blade) in order to protect the engine parts from damaging. Metallic lattice-cored sandwich plates provide a gap (free space) between two face sheets, which helps to arrest the released blade and increases the energy absorption capability of containment rings. Objective: The objective was to investigate numerically the projectile impact response of Body-Centered-Cubic (BCC) Electron-Beam-Melt (EBM) lattice-cored/Ti64 face sheet sandwich plates as compared with that of an equal-mass monolithic EBM-Ti64 plate. Methods: The projectile impact simulations were implemented in LS-DYNA using the previously determined flow stress and damage models and a spherical steel impactor at the velocities ranging from 150 to 500 m s−1. The experimental projectile impact tests on the monolithic plate were performed at two different impact velocities and the results were used to confirm the validity of the used flow stress and damage models for the monolithic plate models. Results: Lower impact stresses were found numerically in the sandwich plate as compared with the monolithic plate at the same impact velocity. The bending and multi-cracking of the struts over a wide area in the sandwich plate increased the energy absorption and resulted in the arrest of the projectile at relatively high velocities. While monolithic plate exhibited a local bent area, resulting in the development of high tensile stresses and the projectile perforations at lower velocities. Conclusions: The numerical impact stresses in the sandwich plate were distributed over a wider area around the projectile, leading to the fracture and bending of many individual struts which significantly increased the resistance to the perforation. Hence, the investigated lattice cell topology and cell, strut, and face sheet sizes and the lattice-cored sandwich plate was shown potentially more successful in stopping the projectiles than the equal-mass monolithic plates. © The Author(s) 2025.Article Citation - WoS: 5Citation - Scopus: 5A Continuously Variable Transmission-Based Variable Stiffness Actuator for Phri: Design Optimization and Performance Verification(American Society of Mechanical Engineers, 2024) Mobedi, Emir; Dede, Mehmet İsmet CanPhysical human–robot interfaces (pHRIs) enabled the robots to work alongside the human workers complying with the regulations set for physical human–robot interaction systems. A variety of actuation systems named variable stiffness/impedance actuators (VSAs) are configured to be used in these systems’ design. Recently, we introduced a new continuously variable transmission (CVT) mechanism as an alternative solution in configuring VSAs for pHRI. The optimization of this CVT has significant importance to enhance its application area and to detect the limitations of the system. Thus, in this paper, we present a design optimization approach (an adjustment strategy) for this system based on the design goals, desired force, and minimization of the size of the system. To implement such design goals, the static force analysis of the CVT is performed and validated. Furthermore, the fabrication of the optimized prototype is presented, and the experimental verification is performed considering the requirements of VSAs: independent position and stiffness variation, and shock absorbing. Finally, the system is calibrated to display 6 N continuous output force throughout its transmission variation range. © 2024 by ASME.Article Citation - WoS: 7Citation - Scopus: 7Investigating the Effects of Pa66 Electrospun Nanofibers Layered Within an Adhesive Composite Joint Fabricated Under Autoclave Curing(American Chemical Society, 2023) Esenoğlu, Gözde; Tanoğlu, Metin; Barışık, Murat; İplikçi, Hande; Yeke, Melisa; Nuhoğlu, Kaan; Türkdoğan, Ceren; Martin, Seçkin; Aktaş, Engin; Dehneliler, Serkan; Gürbüz, Ahmet Ayberk; İriş, Mehmet ErdemEnhancing the performance of adhesively joined composite components is crucial for various industrial applications. In this study, polyamide 66 (PA66) nanofibers produced by electrospinning were coated on unidirectional carbon/epoxy prepregs to increase the bond strength of the composites. Carbon/epoxy prepregs with/without PA66 nanofiber coating on the bonding region were fabricated using the autoclave, which is often used in the aerospace industry. The single lap shear Charpy impact energy and Mode-I fracture toughness tests were