ahmet çetkin - Academia.edu (original) (raw)

Papers by ahmet çetkin

This study is based on the joint quality of zinc-coated EN 10346: 2015 DX52D + Z quality steel sh... more This study is based on the joint quality of zinc-coated EN 10346: 2015 DX52D + Z quality steel sheets with having different thicknesses, which are preferred in the automotive industry due to their formability. Joining problems in clinching applications with different positions and sheets of different thicknesses are discussed and experimental outcomes are discussed in terms of strength of joints. As a result of the tests carried out according to the standards, it has been found that the joining of the sheets with thickness close to each other is relatively good, as the thickness difference increases, the joint quality decreases and sometimes the joint does not form. It has been also found that if the thinner sheet is placed on the bottom die during clinching, a better joint strength is obtained. EN 10346: 2015 DX52D+Z Plakaların Form-Punta Bağlantı Performansları Anahtar kelimeler Perçinleme; Bağlantı dayanımı; Metal şekillendirme; Bağlantı kalitesi; Bağlantı testi; Birbirine kilitlenme Öz Bu çalışma, şekillendirme kabiliyeti nedeniyle daha çok otomotiv endüstrisinde tercih edilen çinko kaplanmış farklı kalınlıktaki EN 10346:2015 DX52D+Z kalite çelik levhaların clinching teknolojisi ile yapılan bağlantılarının bağlantı kalitesi üzerine yapılmıştır. Özellikle clinching uygulamalarında karşımıza çıkan farklı pozisyon ve farklı kalınlıktaki levha birleştirmelerindeki bağlantı problemleri ele alınmış ve bağlantı kalitesi için genel bir değerlendirme yapılmıştır. Standartlara uygun olarak gerçekleştirilen testler sonucunda birbirlerine yakın kalınlıktaki levhaların bağlantılarının nispeten iyi olduğu, kalınlık farkının arttığında, bağlantı kalitesinin azaldığı ve bazen bağlantıların gerçekleşmediği görülmüştür. Bağlantı sırasında daha ince olan plakanın alt matris tarafında olması, çok daha iyi bir bağlantı dayanımının sağlanabilmesinin bir gereği olduğu belirlenmiştir.

Makine Teknolojileri Elektronik Dergisi (elektronik), 2016

El-Cezeri Fen ve Mühendislik Dergisi, 2021

Gears are widely used in motion transmission in machines. For this reason, they work in very diff... more Gears are widely used in motion transmission in machines. For this reason, they work in very difficult conditions. Some damage may occur in the gears depending on the operating conditions. These damages are bending fatigue, pitting, micropitting, scuffing, and wear. This study investigates surface fatigue damages by keeping fixed the material of test gear teeth, rotation speed, lubricating oil, and the applied load, and changing the operating temperatures of oil. In experimental studies, pre-and post-test weights of gear teeth samples were established, surface roughnesses were measured, and micrograph examinations were carried out on teeth surface. As a result, surface roughness and wear were established to increase in proportion to the rise in temperature of oil. Maximum pitting size was measured at about 870 µm at 90 ºC oil temperature, and the lowest pitting size was measured as approximately 450 µm in tests performed at 30 ºC.

