Residual stresses in an electron beam weld of Ti-834: Characterization and numerical modeling

Neutron and synchrotron X-ray strain scanning techniques are used to characterize the residual stresses in an electron beam weld in the near-alpha titanium alloy Ti-834. Measurements are made using the [10 (1) over bar3] and [11 (2) over bar0] lattice planes in both the longitudinal and transverse directions, i.e., both along and normal to the welding direction. The lattice strains are large and positive (several thousand microstrains) in the longitudinal direction; in the fusion zone, the strains measured on the two planes differ by about 30 pct. The strains in the transverse direction are significantly smaller. A numerical model based upon the finite-element method (FEM) is developed in order to rationalize these results. Account is taken of the transfer of heat to the metal and subsequent conduction into the heat-affected zone; convection and radiation effects are neglected. The residual stresses are then estimated using an elastic-plastic analysis with temperature-dependent properties. Despite the limitations of the modeling approach, there is good agreement between experiment and theory, i.e., the sign and extent of the stress field. The plastically upset region extends about 3.5 mm from the weld centerline. The model is used to examine the adequacies of the experimental approach. It is demonstrated that the difference between the lattice strains measured for the two reflections in the fusion zone occurs as a consequence of the micromechanical response of the material, e.g., the partitioning of stress between the grains and the accumulation of intergranular microstrains.