7.1 Introduction

The separation or fragmentation of a solid body into two or more parts, under the action of stresses, is called fracture. The subject of fracture is vast and involves disciplines as diverse as solid-state physics, materials science, and continuum mechanics. Fracture of a material by cracking can occur in many ways, principally the following:

1. Slow application of external loads.

2. Rapid application of external loads (impact).

3. Cyclic or repeated loading (fatigue).

4. Time-dependent deformation (creep).

5. Internal stresses, such as thermal stresses caused by anistropy of the thermal expansion coefficient or temperature differences in a body.

6. Environmental effects (stress corrosion cracking, hydrogen embrittlement, liquid metal embrittlement, etc.)

The process of fracture can, in most cases, be subdivided into the following categories:

1. Damage accumulation.

2. Nucleation of one or more cracks or voids.

3. Growth of cracks or voids. (This may involve a coalescence of the cracks or voids.)

Damage accumulation is associated with the properties of a material, such as its atomic structure, crystal lattice, grain boundaries, and prior loading history. When the local strength or ductility is exceeded, a crack (two free surfaces) is formed. On continued loading, the crack propagates through the section until complete rupture occurs. Linear elastic fracture mechanics (LEFM) applies the theory of linear elasticity to the phenomenon of fracture mainly, the propagation of cracks. If we define the fracture toughness of a material as its resistance to crack propagation, then we can use LEFM to ...