Afyon Kocatepe University Journal of Sciences and Engineering, 2021

This study is based on the joint quality of zinc-coated EN 10346: 2015 DX52D + Z quality steel sh... more This study is based on the joint quality of zinc-coated EN 10346: 2015 DX52D + Z quality steel sheets with having different thicknesses, which are preferred in the automotive industry due to their formability. Joining problems in clinching applications with different positions and sheets of different thicknesses are discussed and experimental outcomes are discussed in terms of strength of joints. As a result of the tests carried out according to the standards, it has been found that the joining of the sheets with thickness close to each other is relatively good, as the thickness difference increases, the joint quality decreases and sometimes the joint does not form. It has been also found that if the thinner sheet is placed on the bottom die during clinching, a better joint strength is obtained. EN 10346: 2015 DX52D+Z Plakaların Form-Punta Bağlantı Performansları Anahtar kelimeler Perçinleme; Bağlantı dayanımı; Metal şekillendirme; Bağlantı kalitesi; Bağlantı testi; Birbirine kilitlenme Öz Bu çalışma, şekillendirme kabiliyeti nedeniyle daha çok otomotiv endüstrisinde tercih edilen çinko kaplanmış farklı kalınlıktaki EN 10346:2015 DX52D+Z kalite çelik levhaların clinching teknolojisi ile yapılan bağlantılarının bağlantı kalitesi üzerine yapılmıştır. Özellikle clinching uygulamalarında karşımıza çıkan farklı pozisyon ve farklı kalınlıktaki levha birleştirmelerindeki bağlantı problemleri ele alınmış ve bağlantı kalitesi için genel bir değerlendirme yapılmıştır. Standartlara uygun olarak gerçekleştirilen testler sonucunda birbirlerine yakın kalınlıktaki levhaların bağlantılarının nispeten iyi olduğu, kalınlık farkının arttığında, bağlantı kalitesinin azaldığı ve bazen bağlantıların gerçekleşmediği görülmüştür. Bağlantı sırasında daha ince olan plakanın alt matris tarafında olması, çok daha iyi bir bağlantı dayanımının sağlanabilmesinin bir gereği olduğu belirlenmiştir.

Journal of Materials and Mechatronics: A, Dec 1, 2021

Metal forming, machining, crashing, etc. in simulations, not only the boundary conditions are giv... more Metal forming, machining, crashing, etc. in simulations, not only the boundary conditions are given perfectly, but also another important input is the properties of the material used. Defining these properties correctly increases the confidence in using the results of the simulation in practice. One of the most well-known parametric models representing the stress-strain relationship at different temperatures and strain rates in simulation programs is the Johnson-Cook flow stress model and ductile damage model. However, the process of obtaining JC parameters for the material is quite long and tiring. Combined evaluation of multiple tests and simulation results, curve fitting, regression and optimization procedures necessitate an organized mathematical operation process. With the program written, it was tried to get both fast and accurate parameter results by using different mathematical solution methods. Parameter constants are obtained automatically by entering different test types, test device result format and simulation report format entries in a hierarchical order using the written program. The user can visually check the tests and results with on the same graphics and intervene in the detection of critical points of the tests when necessary. By using different curve fitting algorithms, finding the most suitable parameters is provided.

Özet Bu çalışma, form punta yöntemiyle ile oluşturulan bağlantıların mekanik özelliklerinin incel... more Özet Bu çalışma, form punta yöntemiyle ile oluşturulan bağlantıların mekanik özelliklerinin incelenmesi amacıyla yapılmıştır. Form punta bağlantıları için özellikle otomotiv endüstrisinde kullanılan galvanizli(St1314) çelik ve alüminyum(Al5754) plakalar seçilmiştir. Numunelere, sırasıyla TS EN ISO 14270 ve TS EN ISO 14273 standardına uygun olarak kesme deneyi ve mekanize soyma deneyleri uygulanmıştır. Keza farklı yerleşim sırası ve farklı plaka kalınlıklarının etkilerini incelemek için mikroskobik analizler de uygulanmıştır. Üstte galvanizli çelik altta alüminyum levhadan oluşan kombinasyonun dayanımı tam tersi kombinasyondan yaklaşık iki kat daha büyüktür. Büyük değerdeki plaka kalınlığı oranlarının, kırılma ve ayrılmalara neden olduğu gözlemlenmiştir. Abstract In this study, mechanical properties of the joints which made with the mechanic clinching were investigated. Galvanized steel (St1314) which is used especially in automotive industry and aluminum (Al5754) sheets were selecte...

