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|Title:||An Experimental Determination of the Effect of Cyclic Stress on Void Growth in Ultra-High-Purity Aluminum During Simultaneous 800 Mev Proton Irradiation|
|Author(s):||Sommer, Walter Frank|
|Department / Program:||Metallurgy and Mining Engineering|
|Degree Granting Institution:||University of Illinois at Urbana-Champaign|
|Abstract:||Conditions of radiation and a simultaneous cyclic stress are inherent in advanced energy system designs, including magnetically and inertially confined controlled thermonuclear fusion reactors (CTR). Walter Green and Johannes Weertman (G & W) had predicted that edge dislocations, set into oscillatory motion by an applied cyclic stress, would "sweep up" excess radiation produced vacancies that would otherwise produce void growth.
A major objective of this research was to test the G & W theory. An applied sinusoidal tension-tension cyclic stress with a mean value of 1/6 the tensile yield stress and a maximum value of 1/3 the tensile yield stress at a frequency of 1/3 Hz decreased void number density in 99.9999% polycrystalline aluminum irradiated with 800 MeV protons to a dose of 0.045 displacements per atom (dpa). Post-irradiation examination by transmission electron microscopy revealed that cavity (void) population in material subjected to a cyclic stress while simultaneously being irradiated was only a third to a quarter of that in identical material that concurrently received an identical radiation history, but was under no applied stress. This result is qualitatively consistent with the G & W theory. In this report, we not only address the G & W theory but also disscuss the role of increased dislocation density, as might be induced by a cyclic load, on void growth kinetics. Ultimately, we conclude that moving dislocations are effective vacancy sinks since their forced presence during simultaneous irradiation leads to measurable decreases in both void number and void size.
The second objective of this experiment was to investigate the potential of using a medium energy (800 MeV) proton source, such as the Clinton P. Anderson Los Alamos Meson Physics Facility (LAMPF) for complicated in-situ mechanical-radiation effects studies. The simulation potential of the 800 MeV proton for CTR 14 MeV neutron effects has been favorably reported, especially since 800 MeV protons yield large amounts of transmutation product gases such as hydrogen and helium; these will also be formed in CTR structural and containment materials but have not been present in material radiation effects data generated by fission reactor experience. It was found that the large experimental volume at LAMPF greatly facilitated use of large, complicated hardware, relative to what can be considered for the core of a fission reactor. In adition, the flux of protons is contained in a beam which is directable through steering magnets and thus can be controlled to irradiate only the sample material and not activate peripheral equipment; this was found to be advantageous during the irradiation period for inspection and repair of equipment and later for rapid sample recovery and preparation.
Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1981.
|Date Available in IDEALS:||2014-12-14|
This item appears in the following Collection(s)
Dissertations and Theses - Metallurgy and Mining Engineering
Graduate Dissertations and Theses at Illinois
Graduate Theses and Dissertations at Illinois