Many of the terms used to describe the mechanical properties of materials, such as strength and toughness, are familiar from everyday speech. In materials science, these terms have specific meanings, and are well defined quantifiable measures of how a material responds to an applied load.

In this section, we will define the most important mechanical properties. Before defining the properties it is important to be familiar with the concepts of elastic and plastic deformation. This exercise helps explain these terms:

Different materials behave very differently under load. Some materials can sustain large plastic deformations before they fail. Other materials do not plastically deform at all, but fail by brittle fracture during the elastic deformation regime.