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Öğe A comparative 3d finite element computational study of stress distribution and stress transfer in small-diameter conical dental implants(Strojarski Facultet, 2021) Kalay O.C.; Karaman H.; Karpat F.; Doğan O.; Yüce, CelalettinThe implant design is one of the main factors in implant stability because it affects the contact area between the bone and the implant surface and the stress-strain distribution at the bone-implant interface. In this study, the effect of different groove geometries on stress-strain distributions in small-diameter conical implants is investigated using the finite element method (FEM). Four different thread models (rectangular, buttressed, reverse buttressed, and symmetrical profile) are created by changing the groove geometry on the one-piece implants, and the obtained results are compared. The stress shielding effect is investigated through the dimensionless numbers that characterize the load-sharing between the bone-implant. It is determined that the lowest stress distribution is observed with rectangular profiled groove geometry. Besides, it is obtained that the buttressed groove geometry minimizes the stress effects transmitted to the periphery of the implant. The symmetrical profiles had better performance than rectangular profiles in stress transfer.Öğe A comparative experimental study on the impact strength of standard and asymmetric involute spur gears(Elsevier Sci Ltd, 2021) Kalay, Onur Can; Dogan, Oguz; Yilmaz, Tufan Gurkan; Yüce, Celalettin; Karpat, FatihGears are one of the main components of the power transmission systems and are used in various fields. Problems caused by sudden load changes in mobile systems are frequently encountered today. Gear dynamics have become more influential due to demands of high power transmission capability, long life, and low-cost. However, inertial forces caused by accelerated movements of gear can have unpredictable results. The impact loads must be calculated correctly. It is inconvenient to determine the impact strength of gear via standard drop-weight test rig due to inhomogeneity and complex geometries. This study investigates how the tooth profile affects the impact load on the involute spur gears. For this reason, a special test setup and experimental approach was proposed to examine the influence of the asymmetric profile on the impact strength. It was observed that the peak force values increased by approximately 15.3% when using 20/30 degrees asymmetric profile gears in comparison with the 20 degrees/20 degrees standard design. This improvement can reach up to 25.8% in terms of peak force energy. The results indicate that the proposed novel test setup and the experimental method can be used for measuring the impact strength of asymmetric involute gears.Öğe A Novel AI-Based Method for Spur Gear Early Fault Diagnosis in Railway Gearboxes(Institute of Electrical and Electronics Engineers Inc., 2020) Karpat, F.; Dirik, A.E.; Dogan, O.; Kalay, O.C.; Korcuklu, B.; Yüce, CelalettinArtificial intelligence (AI) applications have started to take place in our lives due to increasing data collection and processing capabilities with developing technology. In this regard, AI-based early fault diagnosis technologies, which have started to gain reliability in automotive, aviation, and wind turbine fields, have begun to use for railway gearboxes in terms of defect detection and predictive maintenance. Gears are one of the most significant components of powertrain systems. The AIbased fault diagnosis has become more prominent in recent years to predict the remaining useful life of gearbox systems. The gearbox early fault diagnosis plays an important role in both security and reducing high maintenance costs. This issue is of great importance in terms of rail vehicle safety and reliability in a medium to long term perspective. This paper deals with an approach of transferability to railway gearboxes of AI-based gear early fault diagnosis methods from other industries. A vibration-based early fault diagnosis approach and test setup are proposed for railway gearboxes. Early gear crack diagnosis is performed using MATLAB with machine learning algorithms. The proposed test setup allows different degrees of tooth cracks in railway gearboxes to be detected at different operating speeds. As a result, it is observed that the proposed AI-based approach is suitable to identify railway gearbox faults and can be adaptable in rail-based transportation systems. © 2020 IEEE.