Time-dependent deformation under sustained mechanical load. Its rate depends on stress, temperature and microstructure.
A deformation mechanism map shows which deformation process dominates in a specified range of stress, homologous temperature and other controlled variables. Boundaries shift with grain size, composition, pressure, water content and the constitutive laws; they are not universal lines determined by homologous temperature alone.
Dislocation creep is time-dependent crystal deformation through motion and interactions of dislocations. A common constitutive model is with , giving stress-dependent effective viscosity. Unlike diffusion creep, it often has weak grain-size dependence over the regime being modelled.
Water weakening of rocks denotes the reduction of mechanical strength or increase of material creep rate produced by water or hydrogen-related defects under specified conditions. The effect depends on mineralogy, water activity, temperature and deformation mechanism; atmospheric dryness alone does not measure a planet's interior water content.
The approximately constant strain rate in secondary material creep at specified stress, temperature and material state. A lifetime estimate assumes that rate remains representative; evolving area, damage and tertiary material creep can shorten it.
Permanent shape change driven by stress-biased atomic or vacancy diffusion. Different chemical potentials at differently stressed grain surfaces drive material transfer, requiring grain-shape accommodation. Bulk and boundary transport give different grain-size dependencies.
Diffusional material creep dominated by grain-boundary transport. An ideal scaling is . Its stronger grain-size dependence and typically lower transport activation energy distinguish it from bulk-diffusion material creep.
Diffusional material creep dominated by transport through grain interiors. For an equiaxed-grain model, , with geometric factor , atomic volume and grain size . It is linear in stress in this ideal limit.
A regime in which the steady material creep rate varies approximately as a power of stress, , with thermally activated coefficients. In ordinary dislocation-creep fields, glide, climb and recovery give an exponent greater than the linear-stress diffusion-creep limit.
The absolute temperature divided by an appropriate melting temperature, . It is a useful scale for comparing thermally activated deformation; Celsius temperatures cannot be used directly in the ratio.
nucleation and growth of cavities on grain boundaries under high-temperature stress. Coalescence can cause creep rupture. This is distinct from vapour-bubble formation in a liquid.
Relative tangential motion of neighbouring crystal grains along their boundary, requiring accommodation to avoid incompatibility and damage. It can contribute to high-temperature creep.
Time-dependent strain under load that is enhanced or driven by irradiation-produced defects. Stress changes defect capture and dislocation motion; the dependence need not match ordinary thermal creep.
Stress-directed deformation generated by irradiation-defect processes that can operate where ordinary creep is small. The terminology overlaps with irradiation creep in the literature; the mechanism and reference condition should be stated.
Enhancement of a stress-driven creep mechanism by irradiation-maintained point-defect populations, for example accelerated diffusion or dislocation climb. It need not have the creep rate of an unirradiated specimen.
An irradiation creep mechanism in which applied stress makes differently oriented dislocations or dislocation loops absorb point defects at different rates. The resulting directional strain is distinct from stress-free void swelling.
Articles by others on the same topic
Creep is a time-dependent deformation of materials that occurs when they are subjected to a constant stress over an extended period. It is a crucial phenomenon in materials science and engineering, particularly for structures and components that experience prolonged loading conditions, such as bridges, buildings, pipelines, and high-temperature applications like turbines and reactors. Creep typically occurs in three stages: 1. **Primary Creep:** This initial stage involves a rapid rate of strain that gradually decreases over time.