I hope that this information will be helpful.

https://uwspace.uwaterloo.ca/bitstream/handle/10012/4152/mui_jonathan.pdf?sequence=1

From a rheological perspective, the primary difference between a viscoplastic and viscoelastic material is the presence of a yield stress. A viscoplastic material has a yield stress under which it will not deform, whereas a viscoelastic material will deform at any application of stress.

For both types of fluids the rate of strain depends on stress applied and the type of viscoelastic or viscoplastic material you are investigating. Example models of viscoplastic liquids include Bingham plastic, Hershel-Bulkley and Casson (there is a detailed discussion in the link). For Viscoelastic models, the simplest are the Maxwell and Kelvin-Voigt model, which are combined at varying degrees of complexity to form more 'real' responses. These models give a reasonable example of how typical fluids behave at different strains.

As to determining the difference - using rheometric techniques you could simply plot stress over strain and determine the existence of a yield stress. I don't fully understand what you mean by lost strain however, my best guess is either permanent deformation or lost energy after a hysteresis loop. For this I am not sure if there is a measureable difference in the loop itself, however they should start at different points, with viscoelastic liquids deforming as soon as stress is applied and viscoplastic only after the yeild stress.

http://www.bsr.org.uk/rheology-reviews/RheologyReviews/viscoplastic-materials-Mitsoulis.pdf

Thanks a lot 

thank you

Thanks for your answers!

Very nice information..

Thank you Alll

Thank you everyone for sharing information..

Are you interested in particle emission mechanisms? I hope this reference will be useful

https://doi.org/10.1063/1.5047673

In reality most complex materials also show some viscoelastic behavior prior to yielding and have no "sharp" yield point, i.e. it depends on the deformation history. But purely viscoplastic and viscoelastic models are useful simplified descriptions if they are used "with care".

Thank you all, that was worth reading in details.,

The viscoelastic and viscoplastic materials exhibit the behaviour of fluid and solids both. The difference between the two is of deformation. The viscoplastic material will retain some permanent deformation once the applied load or stress is removed while the viscoelastic material will regain its original state with some change is position of molecules. The viscoelastic materials will also release some energy during the cycle of loading and unloading.

Hello,

This question posed in 2015 still arouses interest, which is to say its fundamental nature in materials science. This is answered by first considering the thermodynamic nature of the elastoplastic transformation and then its microscopic nature. There is only a low-intensity stress domain in which the strain is completely reversible. Beyond a limit stress, due to defects which have the effect of producing electronic polarization, atomic polarization and local order modification, there is an accumulation of energy. Depending on the nature of the defects, the intensity of the stress and the temperature, this energy is stable but irreversible. Beyond a limiting internal stress, elastoplaticity, viscoelasticity and viscoplasticity are different words that relate to the non-adiabatic and non-isentropic relaxation of internal energy. This transformation is accompanied by a rise in temperature, shocks, bond breaks, thermal instabilities and particle emissions commonly referred to as thermoemission, exoemission, fractoemission, triboemission. It is also accompanied by a decrease in Young's modulus and an increase in permittivity. Finally, during this transformation the applied stress becomes more and more compressive until it reaches its explosive value. The microscopic processes of this transformation are therefore described by the dielectric function which provides information on the variations of the polarization as a function of the field, the frequency and the temperature. Therefore, the experimental techniques validating all aspects of this approach are based on the dielectric function and on the equations of state. They are used to determine the initial state of the material and the envelope of its final states under stress. The initial state makes it possible to qualify the manufacture. The final states make it possible to know the reliability of the material at each moment of its use. This approach led to the development of defect engineering.

These results led to the creation of a very rapid training of materials experts and whistleblowers because many models are outdated. In a few days I will publish the link to the online training site, in French first then in English a few weeks later.

Cordially

The Gressus