Effects of Needle Peening and Shot Peening for Stainless Steel Welded Joint on the Crack Size Rendered Harmless

Author:  Ryutaro Fueki, Koji Takahashi, Mitsuru Handa
Source:  ICSP-13
Doc ID:  2017120
Year of Publication:  2017
Abstract:  
Introduction: Welded joints are often used in large steel structures. Fatigue cracks tend to initiate at the welded joints (especially at the weld toe) due to tensile residual stresses and stress concentration. Tensile residual stresses result from the effects of heat applied during the welding process. A discontinuous portion of the weld beads cause stress concentration. Peening methods such as needle peening (NP) and shot peening (SP) are expected to be effective for improving fatigue strength of welded joints. Non-destructive inspections are typically conducted prior to performing peening on welded joints in steel structures. However, detection limits are associated with non-destructive inspection, and it is not possible to detect cracks below a certain size. The reliability of welded joints is decreased by the undetected cracks. It is possible to improve reliability of welded joints if peening can be used to mitigate the effect of the fatigue cracks. Recently, Houjou et al. [1] reported that the fatigue limit of a stainless steel welded joint containing a crack-like surface defect at the weld toe could be improved by NP and surface defects could be rendered harmless by NP. However, the effects of SP on the fatigue limit of welded joints with surface defects are unclear.