Improvement of high temperature applications relies on the further development of ultra-high temperature materials (UHTMs). Higher performance and efficiency is driving the need for improvements in energy conversion and propulsion systems. Rocket nozzles, gas turbine engines and hypersonic aircraft depend on a better understanding of a material's performance at high temperatures. More specifically, the characterization of creep properties of high temperature materials is required. Conventional creep testing methods are limited to about 1700 degrees Celsius. Non-contact methods have been developed, which rotate spherical samples up to 33,000 rotations per second. A load is supplied by centripetal acceleration causing deformation of the sample. Non-contact methods have been performed above 2000 degrees Celsius. The induction drive developed in the previous work has decoupled temperature from rotation, greatly expanding the experimental testing range. Creep mechanisms may involve dislocation motion or the diffusional flow of atoms. Creep may be dominated by dislocation glide, dislocation climb, or diffusional-flow mechanisms. Multiple creep mechanisms can be active in a sample, but one is often dominant in a given regime which depends on stress, temperature and grain size. This work studies the creep behavior of samples in regions of transition between dominating creep mechanisms, and the effect on the precision of the measurement. Two finite element models have been developed in the current work. A two-dimensional Norton creep model replaces the more computationally expensive three-dimensional Norton creep model developed in the previous work. Furthermore, a two-dimensional Double Power Law model has been developed to simulate creep behavior of high temperature materials in regimes of mixed dominance. The two-dimensional Norton and Double Power Law models are used to identify and characterize creep in the regions of transition between dominating creep mechanisms. Simulations are analyzed to determine the effect of regimes of mixed dominance on the creep measurements of rotating samples of high temperature materials.
| Identifer | oai:union.ndltd.org:UMASS/oai:scholarworks.umass.edu:theses-1859 |
| Date | 01 January 2012 |
| Creators | Benitz, Maija |
| Publisher | ScholarWorks@UMass Amherst |
| Source Sets | University of Massachusetts, Amherst |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | Masters Theses 1911 - February 2014 |
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