The yield properties and plastic deformation behaviour, as characterized by the tensile test, are usually key mechanical properties.

In many applications, the fracture resistance is also of great importance in design. To understand the methods used for fracture toughness testing, and the interpretation of test results, a basic understanding of the physics controlling fracture is important.

Measures of toughness like K_c and G_c (see property definitions) are based on the application of Linear Elastic Fracture Mechanics (LEFM) theory.

This theory is based on the assumption that unstable crack growth develops in elastically stressed material. This will only be a good assumption for

Fortunately, it is this type of alloy for which fracture toughness is usually an important concern.