This is an asinine question. "Volumetric plastic strains" do not exist.

Plasticity is an inherently shear deformation phenomenon (de-formation = change in form = distortion): the process is produced by shear micro-mechanisms, even though it may be accompanied, favoured or hindered by volumetric strains.

Volumetric strains (no de-formation) and shear strains (distortions) are antinomic.

It is certainly not an asinine question. i found this word in journals.

So what? Do you think anything written in journals is okay?

Please consider my answer , instead.

please consider your answer first

@Syamimi Mohd Yusoff: @Andrea Pavan is right, conceptually "volumetric plastic strain" does not exist.

There are:

Volumetric strain: this is just the change in volume divided by the original volume;

Plastic strain: permanent deformation, which means that after a material reaches its elastic limit (or yielded) further straining will result in permanent deformation.

Cheers,

Humberto.

Thank you Humberto Junior

In small strain theory, it always vanishes. But yes, some do mention that decomposition of plastic strain tensor into pressure part and deviatoric part (again, in small strain realm); and I do not understand why.

Andrea Pavan Syamimi Mohd Yusoff Mohammad Ahmed Basri

I also want to join this discussion, since I think it's quite meaningful. We all know that "volumetric plastic strain" should not exist, since the stress state will not exceed the yield surface along the hydrostatic axis (pressure). However, in the plasticity calculation or the stress correction, we do need to involve a correction of the pressure due to the "volumetric plastic strain". Since right now I'm coding a particle-based approach and this approach calculates the pressure based on EOS, I really want to figure out whether I should make a correction on the pressure based on the flow rule and its corresponding plastic strain. Many thanks.

Volumetric plastic strains is for sure a thing, but its equal to 0 if the material follows von Mises plasticity with associated flow (because the trace of the plastic strain rate is 0). This is due to the assumption that the material is plastically incompressible. Thus, there is no volumetric plastic deformation. However, if the material follows Drucker-Prager, which is pressure-sensitive and non-isochoric (the trace is not 0 and therefore there is volumetric plastic strain) the material is plastically compressible and will have volumetric plastic strains. However, for a material parameter beta = 0, the flow potential does not depend on the pressure and therefore the volumetric plastic strain is 0.

ok I will be able to evaluate your answers in the next four months

Following...

Volumetric plastic strain is that component of strain (as expressed in strain tensor) which leads to compression or expansion of the material body without any shape change. Thus, it is associated with the trace of the strain tensor or its diagonal elements.

The deviatoric plastic strain is the one that causes shape change and is associated with the off-diagonal elements of the strain tensor.

What you incorporate or do not in any given plasticity model or its modification thereof is your choice. The above answer is irrespective of the model that you choose, and is simply an attempt to explain the fundamental definition of the two terms. Kindly update/rectify as needed, whoever reads it. Thanks.

Andrea Pavan Humberto Almeida Jr Shashank Sharma