Makine Mühendisliği Bölümü Koleksiyonu

Permanent URI for this collectionhttps://hdl.handle.net/20.500.12573/206

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Axial free vibration analysis of a tapered nanorod using Adomian decomposition method
(TECHNO-PRESS, 2025) Coskun, Safa B.; Kara, Ozge; Atay, Mehmet T.; AGÜ, Mühendislik Fakültesi, Makine Mühendisliği Bölümü; Atay, Mehmet T.
This study aimed to conduct an analysis of the axial free vibration of tapered nanorods based on nonlocal elasticity theory. The small-scale effect on the free axial vibration of a tapered nanorod was studied employing the Adomian decomposition method (ADM) and the finite difference method (FDM) as a checking tool where a contradiction existed between the results of this study and available results in one highly cited work in the literature, which was used for comparison purposes in this work. Different boundary conditions for the nanorod were considered: fixed-fixed nanorod, fixed-free nanorod, and fixed-linear spring nanorod. The governing equation of the problem is a variable coefficient differential equation for which analytical solutions are strictly limited. For this type of problem, analytical approximate methods are effective, and there are many studies available in the literature on the application of these methods to solve linear/nonlinear ordinary/partial differential equations. ADM is one of the methods and was successfully used in this study to analyze the free vibration of nanorods. The results obtained in this study have shown that the presented technique is so powerful and has potential for applications in nanomechanics based on nonlocal elasticity theory.
Biogas intake pressure and port air swirl optimization to enhance the diesel RCCI engine characteristics for low environmental emissions
(Institution of Chemical Engineers, 2024) Dalha, Ibrahim B.; Koca, Kemal; Said, Mior A.; Rafindadi, Aminu D.; 0000-0003-2464-6466; AGÜ, Mühendislik Fakültesi, Makine Mühendisliği Bölümü; Koca, Kemal
Exhaust emission and combustion control in RCCI (reactivity-controlled compression ignition) focused mainly on the direct-injected fuel parameters, urging to investigate the advantages of port-fuel intake parameters. The engine was modified for port injection of Biogas at the valve and RCCI mode. The influence of port swirl ratio (PSR, 0 – 80%) and biogas injection pressure (BIP, 1 – 4 bar) on the diesel RCCI combustion and emissions was tested and optimized at varied loads and 1600 rpm in a port injection at the valve (PIVE) approach. Established kinetic mechanisms were combined with multi-objective optimization to further investigate, predict, and analyze emissions occurrence and trade-offs for reduced environmental impacts. The results show that the radiation absorption triggered by increased CO2 lowers combustion temperature, resulting in prolonged ignition. Setting the airflow to swirl lowers the in-cylinder pressure at elevated BIP while raising the heat generated across the BIPs. Increasing the PSR slows the combustion while BIP speeds up the process. BIP and PSR show great trade-off reduction ability among all emission parameters. The optimum unburned hydrocarbon, nitrogen oxide, particulate, and carbon monoxide emissions for the injection at the valve were found to be 109.58, 0.577, and 2.336 ppm, and 0.103%, respectively, at low-load, low-BIP, and high-PSR. The emissions were lowered by 6.58, 91.26, 80.65, and 13.45% compared to the premixed RCCI mode, respectively. Therefore, introducing lowpressure biogas amid high swirling air at the valve elevates the in-cylinder condition while lowering the emissions, mitigating their environmental implications.
Characterization of 3D fabric permeability with skew terms
(ELSEVIER SCI LTDTHE BOULEVARD, LANGFORD LANE, KIDLINGTON, OXFORD OX5 1GB, OXON, ENGLAND, 2017) Yun, Minyoung; Sas, Hatice; Simacek, Pavel; Advani, Suresh G.; 0000-0002-5179-2509; 0000-0002-2670-903X; AGÜ, Mühendislik Fakültesi, Makine Mühendisliği Bölümü
Flow simulations can predict resin flow behavior and void formation locations in a preform. One important parameter for simulation is the preform permeability. For thick parts with distribution media on the surface, resin flow is three dimensional and through the thickness permeability is required for simulation. If the fabric is a 3D preform or unbalanced, the through the thickness (Kzz) and two skew components (Kxz and Kyz) must be characterized. The skew terms influence the flow behavior and hence the void formation. In this study, we present a measurement station that provides all six independent components of the permeability tensor from one experiment. The methodology uses the location data of the flow front with time and then couples it to an optimization algorithm and our flow simulation tool, LIMS (Liquid Injection Molding Simulation). The process is automated and experimental results are superimposed on the simulation results to confirm fidelity of the values determined. (C) 2017 Elsevier Ltd. All rights reserved.