Öğe Biofabrication techniques for neural tissue engineering(Elsevier, 2023) Khandaker, Morshed P.H.; Progri, Helga; Kalay, Onur Can; Gürkan Yılmaz, Tufan; Yüce, Celalettin; Karpat, FatihMany researchers fabricated tissue-engineered neural scaffolds to understand brain functions and characteristics in vitro and in vivo. A functional neural scaffold contains a microenvironment for neural cell adhesion that allows regenerating neurons to grow in the damaged brain areas caused by disease and injury and promotes quick recovery. The purpose of this chapter is to explore the current state of research addressing recent advances in electrospun nanofibers-based fabrication techniques for generating neural tissue engineering scaffolds. The chapter will present the impact of nanofibrous material components commonly used in the neural scaffold on scaffolds' structure, properties, and biological efficiency. The following will be reported for each electrospun-based neural tissue scaffold: (1) materials and methods for manufacturing the neural scaffold, (2) structure of the generated scaffold, (3) impact of the material components' composition on the scaffold properties. Finally, we will comment on each electrospun-based neural tissue scaffold's uniqueness, limitations, and potential applications. © 2023 Elsevier Ltd. All rights reserved.Öğe Convolutional neural networks based rolling bearing fault classification under variable operating conditions(Institute of Electrical and Electronics Engineers Inc., 2021) Karpat F.; Kalay O.C.; Dirik A.E.; Dogan O.; Korcuklu B.; Yüce, CelalettinRolling bearings are key machine elements used in various fields such as automotive, machinery, aviation, and wind turbines. Over time, faults may occur in bearings due to variable operating speeds and loads, contamination, etc., and this may cause a severe reduction in performance. In the future, an undetected bearing fault can lead to a fatal breakdown and substantial economic losses or even human casualties. Thus, bearing early fault diagnosis emerges as a critical and up-to-date topic. It is possible to obtain vibration, acoustic, motor current, etc., data that contain crucial diagnostics information regarding the health conditions of mechanical systems with various sensor technologies. With the era of big data, artificial intelligence (AI) algorithms have started to be utilized frequently in industrial applications. In this regard, convolutional neural networks (CNN) are increasingly popular with their capability to capture fault information without expert knowledge. This paper deals with a bearing fault diagnosis method based on one-dimensional convolutional neural networks (1D CNN) using vibration data. A multi-class classification problem was solved by examining different operating conditions for three health classes. Therefore, healthy state, inner raceway, and outer raceway faults were detected under variable operating speeds (900 and 1500 rpm) and loads (0.1 and 0.7 Nm). The effectiveness of the proposed 1D CNN method was evaluated with the Paderborn University (PU) dataset. As a result, rolling bearing early fault diagnosis was performed with an accuracy of 93.97%. It was observed that the proposed method was suitable for bearing fault diagnosis and can be utilized to optimize the rotary machinery maintenance costs by early fault detection.Öğe Effects of drive side pressure angle on gear fatigue crack propagation life for spur gears with symmetric and asymmetric teeth(American Society of Mechanical Engineers (ASME), 2019) Karpat, F.; Dogan, O.; Yilmaz, T.; Yüce, Celalettin; Kalay, O.C.; Karpat, E.; Kopmaz, O.Today gears are one of the most crucial machine elements in the industry. They are used in every area of the industry. Due to the high performances of the gears, they are also used in aerospace and wind applications. In these areas due to the high torques, unstable conditions, high impact forces, etc. cracks can be seen on the gear surface. During the service life, these cracks can be propagated and gear damages can be seen due to the initial cracks. The aim of this study is to increase the fatigue crack propagation life of the spur gears by using asymmetric tooth profile. Nowadays asymmetric gears have a very important and huge usage area in the industry. In this study, the effects of drive side pressure angle on the fatigue crack propagation life are studied by using the finite element method. The initial starting points of the cracks are defined by static stress analysis. The starting angles of the cracks are defined constant at 45°. The crack propagation analyses are performed in ANSYS SMART Crack-Growth module by using Paris Law. Four different drive side pressure angles (20°-20°, 20°-25°, 20°-30° and 20°-35°) are investigated in this study. As a result of the study the fatigue crack propagation life of the gears is increased dramatically when the drive side pressure angle increase. This results show that the asymmetric tooth profile not only decrease the bending stress but also increase the fatigue crack propagation life strongly. Copyright © 2019 ASME.