[brunomramoa]

Hello everyone,

I would like to ask for a clarification of the input in the plasticStrainVsYieldStress .txt file.


For example, in the tutorial tutorials/solids/elastoplasticity/neckingBar it is defined under the mechanicalProperties dictionary that the material has a mechanical law of type neoHookeanElasticMisesPlastic. It then specifies the elastic modulus, density, Poisson coefficient and the location of a file with the plastic strain vs yield stress. In this file there is the following data:
(
(0.000 0.451e9)
(0.006 0.476e9)
(0.019 0.525e9)
(0.038 0.583e9)
(0.066 0.642e9)
(0.147 0.710e9)
(0.500 0.777e9)
(1.000 0.831e9)
)


The epsilon=0; sigma= 0.451e9 is considered the yield strain and yield stress?
epsilon = 1; sigma= 0.831e9 is the strain and stress at break?

image: https://ibb.co/bFjHrW2


Best Regards!

[bigphil]

Originally Posted by brunomramoa

Hello everyone,

I would like to ask for a clarification of the input in the plasticStrainVsYieldStress .txt file.


For example, in the tutorial tutorials/solids/elastoplasticity/neckingBar it is defined under the mechanicalProperties dictionary that the material has a mechanical law of type neoHookeanElasticMisesPlastic. It then specifies the elastic modulus, density, Poisson coefficient and the location of a file with the plastic strain vs yield stress. In this file there is the following data:
(
(0.000 0.451e9)
(0.006 0.476e9)
(0.019 0.525e9)
(0.038 0.583e9)
(0.066 0.642e9)
(0.147 0.710e9)
(0.500 0.777e9)
(1.000 0.831e9)
)


The epsilon=0; sigma= 0.451e9 is considered the yield strain and yield stress?
epsilon = 1; sigma= 0.831e9 is the strain and stress at break?

image: https://ibb.co/bFjHrW2


Best Regards!

Hi Bruno,

The 'plasticStrainVsYieldStress.txt' file specifies the 'plastic (true/log) strain' versus the 'yield (true/Cauchy) stress'.

With reference to https://ibb.co/bFjHrW2, yes 0.451e9 is the yield stress, aka the initial yield stress (as it changes as you apply more deformation), but 0 is not the yield strain (yield total strain), it is instead the plastic strain at first yield, which is always zero by definition at first yield. The subsequent data points are defining how the stress vs plastic strain curve (the link gives stress vs total strain).

You can calculate the plastic strain from the total strain as (from Hooke's law):

plasticStrain = totalStrain - currentYieldStress/YoungModulus

which only makes sense from the initial yield stress.

As regards "breaking", the neoHookeanElasticMisesPlastic law is an elasto-plasticity law and does not include prediction of damage/cracking/breaking; of course, in the neckingBar case the simulation will eventually crash as the cells become severely deformed, but this is not related to the prediction of breaking.

Philip