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Öğe A study of crashworthiness performance in thin-walledmulti-cell tubes 3D-printed from different polymers(WILEY, 2024) Tunay, Merve; Bardakcı, AlperenMulticellular, thin-walled impact tubes have been intensely studied and usedin various engineering fields in recent years due to their lightweight, high per-formance, ease of application, superior energy absorption, and stable deforma-tion characteristics. In this study, energy absorption, crashworthinessperformances, and deformation properties of thin-walled structures manufac-tured from polylactic acid (PLA+) and acrylonitrile butadiene styrene (ABS)using fused deposition modeling (FDM) technology were compared underquasi-static axial compression. Thin-walled structures consist of multicellulartubes connected by concentric corner-edge connections with square and hex-agonal cross-sections. Experimental testing outcomes indicate that the energyabsorption capacity increases with increasing the number of corners in multi-cellular structures. The tubes with square wall-to-wall (S-WW) and hexagonalwall-to-wall (H-WW) cross-sections exhibit superior crashworthiness perfor-mance compared to other cross-sections. Based on the experimental results,the absorbed energy by WW patterned PLA+ square tubes are 19%, 7%, and46% more than that of wall-to-corner (WC), corner-to-wall (CW), and corner-to-corner (CC) patterned tubes, respectively, while it is 11%, 19%, and 80%more in hexagonal cross-section tubes, respectively. This study provides aninformative reference for easier applicability of multicellular energy-absorbingstructures with 3D-print and the design of corner-edge connections of internalconnections in multicellular structures.Öğe Experimental investigation of the axial crushing behavior of aluminum/CFRP hybrid tubes with circular-hole triggering mechanism(ELSEVIER SCI LTD, 2023) Çetin, Erhan; Baykasoğlu, Adil; Erdin, Muhammed Emin; Baykasoğlu, CengizThe current study investigates the axial crushing behavior of filament-wound aluminum/carbon fiber reinforced plastic (Al/CFRP) hybrid tubes with circular-hole triggering mechanism. The proposed hybrid design consists of an inner aluminum thin-walled tube and an outer composite winding of three plies having 30???30??90? angles. The diameter, number, and location of the triggering holes were chosen as design parameters, and Taguchi L9 orthogonal array experimental design was used to find the best configuration of design parameters. For the optimization of multiple responses, Additive Ratio Assessment (ARAS) has also been utilized along with mono-criteria optimization. The experimental results showed that the intact hybrid tube can absorb up to 50% higher crush energy compared with the sum of individual components of the structure. The progressive brittle fracture pattern accompanied by progressive local buckling mode exhibiting favorable energy absorption characteristics were observed in all triggered configurations. Analysis of variance results showed that the trigger location ratio has the most significant effect on the specific energy absorption while the hole diameter was the most significant factor in decreasing the peak crush force. The results revealed that the specific energy absorption and the crush force efficiency of the intact hybrid tubes can be enhanced up to 39.1% and 61.7%, respectively, by the use of optimal levels of design parametersÖğe A fully coupled thermal–microstructural–mechanical finite element processmodel for directed energy deposition additive manufacturing of Ti–6Al–4V(TAYLOR & FRANCIS LTD, 2023) Tuna; Baykasoğlu, Cengiz; Akyıldız, Öncü; C.To, AlbertA fully coupled thermal–microstructural–mechanical finite element modelling framework is developed to investigate the distortion and residual stresses during directed energy deposition (DED) of multi-phase Ti–6Al–4V alloy. The Johnson–Cook constitutive model is used to predict the yield strength of each phase as a function of strain, strain rate and temperature where the flow stress is calculated by a linear mixing rule based on the volumetric phase fractions. A thin-walled rectangular sample is chosen as the reference geometry and the results are compared with experimentally measured in situ thermal history and distortion data, where a reasonable agreement is achieved. The proposed modelling framework with physics-based material constitutive model provides useful information for a better understanding of process–microstructure–property relations in additive manufacturing by DED.