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: 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 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: 3Citation - Scopus: 3Enhancement of Filament Wound Glass Fiber/Epoxy-based Cylindrical Composites by Toughening With Single-Walled Carbon Nanotubes(SAGE Publications, 2022) Ay Solak, Zeynep; Kartav, Osman; Tanoğlu, MetinIn this study, the effect of incorporating nano-sized fillers (noncovalently functionalized with ethoxylated alcohol chemical-vapor-deposition-grown SWCNTs) within an epoxy resin on the performance of filament wound glass fiber (GF)-based cylindrical composites (GFCCs) was investigated. For this purpose, SWCNTs were dispersed with the concentration of 0.05 and 0.1 weight percent (wt.%) within an epoxy resin using mechanical stirring and calendaring (3-roll-milling) techniques. The rheological behavior of the SWCNT incorporated epoxy mixture was characterized to determine the suitability of blends for the filament winding process. It was revealed that the viscosity value of the resin was not significantly affected by the addition of SWCNTs in given concentrations. Moreover, contact angle measurements were also performed on the SWCNT/epoxy blends dropped on the GF for the evaluation of the wettability behavior of the GF in the presence of the SWCNTs in relevant concentrations. Eventually, it was observed that the wettability behavior of GF was not reasonably affected by the presence of the SWCNTs. The double cantilever beam (DCB), flexural, and short beam shear (SBS) tests were performed on the reference and SWCNT-modified GFCC specimens to evaluate the effects of the SWCNT presence on the interlaminar fracture toughness and out-of-plane properties of GFCCs. The fractured surfaces after the DCB and SBS tests were analyzed under the scanning electron microscopy to reveal the toughening mechanisms and the filler morphologies. Consequently, although SWCNT incorporation was on the outermost layer of GFCCs, it was found that the interlaminar shear strength (ILSS) values and Mode I interlaminar fracture toughness values of the curved composite samples were improved up to 22 and 216%, respectively, due to the presence of the SWCNTs.Article Citation - WoS: 13Citation - Scopus: 14The Quasi-Static Crush Response of Electron-Beam Ti6al4v Body-Centred Lattices: The Effect of the Number of Cells, Strut Diameter and Face Sheet(Wiley, 2022) Güden, Mustafa; Alpkaya, Alican Tuncay; Arslan Hamat, Burcu; Hızlı, Burak; Taşdemirci, Alper; Tanrıkulu, A. Alptuğ; Yavaş, HakanThe effect of the number of cells, strut diameter and face sheet on the compression of electron-beam-melt (EBM) Ti6Al4V (Ti64) body-centred-cubic (BCC) lattices was investigated experimentally and numerically. The lattices with the same relative density (~0.182) were fabricated with and without 2-mm-thick face sheets in 10 and 5 mm cell size, 8–125 unit cell (two to five cells/edge) and 2 and 1 mm strut diameter. The experimental compression tests were further numerically simulated in the LS-DYNA. Experimentally two bending-dominated crushing modes, namely, lateral and diagonal layer crushing, were determined. The numerical models however exhibited merely a bending-dominated lateral layer crushing mode when the erosion strain was 0.4 and without face-sheet models showed a diagonal layer crushing mode when the erosion strain was 0.3. Lower erosion strains promoted a diagonal layer crushing mode by introducing geometrical inhomogeneity to the lattice, leading to strain localisation as similar to the face sheets which introduced extensive strut bending in the layers adjacent to the face sheets. The face-sheet model showed a higher but decreasing collapse strength at an increasing number of cells, just as opposite to the without face-sheet model, and the collapse strength of both models converged when the number of cells was higher than five-cell/edge. The decrease/increase of the collapse strengths of lattices before the critical number of cells was claimed mainly due to the size-imposed lattice boundary condition, rather than the specimen volume. The difference in the experimental collapse strengths between the 5- and the 10-mm cell-size lattices was ascribed to the variations in the microstructures—hence the material model parameters between the small-diameter and the large-diameter EBM-Ti64 strut lattices.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: 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.