Internal and Effective Stresses in the Steady-State Creep of Polycrystalline Cadmium at 0.5Tm

High-purity polycrystalline cadmium is creep tested in air at 22°C (0.5 Tm) and the stress-dip test used to determine the effective (σe) and internal (σ1) stresses. The stress-exponent of steady state creep is 2.24 for applied creep stresses, σ, less than about 20 MPa but increases to 6.12 at higher stresses, indicating a possible change in rate controlling mechanism. The internal stress varies with the applied stress, σ, increasing with increasing σ. σi/σ ratios remain constant at 0.93 to 0.98 and do not change at the high σ values where the stress exponent of steady state creep has indicated a change in rate controlling mechanism. σi/σ ratios of 0.9 to 1.0 agree with previous data for pure metals.