CHARACTERIZATION OF 6061 T651 ALUMINUM PLATES SUBJECTED TO HIGH-VELOCITY IMPACT LOADS

Ballistic response of single or multi-layered metal armor systems subjected to kinetic energy pro-jectiles was investigated in many experimental, theoretical and numerical studies.In this study, 6061 T651 aluminum plates impacted by 9 mm bullets were investigated. Microstructural investigations have been carried out using optical microscopy. Microhardness values were used to determine the strength behavior of the plates. Influence of the plate thickness and impact velocity on the microstructure has been evaluated. It was concluded from the study that thinner plates are more prone to deformation hardening with high penetration depth values even at low impact velocities while thick plates are more susceptible to thermal softening with less penetration depths. Maximum hardness values were obtained just below the impact zone in both plate thicknesses

Polietilen destekli AA 7075 T651 levhalarda katman sıralamasının balistik dayanıma etkisi

Using armor systems in battle field is a necessity. These protection tools have been gaining more importance day by day since the wars in the ancient times. Human beings throughout recorded history have used various types of materials to protect themselves from injury in combat and other dangerous situations. At first, protective clothing and shields were made from animal skins. As technology became more advanced, wooden shields and then metal shields came into use. Armor systems, particularly those used for the military purpose must be designed as protection against modern weapons. For this reason, ballistic efficiency of the armor subjected to impact load of specific ammunition is under investigation. Armors designed by using together the ballistic specifications of metal and composite materials used in armor applications provide the desired protection level regarding the weight and ballistic efficiency. Layered structures are generally used in ballistic armor systems. Layered armors basically consist of two main parts: front layer and support layer. Front layers are made from metal or ceramic materials. They aim to deform the nose shape of the projectile and to reduce its ballistic efficiency. Rear or support layers are assigned to absorb the remaining kinetic energy of the projectile. Metal, composite and/or elastomer materials are used in integral armor systems as a support layer. Armor steels, titanium and aluminum alloy materials are most commonly used armor materials. Hardness values of these materials can be at extremely high levels. Aluminum alloys find their use in many different structures such as offshore platforms, bridge decks, train and ship components, etc. Due to their low density, high structural strength and energy absorption capacity, aluminum alloys are also used in lightweight protection systems. Composites have been commonly used in lightweight armor systems. In addition to various advantages, composites are also preferred due to their high energy absorption capacity. At this point, it must be taken into account that quite a high ballistic performance can be acquired in composite armor structures established by using ultra high molecular weight polyethylene fibers. In many studies, it is found that polyethylene has an ultra high energy absorption capacity as well as its low density. In this study, influence of layer sequencing was investigated experimentally on ballistic resistance of aluminum plates supported by using high molecular weight polyethylene plates. In experiments, 7075 aluminum alloys of T651 heat treatment were used. Three different types of layer sequencing were examined in the