Long-term material creep tests
2011-02-21
In most cases creep rupture data for ODS materials that are published by respective suppliers of such materials are based on short-term experiments and results are then extrapolated to mid- and long-term data to predict material durability.
Umicore’s in-house measurements of our FKS material families are usually measured in the same way, with one distinct difference: the relevance of short-term creep test results is usually validated by execution of long-term creep experiments regarding the properties of our FKS material families.
The long-term creep tests are setup in two stages: an intermediate term aimed at lifetimes between 500 and 1.000 hours, and a long term aimed at a lifetime of 10.000 hours. The intermediate term is used as a validation of the extrapolated short-term creep data. If necessary, the test conditions for the long-term tests can then still be adapted accordingly.
Taking the example of our FKS Rigilit PtRh10 material, short- and intermediate-term tests have just been accomplished and the he intermediate results are in very good agreement with the extrapolated short-term data, which already validates the relevance of short-term creep tests. To set up the test conditions for the long-term creep tests (aimed lifetime of 10.000 hours), both the short- and the intermediate-term creep data are used.
It is important to note that for these very long lifetimes a reduction of the sample cross-section occurs due to evaporation in the course of the experiment. Without appropriate compensation, the reduced section leads to a local stress increase and hence a decreased time to rupture. Therefore we have developed modified test procedures that are applied for our long-term creep tests to finally obtain highly accurate figures as the basis for our engineering and design efforts.