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Bad material definition: vumat

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Posts: 26
Topic starter
(@sandra)
Eminent Member
Joined: 15 years ago

Hi,

In my simulation, I use two different sets of material properties and define the constitutive relation using vumat. The material properties and the vumat have been tested individually and they work fine.

When, I use two different sets of material properties simultaneously in simulation, I get the following error

***ERROR: Bad Material definition in element number 136 instance MERGE-1: zero or negative initial dilatational modulus caused by bad material data. Please check your material input and any initial conditions if necessary.

The dilatation modulus (= (stressNew-stressOld)/strainInc for both sets material parameters at t=0 is greater than zero. So i am not really sure, why this error would occur.

I would really appreciate inputs to tackle this problem.

Thanks

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4 Replies
Posts: 26
Topic starter
(@sandra)
Eminent Member
Joined: 15 years ago

I am still lost.

I used a simple cuboid formed by merging two cubes of different material properties. This simulation works provided each cube is meshed as a single brick element. However, when I go for more elements, the simulation thows Bad Material definition error.

B

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4 Replies
Posts: 93
(@kiranckst)
Trusted Member
Joined: 14 years ago

Do the individual vumats work for multiple elements/complex loading conditions?

Could excessive deformation speed/mass be affecting the result with the two merged together?

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Posts: 26
Topic starter
(@sandra)
Eminent Member
Joined: 15 years ago

hi lumpwood,

thanks for your suggestions. i figured out the error. i had a misplaced return statement in the code. now things look brighter..

brunda

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Posts: 26
Topic starter
(@sandra)
Eminent Member
Joined: 15 years ago

hi lumpwood,

thanks for your suggestions. i figured out the error. i had a misplaced return statement in the code. now things look brighter..

brunda

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