What Does Fracture Toughness Mean?
In metallurgy, fracture toughness refers to a property which describes the ability of a material containing a crack to resist further fracture.
Fracture toughness is a quantitative way of expressing a material's resistance to brittle fracture when a crack is present. If a material has high fracture toughness, it is more prone to ductile fracture. Brittle fracture is characteristic of materials with less fracture toughness.
Fracture toughness values may serve as a basis for:
- Material comparison
- Structural flaw tolerance assessment
- Quality assurance
Corrosionpedia Explains Fracture Toughness
Fracture toughness is an indication of the amount of stress required to propagate a pre-existing flaw.
Flaws may appear as:
- Metallurgical inclusions
- Weld defects
- Design discontinuities
A parameter called the stress-intensity factor (K) is used to determine the fracture toughness of most materials. The stress intensity factor is a function of:
- Crack size
- Structural geometry
The purpose of a fracture toughness test is to measure the resistance of a material to the presence of a flaw in terms of the load required to cause brittle or ductile crack extension (or to reach a maximum load condition) in a standard specimen containing a fatigue pre-crack.
The fracture toughness of a material commonly varies with grain direction. It is customary to specify specimen and crack orientations by an ordered pair of grain direction symbols.
Composites exhibiting the highest level of fracture toughness are typically made of a pure alumina or a silica-alumina (SiO2/Al2O3) matrix with tiny inclusions of zirconia (ZrO2) dispersed as uniformly as possible within the solid matrix. Fine ceramics generally possess low fracture toughness—partially-stabilized zirconia, used for products such as scissors and knives, offers significant fracture-toughness improvements.