Part I
Fundamentals
Peter Domone and Marios Soutsos
INTRODUCTION
We conventionally think of a material as being either a solid or a fluid. These states of matter are conveniently based on the response of the material to an applied force. A solid will maintain its shape under its own weight, and resist applied forces with little deformation. An unconfined fluid will flow under its own weight or applied force. Fluids can be divided into liquids and gases; liquids are essentially incompressible and maintain a fixed volume when placed in a container whereas gases are greatly compressible and will also expand to fill the volume available. Although these divisions of materials are often convenient, we must recognise that they are not distinct, and some materials display mixed behaviour, such as gels that can vary from near solids to near liquids.
In construction, we are for the most part concerned with solids, since we use these to carry the applied or self-weight loads, but we do need to understand some aspects of fluid behaviour, for example when dealing with fresh concrete or the flow of water or gas into and through a material.
Intermediate viscoelastic behaviour is also important.
This first part of this book is aimed at both describing and explaining the behaviour of materials in general, without specifically concentrating on any one type or group of materials. That is the purpose of the later sections. This part therefore provides the basis for the later parts, and if you get to grips with the principles, then much of what follows will be clearer.
In the first chapter, we start with a description of the building blocks of all materials – atoms – and how they combine in single elements and in compounds to form gases, liquids and solids. We then introduce some of the principles of thermodynamics and the processes involved in changes of state, with an emphasis of the change from liquid to solid. In the next two chapters, we describe the behaviour of solids when subjected to load and then consider the structure of the various types of solids used in construction, thereby giving an explanation for and an understanding of the behaviour.
This is followed in subsequent chapters by consideration of the process of fracture in more detail (including an introduction to the subject of fracture mechanics), a brief discussion of the behaviour of liquids, viscoelastic materials and gels, the nature and behaviour of surfaces and the electrical and thermal properties of materials.
Chapter 1
Atoms, bonding, energy and equilibrium
As engineers, we are primarily concerned with the properties of materials at the macrostructural level, but in order to understand these properties (which we will introduce in Chapter 2) and to modify them to our advantage, we need an understanding of the structure of materials from the atomic level through bonding forces, molecules and molecular arrangement. Some knowledge of the processes involved in the changes of state, particularly from liquids to solids, is also valuable.
The concept of ‘atomistics’ is not new. The ancient Greeks – and especially Democritus (c. 460 bc) – had the idea of a single elementary particle, but their science did not extend to observation and experiment. For that, we had to wait nearly 22 centuries until Dalton, Avogadro and Cannizzaro formulated atomic theory as we know it today. Even so, very many mysteries still remain unresolved. So in treating the subject in this way, we are reaching a long way back into the development of thought about the universe and the way in which it is put together. This is covered in the first part of this chapter.
Concepts of changes of state are more recent. Engineering is much concerned with change – the change from the unloaded to the loaded state, the consequences of changing temperature, environ...