This dissertation considers the characterisation of the relaxation of residual stress in a component resulting from plasticity induced by externally applied loads with the elastic follow-up factor. Residual stresses are the result of an incompatibility of displacements or strains within a component, i.e. a misfit. However, elastic material surrounding the non-linearly deforming region results in the region experiencing loading conditions between the extremes of fixed-load and fixed-displacement conditions. This is known as elastic follow-up. Greater elastic follow-up, i.e. more compliance in the surrounding material, decreases the relaxation of residual stress with plasticity. An idealised residual stress model was developed to determine the residual component of load acting on a fracture specimen, as a function of the applied component of load, through the plasticity resulting from the total load on the specimen. The effect of elastic follow-up is shown on the rate of residual stress relaxation, additional plastic strain accumulation and the J-integral. The results from the model are compared with the existing and proposed R6 methodology. In general, the existing approach was found to be overly conservative with negligible elastic follow-up, reduced with the g-function approach, otherwise they were reasonably intolerant of elastic follow-up. The recently proposed relaxation equation showed a good agreement with the model for all levels of elastic follow-up. An experiment is presented to characterise the elastic follow-up associated with an idealised one-dimensional residual stress field. It is shown that the elastic follow-up factor is a function of the reduction in eigenstrain or misfit, rather than the increase in plasticity alone, for the associated reduction in residual stress. The rate of relaxation of residual stresses in a component is dependent on the eigenstrain, geometry and post-yield behaviour of the material. It cannot be uniquely described by the elastic follow-up factor as the rate of relaxation is also dependent on the position of all non-linear deformation in the body. Therefore the elastic follow-up factor is position-, loading- and defect-specific.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:650098 |
| Date | January 2013 |
| Creators | Horne, Graeme Christopher Milligan |
| Publisher | University of Bristol |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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