Thesis

Design by analysis methods for ductile collapse modes under static and repeated loading

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Awarding institution
  • University of Strathclyde
Date of award
  • 2024
Thesis identifier
  • T16938
Person Identifier (Local)
  • 201673204
Qualification Level
Qualification Name
Department, School or Faculty
Abstract
  • Pressurised components in civil nuclear power plants are required to operate under extreme thermal and mechanical loading conditions. There are many potential failure mechanisms and the consequences of a component failing could be disastrous. To help solve such a complex problem, dedicated Boiler and Pressure Vessel Design Codes exist to ensure the safe design of pressure vessels for Nuclear application. One widely recognised design code is ASME BPVC Section III Rules for Construction of Nuclear Facility Components. ASME III allows the use of Design by Analysis (DBA) to prevent failure modes such as plastic collapse, ratcheting and fatigue from occurring by carrying out a detailed structural assessment using methods such as Finite Element Analysis (FEA). Linear elastic DBA is commonly used in industry due to the low computational cost compared to non-linear elastic-plastic DBA but requires extensive post-processing. This thesis focuses on the use of elastic and elastic-plastic DBA to prevent failure due to plastic collapse and ratcheting. The advantages and disadvantages of various methods are discussed with an emphasis on the practicality for industrial application. An alternative stress linearisation approach is proposed and is investigated alongside established linearisation methods to determine how the stress distribution in thick components can be better represented using elastic DBA. This study highlights the sensitivity of such methods to complex geometry, loading conditions and code requirements, providing significant insight into the use of elastic DBA for industrial application. By validating the static and cyclic stresses against elastic-perfectly plastic limit load and cycle-by-cycle FEA, it is shown that linearising all 6 stress components proved to be the most reliable and consistent method for the cases studied. number of non-linear DBA methods are investigated using benchmark cases and the results analysed in detail. The ASME VIII Div 2 plastic analysis, twice elastic slope (TES), tangent intersection (TI), plastic work (PW) and plastic work curvature (PWC) methods are all investigated for the prediction of plastic collapse. In particular, the Plastic Work method is shown to provide a reliable method to determine the collapse load of complex nuclear structures whilst maintaining some conservatism. Also, the ASME VIII monotonic stress-strain curve proved to be effective in predicting the structural response of a low carbon steel tubesheet. Combining the ASME VIII material model with the Plastic Work method and using it to assess thick walled nuclear components provides a novel application of both methods. Furthermore, the case studies provide significant evidence of how such an approach could be used to perform robust structural assessments that are complaint with ASME III.
Advisor / supervisor
  • Mackenzie, Donald
  • Bell, Chris
Resource Type
DOI

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