Makine Mühendisliği Bölümü Koleksiyonu

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https://hdl.handle.net/11468/10529

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Investigation failure behaviours of notched composite plates repaired with using adhesive and patch
(Taylor & Francis Inc, 2024) Çelik, Abdullah; Turan, Kadir; Arman, Yusuf
In this study, the damage behaviors of different type-notched composite plates repaired with composite patches were investigated experimentally and numerically. Eight-layer woven glass fiber reinforced epoxy resin matrix composite plates and epoxy-based adhesive were used as materials. Notch type's variations, adhesive thickness, patch length; double-side repair and single-side repair were used as parameter. Although the same size patch was used, the load values varied due to the different positions of the notches. Notched composite samples with the same area dimensions but different locations have different tensile strength values. Patching and bonding processes have different effects on notched samples with different tensile strength values. A feature of this study is that many parameters were compared for many samples under the same experimental conditions in order to improve repair quality and durability in an understandable way. As a result of the repair process, the failure loads were increased from 47% to 307% ratios according to parameters.
A method for the assignment of zeros using frequency response functions
(Springer Heidelberg, 2024) Hüseyinoğlu, Mesut
PurposeIn many engineering structures, undesirable harmonics can occur due to changes in operating conditions. The effects of these unwanted harmonics can be eliminated by assigning the zeros of point or cross Frequency Response Functions (FRFs) of the structure to the frequencies of the unwanted harmonics. In this study, a method is proposed for assigning the zeros of point or cross FRFs to particular frequencies.MethodsThe method is based on Sherman-Morrison (SM) formula known in matrix theory. The inverse structural modification problem was investigated by making spring modifications on a structure to assign zeros.ResultsThe required modifications are calculated by solving the set of equations containing nonlinear combinations of the spring coefficients.ConclusionThere is no need for a physical or modal model of the structure because FRFs are used directly in the method. Therefore, it is quite practical in applications. The accuracy and efficiency of the presented method are illustrated by different numerical simulations and successful results are obtained.
Investigation of the translaminar fracture behavior of the fiber-reinforced composites stitched perpendicular to their plane
(Springer Heidelberg, 2024) Asan, Ahmet Murat; Kaman, Mete Onur; Dag, Serkan; Erdem, Serkan; Turan, Kadir
To increase the fracture toughness, the two-dimensional laminated textiles can be stitched with fibers throughout their thickness. But the stitch properties effect the mechanical behavior of the composite plates. Because of this reason, in this study, translaminar toughness of carbon fiber composites stitched with different densities and angles is investigated for the first time, experimentally and numerically. In the experimental study, fracture tests are performed according to ASTM E1922 standard and critical load; crack tip opening displacements and fracture toughness values are determined. In the numerical study, the critical stress intensity factor is determined using the M-integral method and the displacement correlation method. Modeling and fracture toughness analyses are performed in ANSYS finite element package. In order to find the crack propagation directions numerically, the model prepared in ANSYS is transferred to the LS-DYNA program and progressive failure analysis is performed. Stitching the layered composites perpendicular to the plane has increased the fracture toughness by 23.5-80.6% for plain-woven composites and 1.41-9.38% for UD composites. Fracture toughness values have increased with increasing stitch density. This increase is highest in the specimen stitched in the longitudinal direction where the toughness increased by similar to 15.4% with 100% increase in stitch density. The highest fracture toughness is obtained with double-directional stitching with a stitch density of 1.25 mm. It is determined that the designed heterogeneous model gives more accurate results than the homogeneous model by similar to 1-6%.
FE analyzing of layout types for multi-hole extrusion dies
(Springer Int Publishing Ag, 2014) Bingöl, S.; Keskin, M. S.; Ayer, O.; Sarıkaya, K.; Burucu, O.; Alipur, P.
Extrusion method is an important bulk-forming process to transform materials into semi-finished products in the form of bar, strip, and solid section as well as tubes and hollow sections. One of the basic considerations of die design is to determine the number of die openings based on the shape and size of the profile. In this study, variation of the extrusion load and temperature is investigated for different number and layout of die openings by finite element analysis. Three types of layouts, radial layout of a multi-hole die, flat layout of a multi-hole die and orientation of a shape around its center of gravity, were simulated with four openings in the dies. Moreover, the most commonly used type of them was also simulated for different number of openings in the die to compare the effect of the openings number on the extrusion.
Thermodynamic analysis of a refrigeration system operating with R1234yf refrigerant
(Springer, 2018) Oruç, Vedat; Devecioğlu, Atilla G.
