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#1 2008-02-09 15:15:57

Jacopo
Member
From: Colle di Val d'Elsa, Italy
Registered: 2008-02-05
Posts: 565

Elasto-plastic material

Hello, when I insert the material with elasto-plastic behaviour what kind of curve must be insert?the true stress-true strain curve or engineering stress-strain curve?.
When I red the strain value this are logharitmic (true strain) or engineering?


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#2 2008-04-07 22:11:27

jmp
Member
Registered: 2008-04-07
Posts: 46

Re: Elasto-plastic material

Hello

it depends on your model and hypothesis on strains : small or large

- if your model leads to small displacements and strains, then Cauchy stresses are equivalent to PoilaKirchoff stresses ; the engineering curve is able to modelize stress-strain curve up 5%

- if you have to take into account large displacements, but samll strains, strain tensors are Green-Lagrange, and you have to define DEFORMATION=GREEN. But engineering stress-strain curve is still available

- il you have to modelize large strains, then (with DEFORMATION='SIMO_MIEHE') stress-strain curve is the true one : cauchy stress and logarithmic strains. The when you compute the stesses (with STAT_NON_LINE) they are Caychy stresses, and the strains (with CALC_ELEM) are computes with the hypothesis of large strains.

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#3 2008-04-30 13:56:15

Jacopo
Member
From: Colle di Val d'Elsa, Italy
Registered: 2008-02-05
Posts: 565

Re: Elasto-plastic material

Thx, for you help.
About the definition of plastic zone with command DEFI_FONCTION, if I insert the epsilon and sigma value, the first point of the curve must be the strain value (for example about 0.002 for the steel) and second value the yeld stress...or I must insert the plastic residual value (ABAQUS SW use this formulation so the first point of strain must be 0 and the sigma value the sigma yeld value)?
On the example I see that you use the real value of esilon and sigma and not the plastic residual value but...Can you help me about this my doubt?

Regards
Jacopo


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#4 2008-04-30 14:08:03

Paul CARRICO
Member
From: France
Registered: 2007-12-26
Posts: 294

Re: Elasto-plastic material

The plastic curve is defined as follow :

stress = fonction( total strain)

=> that means the fist abscisse corresponds to the elastic strain : epsilon = yield stress / yound modulus

Paul

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#5 2008-04-30 21:34:53

Jacopo
Member
From: Colle di Val d'Elsa, Italy
Registered: 2008-02-05
Posts: 565

Re: Elasto-plastic material

Ok, you confirm what I image...!!!

Jacopo


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