THE PRESSURE-DEPENDENCE OF CREEP

Constant strain-rate experiments have been conducted at 10** minus **4 and 10** minus **5 s** minus **1, temperatures of 1100-1300 degree C and pressures of 1. 0-3. 0 GPa on a synthetic polycrystal composed of 97% olivine, and 3% enstatite, (Mg, Fe)SiO//3 (to fix the silica activity) prepared by hot isostatic pressing. Over this interval of pressure and temperature, the activation parameters for creep change. Nevertheless, at constant homologous temperature, the pressure dependence of the flow stress vanishes. The authors conclude that DELTA V* need have no simple relationship to the volume of any particular atom or group of atoms and that the correlation of the pressure dependence of creep with the pressure dependence of melting need not necessarily imply diffusion control of creep.