The overall aim behind this work was to gain and apply an understanding of the mechanical effects of welding, in order to mitigate distortions that had previously hampered uniaxial testing of tungsten inert gas (TIG) butt-welded, thin-section, nickel-base superalloy INCONEL 718 (IN718). With this aim achieved, better test data could be obtained, leading to more reliable material data for IN718 welds, which can be used for more accurate life assessments for shell structures and components. ABAQUS finite element (FE) simulations of the arc welding process were used to understand the development of welding-induced distortions and reduce their prevalence. An efficient, distortion-mitigating welding procedure, devised using the numerical simulations, was used to manufacture TIG butt-welded specimens that were free of distortion. Uniaxial tensile, creep and high temperature (620°C) fatigue tests were performed on both welded and non-welded IN718 specimens. It was found that IN718 welds are significantly less ductile than the parent material, and although welded IN718 exhibits comparatively little loss of tensile strength, its creep and high temperature fatigue properties are severely compromised. The lower performance of the welded specimens was attributed to the microstructural differences when compared with the non-welded material. The mechanical properties of the IN718 weld material were calculated and verified using FE analyses, based on the test data obtained. A continuum damage mechanics approach was employed for creep modelling and the necessary material constants were determined. A Smith, Watson and Topper (SWT) strain range parameter was proposed for fatigue life assessment, based on validation obtained using the test data. Three-dimensional, quasi-static elastic-plastic and creep FE analyses were used for a life assessment case study of an IN718 generic spoke structure. The effect of including a weld in a critical region was investigated for both constant (creep) and cyclic loading conditions at 620°C.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:514792 |
| Date | January 2009 |
| Creators | Tanner, David W. J. |
| Publisher | University of Nottingham |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://eprints.nottingham.ac.uk/10796/ |
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