Mechanical Engineering / Makina Mühendisliği
Permanent URI for this collectionhttps://hdl.handle.net/11147/4129
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Article Citation - WoS: 15Citation - Scopus: 15The Effect of Strain Rate on the Compression Behavior of Additively Manufactured Short Carbon Fiber-Reinforced Polyamide Composites With Different Layer Heights, Infill Patterns, and Built Angles(Springer, 2023) Zeybek, Mehmet Kaan; Güden, Mustafa; Taşdemirci, AlperPrevious studies on the fused deposition modelling (FDM) processed short carbon fiber/Polyamide 6 (PA6) matrix composites and neat PA6 have mostly concentrated on the quasi-static mechanical properties. Present study focused on the strain rate-dependent deformation behavior of a short carbon fiber-reinforced PA6 (Onyx) and neat PA6, produced in different layer heights, infill patterns and built angles. As compared with PA6, Onyx showed a higher compression stress at all strain rates investigated. A layer height of 0.2 mm in PA6 specimens promoted a better bonding between [0/90°] infill layers; hence, a higher flow stress than 0.2 mm layer height specimens, while 0.2 mm layer height induced a higher porosity in Onyx specimens, leading to a lower flow stress. The porosities in Onyx [0/90°] infill specimens were due to the constraining effect of 0/90° fiber layers. Changing infill pattern from a [0/90°] to a concentric one decreased porosity at the same layer height and hence increased the compressive flow stress. The highest compressive strength was found in the specimens with the loading axis 90 and 0° to [0/90°] infill plane. The lowest strength was, however, determined in the specimens with the loading axis 30 and 60o to [0/90°] infill plane in quasi-static loading. However, the specimens with the loading axis of 60, 45, 30 and 0° exhibited a brittle behavior in high strain rate loading (1500 s−1). The specimens with the loading axis of 45° had the lowest fracture stress and strain in the high strain rate loading. This signified the importance of loading angle at high strain rates. Finally, the rate sensitivities of PA6 and Onyx specimens were shown to be similar, showing a matrix dominated deformation. However, the strain rate jump tests indicated a slightly higher rate sensitivity of Onyx specimens at quasi-static strain rates (10−3-10−1 s−1).Article Citation - WoS: 3Citation - Scopus: 3Determination of Activation Energy for Carbon/Epoxy Prepregs Containing Carbon Nanotubes by Differential Scanning Calorimetry(SAGE Publications, 2022) Uz, Yusuf Can; Tanoğlu, MetinThe aim of the present study is the thermal characterization of laboratory-scale carbon fiber/epoxy-based prepregs by incorporating single-wall carbon nanotubes (SWCNTs). Investigation of the cure behavior of a prepreg system is crucial for the characterization and optimization of the fiber reinforced polymeric (FRP) composite. To affect dispersion characteristics, SWCNTs were functionalized by oxidizing their surface with carboxyl (-COOH) group using an acid treatment. The modified resin system contained 0.05, 0.1, and 0.2 wt. % functionalized SWCNTs (F-SWCNTs). Carbon fiber (CF) reinforced prepregs containing various amount of F-SWCNTs were prepared using drum-type winding technique. FTIR was performed to identify new bonding groups formed after the functionalization of SWCNTs. Cure kinetics of prepregs prepared with/without F-SWCNTs were investigated using isoconversional methods.Article Citation - WoS: 8Citation - Scopus: 9Experimental Investigation of Air Cooling With/Out Tab Cooling in Cell and Module Levels for Thermal Uniformity in Battery Packs(ASME, 2023) Göçmen, Sinan; Çetkin, ErdalCatastrophic effects of global warming and environmental pollution are becoming more evident each day, and reduction in fossil fuel consumption is an urgent need. Thus, electric vehicles powered by sustainable energy sources are becoming a major interest. However, there are some challenges such as safety, limited range, long charging times, and battery life which are inhibitory to the adaptation of them. One of the biggest reasons for these challenges is the relationship between battery degradation and temperature which can be eliminated if batteries can be kept at the optimum temperature range. Here, the effects of three distinct (natural convection, forced convection, and tab cooling) methodology were experimentally compared at both the cell and module levels (six serial 7.5 Ah Kokam pouch cells, 1P6S) for thermal management of lithium-ion cells. The experiments were conducted at a discharge rate of 3C with ambient temperatures of 24 ◦C and 29 ◦C. The cell-level test results show that the tab cooling yields 32.5% better thermal uniformity in comparison to the other techniques. Furthermore, tab cooling yields better temperature uniformity with and without air convection as the hot spots occurring near the tabs is eliminated. For the module level, the forced air convection method stands out as the best option with a 4.3% temperature deviation between cells and maximum cell temperature of 39 ◦C. Overall, the results show that a hybrid approach with tab cooling would be beneficial in terms of temperature homogeneity especially in high capacity electric vehicle battery cells.Article Enabling Personalization of a Robotic Surgery Procedure Via a Surgery Training Simulator(Cambridge University Press, 2022) Dede, Mehmet İsmet Can; Büyüköztekin, Tarık; Hanalıoğlu, Şahin; Işıkay, İlkay; Berker, MustafaAlthough robotic or robot-assisted surgery has been increasingly used by many surgical disciplines, its application in cranial or skull base surgery is still in its infancy. Master-slave teleoperation setting of these robotic systems enables these surgical procedures to be