Relaxation of Residual Stresses due to Fatigue Loading 600008
MACRORESIDUAL stresses are usually induced in parts during fabrication. These stresses may change if the part is subjected to fatigue loading in service. To make an estimate of the effect of residual stresses on the life of the part, one must know the magnitude and importance of this change.
Axial fatigue results can be used to determine the mechanism by which residual stresses at the surface of a member relax due to fatigue loading.
Such an approach leads to the following conclusions:
Little relaxation of residual stresses should be expected for alternating stresses near the fatigue limit except for “soft” materials.
Because the fatigue limit of “soft” metals is, in general, relatively insensitive to mean stress, partial relaxation of residual stress will affect the fatigue limit only slightly.
For the purpose of estimating the fatigue limit of a member, the initial residual stress at the surface should be considered to remain unchanged during fatigue loading. Treating this stress as part of the service stresses, proceed as in any other fatigue problem in which mean stresses are present.*