Browsing by Author "Kabra, S."
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Item Open Access Control of residual stress and distortion in aluminium wire + arc additive manufacture with rolling(Elsevier, 2018-06-25) Honnige, Jan; Colegrove, Paul A.; Ganguly, Supriyo; Eimer, Eloise; Kabra, S.; Williams, Stewart W.The aluminium alloy wire 2319 is commonly used for Wire + Arc Additive Manufacturing (WAAM). It is oversaturated with copper, like other alloys of the precipitation hardening 2### series, which are used for structural applications in aviation. Residual stress and distortion are one of the biggest challanges in metal additive manufacturing, however this topic is not widely investigated for aluminium alloys. Neutron diffraction measurements showed that the as-built component can contain constant tensile residual stresses along the height of the wall, which can reach the materials' yield strength. These stresses cause bending distortion after unclamping the part from the build platform. Two different rolling techniques were used to control residual stress and distortion. Vertical rolling was applied inter-pass on top of the wall to deform each layer after its deposition. This technique virtually elimiated the distortion, but produced a characteristic residual stress profile. Side rolling instead was applied on the side surface of the wall, after it has been completed. This technique was even more effective and even inverted the distortion. An interesting observation from the neutron diffraction measurements of the stress-free reference was the significantly larger FCC aluminium unit cell dimension in the inter-pass rolled walls as compared to the as-build condition. This is a result of less copper in solid solution with aluminium, indicating greater precipitation and thus, potentially contibuting to improve the strenght of the material.Item Open Access Three-dimensional mapping of the residual stress field in a locally rolled aluminium alloy specimen(Elsevier, 2017-03-08) Coules, Harry E.; Horne, G. C. M.; Kabra, S.; Colegrove, Paul A.; Smith, D. J.Detrimental residual stresses that occur in welded joints can be removed by rolling the weld seam. In this study we show that rolling could be applied to much thicker-section welds than has previously been attempted. A residual stress field introduced by localised rolling of an aluminium alloy specimen was studied to establish whether the plastic deformation caused by rolling would be sufficient to treat thick-section welds. It was modelled using finite element analysis and characterised using detailed neutron diffraction measurements. During rolling, plastic deformation occurs through the entire thickness of the specimen and strongly compressive residual stresses are created in the rolled area. Some features of the three-dimensional residual stress field, such as a region of tensile stress beyond the end of the rolled area, could be detrimental to structural integrity. It is recommended that these should be taken into account in the design of rolling-based weld treatment and surface treatment processes.