Abstract
To extend creep life modelling from classical rupture modelling, a
robust and effective parametric strain model has been developed. The
model can reproduce with good accuracy all parts of the creep curve,
economically utilising the available rupture models. The resulting
combined model can also be used to predict rupture from the available
strain data, and to further improve the rupture models. The methodology
can utilise unfailed specimen data for life assessment at lower stress
levels than what is possible from rupture data alone. Master curves for
creep strain and rupture have been produced for oxygen-free
phosphorus-doped (OFP) copper with a maximum testing time of 51,000 h. Values of time to specific strain at given stress (40–165 MPa) and temperature (125–350 °C)
were fitted to the models in the strain range of 0.1–38%. With typical
inhomogeneous multi-batch creep data, the combined strain and rupture
modelling involves the steps of investigation of the data quality,
extraction of elastic and creep strain response, rupture modelling, data
set balancing and creep strain modelling. Finally, the master curves
for strain and rupture are tested and validated for overall fitting
efficiency. With the Wilshire equation as the basis for the rupture
model, the strain model applies classical parametric principles with an
Arrhenius type of thermal activation and a power law type of stress
dependence for the strain rate. The strain model also assumes that the
processes of primary and secondary creep can be reasonably correlated.
The rupture model represents a clear improvement over previous models in
the range of the test data. The creep strain information from
interrupted and running tests were assessed together with the rupture
data investigating the possibility of rupture model improvement towards
lower stress levels by inverse utilisation of the combined rupture based
strain model. The developed creep strain model together with the
improved rupture model is foreseen to give a sound basis for life
predictions of the OFP copper overpack canister for the spent nuclear
fuel.
Original language | English |
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Pages (from-to) | 25-28 |
Number of pages | 4 |
Journal | Materials Science & Engineering A: Structural Materials: Properties, Microstructure and Processing |
Volume | 510-511 |
DOIs | |
Publication status | Published - 2009 |
MoE publication type | A1 Journal article-refereed |
Event | 11th International Conference of Creep and Fracture of Engineering Materials and Structures, CREEP 2008 - Bad Berneck, Germany Duration: 4 May 2008 → 9 May 2008 |
Keywords
- Creep
- Life prediction
- OFP copper
- Strain modeling