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Residual stresses are those stresses, which remain in the material or body in the absence of any external forces or thermal gradients. They are introduced mostly during manufacturing operations like rolling, welding, forming etc. The quantitative estimation of these stresses is important because they can modify the effective load bearing capacity of the component by getting added to the applied or service stresses and also stimulate stress corrosion failures.
Non-destructive evaluation of residual stresses is in general limited to the near surface of the component. The near surface stresses are seen to have sharp gradients. Quantification of the residual stress distribution with depth till the stress values reach their bulk nominal values is important from point of view of the assessment of structural integrity as these stresses can have magnitudes which can be even more than fifty percent of yield stress. Incremental Hole drilling method, which is relatively simple and fast, is one of the most popularly used semi-destructive methods of residual stress evaluation which can provide the residual stress distribution across the thickness in magnitude, direction and sense. The strains relieved by drilling a small hole of approximately 2 mm diameter are measured using special purpose strain gauges and the residual stresses present in the component are computed from the relieved strains.
The paper presents a case study on the stress field in the heat-affected zones (HAZ) of TIG welded 2219 Aluminium plates and also modifications of the stress field by subsequent weld repairs. The representative values in the bulk of the material are also compared. The stress field due to manual weld is also compared to the field in an automatic weld. The near surface residual stresses are analyzed. Relative merits of the hole drilling method over NDT methods are also discussed.