[Abstract Not Available]
Retrofitting of R-22 Air-conditioning system with R1234ze(E)
(Springer International Publishing Ag, 2020) Devecioğlu, Atilla G.; Oruç, Vedat
In this study, the effect on energy parameters and total equivalent warming impact (TEWI) using R1234ze(E) as a substitute for R22 in an air-conditioning device was investigated. The R22 system was retrofitted with R1234ze(E) changing compressor oil. The experimental data was obtained for three different ambient temperatures (30, 35 and 40 degrees C). It was seen that the power consumption of R1234ze(E) was smaller than that of R22 about by 41%. Although the cooling capacity of R1234ze(E) was 50% lower, its coefficient of performance (COP) was reduced only by 5% compared to R22. Furthermore, refrigerant charging amount of R1234ze(E) was smaller by 16% than R22. The results indicated that TEWI value of R1234ze(E) was lower than that of R22 by 65% due to small GWP (global warming potential) value and proper COP of the alternative refrigerant tested in the study. Hence, it can be expressed that R1234ze(E) can be used in air-conditioners of small capacity as an alternative to R22.
Effect of nanoclay on the mechanical and thermal properties of glass fiber-reinforced epoxy composites
(Springer, 2024) Örçen, Gurbet; Bayram, Duygu
The efects of nanoclay (NC) addition on the thermal and mechanical properties of glass fber-reinforced epoxy composites were investigated experimentally in this study. Nanocomposite plates were produced for this purpose using three diferent NC ratios (0.5%, 1%, and 1.5% by weight). Thermal characteristics of nanocomposites were investigated using dynamic mechanical analysis, diferential scanning calorimetry, and thermogravimetric analysis. The mechanical and thermal results obtained from composites with three diferent NC ratios were compared with the results obtained from pure composites. The structures of nanocomposites were investigated with the help of SEM–EDS analyses. Furthermore, the efect of nanoclay on the failure behavior of composites was also investigated. In this study, the highest values in all mechanical properties were obtained from samples with a 1% NC-added. Obtained from 1% NC-added samples: tensile, compressive, shear strengths, elasticity modulus, shear modulus, and Poisson’s ratio values were 31.06%, 4.25%, 14.30%, 7.35%, 11.94%, and 12.5% higher, respectively, than the values obtained from pure samples. Maximum loss modulus and maximum storage modulus were obtained from samples with 1.5% and 0.5% NC-added, respectively. In samples with 1.5% NC-added, the highest Tan δ value was obtained. Glass transition temperatures increased with the added NC. It was observed that the fber–matrix interfaces were more clearly separated in the samples with 1.5% NC-added.
NF-EEG: A generalized CNN model for multi class EEG motor imagery classification without signal preprocessing for brain computer interfaces
(Elsevier Ltd, 2024) Arı, Emre; Taçgın, Ertuğrul
Objective: Brain Computer Interface (BCI) systems have been developed to identify and classify brain signals and integrate them into a control system. Even though many different methods and models have been developed for the brain signals classification, the majority of these studies have emerged as specialized models. In addition, preprocessing and signal preprocessing methods which are largely based on human knowledge and experience have been used extensively for classification models. These methods degrade the performance of real-time BCI systems and require great time and effort to design and implement the right method. Approach: In order to eliminate these disadvantages, we developed a generalized and robust CNN model called as No-Filter EEG (NF-EEG) to classify multi class motor imagery brain signals with raw data and without applying any signal preprocessing methods. In an attempt to increase the speed and success of this developed model, input reshaping has been made and various data augmentation methods have been applied to the data. Main results: Compared to many other state-of-the-art models, NF-EEG outperformed leading state-of-the-art models in two most used motor imagery datasets and achieved 93.56% in the two-class BCI-IV-2A dataset and 88.40% in the two-class BCI-IV-2B dataset and 81.05% accuracy in the classification of four-class BCI-IV-2A dataset. Significance: This proposed method has emerged as a generalized model without signal preprocessing and it greatly reduces the time and effort required for preparation for classification, prevents human-induced errors on the data, presents very effective input reshaping, and also increases the classification accuracy.
