Fatigue strength of shot-peened as-welded joints and post-weld-treated and subsequently clean-blasted fillet weld joints

Surface treatment methods, such as shot peening and clean blasting, can improve the fatigue strength of welded joints. The aim of the current work is to experimentally evaluate the effects of clean blasting on the fatigue performance of post-weld-treated joints made of normal, high-strength, and ultra-high-strength steels, as well as obtain the fatigue strength improvement gained by the shot peening processes in welded connections made of different steel grades using literature data. A literature review was carried out to extract fatigue test data of welded joints, considering both clean blasting and shot peening processes. This data was statistically re-evaluated and used for a comparison to the results obtained in the current experimental work which focuses on evaluating the improvement gained by the clean blasting after post-weld treatments. Experimental fatigue tests were carried out on non-load-carrying transverse attachment joints prepared with gas metal arc welding, and made of S355, S700, and S1100 structural steels. TIG dressing and HFMI treatment post-weld treatments were implemented and, subsequently, the specimens were blast-cleaned using two different abrasives: corundum and sand. The re-analysis of existing fatigue test data indicated higher improvement by shot peening, i.e., average improvements of 1.71 and 1.52 in the fatigue strength for butt weld and fillet weld joints, respectively, than by clean blasting process for which an average improvement of 1.19 in fatigue strength was obtained. The enhancement factors, however, highly varied among different data sets indicating a clear impact of processing parameters on the improvement level. The statistical re-analyses considering all data sets of shot-peened specimens (butt weld and fillet weld joints) showed that one fatigue (FAT) class higher fatigue strength could be recommended for shot-peened joints compared to the as-welded condition with weld toe failures. The experimental work on the post-weld-treated joints indicated that the fatigue strength of clean-blasted joints was similar to that of non-blasted joints, and thus showing no major advantages or disadvantages by the clean blasting post-weld-treated joints with corundum and sand.