What Does Cleavage Fracture Mean?
Cleavage fracture is a fracture, usually of polycrystalline metal, in which most of the grains have failed by cleavage, resulting in bright, reflective facets.
It is a type of crystalline fracture and is associated with low-energy brittle fracture. It exhibits a river pattern when examined under an electron microscope. It can cause material failures as well as corrosion.
Cleavage fracture is the most brittle form of fracture that can occur in crystalline materials.
Corrosionpedia Explains Cleavage Fracture
Brittle fracture in metals at the microscopic level ("ideal cleavage"or "pure cleavage") occurs only under certain well-defined conditions, primarily when the component is in single-crystal form and has a limited number of slip systems. This is described as cleavage fracture.
Cleavage fracture of metals occurs by direct separation along crystallographic planes due to a simple breaking of atomic bonds. Its main characteristics are that it is associated with a particular crystallographic plane. It is increased by lower temperatures and higher strain rates. More commonly in metals, the fracture surface contains varying fractions of transgranular cleavage and evidence of plastic deformation by slip.
The dividing line between cleavage and cleavage fracture is somewhat arbitrary. The term cleavage fracture applies when significant dimple rupture and/or tear ridges accompany the cleavage morphology.
Many high-strength engineering metals fracture by quasi-cleavage, which is a mixed mechanism involving both microvoid coalescence and cleavage. Cleavage fracture surfaces appear in steels due to:
- Sudden or impact loading
- Low temperature
- High levels of constraint
- Ambient temperature
- Heavily cold-worked parts
The cleavage fracture of steel is generally interpreted by the weakest link mechanism which is differentiated from yielding and work hardening. Under normal circumstances face-centered cubic (FCC) crystal structures do not exhibit cleavage fractures, as extensive plastic deformation always occurs in these materials before cleavage stress is reached.