Volume 20, Issue 6 (November 1992)
Residual Stresses and Fatigue Precracking Techniques for Weldment Fracture Toughness Specimens
This article examines the ability of the local compression, stepwise high R-ratio, and reverse bend weldment fatigue precracking techniques to remove the residual stresses in the uncracked ligaments of as-welded fracture mechanics test specimens. The stepwise high R-ratio and reverse bend techniques appeared to have no significant influence on the residual stresses in the ligament. This was demonstrated by the occurrence of nonuniform fatigue cracks when these techniques were followed by the standard fatigue precracking procedures. Specimens given these treatments, and other specimens fatigue precracked using the standard procedures, showed evidence of crack closure and initial compliances that were lower than normal for these specimen geometries. In contrast, local compression reduced the residual stresses in the uncracked ligaments to low, uniform levels. This was indicated by acceptable fatigue precrack front-straightness and normal specimen compliance. Therefore, of the three precracking techniques investigated, only the local compression technique is recommended.