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 structural performance at low weight or low cost; and so on. Materials technology involves selecting materials with the properties that best meet the service requirements of a component as well as maintaining the performance of the materials over the operating life of the component by resisting corrosion, fatigue, temperature and other damaging events.
Most aerospace engineering work occurs in the field of materials technology, but it is essential to understand the science of materials. The examines the interplay between materials science and materials technology in the application of materials for aircraft structures and jet engines.
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