Abstract
Fatigue properties of a commercial epoxy have been studied at RT, LNT and LHeT. The low temperature reactor irradiation effects have also been studied at LHeT. Repeated flexural stress with frequency of 2Hz was applied to the samples cured into cylindrical shapes of 4.0mm diameter and 30mm length. The samples were in contact with the coolant of liquid helium or liquid nitrogen during the fatigue experiments. Reactor irradiation was performed in Low Temperature Loop of Kyoto University Research Reactor with the fast neutron fluence of about 2.5×1016n·cm-2 and γ doses of 2.8×108rad.
Normally the design parameters at cryogenic temperatures are apt to be based on the data at RT because the temperature decrease brings higher mechanical strength. However the fatigue strength of this epoxy at LHeT was about a half of that at LNT and was as low as that at RT data. For this reason the fatigue data at LHeT where superconducting magnets are used should be accumulated exactly.
On this experimental result, a similar tendency of the fatigue properties between at LNT and at LHeT was observed in the stress-number of cycles curves represented by normalized stress on ordinate against fatigue life on abscissa with logarismic scale. It suggests the possibility of the substitution with fatigue data at LNT for that at LHeT.
Low temperature irradiation brought on the epoxy used in this study the decrease of fatigue strength and the increase of scattering of fatigue strength. These results indicate that careful design should be performed in practical use of these organic materials to fusion reactor.
