Localisation of plastic deformation in friction stir and electron beam copper welds

Abstract

Optical strain measurement through digital image correlation during tensile testing was utilised to study the effect of strain rate and welding defects on localisation of plastic deformation in friction stir welded and electron beam welded phosphorous-alloyed oxygen-free copper. Welds cut from full-size nuclear waste copper canisters and additionally made defective welds were studied. Optical strain measurement represents a new way of studying deformation of materials and obtaining local material data. The data was used to construct strain maps and estimate local true stress–strain curves. Using Gini coefficients to quantify strain localisation, it appears that the lower strain rate resulted in slightly faster localisation of plastic deformation with lower stress level.

Keywords:

• Nuclear waste copper canister
• Friction stir welding (FSW)
• Electron beam welding (EBW)
• Strain rate
• Localisation of plastic deformation
• Optical strain measurement
• Digital image correlation (DIC)
• Welding defects

Acknowledgements

The authors wish to thank the Finnish KYT2018 project for funding, the Swedish Nuclear Fuel and Waste Management Co. (SKB) for the FSW canister weld, and Posiva Oy for the EB welds. Additional thanks go to Kim Widell for help with tensile testing and optical strain measurement, Gianmario Scotti for help with the photolithography, and Mykola Ivanchenko and Kati Savolainen for preliminary work done in the project.

ORCiD

L. Luumi http://orcid.org/0000-0002-3110-7703