Öğe Adsorptive separation of CH4, H2, CO2, and N2 using fullerene pillared graphene nanocomposites: Insights from molecular simulations(SPRINGER, 2023) Mert Balaban, Hümeyra; Deniz, Celal Utku; Baykasoğlu, CengizContext The adsorptive separation performances of fullerene pillared graphene nanocomposites (FPGNs) with tunable micro and meso porous morphology are investigated for the binary mixtures of CH4, H2, CO2 and N2 by using grand canonical Monte Carlo (GCMC) simulations. Diferent fullerene types are considered in designs as pillar to investigate the efects of porosity on the gas separation performances of FPGNs, and the GCMC simulations are performed for an equimolar binary mixture of CO2/H2, CO2/CH4, CO2/N2 and CH4/H2 inspired by industrial gas mixtures. It is found that CO2/N2, CO2/H2 and CH4/H2 selectivity of FPGNs are about 72, 410 and 145 at 298 K and 1 bar, which are higher than those for several adsorbent materials reported. Methods Five diferent FPGN models which contain covalently bonded periodical fullerene and graphene units were constructed using C60, C180, C320, C540 and C720 fullerenes, followed by geometry optimization using Open Babel. All GCMC simulations of adsorption were performed in the RASPA. The adsorption isotherms of FPGNs for pure gases are comparatively examined, and their performances are discussed based on the pore structure and isosteric heat of adsorption. Then, the separation factors of FPGNs for equimolar binary mixtures of these gases are elucidated from the diference in the heat of adsorption and the adsorption selectivityÖğe Biomechanical Behavior Evaluation of Resin Cement with Different Elastic Modulus on Porcelain Laminate Veneer Restorations Using Micro-CT-Based Finite Element Analysis(MDPI, 2023) Mert Eren, Meltem; Çelebi, Alper Tunga; İçer, Esra; Baykasoğlu, Cengiz; Mugan, Ata; Yücel, Taner; Yıldız, EsraThe aim of this study is to evaluate the biomechanical behavior of the porcelain laminate veneer restorations (PLV) of the maxillary central incisor luted with two types of resin cements having different incisal preparations: butt joint and palatal chamfer. Biomechanical analyses were performed using the micro-CT-based finite element models, and von Mises stress and strain values of the PLV, resin cement, adhesive layer, and tooth structure were computed. The PLV with butt joint preparation showed larger stress values than those of restored with palatal chamfer preparation, regardless of the elasticity of the cement and loading conditions. An increase in the elasticity modulus of the resin cement induced slightly larger stresses on the adhesive layer, tooth tissues, and restorative materials. Overall, this study demonstrates the role of the preparation design and luting materials on the mechanical behavior of the PLV restorations and discusses the potential failure mechanisms of the PLV restorations under different loading mechanisms.Öğe Energy absorption of 2D auxetic structures fabricated by fused deposition modeling(SPRINGER HEIDELBERG, 2023) Tunay, Merve; Çetin, ErhanAuxetic structures have become a very popular subject in recent years due to their interesting physical and mechanical properties such as light weight, energy absorption capability, and impact resistance. In this context, the current experimental study presents a detail investigation on the energy absorption performance of re-entrant auxetic structures having diferent design parameters (i.e., strut orientation, strut angle, and strut thickness) under axial quasi-static condition. The auxetic structures were produced by the fused deposition modeling method and the energy absorption performances of the structures were evaluated using various crashworthiness indicators such as energy absorption (EA), specifc energy absorption (SEA), mean crash force (MCF), peak crash force (PCF) and crash force efciency (CFE). Analysis of variance (ANOVA) was also implemented to determine the infuence of design parameters on MCF, SEA and CFE. The results showed that the strut thickness is the highest infuencing parameter on the values for all chosen energy absorption criteria. In particular, the contribution ratios of strut thickness, strut angle and strut orientation on the values of SEA are 74.99, 11.45 and 3.25%, respectively.Öğe Ambient relative humidity effects on mechanical properties of FDM 3D printed PLA components(IOP Publishing Ltd, 2023) Demirtaş, Mehmet Selim; Avcıoğlu, EmirAbstract In this study, poly(lactic acid) samples were printed by using the fused deposition method whereas ambient relative humidity conditions and filling percentages varied. The effects of the relative humidity on the mechanical and thermal properties of the samples were investigated. It was observed that the mechanical properties of the samples decreased as the relative humidity increased and that specimens with low filling percentages were affected more by relative humidity. Differential scanning calorimetry results showed that the glass transition temperature, melting point, and crystallization temperature were inversely correlated with relative humidity. The surface structure was also negatively affected by the relative humidity, and the intensity and size of the voids increased as the relative humidity increased. In addition, this study recommends that the manufacture of materials with a 3D printer be conducted at low humidity to achieve high flexural strength and modulus.