Dear Mr.Deep,

You go to out put results column and read normal stress and shear stresses. Using these values the principal stresses can be calculated and the equation to calculate the principal stresses are available in any strength of material books. The way you have calculated i.e. force divided by area is not correct..ok all the best..

Dear Deep Bakshi,

to extend the answer of Karthigeyan . S, I would say that the stress calculation depends on the type of finite element you are using to model the structure. For example, if you are using a truss element, then your calculation is correct, since only one stress S11 applies, but if you are using 3D finite elements, then you should calculate the S11 stress by taking into account the contributions of all the calculated strains (not only epsilon 11). You may find the expression of Hooke's law for an isotropic material in the following link:

http://www.efunda.com/formulae/solid_mechanics/mat_mechanics/hooke_isotropic.cfm

Regards,

Anargyros

Dear Karthigeyan . S sir thanks for your answer.

My aim is to compare true stress strain obtained from UTM compression test with ABAQUS simulation test, in that Misses Vs LE33 is following the test result but my concern is how it's calcuting that Misses Vs LE33.

As a procedure the stress comes from resistance force and LE comes from displacement so why I am not able to get the same curve from force Vs displacement data after doing manipulation.

Thanks once again and it would be great if you help me through this.

Dear Anargyros Karakalas

Thanks for responding to my doubt, so what I am modelling is 3D deformable cylinder with uniaxial displacement using the rigid plate. Now the misses stress is equal to S11 and the other two S22=S33=0.

But how is S11 is calculated?

If we look at theory engg stress =force /area. Then manipulating we obtain true stress S11. But I am unable to get S11 from the force data.

Your effort in resolving my query is deeply appreciated.

Dear Deep Bakshi,

since you have 3D elements then you should calculate the S11 stress by using the mathematical expression of the Hooke's law in the link I have provided for you.

You can see that given the displacements or strain the stress is calculated using a matrix equation.

I provide again the link:

http://www.efunda.com/formulae/solid_mechanics/mat_mechanics/hooke_isotropic.cfm

Regards,

Anargyros

Dear Anargyros Karakalas,

Thanks a lot, it worked upto Elastic limit can you please tell how to obtain stress and strain beyond elastic limit.

Dear A Rahul,

I have tested at different mesh size as per your suggestion, but as such no much change in result. I have earlier doubt as to how it calculate stress strain from displacement force data. The stress strain that is obtained from abaqus are pretty much close to the desired, i wanted to know the behind calculation.

Thanks a lot for suggestion.

Dear Deep Bakshi,

is your true stress equal to F/(S0(1-u/L0)), where F - force on surface, u - corresponding axial displacement, S0 - initial cylinder cross-section area, L0 - initial cylinder length ?

Dear Victor J. Аdlucky ,

The F/(S0(1-u/L0)) eqution you are talking about is calculating true stress from force displacement, i have been using this only but the answer is different , actually it comes from mathematical expression of Hookes law which Anargyros Karakalas mentioned above.

Thanks a lot for your answer.

Dear Deep Bakshi,

I suppose that if you would like to calculate the plastic stress you will have to use equations of plasticity and possibly write a subroutine. Unfortunately, I am not familiar with plasticity.

Regards,

Anargyros

Dear Deep Bakshi,

I still don't understand why results are differ.

Is abaqus stress state really uniaxial ? If not, then maybe boundary conditions have to be revised.

Dear Victor J. Adlucky,

Yes the stress is unaxial, i have checked that. But stress strain is not coming directly from formula you described.

Dear Deep Bakshi,

Maybe you will find something helpful for yourself in this links

https://www.researchgate.net/post/How_can_I_convert_Logarithmic_Strain_to_Engineering_Strain_in_Abaqus

https://www.researchgate.net/post/Which_strain_outputLE_PE_EE_IE_NE_of_Abaqus_Standard_Explicit_CAE_should_be_taken_in_case_of_non-linear_crimping_analysis_of_nitinol_stents

Thanks Victor J. Аdlucky,

I will go through your suggested link