Bu makalede kenarlari serbest, izotropik dikdortgensel plakalardaki titresim problemlerinin, Dife... more Bu makalede kenarlari serbest, izotropik dikdortgensel plakalardaki titresim problemlerinin, Diferansiyel Quadrature Eleman Metodu (QEM) ile Galerkin?in sonlu elemanlar tekniginin kombinasyonu ile olusturulan Hibrid Eleman Metodu(HEM) yardimiyla elde edilen cozumleri sunulmustur. Kesik, nokta mesnetli ve cizgisel mesnetli dikdortgensel plaka yapilarinda elde edilen cozumler, diger arastirmacilarin cozumleriyle ve/veya sonlu elemanlar analizi ile cozum yapan bir program yardimi ile elde edilen degerlerle karsilastirilmis, cozum degerlerinin birbirleri ile uyumlu oldugu gorulmustur. Anahtar Kelimeler: Dogal titresim, Plaka, Hibrid Quadrature element

Journal of Testing and Evaluation, 2020

In this study, single and duplex aging treatment was applied to the metastable beta titanium allo... more In this study, single and duplex aging treatment was applied to the metastable beta titanium alloy of titanium-15 vanadium-3 aluminum-3 chromium-3 tin with cryogenic treatment. The single-step aging treatment was applied for 20 h at 450°C and 10 h at 550°C. The cryogenic treatment was carried out at −196°C for 24 h, followed by single-step or duplex aging treatment. The results obtained show that the cryogenic treatment causes the formation of martensitic alpha phases. Following the cryogenic treatment, martensitic alpha phases were observed in the sample, which was subjected to aging treatment at 450°C for 20 h, whereas these phases disappeared completely in the sample treated at 550°C for 10 h. Preaging treatment applied after cryogenic treatment prevented the formation of precipitate-free zones by providing a finer and uniform distribution of α phases. Cryogenic treatment followed by preaging treatment at 250°C for 24 h led to the formation of dense metastable prephases. This resulted in a 10% increase in tensile strength, 4% elongation, and 5% hardness compared to preaging at 300°C for 10 h after cryogenic treatment. The optimum mechanical properties in single-step sample groups were obtained in samples aged 20 h at 450°C. In duplex-aged samples, optimum mechanical properties were obtained in cryogenic treatment followed by 250°C/10 h + 450°C/20 h duplex aging treatment.

Journal of Theoretical and Applied Mechanics, 2017

In this study, the hybrid approach of the Quadrature Element Method (QEM) has been employed to ge... more In this study, the hybrid approach of the Quadrature Element Method (QEM) has been employed to generate solutions for point supported isotropic plates. The Hybrid QEM technique consists of a collocation method with the Galerkin finite element technique to combine the high accurate and rapid converging of Differential Quadrature Method (DQM) for efficient solution of differential equations. To present the validity of the solutions, the results have been compared with other known solutions for point supported rectangular plates. In addition, different solutions are carried out for different type boundary conditions, different locations and number of point supports. Results for the first vibration modes of plates are also tested using a commercial finite element code, and it is shown that they are in good agreement with literature.

Applied Mechanics and Materials, 2006

Bending analysis of thick laminated rectangular plates with various boundary conditions is presen... more Bending analysis of thick laminated rectangular plates with various boundary conditions is presented using Generalized Differential Quadrature (GDQ) method. Based on the Reissner first order shear deformation theory, the governing equations include a system of eight first order partial differential equations in terms of unknown displacements, forces and moments. Presence of all plate variables in the governing equations provide a simple procedure to satisfy different boundary condition during application of GDQ method to obtain accurate results with relatively small number of grid points even for plates with free edges .Illustrative examples including various combinations of clamped, simply supported and free boundary condition are given to demonstrate the accuracy and convergence of the presented GDQ technique. Results are compared with other analytical and finite element predictions and show reasonably good agreement.

The method of differential quadrature developed by Richard Bellman in the 1970s is a numerical so... more The method of differential quadrature developed by Richard Bellman in the 1970s is a numerical solution technique for differential systems by means of a polynomial-collocation approach at a finite number of points. In this paper a global method of generalized differential quadrature is presented to solve the problems on deflection, buckling and vibration behaviour of structural components. Furthermore, the applicability of this method to the deflection analysis of beams due to a point load is also demonstrated. An inherent advantage of the approach is its basic simplicity and small computational effort with easy programmability. Results are obtained for various boundary and loading conditions and are compared with existing exact and numerical solutions by other methods. Numerical examples have shown the accuracy, efficiency and great potential of this method for structural analysis.