Öğe A comparative experimental performance evaluation of solar air collector having absorber plate with convex oval-trench dimple(Springer Science and Business Media Deutschland GmbH, 2023) Abuşka, Mesut; Şefik, Seyfi; Özdilli, ÖzgürThe purpose of this research is to examine how convex oval-trench dimples placed staggered on a solar air collector's absorber improved vortex heat transfer. At air mass flow rates of 0.013, 0.027, and 0.036 kg/s, convex oval-trench dimple absorbers with relative roughness heights, e/D=0.2 and e/D=0.4, as well as a flat plate absorber, were evaluated for back-pass and frontpass applications. The oval-trench dimpled absorber plates in the back-pass and front-pass achieved the maximum energy efficiency of 37.5% and 50.6%, respectively, with e/D=0.4 and 0.036 kg/s. The increase in the number of Nu in e/D=0.4 was 26% and 31% more than that of the flat plate for the examined parameter ranges of back-pass and front-pass, respectively. (e/D=0.4)/(flat plate) and (e/D=0.4)/(e/D=0.2) increased by an average of 28% and 24% in back-pass for (Nuotd /Nu0)/(fotd / f0), respectively. In front-pass, (e/D=0.4)/(flat plate) and (e/D=0.4)/(e/D=0.2) improved by 35% and 25%, respectively. The collector with a relative roughness height of 0.4 has the optimal structure for this examination of collectors with an ovaltrench dimple. The results indicated that collectors with convex oval-trench dimples outperform flat plates in terms of surface area expansion and turbulence generation, which boosts thermal efficiency substantially. In addition, when the experiment results were compared, the front-pass implementation outperformed the back-pass approach. As a result, thermal systems may benefit from utilizing the convex oval-trench dimple.Öğe Wear and Service Life of 3-D Printed Polymeric Gears(MDPI, 2022) Tunalıoğlu, Mert Şafak; Ağca, Bekir VolkanPlastic gears are mostly used in the textile, food, and automotive industries due to their silent operation, corrosion resistance, and light and cheap advantages. Plastic gears are generally manufactured by injection molding or hobbing methods. The excess costs of the molds used to produce parts in injection molding and the problems of wastes that occur during production in hobbing lead companies to additive manufacturing, which is an alternative application. In the additive manufacturing method, the desired amount of product is produced without the problem of waste. In this study, the wear resistance of plastic spur gears produced by the Fused Deposition Modeling (FDM) method was determined theoretically. In order to determine the service life of gears, wear tests were carried out in the Forschungsstelle fur Zahnrader und Getriebebau (FZG) type test device at the same load and rotational speeds. polylactic acid (PLA), acrylonitrile butadiene styrene (ABS), and polyethylene terephthalate (PETG) thermoplastic polymer materials were used in the production of gears. When the gears rotate at the same load and rotational speeds, the most wear was observed in ABS, PLA, and PETG at the theoretically calculated wear depths. PETG is the most resistant material in terms of wear.Öğe Weighted superposition attraction-repulsion (WSAR) algorithm for truss optimization with multiple frequency constraints(Elsevier Science Inc, 2021) Baykasoğlu, Adil; Baykasoğlu, CengizStructural optimization of truss structures under multiple frequency constraints is a highly nonlinear and complex optimization problem with non-convex solution space. The optimization method used to solve mentioned problem is expected to provide a very good balance between solution accuracy and computational cost. In this work, the Weighted Superposition Attraction-Repulsion (WSAR) algorithm, which is a recent swarm intelligence based metaheuristic algorithm, is proposed for effective solution of truss optimization problems with multiple natural frequency constraints. The effectiveness and robustness of the WSAR algorithm is studied by solving several planar/space truss structures optimization problems. The optimization results reveal that the successfulness and effectiveness of WSAR in solving truss optimization problems under multiple frequency constraints where WSAR is able to generate the best results in terms of optimized weight and standard deviation compared to the other state-of-the-art metaheuristic algorithms.