NBG–18 graphite is developed by SGL Carbon for the Pebble Bed Modular Reactor
Company (PBMR), and is used as the preferred material for the internal graphite core
structures of a high–temperature gas–cooled nuclear reactor (HTR). The NBG–18
graphite is manufactured using pitch coke, and is vibrationally molded.
To assess the structural behaviour of graphite many destructive techniques have been
performed in the past. Though the destructive techniques are easy and in some cases
relative inexpensive to perform, these methods lead to waste material and require
cumbersome time consuming sample preparations.
To overcome this problem numerous non–destructive testing techniques are available
such as sonic resonance, resonant inspection, ultrasonic testing, low and multifrequency
Eddy current analysis, acoustic emission and impulse excitation techniques.
The Hammer Impulse Excitation technique was used as a method in predicting the
fatigue life of NBG–18 graphite by focussing on the application of modal frequency
analysis of determined natural frequencies. Moreover, the typical fatigue
characteristics of NBG–18 graphite were determined across a comprehensive set of
load ranges.
In order to be able to correlate modal frequency parameters with fatigue life, suitable
uniaxial fatigue test specimen geometry needed to be obtained. The uniaxial fatigue
test specimens were manufactured from two NBG–18 graphite sample blocks. The
relationship between natural frequencies of uniaxial test specimens, fatigue life,
sample positioning and sample orientation was investigated for different principle
stress ratios.
Load ratios R = –oo and R = +2 tested proved to show the highest r–values for the
Pearson correlation coefficients investigated. However, there was no significant trend
found between the natural frequency and the fatigue life. / Thesis (M.Ing. (Nuclear Engineering))--North-West University, Potchefstroom Campus, 2011.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:nwu/oai:dspace.nwu.ac.za:10394/4813 |
| Date | January 2010 |
| Creators | Markgraaff, Renier Francois |
| Publisher | North-West University |
| Source Sets | South African National ETD Portal |
| Detected Language | English |
| Type | Thesis |
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