Brittle Fracture

Definition - What does Brittle Fracture mean?

A brittle fracture is the fracture of a metallic object or other material without appreciable prior plastic deformation. It is a break in a brittle piece of metal that failed because stress exceeded cohesion.

The brittle fracture of normally ductile steels occurs primarily in large, continuous, box-like structures such as:

  • Box beams
  • Pressure vessels
  • Tanks
  • Pipes
  • Ships
  • Bridges
  • Other restrained structures

Brittle fractures that occur in service are invariably initiated by defects that are initially present in the manufactured product or fabricated structure, or by defects that develop during service.

Corrosionpedia explains Brittle Fracture

A brittle fracture is a breakage or cracking of a material into discernible parts, from which no deformation can be identified (a clean break). It is characterized by rapid crack propagation with low energy release and without significant plastic deformation. The fracture may have a bright granular appearance. The fractures are generally of the flat type and chevron patterns may be present.

In brittle crystalline materials, fractures can occur by cleavage as the result of a tensile stress acting normal to crystallographic planes with low bonding (cleavage planes). In amorphous solids, by contrast, the lack of a crystalline structure results in a conchoidal fracture, with cracks proceeding normal to the applied tension.

In a brittle fracture, cracks run close to perpendicular to the applied stress. This perpendicular fracture leaves a relatively flat surface at the break. Besides having a nearly flat fracture surface, brittle materials usually contain a pattern on their fracture surfaces. Some brittle materials have lines and ridges beginning at the origin of the crack and spreading out across the crack surface. Since there is very little plastic deformation before failure occurs, in most cases this is the worst type of fracture because the visible damage cannot be repaired in a part or structure before it breaks.

Brittle fractures display either transgranular or intergranular fracture. This depends upon whether the grain boundaries are stronger or weaker than the grains:

  • Transgranular fracture - The fracture travels through the grain of the material. Cracks choose the path of least resistance.
  • Intergranular fracture - The crack travels along the grain boundaries, and not through the actual grains. This usually occurs when the phase in the grain boundary is weak and brittle.
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