Derin Kriyojenik İşlemin Farklı Bekletme Sürelerinin AISI 4140 (42CrMo4) Çeliğin Mekanik Özelliklerine Etkisi

Bu çalışmada, özellikle otomotiv endüstrisinde yaygın olarak kullanılan AISI 4140 (42CrMo4) çeliğinin mekanik özellikleri üzerinde farklı bekletme süreli derin kriyojenik işlemin etkisi incelenmiştir. Bu amaçla hazırlanan AISI 4140 çeliğinden imal edilen numunelere geleneksel ısıl işlem uygulanmış ve geleneksel ısıl işlemi tamamlayıcı bir işlem olan derin kriyojenik işlem farklı bekletme sürelerinde (12, 24, 36 ve 48 saat)  - 140 °C sıcaklıkta uygulanmıştır. Derin kriyojenik işlem sonrasında numunelere 200 °C’ de temperleme işlemi uygulanmıştır. AISI 4140 çeliğin mekanik özelliklerinin belirlenebilmesi için sertlik ölçüm ve çekme testleri gerçekleştirilmiştir. Bu testlerden elde edilen bulgular analiz edilmiş ve karşılaştırılmıştır. Sonuçlar, farklı bekletme süreli derin kriyojenik işlemin ve derin kriyojenik işlem sonrası uygulanan temperleme işleminin AISI 4140 çeliğin mekanik özellikleri üzerinde önemli etkileri olduğunu göstermiştir. Derin kriyojenik işlemli numunelerde önemli sertlik artışları ve çekme dayanımlarında kayda değer iyileşmeler olmuştur. Ayrıca, mekanik özelliklere etkisi yönünden derin kriyojenik işlemin en uygun bekletme süresinin 36 saat olduğu tespit edilmiştir

TEKNİK EĞİTİM FAKÜLTESİ ÖĞRETMEN ADAYLARININ ÖĞRETMENLİK BECERİLERİ

Bu çalışmada amaç; Düzce Teknik Eğitim Fakültesi son sınıf öğrencilerinin öğretmenlik becerilerini uygulama düzeylerini belirlemektir. Bu öğrenciler sekizinci son dönemde öğretmenlik uygulamasıdersinde öğretmenlik becerilerini okullara uygulamaya gitmektedirler. Bu nedenle, yedinci dönemde öğrencilerin bu beceriler açısından ulaştıklarıdüzeyin belirlenmesi amaçlandı. Araştırmada, survey yöntemi kullanıldı. Araştırma, Düzce Teknik Eğitim Fakültesi Elektrik, Yapıve Mobilya-Dekorasyon Öğretmenliği Bölümleri son sınıf öğrencileri üzerinde yapıldı. Bu bölümlerde son sınıftaki bütün öğrenciler araştırmaya dahil edilmişolduğundan ayrıca örnekleme gidilmemiştir. Öğretmenlik uygulamasıdersinde kullanılan öğretmenlik becerileri ölçeği esas alınarak öğrencilerle birlikte toplam 39 beceri belirlendi. Bunlar: konu alan hakimiyeti, planlama, öğretim süreci, sınıf yönetimi, iletişim ve değerlendirme alt başlıklarından oluşmaktadır. Her alt başlıktan toplam beceri sayısıoranına uygun olarak alınan davranışlarla, öğrencilerin de katkılarıyla üç ayrıölçek oluşturuldu. Her ölçekte 15 beceri yer aldı. Her bir öğrenci bu ölçeklerden birine uygun olarak istedikleri konudan bir ders sunumu hazırlayarak sınıf ortamında sundular. Verileri toplamak için öğretmenlik becerilerinden oluşturulan gözlem formlarıkullanıldı. Öğrenci sunumları, araştırmacıtarafından gözlenerek gözlem formlarıdolduruldu. Toplanan veriler SPSS programıkullanılarak analiz edildi. Araştırmacılar tarafından yapılan gözlemlerin analizi sonucunda öğretmen adaylarının öğretmenlik becerilerini uygulama düzeyleri ortaya konuldu

Farklı Doldurma Şekillerinin Üç Boyutlu Yazıcılarda Üretilen Ürünlerin Mukavemetine Etkisi