This study is based on the joint quality of zinc-coated EN 10346: 2015 DX52D + Z quality steel sh... more This study is based on the joint quality of zinc-coated EN 10346: 2015 DX52D + Z quality steel sheets with having different thicknesses, which are preferred in the automotive industry due to their formability. Joining problems in clinching applications with different positions and sheets of different thicknesses are discussed and experimental outcomes are discussed in terms of strength of joints. As a result of the tests carried out according to the standards, it has been found that the joining of the sheets with thickness close to each other is relatively good, as the thickness difference increases, the joint quality decreases and sometimes the joint does not form. It has been also found that if the thinner sheet is placed on the bottom die during clinching, a better joint strength is obtained. EN 10346: 2015 DX52D+Z Plakaların Form-Punta Bağlantı Performansları Anahtar kelimeler Perçinleme; Bağlantı dayanımı; Metal şekillendirme; Bağlantı kalitesi; Bağlantı testi; Birbirine kilitlenme Öz Bu çalışma, şekillendirme kabiliyeti nedeniyle daha çok otomotiv endüstrisinde tercih edilen çinko kaplanmış farklı kalınlıktaki EN 10346:2015 DX52D+Z kalite çelik levhaların clinching teknolojisi ile yapılan bağlantılarının bağlantı kalitesi üzerine yapılmıştır. Özellikle clinching uygulamalarında karşımıza çıkan farklı pozisyon ve farklı kalınlıktaki levha birleştirmelerindeki bağlantı problemleri ele alınmış ve bağlantı kalitesi için genel bir değerlendirme yapılmıştır. Standartlara uygun olarak gerçekleştirilen testler sonucunda birbirlerine yakın kalınlıktaki levhaların bağlantılarının nispeten iyi olduğu, kalınlık farkının arttığında, bağlantı kalitesinin azaldığı ve bazen bağlantıların gerçekleşmediği görülmüştür. Bağlantı sırasında daha ince olan plakanın alt matris tarafında olması, çok daha iyi bir bağlantı dayanımının sağlanabilmesinin bir gereği olduğu belirlenmiştir.

Makine Teknolojileri Elektronik Dergisi (elektronik), 2016

El-Cezeri Fen ve Mühendislik Dergisi, 2021

Gears are widely used in motion transmission in machines. For this reason, they work in very diff... more Gears are widely used in motion transmission in machines. For this reason, they work in very difficult conditions. Some damage may occur in the gears depending on the operating conditions. These damages are bending fatigue, pitting, micropitting, scuffing, and wear. This study investigates surface fatigue damages by keeping fixed the material of test gear teeth, rotation speed, lubricating oil, and the applied load, and changing the operating temperatures of oil. In experimental studies, pre-and post-test weights of gear teeth samples were established, surface roughnesses were measured, and micrograph examinations were carried out on teeth surface. As a result, surface roughness and wear were established to increase in proportion to the rise in temperature of oil. Maximum pitting size was measured at about 870 µm at 90 ºC oil temperature, and the lowest pitting size was measured as approximately 450 µm in tests performed at 30 ºC.

