Introduction to Aerospace Materials

Adrian P Mouritz

• Publisher: Woodhead Publishing
• Year: 2012
• ISBN:
  9780857095152
• Topic: Technology & Engineering
• Subtopic: Aeronautic & Astronautic Engineering
• Index: Technology & Engineering

The structural materials used in airframe and propulsion systems influence the cost, performance and safety of aircraft, and an understanding of the wide range of materials used and the issues surrounding them is essential for the student of aerospace engineering.Introduction to aerospace materials reviews the main structural and engine materials used in aircraft, helicopters and spacecraft in terms of their production, properties, performance and applications.The first three chapters of the book introduce the reader to the range of aerospace materials, focusing on recent developments and requirements. Following these introductory chapters, the book moves on to discuss the properties and production of metals for aerospace structures, including chapters covering strengthening of metal alloys, mechanical testing, and casting, processing and machining of aerospace metals. The next ten chapters look in depth at individual metals including aluminium, titanium, magnesium, steel and superalloys, as well as the properties and processing of polymers, composites and wood. Chapters on performance issues such as fracture, fatigue and corrosion precede a chapter focusing on inspection and structural health monitoring of aerospace materials. Disposal/recycling and materials selection are covered in the final two chapters.With its comprehensive coverage of the main issues surrounding structural aerospace materials, Introduction to aerospace materials is essential reading for undergraduate students studying aerospace and aeronautical engineering. It will also be a valuable resource for postgraduate students and practising aerospace engineers.

• Reviews the main structural and engine materials used in aircraft, helicopters and space craft in terms of their properties, performance and applications
• Introduces the reader to the range of aerospace materials, focusing on recent developments and requirements, and discusses the properties and production of metals for aerospace structures
• Chapters look in depth at individual metals including aluminium, titanium, magnesium, steel and superalloys

1

Introduction to aerospace materials

1.1 The importance of aerospace materials

The importance of materials science and technology in aerospace engineering cannot be overstated. The materials used in airframe structures and in jet engine components are critical to the successful design, construction, certification, operation and maintenance of aircraft. Materials have an impact through the entire life cycle of aircraft, from the initial design phase through to manufacture and certification of the aircraft, to flight operations and maintenance and, finally, to disposal at the end-of-life.

Materials affect virtually every aspect of the aircraft, including the:

• • purchase cost of new aircraft;
• • cost of structural upgrades to existing aircraft;
• • design options for the airframe, structural components and engines;
• • fuel consumption of the aircraft (light-weighting);
• • operational performance of the aircraft (speed, range and payload);
• • power and fuel efficiency of the engines;
• • in-service maintenance (inspection and repair) of the airframe and engines;
• • safety, reliability and operational life of the airframe and engines; and
• • disposal and recycling of the aircraft at the end-of-life.

Aerospace materials are defined in this book as structural materials that carry the loads exerted on the airframe during flight operations (including taxiing, take-off, cruising and landing). Structural materials are used in safety-critical airframe components such as the wings, fuselage, empennage and landing gear of aircraft; the fuselage, tail boom and rotor blades of helicopters; and the airframe, skins and thermal insulation tiles of spacecraft such as the space shuttle. Aerospace materials are also defined as jet engine structural materials that carry forces in order to generate thrust to propel the aircraft. The materials used in the main components of jet engines, such as the turbine blades, are important to the safety and performance of aircraft and therefore are considered as structural materials in this book.

An understanding of the science and technology of aerospace materials is critical to the success of aircraft, helicopters and spacecraft. This book provides the key information about aerospace materials used in airframe structures and jet engines needed by engineers working in aircraft design, aircraft manufacturing and aircraft operations.

1.2 Understanding aerospace materials

Advanced materials have an important role in improving the structural efficiency of aircraft and the propulsion efficiency of jet engines. The properties of materials that are important to aircraft include their physical properties (e.g. density), mechanical properties (e.g. stiffness, strength and toughness), chemical properties (e.g. corrosion and oxidation), thermal properties (e.g. heat capacity, thermal conductivity) and electrical properties (e.g. electrical conductivity). Understanding these properties and why they are important has been essential for the advancement of aircraft technology over the past century.

Understanding the properties of materials is reliant on understanding the relationship between the science and technology of materials, as shown in Fig. 1.1. Materials science and technology is an interdisciplinary field that involves chemistry, solid-state physics, metallurgy, polymer science, fibre technology, mechanical engineering, and other fields of science and engineering.

1.1 Relationship between materials science and materials technology.

Materials science involves understanding the composition and structure of materials, and how they control the properties. The term composition means the chemical make-up of the material, such as the types and concentrations of alloying elements in metals or the chemical composition of polymers. The structure of materials must be understood from the atomic to final component levels, which covers a length scale of many orders of magnitude (more than 10¹²). The important structural details at the different length scales from the atomic to macrostructure for metals and fibre-polymer composites, which are the two most important groups of structural materials used in aircraft, are shown in Fig. 1.2. At the smallest scale the atomic and molecular structure of materials, which includes the bonding between atoms, has a large influence on properties such as stiffness and strength. The crystal structure and nanoscopic-sized crystal defects in metals and the molecular structures of the fibres and polymer in composites also affect the properties. The microstructure of materials typically covers the length scale from around 1 to 1000 μm, and microstructural features in metals such as the grain size, grain structure, precipitates and defects (e.g. voids, brittle inclusions) affect the properties. Microstructural features such as the fibre arrangement and defects (e.g. voids, delaminations) affect the properties of composites. The macrostructural features of materials, such as its shape and dimensions, may also influence the properties. The aim of materials science is to understand how the physical, mechanical and other properties are controlled over the different length scales. From this knowledge it is then possible to manipulate the composition and structure of materials in order to improve their properties.

1.2 Structural factors at different sizes affect the properties of (a) metals and (b) fibre–polymer composites.

Materials technology (also called materials engineering) involves the application of the material properties to achieve the service performance of a component. Put another way, materials technology aims to transform materials into useful structures or components, such as converting soft aluminium into a high strength metal alloy for use in an aircraft wing or making a ceramic composite with high thermal insulation properties needed for the heat shields of a spacecraft. The properties needed by materials are dependent on the type of the component, such as its ability to carry stress without deforming excessively or breaking; to resist corrosion or oxidation; to operate at high temperature without softening; to provide high st...