Stress analysis and lifetime prediction for Ti-6Al-4V welding joint under fatigue loading

A welded joint has a complex gradient microstructure. The effects of local deformation in the fusion zone, heat-affected zone (HAZ), and other areas, on the macroscopic fatigue properties of an inhomogeneous welded joint, are not fully understood. Thus, it is necessary to correlate the microstructural features and their related local deformation mechanisms with macroscopic fatigue properties. In this study, cyclic stress-strain curves and lifetime model parameters of materials in different HAZs were determined by hardness distribution and base-metal material properties. A user element subroutine was developed in the elastic-plastic finite element analysis to obtain the local stress and strain in the joint. 'Danger points' were selected to predict fatigue lifetime with the Manson-Coffin damage equation. The prediction results agreed closely with experimental observations within the low-cycle fatigue lifetime regime.