employed to examine the effects of PA66 nanofibers on the mechanical properties of the joint region. Scanning electron microscopy (SEM) was used to investigate the nanofiber morphology and fracture modes. The thermal characteristics of Polyamide 66 nanofibers were explored by using differential scanning calorimetry (DSC). We observed that the electrospun PA66 nanofiber coating on the prepreg surfaces substantially improves the joint strength. Results revealed that the single lap shear and Charpy impact strength values of the composite joint are increased by about 79 and 24%, respectively, by coating PA66 nanofibers onto the joining region. The results also showed that by coating PA66 nanofibers, the Mode-I fracture toughness value was improved by about 107% while the glass transition temperature remained constant.Article Citation - WoS: 9Citation - Scopus: 13Analysis of Adhesively Bonded Joints of Laser Surface Treated Composite Primary Components of Aircraft Structures(Elsevier, 2023) Martin, Seçkin; Nuhoğlu, Kaan; Aktaş, Engin; Tanoğlu, Metin; İplikçi, Hande; Barışık, Murat; Yeke, Melisa; Türkdoğan, Ceren; Esenoğlu, Gözde; Dehneliler, SerkanThe performance of the adhesively bonded aerospace structures highly depends on the adhesion strength between the adhesive and adherents, which is affected by, in particular, the condition of the bonding surface. Among the various surface treatment methods, as state of the art, laser surface treatment is a suitable option for the CFRP composite structures to enhance the adhesion performance, adjusting the roughness and surface free energy with relatively minimizing the damage to the fibers. The aim of this study is the validation and evaluation of the adhesive bonding behavior of the laser surface-treated CFRP composite structures, using the finite element technique to perform a conservative prediction of the failure load and damage growth. Such objectives were achieved by executing both experimental and numerical analyses of the secondary bonded CFRP parts using a structural adhesive. In this regard, to complement physical experiments by means of numerical simulation, macro-scale 3D FEA of adhesively bonded Single Lap Joint and Skin-Spar Joint specimens has been developed employing the Cohesive Zone Model (CZM) technique in order to simulate bonding behavior in composite structures especially skin-spar relation in the aircraft wing-box.Article Citation - WoS: 3Citation - Scopus: 3Quasi-Static and Dynamic Brazilian Testing and Failure Analysis of a Deer Antler in the Transverse To the Osteon Growth Direction(Elsevier, 2023) Orhan, Mehmet; Sarıkaya, Mustafa Kemal; Taşdemirci, Alper; Tuncer, Can; Güden, MustafaThe transverse tensile strength of a naturally fallen red deer antler (Cervus Elaphus) was determined through indirect Brazilian tests using dry disc-shape specimens at quasi-static and high strain rates. Dynamic Brazilian tests were performed in a compression Split-Hopkinson Pressure Bar. Quasi-static tensile and indirect Brazilian tests were also performed along the osteon growth direction for comparison. The quasi-static transverse tensile strength ranged 31.5–44.5 MPa. The strength increased to 83 MPa on the average in the dynamic Brazilian tests, proving a rate sensitive transverse strength. The quasi-static tensile strength in the osteon growth direction was however found comparably higher, 192 MPa. A Weibull analysis indicated a higher tensile ductility in the osteon growth direction than in the transverse to the osteon growth direction. The microscopic analysis of the quasi-static Brazilian test specimens (tensile strain along the osteon growth direction) revealed a micro-cracking mechanism operating by the crack deflection/twisting at the lacunae in the concentric lamellae region and at the interface between concentric lamellae and interstitial lamellae. On the other side, the specimens in the transverse direction fractured in a more brittle manner by the separation/delamination of the concentric lamellae and pulling of the interstitial lamellae. The detected increase in the transverse strength in the high strain rate tests was further ascribed to the pull and fracture of the visco-plastic collagen fibers in the interstitial lamellae. This was also confirmed microscopically; the dynamically tested specimens exhibited flatter fracture surfaces. © 2023 Elsevier