Full stress tensor determination in a textured aerospace aluminium alloy plate using synchrotron X-ray diffraction

Abstract

Triaxial strain scanning has been performed on a 7 mm thick 7150-aluminium alloy Variable Polarity Plasma Arc (VPPA) weld using synchrotron X-rays. It has been demonstrated that the use of specific advantageous (hkl) peaks that occur in this highly textured aerospace alloy plate permits fast deep measurements in reflection as well as in transmission. The sin² ψ method was also utilised to monitor the variation in deviatoric stress component (σ₁₁–σ₃₃) across the weld in both the test-piece and a comb like reference specimen used to map the changes in stress-free lattice spacings over the weld. The results suggest that microstresses have little effect on macrostress determination, particularly in the Heat Affected Zones (HAZ). Though small in magnitude, the macrostresses still present in the reference specimen can be allowed for to correct the stress tensor in the plate. Maximum tensile longitudinal stress values remain unchanged, whereas the stress condition in some parts of the HAZ is well described as biaxial after the proposed correction.

Keywords:

• Residual stress
• Synchrotron diffraction
• Texture
• Aluminium variable polarity plasma arc weld

Acknowledgments

The authors wish to thank Dr. A. N. Fitch (beam-line responsible) of ESRF and Dr. J.R. Santisteban of the Open University for their continued support and assistance. We would also like to thank Peter Ledgard for his invaluable help in the preparation of the experiment. We express our gratitude to the Cranfield University Weld Engineering Research Centre for providing the 7150 VPPA weld, to Airbus (UK) and the UK's Engineering and Physical Sciences Research Council for their support via the grant “Weld processing design & durability of welded aircraft assemblies”.