Why creep is a function of Time?

In summary, creep is a phenomenon where a solid material continues to deform slowly under constant load and temperature. This is due to microscopic mechanisms such as diffusion and dislocation creep, where atoms move over time and produce plastic elongation. These mechanisms are a function of time and require atoms to cross an activation energy barrier in order to produce elongation. This explains why creep is a function of time and can occur even at constant load and temperature.
  • #1
koolraj09
167
5
Hi all,
As suggested by the title, i wanted to know as to why creep is a function of time. Since for any component the load and temperature are constant, still it creeps. What happens there at microscopic level? Why does the solid component continues to deform slowly under constant load and temperature?

Thanks
 
Engineering news on Phys.org
  • #2
koolraj09 said:
Hi all,
As suggested by the title, i wanted to know as to why creep is a function of time. Since for any component the load and temperature are constant, still it creeps. What happens there at microscopic level? Why does the solid component continues to deform slowly under constant load and temperature?

Thanks
The solid may not be fully crystalline, and may contain microscopic amorphous regions that are capable of deforming like fluids.
 
  • #3
  • #4
Thanks for the response.
I am not able to connect the deformation w.r.t time due to these mechanisms. Say for example, the diffusion creep. In this, the diffusion process is a function of temperature. At any particular temperature, the diffusion should occur and then stop. Why does it continue at constant temperature and thus make a material deform as a function of time? Similarly if we consider dislocation creep, we don't increase the stress, then what makes the dislocation to further move around? After we reach a particular load and temperature, these things have no reason (from my perspective, currently) to move and make the material deform continuously w.r.t time.
 
  • #5
koolraj09 said:
Thanks for the response.
I am not able to connect the deformation w.r.t time due to these mechanisms. Say for example, the diffusion creep. In this, the diffusion process is a function of temperature. At any particular temperature, the diffusion should occur and then stop. Why does it continue at constant temperature and thus make a material deform as a function of time? Similarly if we consider dislocation creep, we don't increase the stress, then what makes the dislocation to further move around? After we reach a particular load and temperature, these things have no reason (from my perspective, currently) to move and make the material deform continuously w.r.t time.

Hi
Diffusion Creep involves the flow of vacancies and interstitials through a crystal under the influence of applied stress. A tensile stress increases the separation of atoms on grain boundaries that are normal to the stress axis, and the Poisson contraction decreases the separation of atoms on grain boundaries that are parallel to the stress axis. The result is a driving force for diffusional transport of atoms from grain boundaries parallel to the tensile stress to those normal to the tensile stress (there is a flow of vacancies in the opposite direction). Such diffusion produces a plastic elongation.

Diffusion not only needs temperature, but also needs time. As you may know the diffusion distance is proportional to √Dt, where D is the diffusion coefficient. In the diffusion creep, as I described above, atoms should travel the required distance to produce elongation.

Similarly, other creep mechanisms also need time. In fact, creep is an "anelastic effect".
 
  • #6
Hi materials,
Thanks for your response. I understood that diffusion is a function of time.
Secondly, atoms have to cross the activation energy to go to the vacancy site. But if the temperature and stress are uniform which is how the creep is defined, they why does an atom move to the vacancy?
 
Last edited:

FAQ: Why creep is a function of Time?

What is creep?

Creep is a phenomenon in which materials, such as metals and plastics, deform over time when subjected to a constant load or stress. It is a form of slow, permanent deformation and can lead to failure of the material if not accounted for.

How does time affect creep?

Time is a critical factor in creep because creep behavior is dependent on the duration of the applied load. The longer a material is under a constant load, the more likely it is to experience creep and deform over time.

Why is creep a concern in engineering and materials science?

Creep can significantly affect the performance and lifespan of materials in various industries, such as aerospace, automotive, and construction. It can cause unexpected deformations and failures in structures and components, leading to safety hazards and costly repairs or replacements.

What factors influence the rate of creep?

The rate of creep is influenced by several factors, including the type of material, temperature, applied load, and environmental conditions. Different materials have different creep behaviors, and higher temperatures and higher loads typically result in faster creep rates.

How can creep be prevented or controlled?

There are several methods for preventing or controlling creep, depending on the application and material. These include selecting materials with low creep rates, designing structures to minimize stress concentrations, and using heat treatments or coatings to improve the material's resistance to creep. Proper maintenance and regular inspections can also help identify potential creep issues early on.

Similar threads

Back
Top