Afyon Kocatepe University Journal of Sciences and Engineering, 2021

This study is based on the joint quality of zinc-coated EN 10346: 2015 DX52D + Z quality steel sh... more This study is based on the joint quality of zinc-coated EN 10346: 2015 DX52D + Z quality steel sheets with having different thicknesses, which are preferred in the automotive industry due to their formability. Joining problems in clinching applications with different positions and sheets of different thicknesses are discussed and experimental outcomes are discussed in terms of strength of joints. As a result of the tests carried out according to the standards, it has been found that the joining of the sheets with thickness close to each other is relatively good, as the thickness difference increases, the joint quality decreases and sometimes the joint does not form. It has been also found that if the thinner sheet is placed on the bottom die during clinching, a better joint strength is obtained. EN 10346: 2015 DX52D+Z Plakaların Form-Punta Bağlantı Performansları Anahtar kelimeler Perçinleme; Bağlantı dayanımı; Metal şekillendirme; Bağlantı kalitesi; Bağlantı testi; Birbirine kilitlenme Öz Bu çalışma, şekillendirme kabiliyeti nedeniyle daha çok otomotiv endüstrisinde tercih edilen çinko kaplanmış farklı kalınlıktaki EN 10346:2015 DX52D+Z kalite çelik levhaların clinching teknolojisi ile yapılan bağlantılarının bağlantı kalitesi üzerine yapılmıştır. Özellikle clinching uygulamalarında karşımıza çıkan farklı pozisyon ve farklı kalınlıktaki levha birleştirmelerindeki bağlantı problemleri ele alınmış ve bağlantı kalitesi için genel bir değerlendirme yapılmıştır. Standartlara uygun olarak gerçekleştirilen testler sonucunda birbirlerine yakın kalınlıktaki levhaların bağlantılarının nispeten iyi olduğu, kalınlık farkının arttığında, bağlantı kalitesinin azaldığı ve bazen bağlantıların gerçekleşmediği görülmüştür. Bağlantı sırasında daha ince olan plakanın alt matris tarafında olması, çok daha iyi bir bağlantı dayanımının sağlanabilmesinin bir gereği olduğu belirlenmiştir.

Journal of Materials and Mechatronics: A, Dec 1, 2021

Metal forming, machining, crashing, etc. in simulations, not only the boundary conditions are giv... more Metal forming, machining, crashing, etc. in simulations, not only the boundary conditions are given perfectly, but also another important input is the properties of the material used. Defining these properties correctly increases the confidence in using the results of the simulation in practice. One of the most well-known parametric models representing the stress-strain relationship at different temperatures and strain rates in simulation programs is the Johnson-Cook flow stress model and ductile damage model. However, the process of obtaining JC parameters for the material is quite long and tiring. Combined evaluation of multiple tests and simulation results, curve fitting, regression and optimization procedures necessitate an organized mathematical operation process. With the program written, it was tried to get both fast and accurate parameter results by using different mathematical solution methods. Parameter constants are obtained automatically by entering different test types, test device result format and simulation report format entries in a hierarchical order using the written program. The user can visually check the tests and results with on the same graphics and intervene in the detection of critical points of the tests when necessary. By using different curve fitting algorithms, finding the most suitable parameters is provided.

Özet Bu çalışma, form punta yöntemiyle ile oluşturulan bağlantıların mekanik özelliklerinin incel... more Özet Bu çalışma, form punta yöntemiyle ile oluşturulan bağlantıların mekanik özelliklerinin incelenmesi amacıyla yapılmıştır. Form punta bağlantıları için özellikle otomotiv endüstrisinde kullanılan galvanizli(St1314) çelik ve alüminyum(Al5754) plakalar seçilmiştir. Numunelere, sırasıyla TS EN ISO 14270 ve TS EN ISO 14273 standardına uygun olarak kesme deneyi ve mekanize soyma deneyleri uygulanmıştır. Keza farklı yerleşim sırası ve farklı plaka kalınlıklarının etkilerini incelemek için mikroskobik analizler de uygulanmıştır. Üstte galvanizli çelik altta alüminyum levhadan oluşan kombinasyonun dayanımı tam tersi kombinasyondan yaklaşık iki kat daha büyüktür. Büyük değerdeki plaka kalınlığı oranlarının, kırılma ve ayrılmalara neden olduğu gözlemlenmiştir. Abstract In this study, mechanical properties of the joints which made with the mechanic clinching were investigated. Galvanized steel (St1314) which is used especially in automotive industry and aluminum (Al5754) sheets were selecte...