Bu çalışmada, farklı doldurma şekillerinin Ergiyik Depolayarak Modelleme (Fused Deposition Modelling - FDM) yöntemi ile imal edilen ürünlerin mukavemetine etkisi deneysel olarak incelenmiştir. Çalışmada filament malzeme olarak PET-G (Polyethylene Terephthalate Glycol) kullanılmış ve farklı doldurma şekillerinde (Rectilinear, Grid, Triangular, Wiggle, Fast honeycomb, Full honeycomb), doluluk oranı (%30), işleme hızı (4200 mm/dak), nozul çapı (0,40 mm), nozul sıcaklığı (230 ºC), katman kalınlığı (0,20 mm) olmak üzere ISO 527-2 standardına uygun ürünler imal edilmiştir. Bu numunelerin çekme mukavemetlerini incelemek için çekme testleri gerçekleştirilmiş ve testlerden elde edilen sonuçlar karşılaştırılmıştır. Sonuçlar yazdırma şekillerinin ürün mukavemeti üzerinde önemli etkisi olduğunu göstermiştir. Rectilinear doldurma şeklinde imal edilen ürünlerde elde edilen mukavemet değerleri diğer doldurma şekillerine göre yaklaşık % 15 daha yüksek çıkmıştır. Ayrıca, Full honeycomb doldurma şeklinin diğer doldurma şekillerine göre daha fazla uzama gösterdiği görülmüştür

Differential evolution and simulated annealing algorithms for mechanical systems design

In this study, nature inspired algorithms – the Differential Evolution (DE) and the Simulated Annealing (SA) – are utilized to seek a global optimum solution for ball bearings link system assembly weight with constraints and mixed design variables. The Genetic Algorithm (GA) and the Evolution Strategy (ES) will be a reference for the examination and validation of the DE and the SA. The main purpose is to minimize the weight of an assembly system composed of a shaft and two ball bearings. Ball bearings link system is used extensively in many machinery applications. Among mechanical systems, designers pay great attention to the ball bearings link system because of its significant industrial importance. The problem is complex and a time consuming process due to mixed design variables and inequality constraints imposed on the objective function. The results showed that the DE and the SA performed and obtained convergence reliability on the global optimum solution. So the contribution of the DE and the SA application to the mechanical system design can be very useful in many real-world mechanical system design problems. Beside, the comparison confirms the effectiveness and the superiority of the DE over the others algorithms – the SA, the GA, and the ES – in terms of solution quality. The ball bearings link system assembly weight of 634,099 gr was obtained using the DE while 671,616 gr, 728213.8 gr, and 729445.5 gr were obtained using the SA, the ES, and the GA respectively. © 2014 Karabuk Universit

Particle Swarm Optimization for Structural Design Problems

The aim of this paper is to employ the Particle Swarm Optimization (PSO) technique to a mechanical engineering design problem which is minimizing the volume of a cantilevered beam subject to bending strength constraints. Mechanical engineering design problems are complex activities which are computing capability are more and more required. The most of these problems are solved by conventional mathematical programming techniques that require gradient information. These techniques have several drawbacks from which the main one is becoming trapped in local optima. As an alternative to gradient-based techniques, the PSO does not require the evaluation of gradients of the objective function. The PSO algorithm employs the generation of guided random positions when they search for the global optimum point. The PSO which is a nature inspired heuristics search technique imitates the social behavior of bird flocking. The results obtained by the PSO are compared with Mathematical Programming (MP). It is demonstrated that the PSO performed and obtained better convergence reliability on the global optimum point than the MP. Using the MP, the volume of 2961000 mm3 was obtained while the beam volume of 2945345 mm3 was obtained by the PSO

