Font Size: 

Compressive surface residual stresses from shot peening have proven to be
extremely beneficial to fatigue resistance of intermediate and high strength metals
and alloys. Lower strength materials, including steel weldments, often are
believed to not have this significant benefit. This is due to lower yield strengths
that restrict the magnitude of induced residual stresses and the relaxation of
residual stresses during cyclic loading due to local plasticity. Thus, the application
of shot peening, or emerging laser peeening, has not been common in steel
weldments with yield strengths less than about 400 MPa. The limited research
available in the literature concerning these lower strength mild steel weldments,
however, has indicated increased constant amplitude fatigue limits at 2x106 cycles
of between 10 to 90 %.[1-4] Most of these tests were performed with an R-ratio
(Smin/Smax) equal of 0 or 0.1, and included longitudinal and transverse fillet welds,
butt welds and bead-on-welds. Intermediate fatigue lives often showed mixed
results, whereas at shorter life (≤ 4x104 cycles), no benefits from shot-peening
were obtained.