Buckling driven delamination of orthotropic functionally graded materials

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Tezin Türü: Yüksek Lisans

Tezin Yürütüldüğü Kurum: Orta Doğu Teknik Üniversitesi, Mühendislik Fakültesi, Makina Mühendisliği Bölümü, Türkiye

Tezin Onay Tarihi: 2006

Öğrenci: SUPHİ YILMAZ

Eş Danışman: SERKAN DAĞ, FEVZİ SUAT KADIOĞLU

Özet:

In today's technology severe working conditions increase demands on structural materials. A class of materials which are developed to meet these increased demands is Functionally Graded Materials (FGMs). These are inhomogeneous structural materials which are able to withstand large temperature gradients and corrosive environment. Application areas of FGMs are in aerospace industry, nuclear reactors, chemical plants and turbine systems. FGMs have gradual compositional variation from metal to ceramic which give them mechanical strength, toughness and heat resistance. However under high temperature gradients, cracking problems may arise due to thermal stresses. In layered structures the final stage of failure may be delamination due to crack extension. The objective of this study is to model a particular type of crack problem in a layered structure consisting of a substrate, a bond coat and an orthotropic FGM coating. There is an internal crack in the orthotropic layer and it is perpendicular to material gradation of coating. The position of the crack inside the coating is kept as a variable. The steady-state temperature distribution between the substrate and the coating causes a buckled shape along crack face. The critical temperature change, temperature distribution, mixed mode stress intensity values and energy release rates are calculated by using Displacement Correlation Technique. Results of this study present the effects of geometric parameters such as crack length, crack position, etc as well as the effects of the type of gradation on buckling behavior and mixed mode stress intensity factors.