Residual stress in thick titanium-alloy butt-welded plates and effect of hydrogen on fatigue crack propagation

• Investigated the impact of welding residual stress and hydrogen on titanium alloys. • Analyzed fatigue crack initiation/propagation in TC4 titanium butt-welded plates. • Utilized thermo-elastoplastic theory and cohesive zone model to analyze stress. • Established relationship between hydrogen concentration and fatigue life reduction. • Findings enhance safety, reliability of deep-sea structures using titanium alloys. Pressure-resistant titanium-alloy shells are typically fabricated using welding assemblies, making them vulnerable to hydrogen-induced cracking. Consequently, it is of enormous importance to study the crack initiation and fatigue crack propagation of titanium-alloy thick-plate butt welding under the combined action of hydrogen and welding residual stress. In this study, the X-ray non-destructive testing method was used to examine the sheet metal, and the residual stress was numerically calculated. Subsequently, the hydrogen concentration in different regions of a TC4 titanium-alloy butt-welded plate was measured using the thermal conductivity method. Finally, a VUMAT subroutine was developed to simulate the crack initiation and propagation. This enabled us to study the crack initiation and fatigue crack propagation of a TC4 titanium-alloy butt-welded plate under the coupling of hydrogen and residual stress.