Mechanical Engineering

Improvements in the aviation industry raise the usage of titanium and its alloys.  Main reasons of using titanium alloys are superior mechanical properties, high strength-to-density ratio, fatigue and corrosion resistance at moderately high temperatures.  All these superior properties comes with a major disadvantage as poor machinability.  Machining of titanium alloys generates excessive heat in the vicinity of the tool cutting edge so that induces poor tool life.  Cutting parameters of titanium alloys are also limited because of fire risk.  Previous studies show that Ultrasonic Assisted Turning (UAT) technique gives promising results at aviation materials.  UAT changes the relationship between tool and work piece thus reduces cutting force and temperature on the cutting zone.  UAT provides better surface finish and roundness for work piece.  In this study, machining of Ti6Al4 alloy investigated by literature review and 2D finite element analysis performed to understand the effects of UAT in turning process.  UAT simulation results are compared with conventional turning simulation and experimental results performed by previous studies.  It is confirmed that UAT technique alters cutting conditions with specific cutting parameters (cutting force, cutting temperature, chip formation) however, it has some limitations.

Structural health monitoring (SHM); isthe tracking method used to determine the location and size of the damage to the structure and  the  life  of  the  structure.  In  this  study,  the  behavior  of  a  free  piezoelectric  sensor  was  experimentally  tested  using  theelectromechanical impedance method (EMI), taking into account the structures exposed to varying environmental conditions, and simulation studies were performed using the ANSYS finite element program. In the experimental study; impedance measurements were performed between -10 °C and -45 °C after impedance  measurements of the piezoelectric sensor were completed at room temperature. The frequency and amplitude have increased with decreasing temperature. In the simulation studies, harmonic analysis results were obtained by using the ANSYS finite element program of the piezoelectric sensor used in the experimental study. The frequency  and  amplitude  increased  as  the  temperature  decreased,  as  in  the  results  obtained  from  the  experimental  studies.  The results obtained from experimental and simulation studies were found to be close to each other

In the present study, the aim is to predict ice accumulation on a 2-D commercial engine intake. The developed tool mainly consists of four modules: modules for the calculation of the flow-field, droplet trajectories and collection efficiencies, thermodynamics and ice accretion. The flow-field solution is done by a panel method modified for the intake geometry and the required engine mass flow rate using a superposition technique. The droplet trajectories are computed using the Lagrangian approach, while the Extended Messinger Model is implemented in the ice accretion module. The results are compared with numerical literature data.

Railway rails work in contact with railway vehicle wheels.
During this contact high surface contact stresses and
different sliding speeds occur between wheel-rail pair.
Stress values that occur on top and side of rail geometry
are different. This situation causes wear and damage on
rail material in time.
In this study primarily the rail material that is used in our
country was characterized. Wear experiments are
conducted in dry and wet conditions, different contact
stresses and sliding speeds in order to sample rail-wheel
contact. All wear tests were performed according to DIN
50324 standard with WC ball as counter object in a ball on
disc geometry. Wear surfaces were characterized by
optically, SEM microstructure analysis and EDS analysis,
friction coefficients and wear rates were calculated for
every test condition. As a result damage that occurs on rail
material during working conditions were tried to be
determined.

Purpose Plasma transferred arc (PTA) coating is a novel method for surface-coating applications. In this method, the substrate is melted using a plasma arc, and surfacing agents such as carbides are introduced to the melt pool. The purpose of this study is to investigate the effect of boron carbide (B4C) in nickel-based coating on AISI 4140 steel. Design/methodology/approach Samples were tested on a ball-on-disc wear device, and the microstructure, as well as wear properties, were investigated using SEM and XRD. Findings The effect of B4C addition was shown to be linear, with a p-value of 0.0248, indicating strong evidence. The reason for this increase was found to be the increase in third-body generation resulting from hard phases that form couples with the soft base material, nickel. It was concluded that using 6 per cent B4C was the optimal solution. Originality/value In the literature, the effect of neither low temperature on a nickel coating with B4C nor B4C as a single surfaci...

Railway rails work in contact with railway vehicle wheels.During this contact high surface contact stresses anddifferent sliding speeds occur between wheel-rail pair.Stress values that occur on top and side of rail geometryare different. This situation causes wear and damage onrail material in time.In this study primarily the rail material that is used in ourcountry was characterized. Wear experiments areconducted in dry and wet conditions, different contactstresses and sliding speeds in order to sample rail-wheelcontact. All wear tests were performed according to DIN50324 standard with WC ball as counter object in a ball ondisc geometry. Wear surfaces were characterized byoptically, SEM microstructure analysis and EDS analysis,friction coefficients and wear rates were calculated forevery test condition. As a result damage that occurs on railmaterial during working conditions were tried to bedetermined.

Stratolaunch uçağı, uzaya uydu ve insanlı uzay mekiği göndermek amacıyla yapılmış olan bir uçaktır. Uçak dünyada şu ana kadar üretilmiş en büyük uçaktır. Proje, daha önce SpaceShipOne'un yaratılması konusunda işbirliği yapan Microsoft kurucu ortağı Paul G. Allen ve Scaled Composites'in kurucusu Burt Rutan tarafından Aralık 2011'de resmen açıklanmış ve geliştirme maliyetleri başlangıçta 2011 yılında 300 milyon ABD doları olarak öngörülmüştür. Stratolaunch uçağında toplam 6 adet Boeing 747 motoru bulunmaktadır. Kanat açıklığı 117 metre olan dev uçak 226 ton faydalı ağırlık taşıyabilme kapasitesine sahiptir. Uçağın menzilinin yaklaşık 3700 km (2000 NM) kadar olması planlanmaktadır. Uçak yaklaşık 35000 feet (10 km) yüksekliğe kadar çıkıp, uzaya göndereceği uydu veya insanlı mekikleri bırakacaktır. Uçağın toplam üç kişilik bir mürettebatı olması planlanmaktadır. Stratolaunch uçağı projesine 2011 yılında başlanılmıştır. Uçağın ilk yer taksi testleri Aralık 2017'de başlamıştır. Uçak bu testler esnasında pistte saatte 46 km hıza kadar ulaşmıştır. Mart 2018 de yapılan testte ise uçak 75km/h hıza ulaşamayı başarmıştır. Bundan sonraki testte uçağın hızının 130km/h ulaşması, daha sonraki testlerde de 220 km/h düzeyine ulaşması beklenmektedir. Testler başarılı olduğu takdirde 2018 yaz aylarında ilk uçuş testinin yapılması da planlanmaktadır. Paul Allen, Stratolaunch projesi ile uzaya yapılacak olan her türlü uydu ve insanlı mekik gönderiminin daha ucuz, daha az zaman alıcı olmasını ve böylece uzaya gitmenin rutin bir işlem halini almasını (tıpkı gerçekleştirdiğimiz kıtalararası uçak yolculukları gibi) amaçladığını belirtmektedir. Projenin başarılı olması durumunda, aynı uçaktan daha fazla üretilmesi durumunda, geçmiş dönemlere göre çok daha fazla sayıda uzay mekiği uzaya gönderilebilecektir. Bu durum uzay araştırmalarının hızının artmasını sağlayacaktır. Projenin başarılı olması durumunda insanlığın uzay macerasında yeni bir sayfa açılmış olacaktır.