Öğe Experimental and numerical analysis of the splay impact on the performance of splayed cross-cut fin heat sink(Elsevier France-Editions Scientifiques Medicales Elsevier, 2021) Şevik, Seyfi; Özdilli, ÖzgürIn this study, splayed effects on the thermal performance of standard cross-cut heat sink (S-CCHS), fixed-array splayed (FAS-CCHS), and full splayed (FS-CCHS) under natural and forced conditions are studied experimentally and numerically. For this purpose, variable parameters such as splayed ratio, different powers of LEDs, natural and forced conditions, and blowing direction have been studied. The results showed that the thermal performance is significantly impacted by the spread position of the fins, blowing direction, natural and forced conditions of the CCHS but is not very sensitive to LEDs' powers. The results show that the full splayed heat sink occupies the highest physical volume, thus, provides the highest thermal performance by efficiently dissipating heat compared to other heat sinks designs. Experimental and numerical results show that the full splayed effect provides 5.46% and 2.59% lower junction temperature in natural and forced, respectively. Also, FS-CCHS achieved a 7.09% reduction in thermal resistance at natural convection 3 W and a 2.62% reduction at 10 W, respectively, compared to the flat fins and the fixed array wide fin heat sink. For this study, while the most suitable flow direction was determined as push, the most suitable orientation was found to be upward, and the splayed impact was also beneficial.Öğe Grand canonical Monte Carlo simulations of methane adsorption in fullerene pillared graphene nanocomposites(Elsevier Science Inc, 2021) Baykasoğlu, Cengiz; Mert Balaban, Hümeyra; Deniz, Celal UtkuThe objective of this study is to investigate the methane adsorption performance of fullerene pillared graphene nanocomposites (FPGNs) with adjustable micro and meso porous morphology and high surface/weight ratios. Different types of fullerenes are considered as pillar units to adjust the porosity of FPGNs. The gravimetric, volumetric and deliverable methane storage capacities of FPGNs are examined using grand canonical Monte Carlo (GCMC) simulations. The lithium doping strategy is also employed to further improve the methane adsorption performance of FPGNs. GCMC simulations revealed that FPGNs have promising potential for methane storage applications with the appropriate selection of design parameters. In particular, the simulation results demonstrated that the gravimetric absolute methane uptake of FPGNs could reach 12.5 mmol/g at 298 K and 40 bars and, this value could be increased up to 19.7 mmol/g with appropriate doping ratio under the same conditions. (c) 2021 Elsevier Inc. All rights reserved.Öğe Li-doped fullerene pillared graphene nanocomposites for enhancing hydrogen storage: A computational study(Elsevier, 2021) Deniz, Celal Utku; Mert Balaban, Hümeyra; Baykasoğlu, CengizHydrogen physisorption in lithium doped fullerene pillared graphene nanocomposites (Li-FPGNs) having tunable pore structures were examined under different temperature and pressure conditions via grand canonical Monte Carlo (GCMC) simulations. Different forms of fullerenes and Li doping ratios, which have considerable effects on the pore structures and surface properties of FPGNs, were considered to optimize the gravimetric, volumetric and deliverable hydrogen adsorption performances of FPGNs. The GCMC simulations confirmed that the hydrogen adsorption performances of undoped FPGNs could be significantly enhanced with the appropriate selection of the doping ratio and types of fullerenes especially at ambient temperature or low-pressure conditions. Particularly, the GCMC simulations showed that the total gravimetric adsorption capacity of Li-FPGNs with doping ratio of Li:C = 15:100 could reach 9.1 wt% at 77 K and 1 bar, which corresponds to about two times increment in the hydrogen storage performance of undoped FPGNs. Moreover, the GCMC simulations demonstrated that Li doping could enhance the excess hydrogen storage capacity of FPGNs up to three times at ambient temperature. These results revealed that Li-FPGNs are promising candidates in the field of hydrogen storage.Öğe A process-microstructure finite element simulation framework for predicting phase transformations and microhardness for directed energy deposition of Ti6Al4V(Elsevier, 2020) Baykasoğlu, Cengiz; Akyıldız, Öncü; Tunay, Merve; To, Albert C.This paper presents a process-microstructure finite element modeling framework for predicting the evolution of volumetric phase fractions and microhardness during laser directed energy deposition (DED) additive manufacturing of Ti6Al4V. Based on recent experimental observations, the present microstructure evolution model is formulated to combine the formation and dissolution kinetics of grain boundary, Widmanstatten colony/basketweave, massive/martensitic alpha and beta phases of Ti6Al4V. The microstructure evolution algorithm is verified and embedded into a three-dimensional finite element process simulation model to simulate thermally driven phase transformations during DED processing of a Ti6Al4V thin-walled rectangular sample. The microhardness values of different locations of the part, which experience different thermal histories, are computed based on the simulated fractions and hardness values of different phases in the final microstructure. The simulated volumetric phase fractions and related microhardness distribution agree reasonably well with experimental measurements performed on the sample. Thus the proposed simulation model could be useful for designers to understand and control process-microstructure-property relationships in a DED-processed part.