A study on improvement of fatigue performance by shot blasted surface treatment

Recently, the strength of the hull structure including fatigue strength has seen significant improvement because of application of IACS CSR (Common Structure rule), developed by IACS. Various methods which can increase the fatigue strength at welded joints are suggested, since the damage morphology on the recently welded structures was observed to be primarily fatigue failure. In Shipbuilding industry, smoothening of the welding bead toe by grinding is the method that is customarily adopted in order to increase fatigue strength. And recently, peening treatment at the welding bead has also been adopted. The peening treatment can reduce stress concentration by smoothening of the welding bead toe, and a compressive residual stress field generated by the impact of peening. In case of generating compressive residual stress by impact, the same effect could be expected by shot blasting, which is the steel surface treatment before painting. In this study, the condition of the residual stress generated at welding toe by shot blasting was investigated, and then from results of the fatigue test, the increase in fatigue strength due to residual stress is verified.