Repassivation/depassivation Kinetics Of 316l Stainless Steel In Reciprocating Sliding Contacts

Tez (Yüksek Lisans) -- İstanbul Teknik Üniversitesi, Fen Bilimleri Enstitüsü, 2008Thesis (M.Sc.) -- İstanbul Technical University, Institute of Science and Technology, 2008Paslanmaz çelikler, agresif ve korozif çevre etkenlerine karşı yüzeylerinde oluşturdukları nanometre mertebesindeki pasif oksit filmi sayesinde kendilerini korurlar. Bu oksit filmi ortamda oksijen bulunduğu müddetçe kendini daima yenileyebilir. Ancak abrazif bir etki sonucunda bu film lokal olarak bozunabilir veya tamamen sistemden kaldırılabilir. Bu olayı, malzemenin maruz kaldığı çevre koşullarına ve yükleme koşullarına bağlı olarak malzemenin lokal olarak aşınmasına veya o bölgenin tekrar pasif konuma geçmesiyle takip eder. Repasivasyon kinetiği, bu tür pasif malzemelerin korozyon aşınma davranışını kritik olarak etkiler. Bu çalışmada, 316L paslanmaz çeliğine, aktif aşınma bölgesinin çevre koşullarıyla etkileşme süresine bağlı olarak ileri-geri, karşı yüklemeli aşınma testleri uygulandı. Çalışmada, çevre koşullarına maruz kalma süresini kontrol edebilme olanağı sağlayan özel bir mikro aşındırma test düzeneği kullanıldı. Bu süreyi değiştimek kaydıyla, çok sayıda test uygulanarak, sürtünme katsayısı ve aşınma gelişimi analiz edildi. Bu yaklaşımla 316L paslanmaz çeliğinin repasivasyon hızı belirlendi ve tribolojik kontağın etkisine bağlı olarak, karşı yüklemeli aşınma koşulları altındaki aşınma davranışı incelendi.Stainless steels rely on a nanometer degree thick surface oxide passive film for their protection from aggressive and corrosive environments. This oxide film forms instantaneously when oxygen is available in the environment but abrasion can lead to the local rupture or complete removal of these films. This can be followed by a local dissolution or repassivation of the active metal depending on the material-electrolyte system and the loading conditions. The kinetics of repassivation critically affects the corrosion wear of such passive materials. In this work, 316L stainless steel was subjected to reciprocating bidirectional sliding with varying exposure time of the active wear track to the environment. A special experimental set-up was used which allows to control the exposure time by a holding time applying after each reciprocating cycle and keep the reciprocating table at a fixed position for a selected time duration during the fretting tests. Performing large number of tests, evolution of coefficient of friction and the extent of wear was analysed with varying exposure time. In this approach, repassivation rate of 316L stainless steel was indicated. Degredation mechanism of 316L under reciprocating sliding contacts were analysed depending on the role of the contact.Yüksek LisansM.Sc

Effect of loading rate on mechanical properties of micro-sized oak wood

The aim of this study was to investigate the effect of loading rate on the micro-mechanical properties of oak (Quercus petraea) wood. Bending strength, modulus of elasticity in bending, compression strength parallel to the grain and tensile strength parallel to the grain were determined using microsized test samples. Three different loading rates were used for each test. The first loading rates were determined according to related ISO standards and the second and third loading rates were determined for half and a quarter of the standard loading rates. Results showed that the loading rate significantly affected the modulus of elasticity, tensile strength and compression strength of the oak wood, while the bending strength was not affected

Micro-mechanical properties of oak wood and comparison with standard-sized samples

The aim of this study was to investigate micro-mechanical properties of Oak (Quercus petraea) wood and to compare with standard-size test specimens values. Bending strength, modulus of elasticity in bending, compression strength and tensile strength were determined using micro- and standard-size mechanical test samples. In the micro- and standard size samples, bending strengths were evaluated as 71,2 MPa and 99,4 MPa, modulus of elasticity in bending as 2741,3 MPa and 11394,1 MPa tensile strengths as 98,7 MPa and 93,8 MPa and compression strengths as 45,4 MPa and 46,6 MPa respectively.The results showed that the bending strength, modulus of elasticity and compression strength of the micro-size samples were lower compared to the standard-size samples, while the tensile strength was higher in the micro-size samples. The compression strength values of micro- and standard-size samples were not significantly different. The regression analyses indicated a positive linear regression between the mechanical properties of micro- and standard-size samples. Micro-size specimens can be used to estimate the mechanical properties of Oak wood when obtaining standard-size specimens is not possible.   PDF XM

