Understanding Viscoelasticity - Questions Answered

[knoble]

I always get confused while trying to understand viscoelasticity.

As far as I understand,
- In Elastic materials, deformation increases upon application of constant stress and remains constant until the stress/force is removed. Upon removal of force, the deformation reduces and the material attains its original postition.
- In Viscoelastic materials, deformation increases with stress, continues to increase (not constant in this case). When the force is removed, the deformation reduces but the material is induced with a permanent deformation.

Question:
- Dont elastic materials deform permanently upon failure? (or is that if the constant stress applied is lesser than the failure limit, the material does not fail and the deformation is constant)
- Since viscoelastic material also behave similar to Newtonian fluid, why does the stress increase with application of strain and then quickly decline to zero in Newtonian fluid?

It would be great if someone can explain this clearly.

Thanks!
NK

 

[Chestermiller]

Question:
- Dont elastic materials deform permanently upon failure? (or is that if the constant stress applied is lesser than the failure limit, the material does not fail and the deformation is constant)

An ideal elastic material is defined as one that returns to its original configuration once the loading is removed.

- Since viscoelastic material also behave similar to Newtonian fluid, why does the stress increase with application of strain and then quickly decline to zero in Newtonian fluid?

Because the relaxation time for a Newtonian fluid is very short (actually, it's zero in the perfectly Newtonian limit).

Chet