replicated in a virtual reality environment for surgeon training purposes. A variety of teleoperation modes were previously determined with respect to the motion capability of the surgeon's hand that wears the ring as the surgeon handles a surgical tool inside the surgical workspace. In this surgery training simulator developed for a robot-assisted endoscopic skull base surgery, a new strategy is developed to identify the preferred motion axes of the surgeon. This simulator is designed specifically for tuning the teleoperation system for each surgeon via the identification. This tuning capability brings flexibility to adjust the system operation with respect to the motion characteristics of the surgeon.Article Citation - WoS: 2Citation - Scopus: 3Model-Based Detection and Isolation of the Wheel Slippage and Actuator Faults of a Holonomic Mobile Robot(Emerald Group Publishing, 2022) Şahin, Osman Nuri; Dede, Mehmet İsmet CanPurpose: Mobile robots may perform very critical tasks under difficult operating conditions. Faults encountered during their tasks may cause the task to be interrupted or failed completely. In the active fault tolerant control methods, it is very important not only to detect the faults that occur in the robot, but also to isolate these faults to develop a fault recovery strategy that is suitable for that specific type of fault. This study aims to develop a model-based fault detection and isolation method for wheel slippage and motor performance degradation that may occur in wheeled mobile robots. Design/methodology/approach: In the proposed method, wheel speeds can be estimated via the dynamic model of the mobile robot, which includes a friction model between the wheel and the ground. Four residual signals are obtained from the differences between the estimated states and the measured states of the mobile robot. Mobile robot’s faults are detected by using these signals. Also, two different residual signals are generated from the calculation of the traction forces with two different procedures. These six residual signals are then used to isolate possible wheel slippage and performance degradation in a motor. Findings: The proposed method for diagnosing wheel slip and performance degradation in motors are tested by moving the robot in various directions. According to the data obtained from the test results, a logic table is created to isolate these two faults from each other. Thanks to the created logic table, slippage in any wheel and performance degradation in any motor can be detected and isolated. Originality/value: Two different recovery strategies are needed to recover temporary wheel slippage and permanent motor faults. Therefore, it is important to isolate these two faults that create similar symptoms in robot’s general movement. Thanks to the method proposed in this study, it is not only possible to isolate the slipping wheel with respect to the non-slipping wheels or to isolate the faulty motor from the non-faulty ones, but also to isolate these two different fault types from each other.Article Citation - WoS: 1Citation - Scopus: 1Fatigue Life Prediction and Optimization of Gfrp Composites Based on Failure Tensor Polynomial in Fatigue Model With Exponential Fitting Approach(SAGE Publications, 2022) Güneş, Mehmet Deniz; İmamoğlu Karabaş, Neslişah; Deveci, Hamza Arda; Tanoğlu, Gamze; Tanoğlu, MetinIn this study, a new fatigue life prediction and optimization strategy utilizing the Failure Tensor Polynomial in Fatigue (FTPF) model with exponential fitting and numerical bisection method for fiber reinforced polymer composites has been proposed. Within the experimental stage, glass/epoxy composite laminates with (Formula presented.), (Formula presented.), and (Formula presented.) lay-up configurations were fabricated, quasi-static and fatigue mechanical behavior of GFRP composites was characterized to be used in the FTPF model. The prediction capability of the FTPF model was tested based on the experimental data obtained for multidirectional laminates of various composite materials. Fatigue life prediction results of the glass/epoxy laminates were found to be better as compared to those for the linear fitting predictions. The results also indicated that the approach with exponential fitting provides better fatigue life predictions as compared to those obtained by linear fitting, especially for glass/epoxy laminates. Moreover, an optimization study using the proposed methodology for fatigue life advancement of the glass/epoxy laminates was performed by a powerful hybrid algorithm, PSA/GPSA. So, two optimization scenarios including various loading configurations were considered. The optimization results exhibited that the optimized stacking sequences having maximized fatigue life can be obtained in various loading cases. It was also revealed that the tension-compression loading and the loadings involving shear loads are critical for fatigue, and further improvement in fatigue life may be achieved by designing only symmetric lay-ups instead of symmetric-balanced and diversification of fiber angles to be used in the optimization.Article Citation - WoS: 9Citation - Scopus: 10Investigation of Hybridization Effect on Ballistic Performance of Multi-Layered Fiber Reinforced Composite Structures(Sage Publications Ltd, 2022) Üstün, Hikmet Sinan; Toksoy, Ahmet Kaan; Tanoğlu, MetinThe aim of this study is enhancing the ballistic performance of multi-layered fiber reinforced composite structures by hybridization approach against fragment simulating projectile (FSP). For manufacturing of homogeneous and hybrid composite structures, 170 g/m2 twill weave aramid and 280 g/m2 plain weave E-Glass fibers were used with epoxy resin systems and two different thickness values for