Creep tests of sealed specimens as well as unsealed specimens exposed to either pressurized water or air have been conducted at various constant temperatures from 100 to 300°C and durations up to 24 hours. Apart from the need to study multiaxial deformations, the triaxial loading is required to prevent moisture escape from the sealed specimen. The specimens are sufficiently small to achieve uniform temperature and moisture content in less than 3 minutes. Overcoming various difficulties, a triaxial testing device was built. Specimens heated at the time of loading and before loading were tested. Some new and unexpected results are found: (a) unsealed specimens exposed to pressurized hot water creep much less than sealed specimens and the difference in creep rate becomes greater after a few hours; (b) deviatoric creep of sealed specimens is at high temperatures much larger than the volumetric creep; (c) at 100°C, unsealed specimens loaded at the time of heating creep much more than sealed specimens, but at 200°C the situation is reversed; (d) the shrinkage and the additional creep due to drying exhibit great delay after drying. Furthermore, with a several hour increase of the period of preheating before loading, creep is substantially reduced, and the axial creep appears to depend nearly linearly on the axial stress superimposed on a hydrostatic pressure. The results appear to have some new implications for the accident analysis of reactor vessels as well as fire resistance.
ASJC Scopus subject areas