Dear colleague

What is the difference between linear viscoelasticity, viscoelasticity non-linear and the viscoplasticity?

Personally I think that:

nonlinear inelastic rate dependent = creep= viscoplasticity= viscoelasticity non-linear in large deformations! What do you think about ?

Thank you very much to answer.

Hi Hachimi,

the only differences are where the viscosity takes place (in plastic regime or elastic regime) and their dependence in the stress or strain level.

In linear viscoelastic, if you perform a relaxation test by pulling a specimen up to certain strain and then hold at constant strain, regardless until which strain you hold the specimen, the relaxation curves will be the same for all (after normalization). for example, I pull my polymer up to strain 1% and my instantaneous stress is 5 MPa and when I hold it relaxes to 2.5MPa at infinite time. that means the polymer relaxes 50%. In linear viscoelastic case, if I strain up to 2%, and hold, It will always have 50% relaxation (regardless of the applied strain).

Meanwhile, for the nonlinear viscoelastic case, it will be different for each applied strain. I applied 1% it can be relaxes 50 percent, if I applied 2% it relaxes 55% percent and so on. That is why it is called nonlinear viscoelasticity.

Yet, for both cases above, if you release the specimen and wait until sufficient time, there is no permanent strain left (fully elastic but it takes time to recover... therefore, viscoelastic).

In viscoplastic case, after you release the specimen, there will be permanent deformation left.. and thus viscoplasticity.