Surface characteristics and hardness of MDF panels laminated with thermally compressed veneer

WOS: 000313854200080The aim of this study was to investigate surface characteristic (surface roughness and wettability) and hardness of sandwiched panels produced from medium density fiberboard and thermally compressed wood veneer. Oriental beech (Fagus orientalis Lipsky) veneers were compressed at temperature levels of 150 degrees C, 180 degrees C, and 200 degrees C using 4 MPa and 6 MPa pressure for 8 mm. Commercially produced MDF samples were laminated with such thermally compressed veneer sheets. Contact angle (CA) of the panels were measured with a goniometer. The surface roughness (SR) of the samples was determined fine stylus tracing technique and Janka hardness was determined according to ASTM D 1037 standard. The results showed that the SR value of the panels decreased with increasing press pressure and temperature. Press pressure had no significant effect on the CA values of the panels while temperature significantly affected. All of the compressed veneer laminated panels had higher hardness value compared to non-compressed veneer laminated panel. The hardness value of the panels increased with increasing press pressure and temperature. This study showed that press pressure and temperature can be used to improve surface characteristics of non-laminated and laminated MDF panels. Thermally compressed veneer laminated MDF panels can be utilized for structural purposes due to higher hardness. It also would provide more efficient use of adhesive to manufacture plywood and LVL and better surfaces for surface treatments such as painting. (C) 2012 Elsevier Ltd. All rights reserved

Image encryption algorithm with DNA codes

Tez No : 736311RSA şifreleme yöntemi günümüzde de kullanılan güncel bir yöntemdir. RSA, gücünü asalların çarpanlara ayrılamamasından ve iki büyük asalın çarpımı ile elde edilen sayıların kullanılmasından alır. Bu çarpımlar yeterince büyük olduğunda, mevcut yüksek hesaplama gücüne sahip olan, diğer bir değişle süper bilgisayarlarda dahi yıllarca sürebilmektedir. RSA'nın bu denli zor çözülmesi, hatta seçilen asalların yüksek olması, onu genelde görüntü gibi büyük verilerin değil de küçük verilerin şifrelenmesinde kullanılmasına yöneltmiştir. Fakat, bilgisayarların gücü her geçen gün daha da gelişmekte, önceki çözülemez denilen algoritmaların kırılma süreleri azalmaktadır. Hatta şu anda çalışmaları devem etmekte olan kuantum bilgisayarları ile birkaç yıl sürebilecek hesapların birkaç saat içinde çözülebileceği tahmin edilmektedir. Bilgisayarların artan gücü nedeniyle son on yıl içerisinde literatürde de RSA ile görüntü şifreleme çalışmaları olmuştur. Bu tezde, literatürden farklı olarak, DNA'nın kendini tamamlama, karşı zincirini oluşturma, özelliğini ve matematiksel yapılar olan cisimlerden faydalanarak RSA ile kullanılan bir görüntü şifreleme algoritması geliştirilmiştir. Algoritmada, RSA içinde kullanılan gizli anahtarların üzerine ek olarak, DNA'dan cismin elemanlarına çevirme, DNA tamamlama matrisi kullanılmaktadır. Ayrıca RSA şifreleme için her görüntü biti için farklı da seçilebilecek asallardan oluşan matrisler kullanılmaktadır.The RSA encryption method is an up-to-date method that is still used today. RSA draws its strength from the inability to factor primes and the use of numbers obtained by multiplying two large primes. When these multiplications are large enough, they can last for years, even in supercomputers with the high computing power available. The difficulty in solving RSA, and even the high number of primes chosen, has led it to be used for encryption of small data, not large data such as images. However, the power of computers is developing day by day, and the breaking times of algorithms that were previously called unsolvable are decreasing. In fact, it is estimated that the calculations that may take a few years will be solved in a few hours with the quantum computers that are currently working. Due to the increasing power of computers, there have been image encryption studies with RSA in the literature in the last ten years. In this thesis, unlike the literature, an image encryption algorithm used with RSA has been developed by making use of DNA's self-completion, counter-chain formation, and mathematical structures of objects. In the algorithm, in addition to the secret keys used in RSA, conversion from DNA to the elements of the object and DNA complement matrice are used. In addition, for RSA encryption, matrices consisting of primes that can be selected differently for each image bit are used