Öğe Optimal design of truss structures using weighted superposition attraction algorithm(Springer, 2020) Baykasoğlu, Adil; Baykasoğlu, CengizIn this paper, a recently developed swarm based metaheuristic algorithm called weighted superposition attraction (WSA) is implemented for sizing optimization of truss structures first time in literature. The WSA algorithm based on superposition and attracted movement of agents that are observable in many natural systems. The efficiency and robustness of the WSA are investigated by solving five classic 2D and 3D truss-weight minimization problems with fixed-geometry and up to 200 elements. Optimization results demonstrated that WSA is able to generate the best results in terms of optimized weight, standard deviation and number of structural analyses in comparison to all other compared state-of-the-art metaheuristic algorithms.Öğe Crashworthiness of graded lattice structure filled thin-walled tubes under multiple impact loadings(Elsevier Sci Ltd, 2020) Çetin, Erhan; Baykasoğlu, CengizThe objective of this study is to investigate the crashworthiness performances of graded lattice structure filled tubes (GLSFTs) under multiple impact loadings. Different graded body-centered cubic aluminum lattice structures are taken into account in the hybrid tube designs by considering different draft angles and base diameters, and the crashworthiness of those structures are examined by using the validated nonlinear finite element method. The crashworthiness performances of the GLSFTs are also compared with the uniform lattice structure filled tubes (ULSFTs) with the same weights to show the efficiency of GLSFTs by considering several crash worthiness indicators (e.g., initial crush force (ICF), peak crush force (PCF), mean crush force (MCF) and specific energy absorption (SEA)). The results revealed that the graded lattice structure designs enable to obtain variable stiffness throughout the length of hybrid tubes and make possible more folds to be formed without global bending, thus provide significantly better energy absorption performance than their uniform counterparts, especially under oblique loadings. Particularly, the results showed that the GLSFTs can have up to 2 times lower ICF and 3.3 times higher SEA values than that of ULSFTs. The results also revealed that the GLSFTs can absorb up to 146% higher impact energy than the sum of energy absorption of their individual components, and a significant improvement in energy absorption performance of GLSFT can be obtained with appropriate selection of design parameters. Hence, GLSFTs can be recommended as passive protection elements in a broad range of energy absorption applications.Öğe Monte Carlo simulations of hydrogen adsorption in fullerene pillared graphene nanocomposites(Taylor & Francis Ltd, 2020) Mert Balaban, Hümeyra; Deniz, Celal Utku; Baykasoğlu, CengizThe objective of this study is to investigate the hydrogen storage performances of three-dimensional periodic fullerene pillared graphene nanocomposites (FPGNs) consisting of covalently bonded fullerene units between graphene layers. Different forms of fullerenes were used as pillars to adjust porosity and enhance the hydrogen storage capacities of the proposed structures. The gravimetric and volumetric hydrogen uptakes of FPGNs were investigated via grand canonical Monte Carlo calculations under both low- and high -pressure (i.e. 0.01-100 bars) and different thermal (i.e. 77 and 298 K) loading conditions. The simulation results showed that a considerable enhancement in hydrogen adsorption performance could be achieved with the appropriate selection of fullerene size and loading conditions. The simulation results revealed that the FPGNs could uptake 10.3 wt.% hydrogen at 77 K. In addition, the deliverable hydrogen storage capacity of FPGNs could overpass 7.8 wt.% for the charge at 77 K, 100 bar and discharge at 160 K, 5 bar conditions which emphasises the potential of the proposed structures as future ultra-lightweight hydrogen storage media.