Residual stress part 1 - measurement techniques

Abstract

Residual stress is that which remains in a body which is stationary and at equilibrium with its surroundings. It can be very 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 for the measurement of these stresses and to understand the level of information they can provide. After summarising the effect of residual stresses on fatigue lifetimes and structural integrity, Part I of this review deals with the definition and measurement of residual stresses. Different types of stress are characterised according to the characteristic length scale over which they self-equilibrate. By comparing this length to the gauge volume of each technique, the capability of a range of techniques is assessed. Part II goes on to look at the different nature and origins of residual stress for a variety of different classes of materials.

Residual stresses are those that remain in a material after its original cause of stress is removed. It is useful to distinguish between macrostresses (Type I) that span large distances and microstresses (Types II and III) that occur at the grain or atomic level. There exist many measurement techniques, including destructive mechanical methods like hole drilling and non-destructive diffraction methods using X-rays or neutrons. How these stresses influence structural integrity is explained, where tensile stresses may cause failure while compressive stresses can enhance fatigue resistance. It is important to use the techniques that best represents the length scale and engineering problem at hand.