AZ91 Magnezyum Alaşımının Delinmesinde İşleme Parametrelerinin Kesme Kuvveti Üzerine Etkisinin Genetic Expression Modellemesi ile İncelenmesi

This paper is presented a new theoretical model basis on experimental to predict the thrust force on AZ91magnesium alloy in drilling process depend on the various machining parameters. The experiments for modeling were conducted in dry cutting conditions and designed as full factorial using the spindle speed and feed rate with four different kinds of drill bits. The results were modeled with Genetic Expression Programming and the thrust force formulation was obtained. Considering the formulation, the factors effects were analyzed on thrust force for AZ91

Toughening of epoxy adhesives by combined interaction of carbon nanotubes and silsesquioxanes

The extensive use of adhesives in many structural applications in the transport industry and particularly in the aeronautic field is due to numerous advantages of bonded joints. However, still many researchers are working to enhance the mechanical properties and rheological performance of adhesives by using nanoadditives. In this study the effect of the addition of Multi-Wall Carbon Nanotubes (MWCNTs) with Polyhedral Oligomeric Silsesquioxane (POSS) compounds, either Glycidyl Oligomeric Silsesquioxanes (GPOSS) or DodecaPhenyl Oligomeric Silsesquioxanes (DPHPOSS) to Tetraglycidyl Methylene Dianiline (TGMDA) epoxy formulation, was investigated. The formulations contain neither a tougher matrix such as elastomers nor other additives typically used to provide a closer match in the coefficient of thermal expansion in order to discriminate only the effect of the addition of the above-mentioned components. Bonded aluminium single lap joints were made using both untreated and Chromic Acid Anodisation (CAA)-treated aluminium alloy T2024 adherends. The effects of the different chemical functionalities of POSS compounds, as well as the synergistic effect between the MWCNT and POSS combination on adhesion strength, were evaluated by viscosity measurement, tensile tests, Dynamic Mechanical Analysis (DMA), single lap joint shear strength tests, and morphological investigation. The best performance in the Lap Shear Strength (LSS) of the manufactured joints has been found for treated adherends bonded with epoxy adhesive containing MWCNTs and GPOSS. Carbon nanotubes have been found to play a very effective bridging function across the fracture surface of the bonded joints

Olağandışılık kaynaklı ilginçlik öğütlerinin tıbbi veri üzerinde çözümlenmesi.

Peculiar data are regarded as patterns which are significantly distinguishable from other records, relatively few in number and they are accepted as to be one of the most striking aspects of the interestingness concept. In clinical domain, peculiar records are probably signals for malignancy or disorder to be intervened immediately. The investigation of the rules and mechanisms which lie behind these records will be a meaningful contribution for improved clinical decision support systems. In order to discover the most interesting records and patterns, many peculiarity oriented interestingness measures, each fulfilling a specific requirement, have been developed. In this thesis well-known peculiarity oriented interestingness measures, Local Outlier Factor (LOF), Cluster Based Local Outlier Factor (CBLOF) and Record Peculiar Factor (RPF) are compared. The insights derived from the theoretical infrastructures of the algorithms were evaluated by using experiments on synthetic and real world medical data. The results are discussed based on the interestingness perspective and some departure points for building a more developed methodology for knowledge discovery in databases are proposed.M.S. - Master of Scienc

Application of a two-phase flow model for hydrogen evolution in an electrochemical cell

A two-phase mathematical model is applied to numerical investigation of gas evolution in a vertical electrochemical cell. The model comprises transport equations derived from first principles for each phase. Void fraction distribution for both hydrogen and oxygen gases velocity of gas and liquid phases, concentration and current density distribution are calculated. It is found that gas fraction increases towards to the top of the cell. Gas phase confined regions at the vicinity of the electrodes. Gas release significantly affects the velocity profile in the system. The large density differences between two-phase generate flow which modify velocity profile. Gas release is enhanced at high current density however; gas layer accumulated on the electrode surface decreases the active reaction area which adversely affects the reaction rate. © 2003 Elsevier Inc. All rights reserved

Investigation of effects of scale and surface roughness on efficiency of water jet pumps using CFD

