The term "internal stress" is used to refer to residual stresses that are in a material when there is no external load. Internal stresses can arise as a result of plastic deformation, uneven thermal stresses or temperature changes in the material, or due to phase transformations, and generally occur during manufacturing processes.

Key Features:

• Plays out with No External Force: Internal stresses can become "locked-in" to a material after forming, welding, casting, or machining.
• Causes Distortion or Failure: Internal stress must be relieved; if not, it can lead to warping, cracking, or dimensional instability during use.
• Can Be Relieved through Heat Treatment: Heat treatments, such as annealing, stress-relief heating, etc., can relieve or reduce the amount of internal stress present.

Internal stress has the potential to be a major contributor to the performance and reliability of components designed for use in critical industries such as aerospace, automotive, construction, and toolmaking, for example. It can cause parts or components to bend, twist, or otherwise deform over time, irrespective of changes to external loading, which compromises the intended function of the component. Understanding and managing internal stress helps to maintain dimensional accuracy and structural integrity and increase the life of components. Engineers utilize simulation tools, controlled processing, etc., to mitigate internal stresses during manufacturing.