Akıllı malzemelerin mekanik özellikleri
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Dosyalar
Tarih
2017
Yazarlar
Dergi Başlığı
Dergi ISSN
Cilt Başlığı
Yayıncı
Bursa Teknik Üniversitesi
Erişim Hakkı
info:eu-repo/semantics/openAccess
Özet
Akıllı malzemeler, dış uyaranlar (örneğin stres, sıcaklık, elektrik, manyetik alan) etkisi ile özelli klerini değişti rerek tepki verme yetisine sahip ola n malzemelerdir . Aynı zamanda; havacılık, otomotiv, biyomedikal, elektro nik gibi birçok uygulama alanında yer almaktadırlar. A kıllı malzemeler hem yeni bir ürün geliştirilmesiyle hem de konvansiyonel malzemelere geometrik özellikler kazandırılmasıyla oluşabilir. Bu bağlamda bu çalışma içerisinde, konvansiyonel malzemelere geometrik özellik katarak elde edilmiş ve farklı mekanik özelliklerinden dolayı merak konusu olan auxeticlerden bahsedilmiştir. Malzeme olarak k onvansiyonel kabul edilen ve biyomedikal alanda sıkça kullanılan folyo (çok ince) yapıdaki 316L paslanmaz çelik kullanılmıştır. Femtosecond lazer kesim yöntemi ile konvansiyonel malzemeye farklı hücre boyutlarına sahip geometrik şekil işlenerek, Negatif Po isson Oranlı auxetic malzeme elde edilmiştir. Mekanik özelliklerin tespiti için dikdörtgen kesitli numuneler üzerinde çekme testi uygu lanmış, aynı şartlarda testleri yapılan konvansiyonel numuneler ile kuvvet - şekil değişimi ve gerinim - gerilim grafikleri sa yesinde, hücre boyutu, kalınlık ve elastisite modülü parametreleri karşılaştırılıp, sonuçlarıyla beraber kullanım alanına göre tercih seçenekleri sunmuştur. Bu karşılaştırmalar sonucunda, folyo yapıdaki konvansiyonel malzemelerin elastisite modülü, normal elastisite değerinden daha düşük olduğu tespit edilmiştir. Auxeticlerin gözenekli yapılarından dolayı konvansiyonel malzemelere göre daha düşük kuvvetler altında deforme olduğu fakat daha fazla şekil değişimine uğradığı görülmüştür. Aynı zamanda auxeticler in farklı büyüklükteki hücre boyutları ve kalınlıkları arasında kıyas yapıldığında, hücre boyutu küçülüp kalınlık arttıkça, auxetic etkinin daha fazla sürdüğü anlaşılmıştır. Sonlu elemanlar yöntemiyle de eğme kuvveti ile ortaya çıkan sinklastik davranışın ın auxetic numunedeki aldığı görsel in celenmiştir .
Smart materials have the ability to change more than one of its properties with external stimulis (e.g. stress, temperature, electric, magnetic field). These materials have wide range of applications in aerospace, automotive, medical, electronics and more. Thus its significance is rising for the next generations. Smart materials can be obtained either as entirely new developed product or by adding novel features to conventional materials. In this study, auxetic materials were mentioned, which were obtained by adding geometric features to conventional materials and which has an interest due to their different mechanical properties. 316L stainless steel is used in foil (very thin) structure which is accepted as conventional material which is used frequently in biomedical field. By using the femtosecond laser cutting method, a geometric shape with different cell sizes is processed from conventional material and a negative Poisson Ratio auxetic material is obtained. In order to determine the mechanical properties , tensile tests were applied on rectangular samples and the effect of cell size, thickness and elasticity modulus parameters on mechanical behavior is investigated. As a result of these tests , it has been found that the modulus of elasticity of the conven tional materials in foil structure is lower than the steels known elastic modulus obtained from bulk samples . Due to the porous structure of auxetics, it has lower modulus of elasticity than conventional materials but it can bear more deformation prior to failure and show a completely different failure pattern . At the same time, when compared to the size of cells and thicknesses of auxetics, it is understood that the auxetic effect is longer as the cell size is decreased and the thickness is increased. By means of the finite elements, the synclastic behavior, which occurs with the bending forces, has been visually examined in the auxetic sample.
Smart materials have the ability to change more than one of its properties with external stimulis (e.g. stress, temperature, electric, magnetic field). These materials have wide range of applications in aerospace, automotive, medical, electronics and more. Thus its significance is rising for the next generations. Smart materials can be obtained either as entirely new developed product or by adding novel features to conventional materials. In this study, auxetic materials were mentioned, which were obtained by adding geometric features to conventional materials and which has an interest due to their different mechanical properties. 316L stainless steel is used in foil (very thin) structure which is accepted as conventional material which is used frequently in biomedical field. By using the femtosecond laser cutting method, a geometric shape with different cell sizes is processed from conventional material and a negative Poisson Ratio auxetic material is obtained. In order to determine the mechanical properties , tensile tests were applied on rectangular samples and the effect of cell size, thickness and elasticity modulus parameters on mechanical behavior is investigated. As a result of these tests , it has been found that the modulus of elasticity of the conven tional materials in foil structure is lower than the steels known elastic modulus obtained from bulk samples . Due to the porous structure of auxetics, it has lower modulus of elasticity than conventional materials but it can bear more deformation prior to failure and show a completely different failure pattern . At the same time, when compared to the size of cells and thicknesses of auxetics, it is understood that the auxetic effect is longer as the cell size is decreased and the thickness is increased. By means of the finite elements, the synclastic behavior, which occurs with the bending forces, has been visually examined in the auxetic sample.
Açıklama
Anahtar Kelimeler
Makine Mühendisliği, Mechanical Engineering, Smart materials, Negative Poisson's Ratio, Auxetic, Akıllı malzemeler, Negatif Poisson Oranı, Auxetic