study. It was aimed in the choice of the aluminum alloys used in the tests that effects of the support layer on the ballistic performance of the plates must be investigated distinctively. Focusing on this aim, it was decided that using the aluminum alloys whose ballistic performance is well known without support layer is more convenient. It is known from the previous tests that AA 7075 T651 aluminum plates of 4.00 mm thickness are perforated at 383~400 m/s projectile velocity interval and without the support layer. Using this knowledge, influence of three different types of layer sequencing on ballistic performance of the AA 7075 T651 aluminum plates of 4.00 mm thickness with polyethylene support layer was investigated. In experiments, MKEK (Mechanical and Chemical Industry Corporation) made FMJ (Full Metal Jacket)  Parabellum  bullets of 9 mm  diameter and 19 mm length were used. The distance between the target plate holder and the shooting system is 5 meters. All shots were normal to target plates. Oehler Research optical ballistic devices were used for the velocity measurements. To test the one plate of 250x250 mm dimensions for four times by separating the plate, a multi shooting fixture was designed, fabricated and used. It was also used to represent the fully clamped boundary conditions. Plate was placed between the two parts of the fixture and bolted at the middle points of four edges. As a result of the experiments, despite the fact that three of the layer sequencings have the same thickness, it was clearly observed that the best ballistic performance can be obtained by sequencing the aluminum plate as a front layer and the polyethylene support layer at the rear side. Otherwise, it was clearly understood from the test results that plate thicknesses influence the deformation mechanisms due to high velocity impact. Keywords: Ballistic resistance, layered armor, layer sequencing, high velocity impact.Bu çalışmada, yüksek molekül ağırlıklı polietilen levhalar kullanılarak desteklenmiş AA 7075 T651 levhaların balistik dayanımlarına üç farklı katman sıralamasının etkileri deneysel olarak incelenmiştir. Alüminyum alaşımlar, düşük yoğunluk, yüksek yapısal mukavemet ve enerji emiş kapasitesi özellikleri açılarından, yapısal uygulamalar yanında, hafif korunma sistemlerinde de kullanılmaktadır. 4.00 mm kalınlığındaki AA 7075 T651 levhaların, destek katmanı olmadan belirli mermi hızlarında delindikleri yapılan ön testlerde belirlenmiştir. Bu bilgi kullanılarak, farklı katman sıralamalarının balistik dayanıma etkileri deneysel olarak incelenmiştir. İncelenen ilk grupta, ön katman olarak 8.00 mm kalınlığında polietilen ve destek katmanı olarak 4.00 mm kalınlığında AA 7075 T651 levha, ikinci grupta 2.00 mm kalınlığında iki AA 7075 T651 levha arasında 8.00 mm kalınlığında polietilen levha, son grupta ise ön katman olarak 4.00 mm kalınlığında AA 7075 T651 ve destek katmanı olarak 8.00 mm kalınlığında polietilen levha kullanılmıştır. 2’nci HİBM Komutanlığı bünyesinde bulunan atış poligonunda gerçekleştiren deneylerde, MKEK yapımı 9 mm çapında Parabellum mermiler kullanılmıştır. Tüm atışlar 5 m uzaklıktan ve levhaya dik olarak gerçekleştirilmiştir. Yapılan deneyler sonucunda, her üç tasarımın da toplam katman kalınlıkları eşit olduğu halde, destek katmanı olarak kullanılan polietilen levhaların, alüminyum levhaların arkalarına yerleştirildikleri seçeneğin, en yüksek balistik dayanıma sahip tasarım olduğu belirlenmiştir. Deneylerde ayrıca, levha kalınlıklarının, yüksek hızlı çarpma sonucunda oluşan hasar biçimlerini yakından etkilediği gözlenmiştir. Anahtar Kelimeler: Balistik dayanım, katmanlı zırh, katman sıralaması, yüksek hızlı çarpma.&nbsp

