The rate of plastic deformation of thorium has been investigated as a function of stress and strain at temperatures from 0 to 60°C. The rate of creep or plastic deformation was found to depend on the instantaneous values of the stress, strain and temperature and thus could be expressed by a mechanical equation of state. The yield point phenomenon was observed even at the lowest plastic strain rates. A critical stress was found below which no plastic deformation was observed.
Peterson, D. T. and Young, J. D., "The creep of thorium near room temperature" (1964). Ames Laboratory Technical Reports. 77.