Öğe Deep drawing of polymer coated metal sheets(Korean Society of Mechanical Engineers, 2019) Erdin, Muhammed Emin; Özdilli, ÖzgürIn the present study, the deep drawing of polymer coated metallic sheets were experimentally investigated to reduce friction and increase manufacturing efficiency without using a lubricant. Coating of metal sheets with a polymer material before the deep drawing process provides numerous other advantages such as long service life, decorative appearance, corrosion protection, prevention of excessive abrasion. In the experiments, deep drawing ratio, blank holder pressure, and punch speed parameters were varied at various intervals and the obtained values were evaluated via graphs. Experiments of the uncoated metal sheets were conducted as well as the coated ones to compare the results. Results of this study showed that the polymer coating improved the surface quality of the test specimens. As a result of this improvement; the average molding forces decreased, obtained deep drawing ratios increased and defects such as tearing and wrinkling were alleviated by coating metal sheets with polymer material compared to uncoated sheets. © 2019, KSME & Springer.Öğe Multi-objective crashworthiness optimization of lattice structure filled thin-walled tubes(Elsevier Ltd, 2020) Baykasoğlu, Adil; Baykasoğlu, Cengiz; Çetin, ErhanThin-walled tubes have been mostly used in passive vehicle safety systems as crash energy absorber. With the use of additive manufacturing technology, it is possible to produce novel filler materials to further enhance the crashworthiness performance of thin-walled tubes. In this study, optimal designs of novel lattice structure filled square thin-walled tubes are investigated under axial impact loading by using a compromise programming based multi-objective crashworthiness optimization procedure. Types of filler lattice structures (i.e., body-centered cubic, BCC and body-centered cubic with vertical strut, BCC-Z), diameter of lattice member, number of lattice unit cells and tube thickness are considered as design parameters, and the optimum values of these design parameters are sought for minimizing the peak crash force (PCF) and maximizing the specific energy absorption (SEA) values. The validated finite element models are utilized in order to construct the sample design space and carrying out results verification; an artificial neural network is employed for predicting values of the objective functions; the weighted superposition attraction algorithm is used to generate design alternatives and searching for their optimal combination. The compromise programming approach is used to combine multi-objectives and to produce various optimal design alternatives. The optimization results showed that the proposed approach is able to provide good solutions with high accuracy and proper selection of design parameters can effectively enhance the crashworthiness performance of the lattice structure filled thin-walled tubes. The optimum results revealed that BCC hybrid designs have generally superior crashworthiness performance compared to that of their BCC-Z counterparts for the same compromise solutions. In particular, the PCF value of the optimized BCC-Z hybrid structures is up to 44% higher than that of BCC hybrid structures while these structures have similar energy absorption performances. The compromise solutions also show that the SEA of BCC and BCC-Z hybrid structures increases respectively by 29% and 51% depending on the selected weight factors for the design objectives.Öğe Energy absorption of thin-walled tubes enhanced by lattice structures(Elsevier, 2019) Çetin, Erhan; Baykasoğlu, CengizThin-walled structures filled or covered by various materials have been proposed for energy absorption applications in recent years. At this point, additive manufacturing technologies provide an unprecedented opportunity to produce nontraditional low-density filler materials to further improve the energy absorption performance of thin-walled structures. With a similar motivation, novel hybrid structures, in which thin-walled tubes filled with periodic lattice materials, are proposed and the energy absorption behaviors of these structures are investigated under axial impact loading conditions. Two different types of lattice structures (i.e. body-centered cubic structure and body-centered cubic structure with vertical strut) are considered as filler materials, and the effects of number of lattice unit cell, diameter of lattice member and tube thickness on energy absorption characteristics of hybrid structures are examined using validated nonlinear finite element models. The results show that the tube and lattice structures contribute the buckling and bending resistance of each other during progressive deformation of hybrid structures, and a considerable enhancement in energy absorption performance could be achieved with appropriate selection of tube and filler lattice structure parameters. Particularly, the result revealed that the hybrid structures can absorb up to 115% higher impact energy compared with the sum of individual parts of hybrid structures. Besides, the hybrid structures also show promising performance in terms of crashworthiness parameters such as specific energy absorption and crash force efficiency, and thus these structures are recommended as potential candidates for crashworthiness applications.
