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Title: The influence of long-range residual stress on plastic collapse of pressurised pipes with and without flaws
Author: Wu, Guiyi
ISNI:       0000 0004 5921 277X
Awarding Body: University of Bristol
Current Institution: University of Bristol
Date of Award: 2015
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Structural integrity assessments of pressurised pipes include plastic collapse as a potential failure mode. This dissertation uses analytical and numerical models as well as experiments to explore the effect of displacement controlled loading conditions and fixed load conditions on the collapse pressure of pipes with and without flaws. Open- and closed-ended pipes are considered. The displacement controlled uniform stress and bending stress represent long-range or fit-up residual stress. Such long-range residual stress, resulting from misfit between components of an engineering structure, is associated with significant elastic follow-up and is commonly treated as primary stress which contributes to plastic collapse. However, this approach may be incorrect as residual stress can be relaxed. There is little evidence that explores the relationship between longrange residual stress and plastic collapse in a pressurised pipe. In this thesis the finite element method and experiments are developed to consider the effect of long-range residual stress on plastic collapse of pressurised pipes. Pipes in a number of states are considered: short and long pipes with no flaws, part and full circumferential flaws. The flaws consist of either a crack or a slot on the internal or external surface of the pipe. Both local and global collapse pressures are considered. It is found that global collapse of pressurised pipes containing longrange residual stress is not dependent solely on the level of initial stress but also on the length of the pipe, the flaw geometries and the collapse dominated stress. It is shown that the displacement controlled stress can act either as secondary stress or as primary stress. Finally, before considering the role of long-range residual stress in failure assessment diagrams, the level of elastic follow-up for full circumferentially flawed pipes is quantified and closed-form approximations of plastic collapse pressures are proposed to consider when a long-range residual stress is treated as either a secondary stress or a primary stress. The results from this work show that conservative assessments will be made of the collapse pressures of pipes containing flaws if a long-range residual stress is simply taken to be an equivalent form of mechanical loading.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available