WOS: 000332216500002Comparing to pumps with moving parts water-jet pumps have a lower efficiency and surface roughness is an important factor for these types of pumps. The aim of this simulation study is to numerically determine how the scaling-up, downscaling and change in the absolute and relative roughness would impact on the energy efficiency of the pumps, using a commercial computational fluid dynamics (CFD) solver ANSYS FLUENT. In order to select the turbulence model that produces the predictions closest to the actual data from four turbulence models, a preliminary study was conducted on a full-scale jet pump. Using the transition SST model, which gives the best results among all the models, the effects of scale and roughness on the performance of the pumps were investigated in the scale range from 1/4 to 20/1. The optimum efficiencies for different area ratios over a wide range were determined according to the scale and size of roughness. It was seen that the efficiency increases significantly up to a given scale size at a constant absolute roughness, while it is generally independent of the scale size at constant relative roughness. The relative efficiency for the area ratio 5.92 reduces to 60% at the relative roughness value of 0.05. Moreover, CFD appears to be the most appropriate tool for model studies of jet pumps.Selcuk University under the BAP Project [11201037]This research was supported by Selcuk University under the BAP Project No: 11201037

B2-L10 thermoelastic transformation on Ni50Mn29Sb12.5Co8.5 shape memory Heusler alloy

In this study, a series of practically unique and valuable properties that occur with the structural phase transformation on the Shape Memory Ni50Mn29Sb12,5Co8,5 Heusler alloy with comparing different homogenization times, were investigated. From the results of X-ray diffraction (XRD) measurements carried out in this study, B2 → Θ (L10) structural phase transformation was observed. It has been understood that the alloy exhibits a ferromagnetic transition via Vibrating Sample Magnetometer (VSM) as well as the thermoelastic martensitic transformation detected by Differential Scanning Calorimetry (DSC) investigations. At the same time, it has been determined that the paramagnetic β phase has B2 type bcc lattice structure. It has been determined that β (B2) → Θ (L10) diffusionless phase transformation, which is considered as a structural phase transition occurring in the material, includes a martensitic mechanism with narrow temperature hysteresis. It was determined that the average lattice parameter of the B2 lattice was 2.956 Å. It was understood that the thick 110B2 reflection was divided into 110B2 and 111L10 peaks according to the measurements made between 42° and 44° angles. The diffraction peaks obtained in the study prove the existence of parallel L10 lamellae of the martensite phase with habit plane boundaries close to {110}B2. All these findings were supported by scattering electron microscope (SEM) and metal microscopy studies

Analysis of stresses created effect of different temperature in hybrid bonded composite plates