Comparative study on bending behavior and damage analysis of 3D-printed sandwich core designs with bio-inspired reinforcements
(ELSEVIER, 2024) Atahan, M. Gokhan; Erikli, Merve; Ozipek, Enes; Ozgun, Fulya; 0000-0002-8180-5876; 0009-0009-4624-3319; 0009-0009-9408-077X; 0009-0002-8198-4525; AGÜ, Mühendislik Fakültesi, Makine Mühendisliği Bölümü; Atahan, M. Gokhan; Erikli, Merve; Ozipek, Enes; Ozgun, Fulya
In this study, novel sandwich core designs with bio-inspired reinforcements were proposed and their bending behaviors were comparatively examined. The geometrical shapes of alligator osteoderm and chambered nautilus shell were utilized as bio-inspired reinforcements for sandwich core structures. Sandwich core structures were produced through the additive manufacturing method. Experimental tests and finite element analysis were performed to determine the bending performances of the proposed sandwich core structures. The loadcarrying capacity, deformation ability, damage-tolerant capability, energy absorption, and damage mechanisms of the proposed sandwich core structures were comparatively investigated through experimental and numerical methods. The orthotropic material model and Hashin’s damage criterion were used in the numerical model of 3D-printed sandwich core structures to consider the effect of the filament raster orientation on the elastic and damage behavior of the sandwich core structures. Compared to the classical honeycomb sandwich core structure, while bio-inspired reinforcements improved the load-carrying capacity and damage-tolerant capability of sandwich core structures, they reduced the energy absorption ability of sandwich core structures due to reducing the vertical deformation ability of sandwich core structures. Bio-inspired reinforcements significantly affected the stress distribution and damage behavior of the sandwich core structures. They reduced von Mises stress level at the outer cell edges of the sandwich core structures and caused reinforcement damage instead of outer cell damage.
Compensating energy demand of public transport and yielding green hydrogen with floating photovoltaic power plant
(Institution of Chemical Engineers, 2024) Koca, Kemal; 0000-0003-2464-6466; AGÜ, Mühendislik Fakültesi, Makine Mühendisliği Bölümü; Koca, Kemal
The last three decades have seen a dramatic increase in the renewable energy sector as a result of increased human energy consumption and environmental concerns about fossil fuels. Offshore renewable energy sources are the most alluring and promising technologies because of more energy potential, less space, and visual restrictions than onshore ones. Among those, floating solar photovoltaic (FPV) has a remarkable reputation. The present study focuses on a viable way to replace energy resources derived from fossil fuels with renewable solar energy. In this regard, electrical energy demand is investigated where a floating photovoltaic system and integrated hydrogen production unit are employed on water surface of Yamula Dam. Energy demand of public trams would be compensated with electricity generated by FPV and rest of energy would be utilized for hydrogen production. Key results illustrated that in various scenarios, the energy generation amounts were around 31×106 kW, 32×106 kW, and 39×106 kW, while the energy consumption amounts were approximately 24×106 kW. It was evident that the energy created more than offset the amount consumed. It was also note that the total costs of entire system were $94.1 M, $78.5 M and $71.2 M according to the different cases. It was also observed that in October and November, the remaining energy from the Bozankaya tram produced the most hydrogen with 125 kg, whereas in September and October, the remaining energy from the Sirio tram produced approximately 70 kg.
