page_title: Fracture
section_title: Brittle fracture
hierarchical_section_title: Fracture / Types / Brittle fracture
caption_attribution_description: English: A closeup of the fractured edge of a broken drinking glass.
context_page_description: Fracture is the separation of an object or material into two or more pieces under the action of stress. The fracture of a solid usually occurs due to the development of certain displacement discontinuity surfaces within the solid. If a displacement develops perpendicular to the surface of displacement, it is called a normal tensile crack or simply a crack; if a displacement develops tangentially to the surface of displacement, it is called a shear crack, slip band, or dislocation.
  Brittle fractures occur with no apparent deformation before fracture; ductile fractures occur when visible deformation does occur before separation. Fracture strength or breaking strength is the stress when a specimen fails or fractures. A detailed understanding of how fracture occurs in materials may be assisted by the study of fracture mechanics.
context_section_description: In brittle fracture, no apparent plastic deformation takes place before fracture. Brittle fracture typically involves little energy absorption and occurs at high speeds—up to 2133.6 m/s (7000 ft/s) in steel. In most cases brittle fracture will continue even when loading is discontinued.
  In brittle crystalline materials, fracture can occur by cleavage as the result of 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.
  The theoretical strength of a crystalline material is (roughly)
  where: –
   is the Young's modulus of the material,
   is the surface energy, and
   is the equilibrium distance between atomic centers.
  On the other hand, a crack introduces a stress concentration modeled by
   (For sharp cracks)
  where: –
   is the loading stress,
   is half the length of the crack, and
   is the radius of curvature at the crack tip.
  Putting these two equations together, we get
  Looking closely, we can see that sharp cracks (small ) and large defects (large ) both lower the fracture strength of the material.
  Recently, scientists have discovered supersonic fracture, the phenomenon of crack propagation faster than the speed of sound in a material. This phenomenon was recently also verified by experiment of fracture in rubber-like materials.
  The basic sequence in a typical brittle fracture is: introduction of a flaw either before or after the material is put in service, slow and stable crack propagation under recurring loading, and sudden rapid failure when the crack reaches critical crack length based on the conditions defined by fracture mechanics. Brittle fracture may be avoided by controlling three primary factors: material fracture toughness (Kc), nominal stress level (σ), and introduced flaw size (a). Residual stresses, temperature, loading rate, and stress concentrations also contribute to brittle fracture by influencing the three primary factors.
  Under certain conditions, ductile materials can exhibit brittle behavior. Rapid loading, low temperature, and triaxial stress constraint conditions may cause ductile materials to fail without prior deformation.
caption: Brittle fracture in glass
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