Bu çalışmada, karma bağlantı yapılarak birleştirilmiş iki kompozit plakada uygulanan farklı uniform sıcaklıklar etkisiyle meydana gelen gerilmeler analiz edilmiştir. Karma bağlantı, pim ve yapıştırıcının birlikte kullanılması ile meydana getirilmiştir. Analizde sonlu elemanlar metodu (SEM) kullanılmıştır. Modelleme üç boyutlu olarak yapılmıştır. Modelleme ve çözümde, sonlu elemanlar yazılımı olan ANSYS programından yararlanılmıştır. Oluşturulan modele hem çekme yükü hem de uniform sıcaklık yükü aynı anda uygulanmıştır. Sıcaklığın gerilmeler üzerine etkisini gözlemlemek için çekme yükü sabit tutulmuş fakat 50, 70, 90 ve 110 o C’lik üniform sıcaklıklar uygulanmıştır. Elde edilen analiz sonuçlarına göre gerilmeler delik çevresinde yoğunlaşmıştır. Dolayısıyla, karma bağlantı üzerinde başlayacak bir hasarın delik çevresinden başlayacağı anlaşılmıştır. Gerilmelerin değeri, üniform sıcaklık artışındaki miktara bağlı olarak artmaktadır.Mechanical properties of glass-fiber composite materials make them attractive for structural applications where high strength-to-weight and stiffness-to-weight ratios are required. Bolts, pins or rivets have been used extensively in these applications for transferring load between the structural components (Wu and Hahn, 1997). Among the different techniques for joining structural members, mechanical fastening through a pin is a common choice owing to low cost, simplicity, and facilitation of disassembly for repair (Scalea, Cappello and Cloud, 1999). Contrary to many metallic structural members, for which the strength of the joints is mainly governed by the shear and tensile strengths of the pins, composite joints present specific failure modes because of their heterogeneity and anisotropy (Pierron, Cerisier and Grediac, 2000).Adhesive bonding technology is commonly used these days in almost all the industries fields of the world and this is mainly because of its high strength-weight ratio, low cost and high efficiency (You et al., 2007). Nonetheless, the design of safe and cost effective bonded joints is a main challenge. It forces on the engineer to have a good understanding of the effect of material and geometric parameters on the joint’s strength (Derewonko et al., in press). In fact, the adhesive joints experience not only mechanical loads but also thermal loads. Because the adhesive joints consist of materials with different mechanical and thermal properties, the thermal strains in the joint members might cause serious stresses (Apalak and Gunes, 2002). According to literature survey, many researchers have studied either adhesively bonded or pinned single lap joint, double lap joint etc. But, the analysis of hybrid joints designed using both adhesively bonded and pinned single lap joints under both thermal loads and tensile loads has not been analyzed up till now, according to authors’ knowledge. Therefore, in this study stresses created different uniform temperatures effect in two composite plates bonded together with hybrid joint were analyzed. The hybrid joint was created using both pin and adhesive with together. In analysis, the finite element method (FEM) was used. Modeling and solutions were done as three dimensional FEM. During both modeling and solution processes, it was utilized from ANSYS software which is a perfect finite element code. It is known that, the hole is needed if the pin, bolt, rivet etc. are used in the structure for mechanical joint. Therefore, mesh structure is very important around the hole zone for FEM analysis because of stress concentrations. Nonetheless, the generation of mapped mesh is very difficult if the model has hole. However, in this study, the mapped mesh was provided by the author. Both tensile and uniform temperature loads were applied on created model with together. To observe the effect of temperatures on stresses tensile load is applied as single value when selected constant uniform temperature values were performed as 50, 70, 90 ve 110 o C. According to obtained analysis results, it was shown that thermal stresses were concentrated around the pin hole. Therefore, it is understood that any failure may be start from pin hole zone firstly. The magnitudes of stresses were increased by increasing uniform temperature, because the differences of mechanical properties between adhesive and composite adherents cause this result. The thermal expansion coefficient is very important in this increasing, particularl

Numerical analysis of hydrogen storage in metal-hydride beds [Metal-Hidrid Yataklarda Hidrojen Depolanmasinin Sayisal Analizi]

In this study, hydrogen absorption in a metal-hydride bed is numerically investigated. The mathematical model considers the heat and mass transfer and the chemical reaction that take place during the absorption. The hydride bed heats up due to the exothermic reaction. Numerical results show that hydrogen absorption is completed faster near the cooled wall, while it takes longer at the center. Hydriding processes are investigated with the temperature histories, H/M ratio and temperature distributions at several locations in the tank. The estimated H/M ratio is found to agree satisfactorily with the experimental data in the literature

Simulation of laminer film condensation over a horizontal tube using cylindirical and cartesian boundary layer equation

Bu araştırmada; buhar süpürmeli yoğuşma olarak adlandırılan iki fazlı akışın denklemleri sayısal yöntemle çözülerek, yatay tüp üzerinde su buharının yoğuşmasının değişik şartlardaki incelenmesi yapılmıştır. Elde edilen sonuçlar, Shekriladze et al.(3), Rose(1O), ve Homescu et al.(12) tarafından verilen teorik verilerle kıyaslanmış ve sonuçların uyumlu olduğu görülmüştür. Ayrıca silindirik sınır tabaka denklemleriyle yapılan analiz sonuçları ile kıyaslama yapılmıştır. Elde edilen sonuçlar grafikler halinde sunulmuştur.In this study, governing equation of the two phase flow named vapour shear induced flow of condensate has been numerically solved using finite difference method and the condensation over horizontal tubes has been examined under several physical conditions. The results obtained are compared with the previously given results by Shekriladze et al.(3), Rose(1O), and Homescu et al.(12) and found to be in good agreement. In addition the analysis is repeated by means of using cylindirical boundary layer equations and comparison with classical boundary layer equations has been made. Results obtained are given in graphics