Öğe Effects of rim thickness and drive side pressure angle on gear tooth root stress and fatigue crack propagation life(Elsevier Ltd, 2021) Doğan, O.; Yüce, Celalettin; Karpat, F.Gears are the most significant machine elements in power transmission systems. They are used in almost every area of the industry, such as small watches to wind turbines. During the power transmission, gears are subjected to high loads, even unstable conditions, high impact force can be seen. Due to these unexpected conditions, cracks can be seen on the gear surfaces. Moreover, these cracks can propagate, and tooth or body failures can be seen. The fatigue propagation life is related to the gear tooth root stress. If the root stresses decrease, the fatigue life of the gears will increase. In this study, standard and non-standard (asymmetric) gear geometries are formed for four different rim thicknesses and four different pressure angles to examine fatigue crack propagation life. Moreover, the effects of the rim thickness and drive side pressure angle on the root stress are investigated. The static stress analyses are carried out to determine the starting points of the cracks, and the maximum point of the stress is defined as the starting point of the cracks. Fatigue crack propagation analyzes are performed for gears whose crack starting points are determined. The static stress analyses are conducted in ANSYS Workbench; similarly, the fatigue propagation analysis is performed in ANSYS smart crack growth. In this way, the directions of the cracks are determined for different rim thicknesses and drive side pressure angles. Besides, the number of cycles and da/dN graphs is obtained for all cases depending on crack propagation. As a result of the study, maximum stress values were decreased by 66%. The fatigue propagation life was increased approximately fifteen times by using the maximum drive side pressure angle and optimum rim thickness. © 2021 Elsevier LtdÖğe Experimental measurement and numerical validation of single tooth stiffness for involute spur gears(Elsevier Sci Ltd, 2020) Karpat, Fatih; Yüce, Celalettin; Dugan, OguzDynamic characteristics of the spur gears have become a growing field in recent years, due to the high operating speeds and increased power and torque demands. Tooth stiffness is one of the most influential contributing factors of the dynamic behavior of the gear pairs, which varies continuously during the meshing operation. Therefore, the tooth stiffness of the spur gears must calculate accurately. Generally, to calculate the tooth and mesh stiffness of spur gears, analytical equations are used. In this study, single tooth stiffness of involute spur gear was measured experimentally. A special test rig for this purpose was designed, and an experimental technique was proposed to investigate the effects of drive side pressure angle on the stiffness. The validation process of this study was performed using the finite element method. The experiments were repeated in ANSYS Workbench, and the elastic deformations were calculated. Experimental and numerical results were found to be generally consistent. Results showed that, the single tooth stiffness increase nearly 38% with the increase in drive side pressure angle from 20 degrees to 35 degrees. Single tooth stiffness of gear types manufactured by non-traditional methods, including additive manufacturing and forged bimetallic gears, can be investigated experimentally with this technique. (C) 2019 Elsevier Ltd. All rights reserved.Öğe FAULT DIAGNOSIS WITH DEEP LEARNING FOR STANDARD AND ASYMMETRIC INVOLUTE SPUR GEARS(American Society of Mechanical Engineers (ASME), 2021) Karpat, Fatih; Dirik, Ahmet Emir; Kalay, Onur Can; Yüce, Celalettin; Doğan, Oğuz; Korcuklu, BurakGears are critical power transmission elements used in various industries. However, varying working speeds and sudden load changes may cause root cracks, pitting, or missing tooth failures. The asymmetric tooth profile offers higher load-carrying capacity, long life, and the ability to lessen vibration than the standard (symmetric) profile spur gears. Gearbox faults that cannot be detected early may lead the entire system to stop or serious damage to the machine. In this regard, Deep Learning (DL) algorithms have started to be utilized for gear early fault diagnosis. This study aims to determine the root crack for both symmetric and asymmetric involute spur gears with a DL-based approach. To this end, single tooth stiffness of the gears was obtained with ANSYS software for healthy and cracked gears (50-100%), and then the time-varying mesh stiffness (TVMS) was calculated. A six-degrees-of-freedom dynamic model was developed by deriving the equations of motion of a single-stage spur gear mechanism. The vibration responses were collected for the healthy state, 50% and 100% crack degrees for both symmetric and asymmetric tooth profiles. Furthermore, the white Gaussian noise was added to the vibration data to complicate the early crack diagnosis task. The main contribution of this paper is that it adapts the DL-based approaches used for early fault diagnosis in standard profile involute spur gears to the asymmetric tooth concept for the first time. The proposed method can eliminate the need for large amounts of training data from costly physical experiments. Therefore, maintenance strategies can be improved by early crack detection.