Residual stresses can be defined as the self-equilibrating internal stresses that remain in a body in the absence of external forces or thermal gradients. They can arise from kinds of manufacturing processes and thermal treatments, where welding is a common process that generates residual stresses. Residual stresses are known to affect the fatigue, creep and brittle fracture properties of engineering components as well as their structural stability, wear and corrosion behaviour. Techniques that can accurately measure and predict residual stresses are therefore very important. The purpose of this project is to develop and improve the measurement of residual stress using deep hole drilling and neutron diffraction techniques. This is done using experimental methods and finite element analysis methods. Based on these developments, a series of measurements were undertaken to obtain through thickness distributions of residual stress in a variety of welded components. The deep hole drilling residual stress measurement technique is a semi-destructive, mechanical strain relief technique, which the strain components are measured during stress relief from the removal of a small amount of material. Neutron diffraction, a non-destructive technique, is based on Bragg's law and the components of strains are obtained from measurement of lattice spacing of polycrystalline material. The standard deep hole drilling, a newly developed incremental deep hole drilling techniques and the neutron diffraction technique were applied to a variety of metal welds to characterise the through thickness residual stresses generated by different welding methods, validate and develop the application range of these techniques. The finite element method was adopted for a ring weld specimen to simulate the welding process to obtain the residual stress field and to simulate the deep hole drilling techniques. An over-core deep hole drilling mcthod, a development from previous deep hole drilling techniques, was examined in this study. The extraction step in the over-core deep hole drilling technique allowed a hybrid procedure to combine the deep hole drilling and neutron diffraction techniques and increased the accuracy and reliability of residual stress measurements.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:618551 |
| Date | January 2013 |
| Creators | Gang, Zheng |
| Publisher | University of Bristol |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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