LtdArticle Citation - WoS: 3Citation - Scopus: 3Computation Time Reduction of Pcm Melting Process by Changing Modeling Parameters(Taylor & Francis, 2022) Demirkıran, İsmail Gürkan; Çetkin, ErdalThis study can be considered as a helpful reference for whom endeavor to boost the computation efficiency of the PCM melting process. Researchers sacrifice accuracy to decrease computation time since computational fluid dynamics (CFD) solutions of PCM melting processes require comparatively very long time, i.e., from hours to days or weeks, depending on the system geometry. The present study compares the approaches recommended in the literature in terms of their influence on computation time reduction and accuracy. A horizontally finned tube LHTES unit is modeled in 2-D space using ANSYS Fluent, the most common commercial CFD software for the considered problem in the literature. The outcomes obtained from the attempts to boost the computation efficiency are as follows: adaptive time step size approach causes 72% enhancement in computation time (from 90 hours to 25 hours), frozen flux algorithm and constant thermophysical properties have almost no influence on computation time. Even though low convergence criteria and neglecting natural convection reduces computation time drastically, the errors in accuracy are not in acceptable level.Article Citation - WoS: 7Citation - Scopus: 10The Computational Approach To Predicting Wear: Comparison of Wear Performance of Cfr-Peek and Xlpe Liners in Total Hip Replacement(Taylor & Francis, 2022) Alpkaya, Alican Tuncay; Mihçin, ŞenayWear on articulating bearing surfaces is a key factor causing revision in total hip replacement (THR). Wear debris that releases particles from bearing surfaces might result in adverse soft tissue reactions requiring revision surgeries. In this study, a comprehensive computational wear model based on the Archard wear equation was performed to investigate the wear performance under a three-dimensional (3D) physiological gait cycle, mimicking a normal walking condition (5 million cycles). The study shows that the accuracy of the model is highly dependent on the mesh convergence, the wear fraction, and the scaling factor. The simulations were run to provide a vast amount of detail for the reproducibility of the work. Cobalt chromium (CoCr) on cross-linked polyethylene (XLPE) and CoCr on carbon-fiber-reinforced polyether ether ketone (CFR-PEEK) prototype models were created in silico. The volumetric wear rates for CoCr-on-XLPE were calculated as 0.2989 (Formula presented.) for CoCr head and 21.0271 (Formula presented.) for XLPE liner, while for CoCr-on-CFR-PEEK they were 0.3484 (Formula presented.) for CoCr head and 1.8476 (Formula presented.) for CFR-PEEK liner. When compared to in vivo and in vitro studies, the wear patterns of these two prototypes are consistent with those of the conventional polyethylene liners in the literature. Although the volumetric wear rate of the CFR-PEEK liner is about 11 times lower than the counterpart of XLPE in MoP implants, the wear rate of CoCr was higher when compared to its use with XLPE. Therefore, CFR-PEEK articulating against orthopa\edic metals may not be as good an alternative as XLPE, due to higher indicative metallic wear. This detailed computational wear modeling methodology could be utilized in design improvements of implants.Article Citation - WoS: 5Citation - Scopus: 7Enhanced Temperature Uniformity With Minimized Pressure Drop in Electric Vehicle Battery Packs at Elevated C-Rates(Wiley, 2022) Güngör, Şahin; Çetkin, ErdalThe trend of transition from fossil fuel to electrification in transportation is a result of no carbon emission produced by electric vehicles (EVs) during their daily operations. Furthermore, the global carbon footprint of EVs can be minimized if the electricity is generated from renewable sources such as wind and solar. On the other hand, there are some drawbacks of these vehicles such as charging time being very long and the mileage range of vehicles not at the desired level. Battery cells are being charged at relatively high C-rates to eliminate these problems, yet high current rates accelerate the aging of batteries and capacity losses due to the generated heat. Generated heat causes overheating, and excess temperature triggers degradation and thermal runaway risks. This paper uncovers how the battery