Pivoted-pad journal bearings lubrication design

WOS: 000292064700007Purpose - This paper aims to utilize an evolutionary algorithm as an optimization technique to solve design optimization of a pivoted-pad journal bearing performance characteristics considering objective functions which are contradictory to each other. These functions include fluid film thickness, film temperature, and power loss along with design variables vector, which consists of pad axial length to journal diameter ratio, pad arc length, bearing radial clearance, pad offset factor, and pad preload factor. Design/methodology/approach - In order to improve performance characteristics of the pivoted-pad journal bearing, the genetic algorithm (GA) was employed and the modeling of the bearing was represented with the finite element method. Also, a numerical method, global criterion, was conducted to validate the efficiency and applicability of the proposed method. Findings - This paper utilizes the GA to solve multi-objective optimization of the pivoted-pad journal bearing performance governed by design variables such as pad axial length to journal diameter ratio, pad arc length, bearing radial clearance, pad offset factor, and pad preload factor for a range of rotational speed. The global criterion method (GCM) proves that the proposed method is very efficient and useful for the optimal design of the pivoted-pad journal bearings. An acceptable results agreement between the GA and the GCM has been obtained. The GA is well suited to find the optimum solutions with a high probability since it starts with an initial set of solutions rather than a single solution. The GA explores different areas of search space in parallel and, it is good at exploitation. Originality/value - With the help of the proposed method, it will be possible to have an idea about bearing geometric parameters on a more rational basis, and to better predict the dynamic performance of rotor systems supported on the pivoted-pad journal bearings

Improving the dynamic characteristics of a rotor system using an evolutionary algorithm [Izboljšanje dinami?nih zna?ilnosti rotorskega sistema z razvojnim algoritmom]

In this paper the optimum design for improving the dynamic characteristics of a flexible, overhung rotor system is studied. The design of a flexible rotor system is a complicated process due to the large number of geometrical parameters of hydrodynamic bearings, which play an important role in the prediction of the dynamic behavior of the rotor system. There are a number of design requirements added to the rotor-system configuration that improve the dynamic characteristics within the rotor's speed range. To improve the dynamic characteristics of the rotor system, a genetic algorithm was employed and the modeling of the components of the rotor system was made with the finite-element method. Also, the method of feasible directions was used in order to validate the efficiency and applicability of the proposed method, and it proved that the proposed method in the rotor-system design is very efficient and useful for improving the dynamic characteristics of the rotor system. © 2007 Journal of Mechanical Engineering. All rights reserved

Improving the dynamic characteristics of a rotor system using an evolutionary algorithm

WOS: 000253220400008In this paper the optimum design for improving the dynamic characteristics of a flexible, overhung rotor system is studied. The design of a flexible rotor system is a complicated process due to the large number of geometrical parameters of hydrodynamic bearings, which play an important role in the prediction of the dynamic behavior of the rotor system. There are a number of design requirements added to the rotor-system configuration that improve the dynamic characteristics within the rotor's speed range. To improve the dynamic characteristics of the rotor system, a genetic algorithm was employed and the modeling of the components of the rotor system was made with the finite-element method. Also, the method of feasible directions was used in order to validate the efficiency and applicability of the proposed method, and it proved that the proposed method in the rotor-system design is very efficient and useful for improving the dynamic characteristics of the rotor system. (c) 2007 Journal of Mechanical Engineering. All rights reserved

DESIGNING OPTIMUM OIL THICKNESS IN ARTIFICIAL HUMAN KNEE JOINT BY SIMULATED ANNEALING

WOS: 000265362900003In human knee joints, synovial fluid film covers the surface of synovium and cartilage within the joint space. Synovial joints acts as bearing in mechanical system. Although the artificial human joints differ from most mechanical bearings in their nature, they have been modeled and analyzed in terms of hydrodynamic bearing of engineering. In this study, nature inspired an algorithm, the simulated annealing (SA), is used to find minimum fluid film thickness in artificial human knee joints. It is important to optimize the film thickness of the bearing in terms of successful operation and lifetime of the implant in terms of friction and wear. The problem is complex and a time consuming process due to design variables and constraints imposed on the objective function. It is demonstrated that the SA performed and obtained convergence reliability on the optimum point

DESIGNING OPTIMUM OIL THICKNESS IN ARTIFICIAL HUMAN KNEE JOINT BY SIMULATED ANNEALING

WOS: 000265362900003In human knee joints, synovial fluid film covers the surface of synovium and cartilage within the joint space. Synovial joints acts as bearing in mechanical system. Although the artificial human joints differ from most mechanical bearings in their nature, they have been modeled and analyzed in terms of hydrodynamic bearing of engineering. In this study, nature inspired an algorithm, the simulated annealing (SA), is used to find minimum fluid film thickness in artificial human knee joints. It is important to optimize the film thickness of the bearing in terms of successful operation and lifetime of the implant in terms of friction and wear. The problem is complex and a time consuming process due to design variables and constraints imposed on the objective function. It is demonstrated that the SA performed and obtained convergence reliability on the optimum point