A comprehensive experimental and modeling study of the strain rate- and temperature-dependent deformation behavior of bio-degradable Mg-CeO2 nanocomposites
(ELSEVIER, 2024) Deka, Surja; Mozafari, Farzin; Mallick, Ashis; 0000-0001-8218-4410; AGÜ, Mühendislik Fakültesi, Makine Mühendisliği Bölümü; Mozafari, Farzin
A comprehensive study was undertaken on the temperature-dependent and strain rate-sensitive deformation behavior of near-dense low-volume fraction magnesium-cerium dioxide (Mg-CeO2 ) nanocomposites synthesized by powder metallurgy technique. The process involved ball milling of elemental powders → cold compaction → sintering in an inert atmosphere, and in-situ hot extrusion. The Mg-CeO2 nanocomposites displayed strain rate and temperature sensitivity, exhibiting higher yield strength, superior compressive characteristics, greater hardness, and improved ductility compared to pure Mg and most commercial Mg alloys. Furthermore, a thorough micro-structural investigation was conducted to characterize the distributions of ceria nanoparticles, grain refinement degree, ceria-magnesium interface, formation of deformation twins and interfacial bonding between the reinforcement and matrix. The present study has proposed two modeling approaches, the Johnson– Cook (J–C) constitutive model and a machine learning-assisted model, to predict the mechanical behavior of monolithic Mg and Mg-CeO2 nanocomposites. The models effectively explained the deformation behavior under various strain rates and temperatures.
Compression performance of 3D-printed ant-inspired lattice structures: An innovative design approach
(Sage Journals, 2025) Atahan, Mithat Gokhan; Saglam, Selman; 0000-0002-8180-5876; AGÜ, Mühendislik Fakültesi, Makine Mühendisliği Bölümü; Atahan, Mithat Gokhan; Saglam, Selman
In this study, three different ant-inspired lattice design types: single, double, and inverted double structures were considered due to ants' excellent load-carrying weight ratio. Lattice structures were fabricated using the 3D printing method and polylactic acid filament was used as a printing material. The true blueprint images of the ant were used to obtain the parametric dimensions of the ant-inspired lattice structure. Hence, the presented innovative method for designing lattice structures can be a promising option for industrial sectors requiring high-strength structures. The quasi-static axial compression tests were conducted to evaluate the compression performance of the novel lattice structures. The compression performance of ant-inspired single lattice structures was compared based on specific force, specific energy absorption, and specific stiffness at different height values. The deformation stages and damage regions of ant-inspired lattice structures were analyzed to identify their critical regions during compression tests. The results indicated that as the height value increased, there was a notable decrease in specific force, specific energy absorption, and specific stiffness, along with buckling damage in the ant-inspired single lattice structures. Among the three design types, the ant-inspired inverted double lattice structure showed better compression performance compared to the ant-inspired double lattice structure; however, the ant-inspired single lattice structure with a height of 30 mm exhibited the highest overall compression performance.
Corrosion behavior of novel Titanium-based high entropy alloys designed for medical implants
(ELSEVIER SCIENCE SA, PO BOX 564, 1001 LAUSANNE, SWITZERLAND, 2020) Yagci, Mustafa Baris; Bal, Bekir Cihad; Canadinc, Demircan; Gurel, S.; 0000-0001-9961-7702; 0000-0002-3176-2388; AGÜ, Mühendislik Fakültesi, Makine Mühendisliği Bölümü
This paper reports on the corrosion behavior of three TiTaHf-based high entropy alloys (HEAs) in simulated body fluid (SBF) and artificial saliva (AS) in order to assess their potential utility as implant materials. Specifically, TiTaHfNb, TiTaHfNbZr and TiTaHfMoZr HEAs were subjected to static immersion experiments in SBF and AS, and both the surfaces of the samples and the immersion fluids were thoroughly examined with the state of the art techniques. The experimental results presented herein revealed that the presence of Zr and Nb in the TiTaHf-based samples enhanced corrosion performance with reduced ion release and better surface properties, while Mo addition resulted in an inhomogeneous microstructure, leading to dendrite structures and significant amount of ion release upon immersion in both media. Furthermore, a protective passive layer formation or crystallization was present on all HEA surfaces, implying that corrosion resistance can be sustained in long-term applications. Overall, the set of findings presented herein constitute an early indication of the potential of the TiTaHf-based HEAs to be utilized as implant materials.
