Advanced manufacturing of titanium propellant tanks for space applications part 2: a comparative study of residual stresses

Friction stir welding (FSW) was used to join cast Ti–6Al–4V hemisphere and cylinder parts to produce a spacecraft propellant tank with reduced costs and lead time compared to conventional manufacturing. As a potential source for failure, the weld was inspected for residual stresses using three different methods: non-destructive neutron and X-ray diffraction as well as destructive hole drilling. The results showed lower residual stresses in the friction stir weld compared to results from conventional welding techniques such as electron beam welding or tungsten inert gas welding. In the hoop direction, a typical M-shaped residual stress profile centered around the weld was observed for both neutron and X-ray diffraction. According to the acquired data, the peak residual stresses (tensile) were measured in the heat-affected zone, up to a maximum of ~ 200 MPa. The results from the three different techniques generally compared well with each other, considering the rather significant differences between the methods.