Residual stress is that which remains in a body that is stationary & at equilibrium with its surroundings. It can be detrimental to the performance of a material or the life of a component. Alternatively, beneficial residual stresses can be introduced deliberately. Residual stresses are more difficult to predict than the in-service stresses on which they superimpose. For this reason, it is important to have reliable methods of measurement of these stresses & to understand the level of information they can provide. In this paper, the first of a 2-part overview, the effect of residual stresses on fatigue lifetimes & structural integrity are first summarised, followed by the definition & measurement of residual stresses. Different types of stress are characterised according to the characteristic length scale over which they self-equilibriate.