Non-destructive evaluation of beech and oak wood bent at different radii

AS, Nusret/0000-0002-5269-1574WOS: 000316042600011The aim of this study was to investigate the parallel and perpendicular velocity and transmission time of beech and oak wood bent at different radii. Two trees from each wood species, having straight trunks of approximately 40 cm in diameter, were selected, and two 4-m logs were cut from each tree. The prepared samples, except those from the control groups, were steamed, bent and set. The samples were bent at three different radii (300 mm, 200 mm and 100 mm) in the tangential direction. The density, parallel and perpendicular (radial and tangential) velocity and transmission times of the beech and oak wood were determined. The results of this study showed that the bent samples of beech and oak wood had higher density compared to the unbent groups. The density of both wood species increased with the decreasing bending radius. The highest velocity parallel to the fibers was measured on the convex surface, while the lowest was measured on the concave surface. The parallel and perpendicular velocity decreased as the bending radius decreased. (c) 2013 Elsevier Ltd. All rights reserved

Prediction of optimum CNC cutting conditions using artificial neural network models for the best wood surface quality, low energy consumption, and time savings

This study aimed to predict the CNC cutting conditions for the best wood surface quality, energy, and time savings using artificial neural network (ANN) models. In the CNC process, walnut, and ash wood were used as materials, while three different cutting tool diameters (3 mm, 6 mm, and 8 mm), spindle speed (12000 rpm, 15000 rpm, and 18000 rpm), and feed rate (3 m/min, 6 m/min, and 9 m/min) were determined as cutting conditions. After the cutting processes were completed with the CNC machine, energy consumption and processing time were determined for all groups. Surface roughness and wettability tests were performed on the processed wood samples, and their surface qualities were determined. The experimentally obtained data were analysed in ANN, and the models with the best performance were obtained. By using these prediction models, optimum cutting conditions were determined. Using the findings of the study, the optimum cutting condition values can be determined for walnut and ash wood with the smoothest and best wettable surface. Furthermore, in CNC processes using such materials, minimum energy consumption and shorter processing time can be obtained with optimum cutting conditions

Effects of Moisture Content on Mechanical Properties of Micro-size Oak Wood

WOS: 000493997400005Effects of moisture content (MC) were investigated for the mechanical properties of oak wood (Quercus petraea Liebl.) using micro-size test specimens. The micro-size specimens for bending, tensile, and compression tests were prepared and divided into five groups. Each group was conditioned at a different relative humidity and temperature to achieve MC values of 8%, 12%, 16%, 20%, and above-fiber-saturation-point MCs. After conditioning, the bending strength, modulus of elasticity (MOE) in bending, tensile strength, and compression strength values were determined. The results showed that MC had statistically significant effects on all the measured mechanical properties in the micro-size oak wood samples. The greatest decrease was observed for the compression strength, while the lowest decrease was observed for the tensile strength, when MC increased. The changing rates induced by 1% MC were calculated as 3% for bending strength, 2.5% for the MOE, 2.0% for the tensile strength, and 3.1% for the compression strength.Scientific and Technological Research Council of Turkey (TUBITAK)Turkiye Bilimsel ve Teknolojik Arastirma Kurumu (TUBITAK) [112O815]; Duzce UniversityDuzce University [BAP-2017.02.03.718]This work was supported by the Scientific and Technological Research Council of Turkey (TUBITAK Project Number: 112O815) and Duzce University (Project Number: BAP-2017.02.03.718)

PHYSICAL AND MECHANICAL PROPERTIES OF PARTICLEBOARD LAMINATED WITH THERMALLY COMPRESSED VENEER

The aim of this study was to investigate the effects of thermally compressed veneer laminating on some of the physical and mechanical properties of particleboard. Oriental beech (Fagus orientalis Lipsky) veneers were compressed under various press conditions. Commercially produced particleboard samples were laminated with such compressed veneer sheets. The density, 2-h and 24-h water absorption (WA) and thickness swelling (TS), bending strength (MOR), and modulus of elasticity (MOE) in the parallel and perpendicular directions to grain orientation were measured. The results showed that all of the particleboards laminated with compressed veneer had higher MOR and MOE values compared to unlaminated particleboard and particleboard laminated with non-compressed veneer. In the sandwiched panels, particleboards laminated with veneer sheets and compressed at a pressure of 4 MPa and a temperature of 150 oC had the highest MOR and MOE values. The MOR and MOE values decreased with increasing temperatures higher than 150 oC. The TS value for 2-h and 24-h immersion times decreased with increasing press temperature. The findings of this work could provide some insight in producing sandwich-type panels with improved properties. It appears that compressed veneer using different press temperatures and pressures could be considered as an alternative way of developing sandwich-type products with satisfactory structural properties