each composite panel were fabricated and tested to obtain a relationship between areal density and V50 parameters. Tensile, 3-point bending, and short beam strength tests of composite panels were performed, and ballistic performance of composite structures were measured by V50 test method with 1.1 g FSP threat. Ballistic performance of hybrid composite structures was compared with high-performance composite ballistic panel test results reported in literature. As a result, it was found that E-Glass fabric layers together with aramid fabrics increased the energy absorbing capability of hybrid composite panels and ballistic performance was enhanced to be similar or higher than ballistic fiber reinforced composites. Hence, hybridization was found to be an effective way to enhance ballistic performance of fiber reinforced composite structures.Article Citation - WoS: 22Citation - Scopus: 22Simultaneous Validation of Wearable Motion Capture System for Lower Body Applications: Over Single Plane Range of Motion (rom) and Gait Activities(Walter de Gruyter GmbH, 2022) Mihçin, ŞenayExtracting data from {Zhu, 2019 #5} daily life activities is important in biomechanical applications to define exact boundary conditions for the intended use-based applications. Although optoelectronic camera-marker based systems are used as gold standard tools for medical applications, due to line-of-sight problem, there is a need for wearable, affordable motion capture (MOCAP) systems. We investigate the potential use of a wearable inertial measurement unit (IMU) based-wearable MOCAP system for biomechanical applications. The in vitro proof of concept is provided for the full lower body consisting of hip, knee, and ankle joints via controlled single-plane anatomical range of motion (ROM) simulations using an electrical motor, while collecting data simultaneously via opto-electronic markers and IMU sensors. On 15 healthy volunteers the flexion-extension, abduction-Adduction, internal-external rotation (ROM) values of hip and, the flexion-extension ROM values of the knee and ankle joints are calculated for both systems. The Bland-Altman graphs showed promising agreement both for in vitro and in vivo experiments. The maximum Root Mean Square Errors (RMSE) between the systems in vitro was 3.4° for hip and 5.9° for knee flexion motion in vivo, respectively. The gait data of the volunteers were assessed between the heel strike and toe off events to investigate the limits of agreement, calculating the population averages and standard deviation for both systems over the gait cycle. The maximum difference was for the ankle joint <6°. The results show that proposed system could be an option as an affordable-democratic solution.Article Design, Prototyping and Tests of a Rollable Ramp for Temporary Use(Springer, 2021) Doğan Kumtepe, Elvan; Kiper, GökhanPortable ramps, used generally by wheelchair users, offer temporary solution to increase accessibility and mobility. Preferably these ramps should be compact and lightweight for ease of handling and storage. Different types of portable ramps in the market that are used by wheelchair users are generally made of aluminum and require several improvements, especially in terms of lightweight and compactness. Based on wheelchair users’ inclinations a compact and lightweight rollable ramp is designed in this study. A parametric model of the links of the ramp are derived and the rolled geometry is optimized using convex hull and smallest enclosing circle algorithms. The side bars of the links are designed and manufactured from aluminum and the load-bearing panels are manufactured from sandwich composite structures with honeycomb core. Strength calculations are performed analytically and also with finite-element analysis. After the design is finalized, a prototype is manufactured. The designed ramp is 15.4% more compact and has 18.9% less weight compared to the best rival product available in the market. Load tests and functional tests are performed with voluntary wheelchair users. Several positive feedbacks are received from the participants about the ramp being practical, easy to use and store, lightweight, advantage of the anti-slip surface.Article Citation - WoS: 8Citation - Scopus: 8Comparing Compression Deformation and Rate Sensitivity of Additively Manufactured and Extruded-Annealed 316l Alloys(Springer, 2021) Enser, Samed; Yavaş, Hakan; Arslan Hamat, Burcu; Aydın, Hüseyin; Kafadar, Gülten; Tanrıkulu, A. Alptuğ; Zeytin Kazdal, Havva; Öztürk, Fahrettin; Güden, MustafaThe deformation behavior of a selective-laser-melt-processed 316-L alloy (SLM-316L) under compression was determined together with a commercial annealed-extruded 316L alloy bar (C-316L) for comparison. Strain rate jump tests and hardness tests on the untested and compression tested samples were also performed. Extensive microscopic observations on the deformed and undeformed samples showed a twinning-dominated deformation in SLM-316L, similar to twinning-induced-plasticity steels, while a martensitic transformation-dominated deformation in C-316L alloy, similar to transformation-induced-plasticity steels. Within the studied quasi-static strain rate regime, the measured higher strain rate sensitivity of SLM-316L was ascribed to the lower distances between the nano-twins, in the level of 100 nm, than the distances between martensite plates, in the level of 1000 nm. A higher hardness increase in the martensite transformation region as compared with the twinned region proved the higher work hardening of C-316L. The hardness tests in the micron and sub-micron levels further confirmed the previously determined relatively low resistances of the dislocation cell walls (sub-grain) to the dislocation motion in SLM-316L alloy.