Abstract:
Riveting is a traditional joining technique mostly used in the manufacturing of aircraft
structures.
Manufacturing studies on the next generation of wide body commercial
aircraft have' indicated that the achievement of
acceptable cost/benefit goals would
require the» application of highly cost-effective joining processes. Although riveting
provides good structural performance, it is expensive and time consuming. Welding is a
candidate
process t be used to manufacture large aircraft structures allowing sensible
cost reductions and structural
efficiency.
Welded aluminium 2024-T351 structural
joints produced .with a new generation of
welding processes, such a Friction Stir Welding ( SW) and Plasma welding were
characterised in terms of
rnicrostructure, hardness and weld residual stress. Tensile
properties and stress-strain behaviour of the FSW joints was investigated and discussed
using simple mechanical models. The investigation of the fatigue properties of the FSW
and Plasma Welded structural
joints revealed the superior behaviour of the FSW joints.
It was found that
fatigue strength in FSW joints is dominated by surface irregularities
produced by the welding process. Weld surface skimming greatly improved fatigue
strength by removing surface stress concentrations. Initiation in skimmed joints
occurred at locations of minimum hardness.
Fatigue endurance behaviour of skimmed
joints was equal or superior to that reported in riveted aluminium joints. Fatigue crack
propagation studies were carried out on FSW 2024-T351 joints for cracks parallel and
orthogonal to the weld direction. Crack propagation behaviour was sensitive t both
weld orientation and the distance of the crack from the weld line. Growth rates both
faster and slower than in the
parent material were observed, depending on the crack
orientation and distance from the weld. Residual stress was
mechanically relieved and
the effects on crack
propagation observed. A comparative analysis of the results
associated with crack closure measurements indicated that crack
growth behaviour in
the FSW
joints was generally dominated by the weld residual stress. Possible design
solutions for
damage tolerant Welded aircraft structural components were identified and
discussed in the
light of the experimental results.