pack temperature uniformity and strict thermal control can be achieved with heat transfer enhancement by conduction (cold plates) and convection (vascular channels). We aimed to reduce the energy consumption of the EV battery pack system while increasing the thermal performance. The impact of the thermal contact resistance is also considered for many realistic scenarios. The results indicate that an integrated system with cold plates and vascular channels satisfies the temperature uniformity requirement (over 81%) with comparatively less pumping power (∼72%) of advanced electric vehicles for relatively high C-rates. Furthermore, findings show the temperature level can increase up to 4°C as thermal contact resistance increases. The proposed cooling technique, which has low cost, easy application, and lower energy consumption superiorities, can be implemented in palpable EV battery packs.Article Citation - WoS: 8Citation - Scopus: 10Spray Analysis of Biodiesels Derived From Various Biomass Resources in a Constant Volume Spray Chamber(American Chemical Society, 2022) Ulu, Anılcan; Yıldız, Güray; Rodriguez, Alvaro Diez; Özkol, ÜnverThis research aimed to analyze the spray characteristics of various biodiesels, which have rarely been investigated in terms of spray analysis in the literature compared to fossil diesel. For this purpose, four different methyl ester-type biodiesels were produced from canola, corn, cottonseed, and sunflower oils. These feedstocks were selected due to their wide availability in Turkey and being among the significant resources for biodiesel production. Measured physical properties of biodiesel samples showed that biodiesel fuels had, on average, 1.7 to 1.9 times higher viscosities, 5.3 to 6.6% larger densities, and 37 to 39.1% higher contact angle values than the reference diesel fuel. Spray characteristics of all fuels were experimentally examined in a constant volume spray chamber under chamber pressures of 0, 5, 10, and 15 bar and injection pressures of 600, 800, and 1000 bar. All tested biodiesels performed, on average, 3 to 20% longer spray penetration lengths, 5 to 30% narrower spray cone angles, and 5-18% lesser spray areas than the reference diesel fuel under chamber pressures of 5 and 10 bar. No significant differences occurred at 15 bar ambient pressure between biodiesels and diesel. In addition, analytical and empirical predictions showed that biodiesels had around 21.2-35.1% larger SMD values and approximately 7% lower air entrainment.Article Citation - WoS: 9Citation - Scopus: 11Experimental Investigation of Spray Characteristics of Ethyl Esters in a Constant Volume Chamber(Springer, 2022) Ulu, Anılcan; Yıldız, Güray; Özkol, Ünver; Rodriguez, Alvaro DiezAbstract: Biodiesels are mainly produced via the utilization of methanol in transesterification, which is the widespread biodiesel production process. The majority of this methanol is currently obtained from fossil resources, i.e. coal and natural gas. However, in contrast with methanol, biomass-based ethanol can also be used to produce biodiesels; this could allow the production line to become fully renewable. This study aimed to investigate the spray characteristics of various ethyl ester type biodiesels derived from sunflower and corn oils in comparison to methyl esters based on the same feedstocks and reference petroleum-based diesel. Spray penetration length (SPL) and spray cone angle (SCA) were experimentally evaluated in a constant volume chamber allowing optical access, under chamber pressures of 0, 5, 10 and 15 bar and injection pressures of 600 and 800 bar. Sauter mean diameter (SMD) values were estimated by using an analytical correlation. Consequently, ethyl esters performed longer SPL (2.8–20%) and narrower SCA (5.1–19%) than diesel under ambient pressures of 5 and 10 bar. Although the SMD values of ethyl esters were 48% higher than diesel on average, their macroscopic spray characteristics were very similar to those of diesel under 15 bar chamber pressure. Moreover, ethyl esters were found to be very similar to methyl esters in terms of spray characteristics. The differences in SPL, SCA and SMD values for both types of biodiesels were lower than 4%. When considering the uncertainty (± 0.84%) and repeatability (±5%) ratios, the difference between the spray characteristics of methyl and ethyl esters was not major.