Variation Of Creep Rate Research Articles

Soil Creep As A Rate Process

The fundamental equation of the theory of absolute reaction rates has been adapted for use in the study of time-dependent soil deformations. Results of constant stress creep tests have established that the basic form of this equation supports the assumption of a thermally activated creep process, the predicted relationship between experimental activation energy and creep stress, and the predicted stress dependence of creep rate. Some modification of the equation is needed, however, to account for the variation of creep rate with time. Techniques are described for study of deformation mechanisms in soils and test results suggest that interparticle bonding is probably of the primary valence type. Resistance to shear stresses cannot be accounted for in terms of viscous water films, and interparticle contacts must be effectively solid to solid.

High-Temperature Steady-State Creep Rate in Single-Crystal MgO

Steady-state, three-point bending deflection rate measurements on single-crystal MgO samples in the temperature range of 1450°–1700°C show that creep is a thermally activated process without an unique activation energy. The measured energies range from 3.5 to about 7 eV. This range of energies can be explained in terms of self-diffusion data if it is assumed that the creep rate is limited by self-diffusion. Small deviations from stoichiometry are shown to be very important in controlling the creep rate as they are in all ionic or electron transport processes. Understanding and control of these deviations are necessary to obtain a quantitative understanding of either steady-state creep or diffusion. The variation of creep rate with stress can be described by a power law with an exponent varying from 4 to 7. This range of exponent lends some support to the theory based on edge dislocation climb over barriers as the rate limiting step. On the other hand, such barriers have not been observed in single crystals of MgO and other substances, so that some other mechanism in which diffusion is rate limiting may be operating. The creep rate is apparently independent of subgrain structure, precipitates observed at room temperature, surface roughness, spectroscopically determined impurity content, the valence state of the iron impurity, and dislocation strain pattern after bending.