Öğe Investigations on the microstructure and mechanical properties of laser welded dissimilar galvanized steel-aluminum joints(Springer London Ltd, 2019) Yüce, Celalettin; Karpat, Fatih; Yavuz, NurettinIn this study, galvanized high-strength steel and aluminum alloy sheets were laser-welded in zero-gap lap joint configuration. In order to determine the influences of the heat input levels, microstructural and mechanical properties of the joints were investigated. The weld bead geometry, microstructure, and intermetallic phases at the interface of welded joints were investigated using an optical microscope and scanning electron microscopy (SEM) with energy-dispersive spectroscopy (EDS) at different heat input levels. Mechanical properties and microhardness distribution of the welded joints were examined according to the weld bead dimension. The results revealed that there is a correlation between the weld seam geometry and intermetallic phase formation. At relatively high heat input level, the penetration depth increased, and thick Al-rich intermetallic layer was observed at the interface of the weld seam, which deteriorated the tensile strength of the joint. It has been found that without the need for any additional precaution, the thickness of the IMC layer can be limited to 5-15 mu m when the optimum welding parameters were conducted. The experimental results showed that with limited heat input and penetration depths, up to 108.7-N/mm tensile strength could be achieved and fracture initiated at the weld seam-steel interface.Öğe Multi-objective optimisation for indentation rate, nugget diameter and tensile load in resistance spot welding using Taguchi-based grey relational analysis(Inderscience Publishers, 2021) Yüce, CelalettinIn this study, a multi-objective optimisation method based on grey relational analysis with weighted responses is conducted to optimise the RSW parameters of electrode force, welding current, and welding time. Three objectives, such as indentation rate, nugget diameter, and tensile load, are simultaneously optimised. In order to assign the optimum level for each parameter individually, the Taguchi technique was applied. ANOVA results showed that the most influential parameters on indentation rate, nugget diameter, and tensile load are welding current, welding time, and welding current, respectively. In the grey relational analysis, the grey relational grades were obtained using weighted responses. The weight factors for the indentation rate, nugget diameter, and tensile load are 33.24%, 35.67%, and 31.1%, respectively. The optimum parameter combination was obtained as 2,500 N, 9 kA, and 0.5 s. Under these parameter combinations, indentation rate, nugget diameter, and tensile load were 26.2%, 8.34 mm, and 20.04 kN, respectively.Öğe Paslanmaz Çelik Malzemelerin Fiber Lazer Kesiminde Proses Parametrelerinin Optimizasyonu(Bursa Uludağ Üniversitesi, 2019) Yüce, CelalettinGünümüzde lazer ışını ile kesme yöntemi modern malzeme kesme yöntemleri arasında maliyet ve kalite açısından üstün özellikleri nedeni ile öne çıkmaktadır. Özellikle lazer kesme yöntemi, imalat sektöründeki birçok uygulamada kullanılan paslanmaz çeliklerin kesilmesinde çok önemli avantajlara sahiptir. Bu çalışma kapsamında 304 kalite paslanmaz çelik malzemenin fiber lazer ile kesilmesinde lazer gücü, kesme hızı ve odak mesafesinin kesilen yüzeylerin pürüzlülüğü ve kerf genişliği üzerindeki etkileri incelenmiştir. Box-Behnken deney tasarımına göre parametre çiftleri belirlenerek kesme işlemi gerçekleştirilmiş ve yüzey pürüzlülükleri ile kerf genişlikleri ölçülmüştür. İşlem parametrelerinin tekil ve etkileşimli etkilerini belirlemek için varyans analizi (ANOVA) uygulanmıştır. Yüzey pürüzlülükleri ve kerf genişlikleri için cevap yüzeyi fonksiyonları belirlenmiş ve istenebilirlik fonksiyonu yaklaşımı ile optimum proses parametreleri tespit edilmiştir. Yapılan çalışma sonucunda yüzey pürüzlülüğü ve kerf genişliği üzerindeki en etkili parametrenin odak mesafesi olduğu, ilerleme hızının etkisinin sınırlı kaldığı görülmüştür.Öğe PMMA ve ABS MALZEMELERİN LAZER İLETİM KAYNAĞI İLE BİRLEŞTİRİLMESİNDE PROSES PARAMETRE ETKİLERİNİN İNCELENMESİ(Bursa Uludağ Üniversitesi, 2021) Küçükoğlu, Ayça; Yüce, Celalettin; Karpat, Fatih; Okar, Halil; Sözer, İbrahim Emrah; Kurt, NiyaziOtomotiv endüstrisindeki araç aydınlatma sistemlerinde kullanılan termoplastik malzemelerin birleştirilmesinde lazer iletim kaynağı üstün özellikleri nedeni ile öne çıkmaktadır. Ancak, proses parametreleri kaynak kalitesini doğrudan etkilediği için etkilerinin tespit edilmesi oldukça önemlidir. Bu çalışmada 2,7 mm kalınlığındaki Akrilonitril bütadien stiren (ABS) ve şeffaf Polimetil metakrilat (PMMA) malzemeler LPKF Twinweld 3D 6000 lazer cihazı ile birleştirilmiştir. Lazer iletim kaynağındaki önemli parametreler olan lazer gücü, baskı kuvveti ve ilerleme hızının etkileri incelenmiştir. Yapılan çalışmada lazer gücü 20-50 W aralığında, ilerleme hızı 30-150 mm/s aralığında ve baskı kuvveti 55-85 N aralığına çalışılmıştır. Farklı parametre kombinasyonlarında birleştirilen numuneler çekme testlerine tabi tutularak mekanik dayanımları incelenmiş ve parametreler ile ilişkilendirilmiştir. Yapılan testler sonucunda en yüksek ortalama mekanik dayanım ve ortalama kopma uzaması 30 W, 70 mm/s ve 70 N parametre kombinasyonunda elde edilmiştir. Diğer tüm parametrelerin sabit tutulduğu durumda mekanik dayanım üzerindeki en etkili parametrenin lazer gücü olduğu görülmüştür.