On wing life optimization of commercial turbofan aircraft engines

Bir havayolu işletmesinde, turbofan uçak motorlarından sorumlu olan mühendisliğin birincil önceliği, motorların teknik olarak uçuşa elverişliliğini sağlayacak şekilde yönetilmesi ve bununla birlikte uçak motorlarının kullanım maliyetinin, güvenilirliğinin, emniyetinin ve operasyonel esneklik açısından motor performanslarının yeterli seviyelerde olmasının temin edilmesidir. Motorların uçak üzerinden sökülmesi ve motora gereken iyileştirme işlemlerinin yapılması gereken optimum bir zaman aralığı olduğu bilinmektedir. Optimum zaman aralığından önce gerçekleştirilen sökümlerde henüz kullanılabilir durumdaki parçaların vaktinden önce tamir edilmesi nedeniyle, kullanılabilecek parça ve motor ömrü ek bir maliyet olarak ortaya çıkacaktır. Optimum zaman aralığından sonra gerçekleştirilen sökümlerde, tamir edilmesi gereken parçaların sayılarının artması, tamirlerin zor ve maliyetli olması ek bir maliyet olarak ortaya çıkmaktadır. Söz konusu optimum uçuş ömrünün belirlenebilmesi amacıyla bir operatörün motorlarına ait veriler hem analitik hem de istatiksel olarak analiz edilmiştir. Gerçek problemin özelliklerini bozmayacak yaklaşımlarla, problem matematiksel olarak modellenmiştir. Bakım maliyeti, performans, güvenilirlik ve emniyet hedefleri bir arada düşünülmesi gerektiğinden, problem çoklu amaç fonksiyonlu bir optimizasyon problemi şeklinde çözülmüştür. Söz konusu çoklu amaç fonksiyonlu problem, bir havayolu mühendisliğinin öncelikleri göz önüne alınarak dayanıklılık fonksiyonu şekline dönüştürülmüş ve optimizasyon genetik algoritma yöntemi kullanılarak gerçekleştirilmiştir. Optimizasyon sonunda elde edilen sonuçlara göre, ele alınan motor tipi için bir optimum uçuş ömrü, bir başka değişle, optimum söküm aralığı bulunmuşur. Anahtar Kelimeler: Uçak motor bakımı, uçuş ömrü, optimizasyon.The primary objective of an airline powerplant engineer responsible from turbofan aircraft engines is to technically manage the engines to be available for revenue flight, while achieving the desired goals of cost of use, reliability and safety, with adequate engine performance level for operational flexibility. For an airline, flight safety is a must. Thus, aviation authorities throughout the world strictly bound the range in which an airline could move to meet the above goals. Since, approximately 40-45% of total aircraft maintenance cost is directly arising from engine maintenance costs, meeting these objectives becomes a very important issue as far as the competitiveness of the airline business is concerned. Under these circumstances, airlines always seek to find and explore methods in order keep the powerplants running with an optimized cost versus on wing life. The engine on wing maintenance concept is known as "on-condition maintenance". In this concept, engines are continuously monitored during their on wing operation in order to prevent failures and to meet goals on reliability and safety. In other words, engines are kept on wing as long as reliability, safety and performance levels are acceptable. All of the above conditions end up with raising the following important question: What is the time on wing of an aircraft engine that will fulfill all of these goals at the required levels This question forms the basis of analyzes performed in this study. It is known that there is an optimum time at which engine should have essential restoration done, in order to meet an optimized cost for removal. In other words, at times prior to the optimum one; the opportunity costs which are arising due to repairing an engine before all its useful life is consumed result in an increase in maintenance cost. At times greater than the optimum; the number of parts which need repair, the difficulty and cost of repair and the number of parts which must be scrapped increase. As a result, the maintenance cost increases. In order to search for this optimum, available data is gathered from one airline and analyzed both analytically and statistically. The problem is mathematically modeled by making assumptions, without effecting the accuracy of the real problem. In order to achieve a better understanding, the objectives (maintenance cost, performance, reliability and safety) are studied as sub problems. The data relating these objectives to the engine on wing time are searched and analyzed. For each of these objectives, mathematical expressions are derived. As far as the integrity of the goals of maintenance cost, performance, reliability and safety is concerned, a multi objective optimization problem is proposed. The model is converted into a fitness function form by an airline engineering perspective and multi objective problem of on wing life optimization is solved by using a Genetic Algorithm based solver. Genetic Algorithm method has been selected as being a robust and reliable technique for multi objective engineering optimization problems. Since performance deterioration characteristics end up with three different types of deterioration curves, three sub problems have been solved. This ensured the diversity in terms of actual engine performance deterioration characteristics, which is a result of operational, configurational and manufacturing diversities encountered in the real operation. Performance related diversity is believed to cover the above mentioned facts of the actual problem and enables a better forecast on the optimum on wing life of commercial turbofan aircraft engines. All the results are gathered considering airline engineering priorities and the optimum on wing life of a CFM56-3C1 engine is calculated. A removal planned within this optimum removal interval will achieve all the priorities in terms of minimum maintenance cost, adequate performance, while not sacrificing from reliability and safety. The result of the optimization is compared with the actual removals and found to be in line with the actual removal time frame. This proves the proficiency of proposed method and the mathematical model. Additionally, the operational factors affecting the aircraft engine on wing life is discussed in order to derive a generalized mathematical model for adaptation to other airline engine fleets and to other engine types. Thus, a generaized model is formulated in order to find the optimum time on wing for any type of commercial turbofan engine operated in any fleet. Keywords: Aircraft engine maintenance, on wing life, optimization

