Discontinuity

Definition - What does Discontinuity mean?

Discontinuity is an interruption in the normal physical structure or configuration of an article. A discontinuity may or may not affect the usefulness of the article.

Discontinuities in structures can cause local increases in stress, leading to:

  • Cracks
  • Laps
  • Seams
  • Inclusions
  • Porosity
  • Hydrogen cracks
  • Fatigue
  • Tears
  • Segregations

Discontinuity creates areas where abrupt changes in geometry, material or loading occur. These areas are known as discontinuity regions, and the stresses associated with them are called discontinuity stresses.

Corrosionpedia explains Discontinuity

A discontinuity is not necessarily a defect. During non-destructive inspection, the inspector looks for discontinuities in the object and identifies their nature and size. Those discontinuities are evaluated according to an acceptance criterion to determine if they are considered to be defects.

Any imperfection that is found by the inspector is called a discontinuity until it can be identified and evaluated as to the effect it may have on the service of the part or to the requirements of the specification. A certain discontinuity may be considered to be a defect in some cases and not a defect in other cases because the definition of defect changes with the type of component, its construction, its materials and the specifications being used.

Discontinuities are categorized in following four groups:

  • Inherent discontinuities - Originating during the initial casting process. Some known discontinuities in this stage are: cold shut, shrinkage cavities, blowhole and porosity, nonmetallic inclusions, segregations
  • Primary processing discontinuities - Originating during hot or cold forming processes, such as seams, laminations, cooling cracks, forging and rolling laps, bursts, hydrogen flakes, hot & cold cracks
  • Secondary processing discontinuities - Originating during grinding, machining, heat treating, plating and related finishing operations, such as grinding, plating & pickling cracks, machining tears
  • Service discontinuities - Originating or developing while the component is in service. Known examples are: fatigue & creep cracks, stress corrosion cracks and hydrogen cracks

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