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Both terms concern time-dependent strain under stress. Here radiation-enhanced creep means irradiation accelerating a mechanism that also operates thermally, whereas radiation-induced creep emphasises deformation driven by irradiation-specific defect fluxes. The literature sometimes uses irradiation creep as an umbrella, so identifying the mechanism is more informative than treating the names as mutually exclusive experimental categories.

radiation-enhanced diffusion maintains mobile point-defect concentrations above their thermal equilibrium values. Under a load, this can accelerate diffusion-mediated deformation or dislocation climb and thereby enhance a creep mechanism. The effect depends on temperature, defect production, recombination and sinks; simply raising the specimen temperature by radiation heating is a different explanation and must be controlled.

radiation-induced creep can remain important where unirradiated creep is small. stress-induced preferential absorption gives differently oriented dislocations unequal capture of irradiation-produced defects, producing directional climb. Climb can also enable further glide by relieving obstacles. A schematic low-stress relation iswith a condition-dependent compliance $B_{\mathrm{irr}}$, not a universal constitutive law. Coupling to void swelling and evolving sinks can add further terms.

Compare stressed and unstressed specimens in and out of irradiation at matched actual temperature, and resolve longitudinal, transverse and volumetric strains. Unstressed irradiation growth or void swelling is not itself evidence of creep, and stress-enhanced void swelling must not be included automatically in a fitted creep strain. These controls distinguish a mechanical response to irradiation defects from ordinary creep or a different dimensional-change mechanism.

Irradiation creep adds stress-directed, time-dependent strain driven by the irradiation-generated defect population. It can be appreciable where ordinary thermal material creep would be slow, because irradiation maintains mobile point defects far above their equilibrium populations.

Absorption or emission of vacancies and self-interstitials permits dislocation climb. Applied stress can make differently oriented dislocations or dislocation loops absorb defects at different rates: stress-induced preferential absorption then produces a directional strain. Climb can also allow a pinned dislocation to bypass an obstacle and continue dislocation glide, providing a second route to strain.

A useful small-strain empirical form, over a limited range of conditions, isfor constant stress $\sigma$ and approximately constant irradiation-creep compliance $B$. Here $d$ is the accumulated displacements per atom and $\dot{d}$ the displacement dose rate; $B$ is measured per unit stress and per unit dpa. This relation explains why creep can scale approximately with both stress and neutron flux when the damage spectrum is fixed. It is not a constitutive law valid at every dose or temperature.

The total strain can also include thermal material creep, void swelling, irradiation growth and changes due to precipitation or recovery. Stress-free swelling is not itself irradiation creep. Experiments on pressurized type316 tubes separated these contributions and found that correcting stress-enhanced swelling materially affected comparisons between annealed and specimens strengthened by cold working.^[ref]

At sufficiently high temperature, thermal material creep can dominate. Changes in microstructure caused by irradiation hardening, softening, bubbles and cavities can either alter the creep rate or shorten rupture life. Thus enhanced defect-driven creep is the central effect, while the net rate and lifetime remain material- and history-dependent.