ALÜMİNYUM LEVHALARIN YÜKSEK HIZLI ÇARPMA DAVRANIŞLARI İÇİN AMPİRİK BİR MODEL

Due to their low density, high structural strength and energy absorption capacity, aluminum alloys are frequently used in lightweight armor systems such as aeronautics applications, offshore platforms, ship components, bridge decks, etc. This wide application area considering behavior of materials subjected to high velocity impact load increases the importance of the investigations about developing analytical solutions to determine the failure mechanisms and penetration depth caused by high velocity impact. In this study, an exponential equation was proposed that can be used to determine the penetration depth of the 2024 aluminum alloys of T351 condition. Comparing the analytical results with the results of previous experimental study which used the 9 mm Parabellum bullets, it was determined that equation proposed efficiently model the penetration depth of the AA 2024 T351 plates under impact load at velocity level in experiments

YÜZEY KAPLAMASI VE DESTEK KATMAN İLAVESİNİN ALÜMİNYUM LEVHALARIN BALİSTİK PERFORMANSINA ETKİLERİ

Due to their low density, high structural strength and energy absorption capacity, aluminum alloys are frequently used in lightweight armor systems such as aeronautics applications, offshore platforms, ship components, bridge decks, etc. Impacts or other types of high-speed loading conditions are thus a relevant issue for several of these applications. In these applications, weight of a structure is an important design criterion. For this reason, it’s known that aluminum alloys are preferred instead of conventional steel or concrete. This wide application area considering behavior of materials subjected to high velocity impact load increases the importance of the investigations about solutions to decrease the penetration depth caused by high velocity impact. In this study, influences of ballistic performance improving techniques e.g. surface coating and adding support on high velocity normal impact resistance of aluminum plates were analyzed and compared experimentally

YÜKSEK HIZLI ÇARPMA YÜKLERİNE MARUZ 6061 T651 ALÜMİNYUM LEVHALARIN KARAKTERİZASYONU

Kinetik enerjiye sahip mermilere karşı, tek veya çok katmanlı metal zırh sistemlerinin gösterdiği balistik davranış, çok sayıda deneysel, teorik ve sayısal çalışmayla araştırılmıştır. Bu çalışmada, 9 mm mermilerle üzerine atış yapılan 6061 T651 alüminyum levhalar incelenmiştir. Mikroyapı incelemesi optik mikroskop kullanılarak gerçekleştirilmiştir. Levhaların mukavemet davranışlarının belirlenmesinde mikrosertlik değerleri kullanılmıştır. Levha kalınlığı ve çarpma hızının mikroyapı üzerindeki etkisi değerlendirilmiştir. Çalışma sonucunda; ince levhaların, düşük çarpma hızlarında bile yüksek nüfuziyet derinliğiyle deformasyon sertleşmesine daha duyarlı olduğu, kalın levhaların ise düşük nüfuziyeti derinliğiyle termal yumuşamaya eğilimli olduğu değerlendirilmiştir. Maksimum sertlik değerleri her iki levha kalınlığında da çarpma bölgesinin hemen altında elde edilmiştir

THE IMPACT OF HARBOR USE ON ZOOBENTHOS

In 7 different region which represent most used harbors, ports and fishing shelters in the Sea of Marmara and Black Sea in Turkey coasts. Ecological Quality Status was assesed by sampling soft -bottom macrozoobenthos from 22 stations in 2014