Deformation behavior of nanostructured aluminum: Experiment and computational study
(Elsevier Ltd, 2023) Deka, Surja; Mozafari, Farzin; Mallick, Ashis; 0000-0001-8218-4410; AGÜ, Mühendislik Fakültesi, Makine Mühendisliği Bölümü; Mozafari, Farzin
Nanocrystalline metals have been processed from powder predecessors in recent times in significant ways, and nowadays, materials are starting to be manufactured which are not only strong but also ductile. Nanocrystalline aluminum (Average grain size 51 nm) was synthesized through high-energy ball milling at the room temperature of microcrystalline powder. The particle size and crystallite sizes were obtained by Williamson Hall and found to be in good correlation with transmission spectroscopy (TEM) data. There was a significant increase in the mechanical properties of nanostructured aluminum in comparison to coarse-grained aluminum. Moreover, a phenomenological model of large-deformation, isotropic, rate-dependent plasticity is developed, which takes into account pressure dependency, plastic dilatation, and non-normal flow. The model has been incorporated into a finite element program. Compression and tension experiments were performed on nanocrystalline aluminum, and the constitutive parameters within the model were estimated from these experiments. The present study shows that the constitutive model successfully simulates the mechanical response of nanocrystalline aluminum with reasonable accuracy using our numerical finite-element capability.
Design analysis of a wave energy converter for hydrogen generation near shoreline of Black Sea
(Institution of Chemical Engineers, 2024) Bekçi, Eyüp; Koca, Kemal; Bashir, Muhammad Farhan; 0000-0003-2464-6466; AGÜ, Mühendislik Fakültesi, Makine Mühendisliği Bölümü; Bekçi, Eyüp; Koca, Kemal
The generation of electricity from waves has attracted a lot of attention from researchers lately. Despite the vastness and accessibility of wave energy across the majority of the planet, there is a dearth of literature on the production of electricity and hydrogen from wave power. In this paper, a comprehensive simulation related to hydrogen production with an oscillating wave surge converter (OWSC) system was employed for the Black Sea region. The simulations were performed by means of Homer-Pro software and the data were provided thanks to European Marine Observation and Data Network (EMODnet) as well as a novel web-based tool with regards to wave resources. Initial results of web-based tool showed that the hydrogen generation was directly impacted by considerable wave height and wave energy period. As a result, it may change based on the days and months. May had the lowest monthly energy production (3 MWh), while December had the highest monthly energy production (27 MWh). Moreover, the electrolyzers with different efficiencies were investigated with Homer-Pro. The electrolyzer with an efficiency of 85% at 100 kW produced 3301 kg annually, whereas the electrolyzers with 90% and 95% efficiency at 100 kW produced 3419 kg annually and 3422 kg annually, respectively. Apart from those findings, when more efficient electrolyzers were employed in the system, both the capital and replacement costs dropped at the same time.
A detailed investigation of the effect of hydrogen on the mechanical response and microstructure of Al 7075 alloy under medium strain rate impact loading
(PERGAMON-ELSEVIER SCIENCE LTD, THE BOULEVARD, LANGFORD LANE, KIDLINGTON, OXFORD OX5 1GB, ENGLAND, 2020) Bal, Burak; Okdem, Bilge; Bayram, Ferdi Caner; Aydin, Murat; AGÜ, Mühendislik Fakültesi, Makine Mühendisliği Bölümü
Effects of hydrogen and temperature on impact response and corresponding microstructure of aluminum (Al) 7075 alloy were investigated under medium strain rate impact loading. The specimens were subjected to impact energy of 12 J and 25 J, corresponding to impact velocities of 2.13 m/s and 3.08 m/s, respectively. These energy levels were decided after a couple of impact tests with different impact energy values, such as 6 J, 10 J, 12 J, 25 J. The experiments were conducted at five different temperatures. Electrochemical charging method was used for hydrogen charging. Microstructural observations of hydrogen uncharged and hydrogen charged specimens were carried out by scanning electron microscope. Hydrogen changed the crack propagation behavior of Al 7075 alloy depending on the temperature. Coexistence of several hydrogen embrittlement mechanisms, such as hydrogen enhanced decohesion (HEDE) and hydrogen enhanced localized plasticity (HELP) were observed under impact loading. The impact response of Al 7075 was significantly deteriorated by the hydrogen charging and changing temperature affected the absorbed energy of hydrogen-charged specimens. In addition, molecular dynamics simulations were conducted to uncover the atomistic origin of hydrogen embrittlement mechanisms under impact loading. In particular, hydrogen decreased the cohesive energy and enhanced the average dislocation mobility. Therefore, the experimental results presented herein constitute an efficient guideline for the usage of Al alloys that are subject to impact loading in service in a wide range of temperatures. (C) 2020 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.
