ABSTRACT
An important consequence of the structures of solids is the nature of the fracture and cracking processes when subject to sufficiently high stress. This is the subject of the branch of materials science called fracture mechanics; this chapter introduces some of the concepts, including the important property of toughness. To fracture a material, it is need to break the bonds between the individual atoms and make sure that they do not reform. There are both attractive and repulsive forces, which balance one another when the atoms are in equilibrium. When considering the balance between the energy consumed by the crack propagation that is available from the internal strain energy, it is essential to consider more than just the energy of the new crack surface. The value of the critical yield crack length aycrit is a significant property, since if the material contains cracks larger than this failure will not only occur at a stress lower than expected but also without warning.
