5
$\begingroup$

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?

$\endgroup$

1 Answer 1

6
$\begingroup$

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:

enter image description here

Observe the sagging of lead pipes decades after installation:

enter image description here

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.

$\endgroup$
4
  • $\begingroup$ You said there is a non zero chance to creeping at non zero temperatures. Does that mean the rate of creeping is not continuous at any stage even if the material is free from defects (manufacturing defects)? I think you meant defects in the answer in the meaning that they are caused by chance due to non-zero temperature. $\endgroup$ Jul 6, 2023 at 17:40
  • 1
    $\begingroup$ I edited my answer to clarify. The kind of defect I’m referring to is a thermally induced defect; no material is free of them. The flow is modeled as continuous because of how many atoms (and vacancies) exist in a typical sample. $\endgroup$ Jul 6, 2023 at 17:44
  • $\begingroup$ Thanks. But , there are mentions of a threshold for some materials below which it is said to be no creep. : sciencedirect.com/science/article/abs/pii/S1359646202001653 Is that approximation only or do such materials exist? $\endgroup$ Jul 6, 2023 at 17:52
  • 1
    $\begingroup$ That paper is looking only at dislocation-mediated creep and implicitly ignoring the background diffusional creep as negligible. $\endgroup$ Jul 6, 2023 at 18:02

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.