On the Simulation of Progressive Deformation in Nuclear Piping
In this thesis the performance of different constitutive models in ratchet simulation is investigated. Ratcheting is accumulated plastic strains which may occur when a structure is subjected to a constant load in combination with cyclic loading. In the assessment of nuclear class 1 pressure retainin...
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Format: | Dissertation |
Sprache: | eng |
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Zusammenfassung: | In this thesis the performance of different constitutive models in ratchet simulation is investigated. Ratcheting is accumulated plastic strains which may occur when a structure is subjected to a constant load in combination with cyclic loading. In the assessment of nuclear class 1 pressure retaining component ratcheting is one of the three failure modes that are addressed and may limit the design life of nuclear pressurized components and piping systems.A steel structure subjected to a constant load in combination with cyclic loading into the plastic region undergoes a change of the material characteristics in several aspects. These cyclic material characteristics are complex and may vary for different load situations, load levels, temperatures and materials. In addition to this, the presence of a mean stress may also affect the material cyclic characteristics.In previous numerical investigations on ratcheting there has not been a sufficiently robust case of simulation. However, in most of these investigations, the simulation response is compared with ratcheting experiments which either are conducted under load levels which are not common for a nuclear pressurized component, the experimental specimen is not comparable with a pressurized component or only a few experimental tests have been conducted. Hence, it has not been settled which material characteristics need to be considered to accurately simulate ratcheting in a pressurized piping component under load levels common in a nuclear power plants. As a result of this, it is not obvious which types of constitutive material models is needed and how the model parameters should be calibrated in order to simulate ratcheting in a nuclear component accurately.As part of this thesis an extensive experimental program has been conducted on pressurized tube specimens. In total 30 test specimens made of two different materials, 316L and P235, have been manufactured and tested. In order to determine material properties, monotonic tensile load and internal pressure experiments have been performed. The remaining test specimens have been used for ratcheting experiments.The experimental results show ratcheting in the hoop direction when the tube is subjected to certain combinations of internal pressure and cyclic axial strains. The higher the pressure is and the larger the strain ranges are, the higher the ratcheting response becomes. In addition to this, also the cyclic hardening and softening behavior in the tubes axi |
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