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[Solved] question about vumat_nh

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Posts: 1
Topic starter
(@dolbynormal)
New Member
Joined: 16 years ago

Special considerations for hyperelasticity

Hyperelastic constitutive models in VUMAT should be defined in a corotational coordinate system in which the basis system rotates with the material. This is most effectively accomplished by formulating the hyperelastic constitutive model in terms of the stretch tensor, , instead of in terms of the deformation gradient, . Using the deformation gradient can present some difficulties because the deformation gradient includes the rotation tensor and the resulting stresses would need to be rotated back to the corotational basis.

refer Abaqus User Subroutines Reference Guide (1.2.18 VUMAT).

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Posts: 1
(@cedricxie)
New Member
Joined: 10 years ago

[B][I]Special considerations for hyperelasticity[/I][/B]

Hyperelastic constitutive models in VUMAT should be defined in a corotational coordinate system in which the basis system rotates with the material. This is most effectively accomplished by formulating the hyperelastic constitutive model in terms of the stretch tensor, , instead of in terms of the deformation gradient, . Using the deformation gradient can present some difficulties because the deformation gradient includes the rotation tensor and the resulting stresses would need to be rotated back to the corotational basis.

refer Abaqus User Subroutines Reference Guide (1.2.18 VUMAT).

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Posts: 3998
(@jorgen)
Member
Joined: 5 years ago

I agree with Vinayb.
You can also use the deformation gradient, but then you need to rotate things properly.

-Jorgen

Posts: 9
(@lin987)
Active Member
Joined: 8 years ago

This is my understanding:

B should be calculated as : B = R * U^2 * Rt = R * B_corot* Rt

but in VUMAT, the rotation is taken care of by Abaqus, so the user only needs to calculate the corotational portion, which is U^2

Posts: 10
(@Dhafer)
Active Member
Joined: 6 years ago

In addition to the responses above, you may find the link in response #13 at this thread helpful:

[url] https://polymerfem.com/forum/polymerfem-downloads/computer-software/88-abaqus-vumat-for-the-neo-hookean-model [/url]

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