Elasto-plastic stress analysis in laminated thermoplastic composite plates with an elliptic hole
(Association for Scientific Research, 2013) Örçen, Gurbet; Gür, Mustafa
In this paper, elasto-plastic stress analysis in laminated thermoplastic composite plates having an elliptic hole in the middle is examined by using finite element method. Composite plates consist of four orthotropic laminations and bonded symmetrically [θ0/-θ0]. Uniform loadings in vertical direction are applied to the selected composite plates. The loading and reinforcement angle are gradually increased from the yield point of the plate. The load steps increased as 0.0001 MPa at each iteration. Iteration numbers are chosen 25, 50, 75 and 100. A quarter of the plate is taken into consideration due to symmetry. Elasto-plastic stresses are obtained according to load steps and orientation angles.
A method for substructure decoupling of mechanical systems by using frequency response functions
(Springer Science and Business Media Deutschland GmbH, 2024) Hüseyinoğlu, Mesut
The need for modification in many mechanical systems occurs due to the parameters that are not taken into account during the design process and the changes made on the main structure. This can be in the form of removing a substructure from the main structure. Although the dynamic properties of the main structure are known, it is important to know what the dynamic properties of the new structure will be formed by the substructure removed from the main structure. In this study, a method for substructure decoupling of mechanical systems based on the Sherman–Morrison formula is presented. The frequency response functions (FRFs) of the main structure relating to the decoupling coordinates are directly used in the developed method. The main highlight of the presented method is needed neither a physical model nor a modal model, since FRFs are directly used. It is also more useful than methods using modal properties, since a limited number of FRFs are used for decoupling coordinates.
Artificial neural networks based computational and experimental evaluation of thermal and drying performance of partially covered PVT solar dryer
(Institution of Chemical Engineers, 2024) Gupta, Ankur; Das, Biplab; Arslan, Erhan; Das, Mehmet; Koşan, Meltem; Can, Ömer Faruk
This study proposes a mixed-mode dryer with a semi-transparent photovoltaic thermal (PVT) collector for the assessment of drying and thermal performance using computational and experimental findings. The thermal behavior and fluid flow characteristics have been analyzed to optimize the air flow rate in the PVT solar dryer by considering three different inlet velocities of 0.048 m/s (Case 1), 0.096 m/s (Case 2), and 0.144 m/s (Case 3). The temperature distribution is obtained more uniformly for the PVT collector and dryer cabin in Case 2. The results of the investigation show that Case 3 has a positive impact on the PVT solar dryer performance. In numerical and experimental methods, the enhanced thermal efficiency is attained as 30.78% and 29.78% for Case 2, and 33.20% and 31.14% for Case 3, respectively, in comparison to Case 1. Case 3 has improved Reynolds and Nussselt numbers by 3.06 and 2.45 times, respectively compared to Case 1. Experimental results varied by 2.24 to 4.90% from simulated outcomes obtained from CFD. The machine learning approach of ANN has been implemented with different hidden layers network models to choose the best drying conditions by predicting the drying performance parameters.
Experimental and numerical study on the strength of aluminum extrusion welding
(MDPI, 2015) Bingöl, Sedat; Bozacı, Atilla
The quality of extrusion welding in the extruded hollow shapes is influenced significantly by the pressure and effective stress under which the material is being joined inside the welding chamber. However, extrusion welding was not accounted for in the past by the developers of finite element software packages. In this study, the strength of hollow extrusion profile with seam weld produced at different ram speeds was investigated experimentally and numerically. The experiments were performed on an extruded hollow aluminum profile which was suitable to obtain the tensile tests specimens from its seam weld's region at both parallel to extrusion direction and perpendicular to extrusion direction. A new numerical modeling approach, which was recently proposed in literature, was used for numerical analyses of the study. The simulation results performed at different ram speeds were compared with the experimental results, and a good agreement was obtained.
Effect of cobalt nanoparticles on mechanical properties of Sn–58Bi solder joint
(Springer, 2022) Bashir, M. Nasir; Saad, Hafız Muhammad; Rizwan, Muhammad; Bingöl, Sedat; Channa, Iftikhar Ahmed; Haseeb, Abdul S.Md Abdul; Naher, Sumsun
Brittle phases are responsible for crack formation and propagation in tin–bismuth (Sn–58Bi) solder material. The purpose of this work is to investigate the effects of various cobalt (Co) nanoparticle (NP) concentrations on the tensile properties of the Sn–58Bi solder matrix. Different aging times were studied to find out the effect of Co NP on ultimate tensile strength. Tin–bismuth solder joints of different Co NP concentrations of 0%, 0.5%, 1%, and 2% were prepared. The reflow process was done at 180 °C for 1 min. Scanning Electron Microscopy and Energy-Dispersive X-ray spectroscopy were used to analyze the solder joints. The tensile test was carried out for the Sn–58Bi and Sn–58Bi–xCo (x = 0.5, 1, and 2) solder joints. The tensile test was run before and after aging time. The tensile results reveal that the addition of Co NP increased the tensile strength significantly at different concentrations of Co NP. The Tensile test revealed that ductility was improved as the temperature was increased. As the aging time increased, the ultimate tensile strength of all samples decreased.
