Creep of the materials

Question

Does creep exists for all materials at any stress at room temperature? I searched for this and could not find any answer other than creep isn't significant at low stresses and low temperatures. What I want to know is if the creep is present at low temperatures (way below the melting point) and even at the slightest of stress (way below yield strength) even if in the smallest negligible amount (creep) so that deformation or elongation will happen noticeably if we waited for a sufficient time period (even if very long). For example, a structural-grade steel cube suspended by a string from above will/will not elongate under its own weight and become a long and thin wire that ultimately touches down to the ground if we observe it for say 100 000 or more years? Or is there a creep threshold which determines that below that no irreversible creep is possible?

Answer 1

Yes, creep occurs at all temperatures, although the dropoff is exponential. The reason is that at any nonzero temperature (which is all temperatures), there’s a nonzero chance for a thermal defect such as a vacancy to form, and to minimize strain energy, these defects preferentially resolve in a manner that relieves the existing stress state. This results in viscous flow.

The flow rate is marked on some deformation mechanism maps:

Observe the sagging of lead pipes decades after installation:

You can expect to wait the longest (or gain the longest safe operating time, however you look at it) for strong, refractory materials at low temperatures and load states.