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Modified Armstrong-Frederick Relation for Handling Back Stresses in FEM Computations
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Technology.ORCID iD: 0000-0002-8494-3983
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Technology.
2009 (English)In: CREEP & FRACTURE IN HIGH TEMPERATURE COMPONENTS: DESIGN & LIFE ASSESSMENT ISSUES, PROCEEDINGS / [ed] Shibli IA, Holdsworth SR, LANCASTER: DESTECH PUBLICATIONS, INC , 2009, 836-847 p.Conference paper, Published paper (Refereed)
Abstract [en]

If transient phenomena are important in creep design, a non-stationary creep model must be applied. One way of achieving this is to apply a back stress. The back stress reflects the history of the creep deformation. During primary creep the back stress normally increases from zero to a stationary value representing secondary creep. A common way to derive the back stress in FEM-modelling is to use the Armstrong-Frederick relation. It is demonstrated that this can give rise to unexpected results in the sense that back stress components can be much larger than the corresponding applied stress components. Modification of the Armstrong-Frederick relation are proposed that avoid this problem. An alternative approach is also given. In this case the back stress is assumed to be a scalar. Then its value can be derived in the same way as in the uniaxial case, for example using the Bergstrom-Kocks-Mecking model for FCC alloys. In the Odqvist equation for the creep rate, the effective stress is reduced with the back stress, but the stress deviator is left unmodified. The models are applied to copper canisters for storage of nuclear waste. It is demonstrated that the models give virtually the same result.

Place, publisher, year, edition, pages
LANCASTER: DESTECH PUBLICATIONS, INC , 2009. 836-847 p.
Keyword [en]
creep, copper, FEM, back stress
National Category
Materials Engineering
Identifiers
URN: urn:nbn:se:kth:diva-30846ISI: 000266610600074ISBN: 978-1-60595-005-1 (print)OAI: oai:DiVA.org:kth-30846DiVA: diva2:402492
Conference
2nd International Creep Conference Zurich, SWITZERLAND, APR 21-23, 2009
Note
QC 20110308Available from: 2011-03-08 Created: 2011-03-04 Last updated: 2011-03-08Bibliographically approved

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Sandström, Rolf

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