simple stress/strain validation
simple stress/strain validation
(OP)
Hi,
I am a structural engineer, and I have recently began using the Abaqus as a finite element software. After numerous attempts and researching a lot of information, I have not been able to validate a simple test.
What I am trying to do is model a non-linear steel part in 3D (as a solid) and trying to validate the stress/strain curve I receive from the Abaqus to the one I have inputted into the material property. I used the elastic and plastic models in the Abaqus/CAE. In all honesty the numbers are not important me (i.e. which structural steel, it could be 60 ksi grade or whatever), but I just want to know how to model it correctly so that the stresses and strains match up. I have read several topics here, but none seem to help.
Does anyone have a very basic input file they could share that has a working non-linear structural steel material property that matches the Abaqus stress/strain to the theory/actual stress/strain.
This problem has me stumped and I have been stuck on something so seemingly simple for a while now.
Thank you for any help you may provide.
I am a structural engineer, and I have recently began using the Abaqus as a finite element software. After numerous attempts and researching a lot of information, I have not been able to validate a simple test.
What I am trying to do is model a non-linear steel part in 3D (as a solid) and trying to validate the stress/strain curve I receive from the Abaqus to the one I have inputted into the material property. I used the elastic and plastic models in the Abaqus/CAE. In all honesty the numbers are not important me (i.e. which structural steel, it could be 60 ksi grade or whatever), but I just want to know how to model it correctly so that the stresses and strains match up. I have read several topics here, but none seem to help.
Does anyone have a very basic input file they could share that has a working non-linear structural steel material property that matches the Abaqus stress/strain to the theory/actual stress/strain.
This problem has me stumped and I have been stuck on something so seemingly simple for a while now.
Thank you for any help you may provide.





RE: simple stress/strain validation
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RE: simple stress/strain validation
Input File
would you like me to just paste it in, or is the above link alright?
Thank you for your quick reply
RE: simple stress/strain validation
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RE: simple stress/strain validation
For some reason, the analysis is not capturing the linear and non-linear behavior very accurately. The non-linear also seems to be more accurate than the linear results, because the slope of the elastic region is not even close to 28-29 million psi.
RE: simple stress/strain validation
CODE --> Abaqus_input
However, you still need to create a uniaxial strain/stress state. A quick and easy way to do this is to create one cube of unit dimensions, use equation constraint just as you did previously, and the output RF and U will automatically be equal to stress and strain.
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RE: simple stress/strain validation
RE: simple stress/strain validation
Are you new to this forum? If so, please read these FAQ:
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RE: simple stress/strain validation
Yes I tried it on a cube, and applied a uniaxial strain, and the results match very nicely.
I am currently doing the same on a concrete cube, using the Concrete Damage Plasticity Model where I am required to input Compression and Tension Behavior of the Concrete. However, this will obviously be a bit more involved than steel due to the nature of concrete material properties.
For some reason, the tension test on the concrete matches the theoretical data quite nicely. Meaning when I apply an upward (tensile) displacement, the stress/strain curve from Abaqus matches nicely with the theoretical data.
But when it comes to the compression test, where I apply a downward (compressive) displacement, the stress/strain curve from Abaqus does not match as nicely. The data in the elastic region matches in a relatively good way, however, in the plastic region my concrete cube will not fail like the steel cube did. The stress keeps increasing as the strain increases without actually me seeing a drop off. So I am suspicious as to why that is, because the tension test saw a failure behavior in the Abaqus results, but the compression test seems to never fail. If you have some insight on this matter, that would be greatly appreciated as well.
RE: simple stress/strain validation
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RE: simple stress/strain validation
** MATERIALS
**
*Material, name=Concrete-CDP-Cube
*Density
0.0002246,
*Elastic
3.56045e+06, 0.2
*Concrete Damaged Plasticity
31., 0.1, 1.16, 0.666667, 0.
*Concrete Compression Hardening
356.028, 0.
699.719, 3.45483e-06
1029.01, 1.09436e-05
1343.13, 2.26845e-05
1641.87, 3.8735e-05
1925.35, 5.90599e-05
2193.91, 8.35659e-05
2448.02, 0.000112122
2688.21, 0.000144575
2915.1, 0.000180757
3129.29, 0.000220492
3331.43, 0.000263604
3522.14, 0.000309916
3702.04, 0.000359256
3871.71, 0.000411454
4031.75, 0.000466351
4736.28, 0.00315966
4881.3, 0.00712494
5264.16, 0.0742979
*Concrete Tension Stiffening
360.536, 0.
342.657, 0.000104944
291.385, 0.000219139
259.737, 0.000327882
237.582, 0.000433981
220.894, 0.000538555
207.706, 0.000642148
196.923, 0.000745063
187.879, 0.000847487
180.144, 0.000949537
173.422, 0.0010513
167.507, 0.00115282
162.245, 0.00125416
157.522, 0.00135533
153.25, 0.00145637
149.359, 0.0015573
145.795, 0.00165812
142.514, 0.00175886
139.479, 0.00185951
136.66, 0.0019601
134.032, 0.00206062
131.574, 0.00216109
129.268, 0.00226151
127.099, 0.00236187
125.053, 0.0024622
123.118, 0.00256248
121.286, 0.00266272
119.546, 0.00276293
117.892, 0.00286311
116.315, 0.00296325
**
I have been reading up as much as possible, trying to find out more information on this material model. I have yet to determine how I would define "damage parameters" as that is an additional option for Concrete Damage Plasticity, even though I have read up on the information, it might be difficult to get some values without test data, which I don't have. But then I am not sure if I need the "damage parameters" since my tension behavior matched nicely and showed the decreasing branch of the stress/strain curve, and I did not define "damage parameters" for that.
RE: simple stress/strain validation
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RE: simple stress/strain validation
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RE: simple stress/strain validation
So I would like to thank you for that. I have been also to confirm my stress-strain data for compression and tension thanks to this thread. Currently, I am working on shear behavior though, as that is my main concern so if that might be a future concern of yours I look forward to seeing what help can be provided through this thread.
RE: simple stress/strain validation
Shear and Flexure are also an interest to me, but I have not read up on that to see which material model would be bested suited for this. (I have taken a look at your thread). As far as I can tell, the Concrete Damage Plasticity model is acceptable for compression/tension behavior, but I am not sure how to capture the shear behavior in an accurate manner.
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RE: simple stress/strain validation
All you need to do is make sure the element type allows the type of deformation you expect in your problem - which can easily be done by reading the documentation for any given element type.
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RE: simple stress/strain validation
entail that the incorrect element type is being used for the expected deformations?
RE: simple stress/strain validation
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RE: simple stress/strain validation
RE: simple stress/strain validation
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RE: simple stress/strain validation
Moving on to a column (which is not a unit cube), let's say that I have loaded this column in shear, how would I determine the failure load? Meaning, after applying a displacement, how would I get the output for the failure load, assuming I am still using the Concrete Damage Plasticity Model.
For the unit cube, I just examined the force vs displacement at the "Load Node" which is the node I applied the displacement to. However, for a column, you don't necessarily know the exact point, how would I extract that information. I will post a picture to show you the column setup I have. I am applying the displacement on the top part above the column but want to determine the failure load in the column.
Here is the link: Link
Not sure if I can post it this way but I will try:
RE: simple stress/strain validation
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