PolymerFEM - Constitutive Models

Using F-d curve for NL springs

themig — Sat, 18 May 2013 06:42:58 GMT

Hello users,

My first post in this forum.

I am working on a project wherein there is a rubber material which gets compressed. Now I have the force-displacement curve for this rubber material. I intend to represent the rubber with NL springs.

1. he F-d curve mentions the specimen details as 5*100 mm. This i believe is the dimension of tested specimen. Do I need to consider this for the whole rubber model??? The rubber model has a perimeter of 2000 mm

2. I have 'n' number of springs connected in parallel. Do I need to consider this as well while using F-d curve. Effective stiffness when springs connected in parallel is Keff = K1 + K2 + ....Kn

Kindly let me known your thoughts

Thanks.

Curve fitting in ANSYS

kavitharun — Fri, 17 May 2013 05:33:02 GMT

Hi

I am doing hyper elastic modelling. I have Uni axial stress strain data. I am using curve fitting tool in ANSYS. Should I give the same stress strain data as input to curve fitting tool or should I convert the strain into stretch ratio and then give as input? pls help me in this.

After fitting the model in curve fitting tool in ANSYS hyper elastic modelling, I am getting the fitted model parameters alone but how do I get the corresponding stress and strain values fitted for model. so that I can import to Matlab.

I am struggling in that. So please help me. Thanks in advance.

Kavitha

Modelling Hyperelastic Material-aborting

KarimO — Wed, 15 May 2013 03:20:49 GMT

Hello,

I am fairly new to Abaqus, I have been trying to model a material with a skin around it made of rubber. I have inputed the properties of the rubber using Neo-hookean model that I have obtained from another FEA fit. My model without using the hyperelastic material properties for the rubber will converge however, when I add the hyperelastic material properties the simulation will be submited and run to only abort. If anyone has any insight that would be great.

problem to define steel for X-bracing system

max_wolf — Sun, 12 May 2013 14:07:32 GMT

hi all freind ,
To reach the buckling behavior of the X-bracing system in cyclic loading , how it should be steel behavior model in Abaqus? Behavioral model is applied to the definition of the material or analysis step?
In fact I want to get under Figure.
thanks

Attached Images

scbf hys.jpg (36.3 KB)

Connection between ABAQUS and Fortran

yeqwang — Fri, 10 May 2013 15:39:19 GMT

Dear all,

I have installed ABAQUS 6.12-1 and Intel Fortran 11.1.060. And I believe that I had done all the necessary configurations for updating all the environment variables.

The problem that I am dealing with is writing a material model UMAT in ABAQUS. Before doing that, I have to make sure that UMAT works in ABAQUS on my computer, so I ran the benchmark NEO-HOOKEAN material model in ABAQUS. But, unfortunately, I got some messages popped up below.

The way that I tested the benchmark problem was: Typing "abaqus make library=umat.for" in the abaqus command window. "umat.for indicates the neo-hookean UMAT code"

The error messages are:

C:\Temp>abaqus make library=umat.for
Abaqus JOB umat.for
Begin Compiling Abaqus/Standard User Subroutines
5/10/2013 10:36:58 AM
End Compiling Abaqus/Standard User Subroutines
5/10/2013 10:36:58 AM
Begin Linking Abaqus/Standard User Subroutines
5/10/2013 10:36:58 AM
Traceback (most recent call last):
File "SMAPyaModules\SMAPyaDriverPy.m\src\make.py", line 906, in
File "SMAPyaModules\SMAPyaDriverPy.m\src\application.py ", line 149, in run
File "SMAPyaModules\SMAPyaDriverPy.m\src\make.py", line 93, in execute
File "SMAPyaModules\SMAPyaDriverPy.m\src\make.py", line 844, in makeUserSubSha
redLib
File "SMAPyaModules\SMAPyaDriverPy.m\src\driverSharedLi brary.py", line 210, in
run
File "SMAPyaModules\SMAPyaDriverPy.m\src\driverSharedLi brary.py", line 351, in
link
File "SMAPython\SMAPytLibPy.m\src\subprocess.py", line 444, in call
return Popen(*popenargs, **kwargs).wait()
File "SMAPython\SMAPytLibPy.m\src\subprocess.py", line 595, in __init__
errread, errwrite)
File "SMAPython\SMAPytLibPy.m\src\subprocess.py", line 804, in _execute_child
startupinfo)
WindowsError: [Error 2] The system cannot find the file specified

Any help or suggestions will be greatly appreciated!

