Study on fatigue crack growth performance of EH36 weldments by laser shock processing

EH36 ship steel plates are widely used under harsh environment of ships and offshore platforms because of high specific strength, good low temperature impact toughness, good weldability, and good corrosion resistance. However, welded ship steel plates produce unforeseen crack and fatigue failure during service. In order to improve the fatigue resistance of EH36 weldments, the influence of impact pressure, spot diameter, and laser shock processing (LSP) on the fatigue crack growth (FCG) rate of EH36 weldment was studied. LSP experiments and fatigue tests on EH36 compact tension (CT) weldments were carried out. The surface compressive residual stress and the microhardness in the welding zone (WZ) with LSP-3 are 230 MPa and 270 HV, and grain size in the surface layer of WZ was refined. Fatigue life of EH36 weldments with LSP-3 increases by 270% compared to that of them without LSP. FCG rate obviously decreases because of the secondary cracks and narrow and dense fatigue striations occurring in the fatigue fracture. Moreover, large and deep dimples on the fatigue fracture effectively improve the plasticity of weldments. The proposed research provides the instruction to predict the fatigue life of EH36 weldments by LSP.