Flow frictional resistance in pneumatic conveying of solid particles through inclined lines
(Elsevier, 2002) Çarpınlıoğlu, Melda Ö.; Özbelge, Tülay A.; Oruç, V.
The frictional behaviour of fully suspended dilute flow of granular solid particles in air through the transport lines of various angularities, α, with the horizontal plane in the range of 0°≤α≤30° is presented in this paper. The friction factor determination is based on the measurements of local static pressure gradients. The experiments were mainly directed to determine the effects of transport line inclination, particle physical characteristics, the ratio of mass flow rate of particles to that of air, Mp/Ma, and the flow Reynolds number, Re, on the two-phase friction factor. A variety of solid particles whose average diameter, dp, and apparent density, ρp, being in the respective ranges of 75.5 μm≤dp≤275 μm and 467.95 kg/m3≤ρp≤824.17 kg/m3 were used, with 5%≤Mp/Ma≤30%, at 50 000≤Re≤100 000, for this purpose. The results were expressed in terms of two-phase friction factor, fp+a, correlations proposed under the light of the state of art. The experimental data was also evaluated via solids friction factor, fs, correlated previously by Özbelge [Int. J. Multiphase Flow 10 (1984) 459] based on a theoretical analysis of vertical upward flow fields [Int. J. Multiphase Flow 9 (1983) 437] as well as to confirm the validity of the method in non-vertical upward flows.
Theoretical approximations to analyse the onset of self-excited oscillations in flow through collapsible tubes
(Sage Publications INC., 2010) Oruç, V.; Çarpınlıoğlu, M.Ö.
In this study, flow through collapsible tubes is analysed theoretically for the case of the onset of collapse which induces self-excited oscillations. The basic tools in the theoretical calculations are the linear stability theory and the tube law. The experimental data in the form of measured oscillation frequency at the onset of collapse of an elastic tube is supplied as a base input parameter for the theoretical approximations. The calculations offer a possibility for estimating the unmeasured parameters such as critical oscillation speed, speed index, and tube cross-sectional area at the onset of collapse. It was seen by referring to the obtained results that theoretical predictions agreed with the experimental measurements.
Experimental assessment of the retrofit of an internal heat exchanger in refrigeration systems: The effect on energy performance and system operation
(Pergamon-Elsevier Science LTD, 2020) Oruç, Vedat; Devecioğlu, Atilla G.
The aim of this experimental study is to retrofit a refrigeration system with an internal heat exchanger (IHX) and to assess its effect on the energy performance of the system. The separate IHX cases in the investigation are tube-in-tube type and plate type and these are also compared with the system without any IHX. R404A and R442A refrigerants are tested in a single stage vapour compression refrigeration system. In the experimental work evaporation temperatures of −5°C and 0°C are considered while the condenser temperatures are 30°C and 50°C. The results indicated that both utilised types of IHX elements improved the energy performance of the system while the benefit with the tested plate type IHX case was better. Also, the alternative refrigerant R442A can be preferred as a substitute for R404A due to the enhanced energy performance of the system. The thermal effectiveness of IHX devices and the volumetric efficiency of the compressor are considered as well for the evaporation and condenser temperatures covered.
Experimental investigation of a solar air heater with copper wool on the absorber plate
(Taylor & Francis, 2020) Biçer, Ayşe; Devecioğlu, Atilla G.; Oruç, Vedat; Tuncer, Zafer
The thermal performance of a novel solar air heater was experimentally studied in this paper. For this aim, a new solar air collector was designed using copper wool on its absorber plate to be a selective surface. Hence, the area of absorber plate was enhanced to absorb much amount of heat energy. The experimental study was conducted for both cases (presence and absence of copper wool on the absorber plate) to determine the effect of copper wool on the thermal efficiency of the collector. The mass flow rate values of the study were 0.035 and 0.044 kg/s. The results pointed out that fluid temperature at outlet of collector with copper wool was increased by about 8 to14%. Therefore, these collectors may be suitable for space heating and drying of food applications. However, copper wool caused more pressure loss through the collector by 40% compared to simple case of collector. The thermal efficiency of the collectors was obtained as 34 to 83% depending on experimental variable parameters. Similarly, effective efficiency of collectors was computed to be 24 to 70%. It is found that efficiency of the collector was improved when using copper wool on the absorber plate as well as increasing mass flow rate of air.
