What are residual stresses?
Residual stresses are the internal stresses existing in a component or material without any external load stresses applied.
The residual stresses can be either of tensile- or compressive- type. They are locked inside the material and are a result of the component’s history.
The residual stresses are very important for the fatigue life of the component. Compressive stresses are said to be beneficial, while tensile stresses are detrimental.
The highest stresses during loading of the component will be in the surface. That’s why we would like to have compressive residual stresses in the surface of the component to overcome possible tensile load stresses.
If we don’t have compressive residual stresses, and have a small defect or crack in the surface, the crack can start to grow and open more and more for every load cycle, And finally we will have a fatigue failure.
The compressive residual stresses can then stop the crack to grow and our fatigue life will be extended.