Abstract
This paper reports creep crack growth modelling of Grade 91 vessel weldments at high temperature using a modified ductility-based continuum damage mechanics (CDM) model, which is based on the Kachanov-Rabotnov CDM and utilizing the concept of ductility exhaustion. The proposed model holds a key advantage over existing models in that it requires fewer material constants to be identified and calibrated. The new modified model was implemented into a user-defined subroutine in ABAQUS and then used to predict the creep crack growth of Grade 91 vessel weldments. Creep crack initiation and growth in the vessels were predicted to occur in the heat-affected zones of the weldments associated with the end closures, which is in good agreement with the corresponding vessel tests. Further, the predicted creep rupture lives of the notched bars and the vessels using the proposed model correlated reasonably well against the experimental results. This suggests that the modified ductility-based damage model can be used for creep crack growth and life prediction for high temperature structures with confidence.
Highlights
With the increasing derive to enhance the thermal efficiency and reduce carbon emissions, energy conversion systems such as power plants are expected to operate under high temperature and pressure conditions
Creep Strength Enhanced Ferritic (CSEF) steels including 9–12%Cr steels have been extensively used in the construction of highenergy components owing to their good mechanical performance, such as creep strength and oxidation resistance (Masuyama, 1999; Choudh ary and Palaparti, 2012)
The evolution of damage is based on the rupture stress cri terion, while the latter approaches assume that material failure at a given point occurs when the locally accumulated creep strain reaches its critical value (Wen et al, 2016; Meng and Wang, 2019)
Summary
With the increasing derive to enhance the thermal efficiency and reduce carbon emissions, energy conversion systems such as power plants are expected to operate under high temperature and pressure conditions. Hyde et al (2001) have proposed a stress-based damage mechanics approach to predict creep damage initiation and growth in power plant steels weldment. Similar work has been used to model the high-temperature creep damage and crack growth in P91 steel weldments through the applications of stress-based CDMs (Hyde et al, 2010b, 2010c). Cocks and Ashby (1980) proposed a multi-axial creep ductility-based model assuming that cavity growth is governed by the power law creep This model has been widely used to investigate creep damage behaviour of steels and the related failure mechanisms (Shlyannikov and Tumanov, 2018b; Oh et al, 2011; Kim et al, 2013; Alang and Nikbin, 2018).
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