Effect of Shot and Laser Peening on SAE 1010 Steel Tubes with a Transverse Center Weld

Author:  L.D. Vo, R.I. Stephens
Source:  ICF 12, July, 2009
Doc ID:  2009031
Year of Publication:  2009
Abstract:  
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. Laser peening produces deeper penetration of compressive residual stresses than shot peening and hence may produce better fatigue resistance than shot peening for mild steel weldments. Laser peening has been very successful in higher strength materials involving aluminum, steel and titanium alloys.[5,6] However, it is significantly more expensive than shot peening. The goals of this research were to compare the fatigue resistance of both shot and laser peened mild steel weldments under constant and variable amplitude loading as part of the Society of Automotive Engineers Fatigue Design and Evaluation (SAEFDE) committee's fatigue of weldments program.