Development of a Nanoparticle-Embedded Chitosan Sponge for Topical and Local Administration of Chemotherapeutic Agents
(American Society of Mechanical Engineers (ASME), 2014) Goldberg, Manijeh; Manzi, Aaron; Aydin, Erkin; Singh, Gurtej; Khoshkenar, Payam; Birdi, Amritpreet; LaPorte, Brandon; Krauskopf, Alejandro; Powell, Geralle; Chen, Julie; Langer, Robert; 0000-0001-7811-2959; AGÜ, Mühendislik Fakültesi, Makine Mühendisliği Bölümü; Aydin, Erkin
The following work describes the development of a novel noninvasive transmucosal drug delivery system, the chitosan sponge matrix (CSM). It is composed of cationic chitosan (CS) nanoparticles (NPs) that encapsulate cisplatin (CDDP) embedded within a polymeric mucoadhesive CS matrix. CSM is designed to swell up when exposed to moisture, facilitating release of the NPs via diffusion across the matrix. CSM is intended to be administered topically and locally to mucosal tissues, with its initial indication being oral cancer (OC). Currently, intravenous (IV) administered CDDP is the gold standard chemotherapeutic agent used in the treatment of OC. However, its clinical use has been limited by its renal and hemotoxicity profile. We aim to locally administer CDDP via encapsulation in CS NPs and deliver them directly to the oral cavity with CSM. It is hypothesized that such a delivery device will greatly reduce any systemic toxicity and increase antitumor efficacy. This paper describes the methods for developing CSM and maintaining the integrity of CDDP NPs embedded in the CSM.
Development of an optical measurement system for surface depth measurements and study of focus effect on determination of steel inclusion content by EN-10247
(SPIE-SOC PHOTO-OPTICAL INSTRUMENTATION ENGINEERS1000 20TH ST, PO BOX 10, BELLINGHAM, WA 98225, 2021) Durkaya, Goksel; Kurtuldu, Huseyin; Cetin, Baris; Bal, Burak; AGÜ, Mühendislik Fakültesi, Makine Mühendisliği Bölümü; Bal, Burak
Surface inspections are important in steelmaking processes to characterize the final product's quality. We present a method to measure surface depth profile using laser scattering geometry. This technique is used to analyze the focus effect on microscopic analyses of steel inclusions using the EN-10247 standard. The results presented herein offer promising new perspectives for the metal manufacturing industry through cost-effective solutions that attain quasi in-line process inspection capabilities. (C) 2021 Society of Photo-Optical Instrumentation Engineers (SPIE)
Development of high-performance nanostructured aluminum and its constitutive modeling
(Taylor and Francis Ltd., 2023) Deka, Surja; Mozafari, Farzin; Mallick, Ashis; Thamburaja, Prakash; Gupta, Manoj; 0000-0001-8218-4410; AGÜ, Mühendislik Fakültesi, Makine Mühendisliği Bölümü; Mozafari, Farzin
A new technique, an in-situ hot-extrusion-based synthesizing process, is proposed to develop high-performance nanocrystalline aluminum (nc-Al) with an optimally tuned strength-to-ductility ratio suitable for various technologically relevant applications. Comprehensive investigations are conducted by characterizing mechanical and microstructural properties to realize the influence of various synthesizing variables on the properties of the bulk nc-Al. Furthermore, a continuum-scale constitutive modeling approach is proposed based on dominant microstructural mechanisms of plastic deformation and implemented into a finite element solver using a user-defined material interface. It is shown that the proposed theory can provide a versatile platform to predict the nanocrystalline aluminum mechanical response quite well.
