Everything that surrounds us is matter. The origin of the word matter is mater (Latin) or matri (Sanskrit), for mother. In this sense, human beings anthropomorphized that which made them possible – that which gave them nourishment. Every scientific discipline concerns itself with matter. Of all matter surrounding us, a portion comprises materials. What are materials? They have been variously defined. One acceptable definition is “matter that human beings use and/or process.” Another definition is “all matter used to produce manufactured or consumer goods.” In this sense, a rock is not a material, intrinsically; however, if it is used in aggregate (concrete) by humans, it becomes a material. The same applies to all matter found on earth: a tree becomes a material when it is processed and used by people, and a skin becomes a material once it is removed from its host and shaped into an artifact.
The successful utilization of materials requires that they satisfy a set of properties. These properties can be classified into thermal, optical, mechanical, physical, chemical, and nuclear, and they are intimately connected to the structure of materials. The structure, in its turn, is the result of synthesis and processing. A schematic framework that explains the complex relationships in the field of the mechanical behavior of materials, shown in Figure 1.1, is Thomas's iterative tetrahedron, which contains four principal elements: mechanical properties, characterization, theory, and processing. These elements are related, and changes in one are inseparably linked to changes in the others.