Investigation of structural creep strain recovery and its impact on structural integrity

Cho, Nak-Kyun and Chen, Haofeng (2017) Investigation of structural creep strain recovery and its impact on structural integrity. In: 24th International Conference on Structural Mechanics in Reactor Technology, 2017-08-20 - 2017-08-25, BEXCO/Centum Hotel.

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The creep strain recovery in steels is a material phenomenon of the time-dependent recovery of creep strain after unloading. Effects of the recovery has been commonly neglected or considered insignificant when designing steel components or structures. However, a different mechanism of the structural creep strain recovery, which affects the lifetime of the component, can be identified by nonlinear finite element analyses. The aim of this paper is to analyse this structural creep strain recovery mechanism, which can take place under the cyclic thermal and uniaxial tensile loads, and its impact on the structural integrity. It is identified that the mechanism can occur within a peak dwell due to dwell stress relaxations of thermally induced stresses for a certain type of cyclic thermal and mechanical load condition. Further analyses and discussions are provided to investigate the root cause of the mechanism. Various tensile load conditions with a dwell at the peak thermal load are analysed to define factors influencing the structural creep recovery mechanism, and to investigate how the mechanism affects the lifetime of the component. Practical problems and appropriate methods for estimating creep-fatigue damage associated with the mechanism are discussed. From the investigations, it is concluded that the structural creep recovery mechanism during the peak dwell may significantly increases the plastic strain during unloading phase, leading to a creep ratchetting behaviour of the structure.


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