Experimental comparison of R404A and R452A in refrigeration systems
(Taylor & Francis, 2021) Devecioğlu, Atilla G.; Oruç, Vedat
In this study, R404A and R452A refrigerants used in refrigeration systems were compared experimentally. The energy performance of the system was investigated for widely used evaporation temperatures (−5, 0, +5 °C) and condenser temperatures (25, 35, 45 °C). It was seen that COP was higher but power consumption of system was lower using R452A as a substitute for R404A. When R452A was used, COP was improved about by 3% to 8% compared to R404A. Furthermore, cooling capacity decreased about by 2% for condenser temperatures of 25 and 35 °C while it increased at condenser temperature of 45 °C. Power consumption of system was also reduced nearly by 5%. Mass flow rate of refrigerant was lower when the system was operated with R452A. In the middle term, R452A could be a suitable alternative refrigerant for commercial refrigeration applications due to its low GWP value and better energy performance compared to R404A.
Drop-in assessment of plug-in R404A refrigeration equipment using low-global warming potential mixtures
(Oxford University Press, 2022) Devecioğlu, Atilla G.; Oruç, Vedat
This study analyzes the performance of plug-in refrigeration equipment, which has the condenser on the system and delivers heat to the indoor medium, using mixtures with low-global warming potential (GWP). The theoretical drop-in replacement of R404A that is widely used in the plug-in refrigeration equipment is investigated utilizing refrigerants with GWP < 150 such as R454C, R455A, R457A and R465A. In the study, four cases of evaporation temperatures (−25°C, −15°C, −5°C and 0°C) and two cases of condenser temperatures (30°C and 40°C) were considered for freezer and chiller modes of the equipment. According to the obtained results, the power consumption of R404A is determined to be higher than other refrigerants for both studied condenser temperatures. The mass flow rate circulating in the system decreases using R404A’s alternatives. Furthermore, the highest coefficient of performance (COP) is reached with R457A, which has a greater COP than R404A about by 8.5%. The compressor discharge pressures of alternative refrigerants are smaller compared with R404A as well. The reduction in CO2 emission is also presented in terms of total equivalent warming impact (TEWI) computations. The conducted analysis points out that it will be possible to use directly the investigated mixtures (especially R457A and R455A are most promising ones) in plug-in refrigeration devices as alternatives to R404A without performing any constructional modification in the system.
Flow around a cylinder surrounded by a permeable cylinder in shallow water
(Springer, 2012) Özkan, Göktürk M.; Oruç, Vedat; Akıllı, Hüseyin; Şahin, Beşir
The change in flow characteristics downstream of a circular cylinder (inner cylinder) surrounded by an outer permeable cylinder was investigated in shallow water using particle image velocimetry technique. The diameter of the inner cylinder and the water height were kept constant during the experiments as d = 50 mm and h w = 25 mm, respectively. The depth-averaged free-stream velocity was also kept constant as U = 170 mm/s which corresponded to a Reynolds number of Red = 8,500 based on the inner cylinder diameter. In order to examine the effect of diameter and porosity of the outer cylinder on flow characteristics of the inner cylinder, five different outer cylinder diameters (D = 60, 70, 80, 90 and 100 mm) and four different porosities (β = 0.4, 0.5, 0.6 and 0.7) were used. It was shown that both porosity and outer cylinder diameter had a substantial effect on the flow characteristics downstream of the circular cylinder. Turbulent statistics clearly demonstrated that in comparison with the bare cylinder (natural case), turbulent kinetic energy and Reynolds stresses decreased remarkably when an outer cylinder was placed around the inner cylinder. Thereby, the interaction of shear layers of the inner cylinder has been successfully prevented by the presence of outer cylinder. It was suggested by referring to the results that the outer cylinder having 1.6 ≤ D/d ≤ 2.0 and 0.4 ≤ D/d ≤ 0.6 should be preferred to have a better flow control in the near wake since the peak magnitude of turbulent kinetic energy was considerably low in comparison with the natural case and it was nearly constant for these mentioned porosities β, and outer cylinder to inner cylinder diameter ratios D/d.

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