Bu makalede kenarlari serbest, izotropik dikdortgensel plakalardaki titresim problemlerinin, Dife... more Bu makalede kenarlari serbest, izotropik dikdortgensel plakalardaki titresim problemlerinin, Diferansiyel Quadrature Eleman Metodu (QEM) ile Galerkin?in sonlu elemanlar tekniginin kombinasyonu ile olusturulan Hibrid Eleman Metodu(HEM) yardimiyla elde edilen cozumleri sunulmustur. Kesik, nokta mesnetli ve cizgisel mesnetli dikdortgensel plaka yapilarinda elde edilen cozumler, diger arastirmacilarin cozumleriyle ve/veya sonlu elemanlar analizi ile cozum yapan bir program yardimi ile elde edilen degerlerle karsilastirilmis, cozum degerlerinin birbirleri ile uyumlu oldugu gorulmustur. Anahtar Kelimeler: Dogal titresim, Plaka, Hibrid Quadrature element

Journal of Testing and Evaluation, 2020

In this study, single and duplex aging treatment was applied to the metastable beta titanium allo... more In this study, single and duplex aging treatment was applied to the metastable beta titanium alloy of titanium-15 vanadium-3 aluminum-3 chromium-3 tin with cryogenic treatment. The single-step aging treatment was applied for 20 h at 450°C and 10 h at 550°C. The cryogenic treatment was carried out at −196°C for 24 h, followed by single-step or duplex aging treatment. The results obtained show that the cryogenic treatment causes the formation of martensitic alpha phases. Following the cryogenic treatment, martensitic alpha phases were observed in the sample, which was subjected to aging treatment at 450°C for 20 h, whereas these phases disappeared completely in the sample treated at 550°C for 10 h. Preaging treatment applied after cryogenic treatment prevented the formation of precipitate-free zones by providing a finer and uniform distribution of α phases. Cryogenic treatment followed by preaging treatment at 250°C for 24 h led to the formation of dense metastable prephases. This resulted in a 10% increase in tensile strength, 4% elongation, and 5% hardness compared to preaging at 300°C for 10 h after cryogenic treatment. The optimum mechanical properties in single-step sample groups were obtained in samples aged 20 h at 450°C. In duplex-aged samples, optimum mechanical properties were obtained in cryogenic treatment followed by 250°C/10 h + 450°C/20 h duplex aging treatment.

Journal of Theoretical and Applied Mechanics, 2017

In this study, the hybrid approach of the Quadrature Element Method (QEM) has been employed to ge... more In this study, the hybrid approach of the Quadrature Element Method (QEM) has been employed to generate solutions for point supported isotropic plates. The Hybrid QEM technique consists of a collocation method with the Galerkin finite element technique to combine the high accurate and rapid converging of Differential Quadrature Method (DQM) for efficient solution of differential equations. To present the validity of the solutions, the results have been compared with other known solutions for point supported rectangular plates. In addition, different solutions are carried out for different type boundary conditions, different locations and number of point supports. Results for the first vibration modes of plates are also tested using a commercial finite element code, and it is shown that they are in good agreement with literature.

Applied Mechanics and Materials, 2006

Bending analysis of thick laminated rectangular plates with various boundary conditions is presen... more Bending analysis of thick laminated rectangular plates with various boundary conditions is presented using Generalized Differential Quadrature (GDQ) method. Based on the Reissner first order shear deformation theory, the governing equations include a system of eight first order partial differential equations in terms of unknown displacements, forces and moments. Presence of all plate variables in the governing equations provide a simple procedure to satisfy different boundary condition during application of GDQ method to obtain accurate results with relatively small number of grid points even for plates with free edges .Illustrative examples including various combinations of clamped, simply supported and free boundary condition are given to demonstrate the accuracy and convergence of the presented GDQ technique. Results are compared with other analytical and finite element predictions and show reasonably good agreement.

The method of differential quadrature developed by Richard Bellman in the 1970s is a numerical so... more The method of differential quadrature developed by Richard Bellman in the 1970s is a numerical solution technique for differential systems by means of a polynomial-collocation approach at a finite number of points. In this paper a global method of generalized differential quadrature is presented to solve the problems on deflection, buckling and vibration behaviour of structural components. Furthermore, the applicability of this method to the deflection analysis of beams due to a point load is also demonstrated. An inherent advantage of the approach is its basic simplicity and small computational effort with easy programmability. Results are obtained for various boundary and loading conditions and are compared with existing exact and numerical solutions by other methods. Numerical examples have shown the accuracy, efficiency and great potential of this method for structural analysis.