Development of highly transparent Pd-coated Ag nanowire electrode for display and catalysis applications
(ELSEVIER, 2015) Canlier, Ali; Ucak, Umit Volkan; Usta, Hakan; Cho, Changsoon; Lee, Jung-Yong; Sen, Unal; Citir, Murat; 0000-0002-0618-1979; 0000-0003-3736-5049; 0000-0002-6666-4980; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü; Canlier, Ali; Ucak, Umit Volkan; Usta, Hakan; Sen, Unal; Citir, Murat
Ag nanowire transparent electrode has excellent transmittance (90%) and sheet resistance (20 Omega/sq), yet there are slight drawbacks such as optical haze and chemical instability against aerial oxidation. Chemical stability of Ag nanowires needs to be improved in order for it to be suitable for electrode applications. In our recent article, we demonstrated that coating Ag nanowires with a thin layer of Au through galvanic exchange reactions enhances the chemical stability of Ag nanowire films highly and also helps to obtain lower haze. In this study, coating of a thin Pd layer has been applied successfully onto the surface of Ag nanowires. A mild Pd complex oxidant [Pd(en)(2)](NO3)(2) was prepared in order to oxidize Ag atoms partially on the surface via galvanic displacement. The mild galvanic exchange allowed for a thin layer (1-2 nm) of Pd coating on the Ag nanowires with minimal truncation of the nanowire, where the average length and the diameter were 12.5 mu m and 59 nm, respectively. The Pd-coated Ag nanowires were suspended in methanol and then electrostatically sprayed on flexible polycarbonate substrates. It has been revealed that average total transmittance remain around 95% within visible spectrum region (400-800 nm) whereas sheet resistance rises up to 175 Omega/sq. To the best of our knowledge, for the first time in the literature, Pd coating was employed on Ag nanowires in order to design transparent electrodes for high transparency and strong chemical resistivity against nanowire oxidation. The current Pd-coated Ag nanowires may render an excellent catalyst system for fuel cell applications, as well as in organic synthesis with relatively low costs since our approach enables the fabrication of these nanowires with a very thin layer of Pd. We believe that mesh form of Pd-coated Ag nanowires will coin a new catalyst concept to the related areas since their sheet conductivity is high enough, and also little amount of Pd displays a large surface area as thin layers. (C) 2015 Elsevier B.V. All rights reserved.
The Digitized Shoulder: From Preoperative Planning to Patient-Specific Guides
(SPRINGER LINK, 2022) Sadeghi, Majid Mohammad; Kapicioglu, Mehmet; Kececi, Emin Faruk; Bilsel, Kerem; 0000-0001-8561-6960; AGÜ, Mühendislik Fakültesi, Makine Mühendisliği Bölümü; Kececi, Emin Faruk
As the information and computer technologies improve, it can change how the shoulder surgeries and treatments are done. Digitalization of the shoulder joint acquired via MR and CT (1) shows the surgeons the pathology in a more easily understandable way, (2) generates models for preoperative planning, and (3) uses special software to generate patient-specific instruments. Digitalization of the shoulder will make the shoulder disorder’s treatment easier and more accurate in the future.
Edge dislocation depinning from hydrogen atmosphere in α-iron
(Acta Materialia Inc, 2024) Kapci, Mehmet Fazil; Yu, Ping; Liu, Guisen; Shen, Yao; Li, Yang; Bal, Burak; Marian,Jaime; 0000-0002-7389-9155; AGÜ, Mühendislik Fakültesi, Makine Mühendisliği Bölümü; Kapci, Mehmet Fazil; Bal, Burak
Understanding the dislocation motion in hydrogen atmosphere is essential for revealing the hydrogen-related degradation in metallic materials. Atomic simulations were adopted to investigate the interaction between dislocations and hydrogen atoms, where the realistic hydrogen distribution in the vicinity of the dislocation core was emulated from the Grand Canonical Monte Carlo computations. The depinning of edge dislocations in α-Fe at different temperatures and hydrogen concentrations was then studied using Molecular Dynamics simulations. The results revealed that an increase in bulk hydrogen concentration increases the flow stress due to the pinning effect of solute hydrogen. The depinning stress was found to decrease due to the thermal activation of the edge dislocation at higher temperatures. In addition, prediction of the obtained results was performed by an elastic model that can correlate the bulk hydrogen concentration to depinning stress.
Effect of bio-mimicked surface texturing on the shear strength of additively manufactured metal single-lap joints: An innovative approach
(PERGAMON-ELSEVIER SCIENCE LTD, 2025) Atahan, M. Gokhan; Maskery, Ian; Ashcroft, Ian; Apalak, M. Kemal; Pappas, Athanasios; 0000-0002-8180-5876; AGÜ, Mühendislik Fakültesi, Makine Mühendisliği Bölümü; Atahan, M. Gokhan
In this paper, we investigate the mechanical performance of metal single-lap joints featuring bio-mimicking surface textures. The inspiration for the surface textures was the foot and toe of the gecko, a creature whose ability to climb smooth shear surfaces is attributed to the mesoand micro-structures of its feet. Three surface textures were investigated: a hexagonal texture based on the central region of the foot, a lamellae-like texture based on the toe, and a mixed texture of both. Metal adherends with these textures were produced using the laser powder bed fusion (LPBF) additive manufacturing method. Finite element analysis was performed to examine the influence of surface texture on stress distribution in the adhesive layer, while mechanical testing was used to determine joint strength and failure mode. Compared to the as- printed surface texture, bio-mimicking surface textures improved the wettability of the bonding surfaces, and significantly improved the lap shear strength of the joints. Mechanical interlocking due to surface texture was more effective than the increase in bonding surface area in enhancing joint strength. The bio-mimicking textures improved the damage tolerance capacity of the joints by reducing local stress concentrations at the overlap edges of the adhesive layer and ensured that the adhesive failure type was mixed mode due to the mechanical interlocking effect. The presented novel bio-mimicked surface texture method offers promising results for both industrial applications and scientific studies.
