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Interfaces of Ceramic-Matrix Composites
Design, Characterization and Damage Effects
Longbiao Li
Author
Prof. Longbiao Li
Nanjing University of Aeronautics and
Astronaut
College of Civil Aviation
No. 29 Yudao St.
210016 Nanjing
China
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Print ISBN: 978‐3‐527‐34778‐0
ePDF ISBN: 978‐3‐527‐82803‐6
ePub ISBN: 978‐3‐527‐82805‐0
oBook ISBN: 978‐3‐527‐82804‐3
To Shengning
Preface
To realize the advantages of operating systems under high temperature conditions, it is necessary to master the properties of a large number of high temperature materials and components. For example, a significant increase in the gas temperature will significantly increase the gas turbine efficiency. The introduction of new materials and new technology has gradually improved the high‐temperature performance of gas turbine engine for more than 70 years, but the development of cooling methods and solutions has contributed more than 75% to the performance improvement. Although component cooling methods and engine material properties have improved significantly, most high‐temperature alloys currently operate at temperatures above 90% of their original melting point. Higher operating temperatures are required for more efficient engines, which will require higher component temperatures. As the operating temperature continues to increase, new materials with higher thermo‐mechanical and thermo‐chemical properties are required to meet high‐temperature structural applications. Ceramic‐matrix composites (CMCs) are considered to have the potential to provide high strength, high toughness, creep resistance, low notch sensitivity, and environmental stability to meet the needs of future high‐performance turbine engines.
For a monolithic ceramic material, when it is subjected to tensile stress, it appears as elastic deformation at low stress level; as the stress increases, cracks occur in the defect region of the material, and the cracks rapidly expand, causing the material to undergo brittle fracture. When the CMC material is subjected to tensile stress, it is elastically deformed before matrix cracks; as the tensile stress increases, the matrix begins to crack, and the fibers begin to debond and play a role of crack bridging; as the tensile stress increases further, the cracks become saturated, and the bridging fibers begin to pull out; as the tensile stress continues to increase, the fibers begin to break until the material reaches the highest strength. The fracture modes of monolithic ceramics and CMCs are different, mainly because the interface plays a role in the fracture process of CMCs. The interface is a special domain between the matrix and the reinforcement. It is the link between the fiber and the matrix, and also a bridge for load transfer. The structure and properties of interphase directly affect the strength and toughness of CMCs. This book focuses on the time‐dependent mechanical behavior of CMCs at elevated temperatures, as the following:
1 (1) The definition, function, and design of interface in different fiber‐reinforced CMCs are given. The interphase plays an important role in the mechanical behavior of non‐oxide and oxide/oxide CMCs at room and elevated temperatures. The interface phase has two basic functions. One is mechanical fuse function that is to deflect crack growth to protect the fiber, which