Residual stresses are stresses that remain in a material after subjection to external loads or treatment. These stresses act like pre-stressing, thereby pre-loading the structure affecting its response to external loads.
Compressive residual stresses generally decrease resistance to instability phenomena driven by compressive stresses because they add to the compressive loads, thereby decreasing the critical load required to trigger instability.
In contrast, tensile residual stresses are less commonly associated with instability, but can act beneficially by opposing any compressive load and subsequently increasing the external load capacity with regard to instability.