Effect of hydrogen on fracture locus of Fe-16Mn-0.6C-2.15Al TWIP steel
(PERGAMON-ELSEVIER SCIENCE LTD, THE BOULEVARD, LANGFORD LANE, KIDLINGTON, OXFORD OX5 1GB, ENGLAND, 2020) Bal, Burak; Cetin, Baris; Bayram, Ferdi Caner; Billur, Eren; AGÜ, Mühendislik Fakültesi, Makine Mühendisliği Bölümü
Effect of hydrogen on the mechanical response and fracture locus of commercial TWIP steel was investigated comprehensively by tensile testing TWIP steel samples at room temperature and quasi-static regime. 5 different sample geometries were utilized to ensure different specific stress states and a digital image correlation (DIC) system was used during tensile tests. Electrochemical charging method was utilized for hydrogen charging and microstructural characterizations were carried out by scanning electron microscope. Stress triaxiality factors were calculated throughout the plastic deformation via finite element analysis (FEA) based simulations and average values were calculated at the most critical node. A specific Python script was developed to determine the equivalent fracture strain. Based on the experimental and numerical results, the relation between the equivalent fracture strain and stress triaxiality was determined and the effect of hydrogen on the corresponding fracture locus was quantified. The deterioration in the mechanical response due to hydrogen was observed regardless of the sample geometry and hydrogen changed the fracture mode from ductile to brittle. Moreover, hydrogen affected the fracture locus of TWIP steel by lowering the equivalent failure strains at given stress triaxiality levels. In this study, a modified Johnson-Cook failure mode was proposed and effect of hydrogen on damage constants were quantified. (C) 2020 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.
Effect of pre-rolling temperature on the interfacial properties and formability of steel-steel bilayer sheet in Single Point Incremental Forming
(SAGE PUBLICATIONS LTD1 OLIVERS YARD, 55 CITY ROAD, LONDON EC1Y 1SP, ENGLAND, 2021) Hassan, Malik; Hussain, Ghulam; Ali, Aaqib; Ilyas, Muhammad; Malik, Sohail; Khan, Wasim A.; AGÜ, Mühendislik Fakültesi, Makine Mühendisliği Bölümü; Bal, Burak
The aim of this research was to investigate the effect of pre-rolling temperature on the interfacial properties in delamination modes 1 and 2; and formability in Single Point Incremental Forming (SPIF) of Steel-Steel (St-St) bilayer sheet prepared by roll bonding process. The roll bonding process was performed at three pre-rolling temperatures, 700 degrees C, 800 degrees C, and 950 degrees C, with a constant thickness reduction ratio of 58%. The bond strength and critical strain energy release rate (CSERR) were measured to characterize the interface of St-St bilayer sheet. T-peel test for mode 1 and tensile shear test for mode 2 were conducted to determine the interfacial properties. The formability of St-St bilayer sheet in SPIF was measured in terms of maximum wall angle. The results showed that the increase in pre-rolling temperature from 700 degrees C to 950 degrees C enhanced the bond strength and CSERR, in both mode 1 and 2. The enhancement in bond strength with an increase in pre-rolling temperature was 149.5% and 203% in mode 1 and 2, respectively. However, the increase in CSERR in mode 1 and 2 was 115% and 367%, respectively. The formability of St-St bilayer sheet also showed an increasing trend with an increase in pre-rolling temperature. Moreover, a consistent relation between formability and interfacial parameters was observed. It was also found that to successively deform the bilayer sheet into the desired shape, it is necessary for the sheet to be heated above the critical temperature during fabrication to facilitate good bonding between two sheets.

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