Thanks a lot!

How to simulate a varied stiffness model using VUMAT

cuba20052001 — Thu, 09 May 2013 11:07:00 GMT

Dear all,

I want to simulate a varied stiffness and elastic model in ABAQUS like this: A simple rectangular specimen, an impact load on the right side. For the sake of simplicity, supposing only shear stiffness component is strain rate dependent, for instance, it can be expressed as: Qss=a+b*log(Ess_rate), where a and b are constants, Ess_rate is shear strain rate. Now I am not sure whether this model can be implemented using VUMAT:confused::confused:. Who can help me about this issue?Thanks a million.
Best,
Haibin

Abaqus verification

d_ak — Thu, 09 May 2013 06:55:44 GMT

Hello everyone
I have a question about Abaqus verification for a Mooney-Rivlin hyperelastic material example which exist in ABAQUS Documentation/Abaqus Verification Manual/2.2.1 Elastic materials/VIII. Hyperelasticity with Mooney-Rivlin strain energy function. In the example for a Test data input-uni axial tension the company Defined a stress-strain curve as input for material property(Nominal stress-Nominal strain). But when I plot these parameters(Stress -nominal strain) as output of the software the result shows a significant difference between Input data and out put data,and I don't know why?!
Any comment about this will be highly appreciable
this is the input file which I'm discussing about:
*HEADING
- COMPR. HYPEREL. (MOONEY-RIVLIN), TEST DATA INPUT, UNIAXIAL TENSION
*NODE,NSET=ALL
1,
2,1.
3,1.,1.,
4,0.,1.,
5,0.,0.,1.
6,1.,0.,1.
7,1.,1.,1.
8,0.,1.,1.
*NSET,NSET=FACE1
1,2,3,4
*NSET,NSET=FACE2
5,6,7,8
*NSET,NSET=FACE3
1,2,5,6
*NSET,NSET=FACE4
2,3,6,7
*NSET,NSET=FACE5
3,4,7,8
*NSET,NSET=FACE6
4,1,8,5
*ELEMENT,TYPE=C3D8RH,ELSET=ONE
1,1,2,3,4,5,6,7,8
*SOLID SECTION,ELSET=ONE,MATERIAL=MOONEY
*MATERIAL,NAME=MOONEY
*HYPERELASTIC, MOONEY-RIVLIN, TEST DATA INPUT
*UNIAXIAL TEST DATA
1.5506, 0.1338
2.4367, 0.2675
3.1013, 0.3567
4.2089, 0.6242
5.3165, 0.8917
5.9810, 1.1592
6.8671, 1.4268
8.8608, 2.0510
10.6329, 2.5860
12.4051, 3.0318
16.1709, 3.7898
19.9367, 4.3694
23.4810, 4.8153
27.4684, 5.1720
31.0127, 5.4395
34.5570, 5.7070
38.3228, 5.9299
42.0886, 6.0637
45.6329, 6.1975
49.3987, 6.3312
53.1646, 6.4650
56.9304, 6.5541
64.2405, 6.6433
*BIAXIAL TEST DATA
0.9384, 0.0200
1.5900, 0.0600
2.4087, 0.1100
2.6220, 0.1400
3.3240, 0.2000
4.4278, 0.3100
5.1830, 0.4200
6.6024, 0.6800
7.7794, 0.9400
9.7857, 1.4900
12.6351, 2.0300
14.6804, 2.4300
17.4000, 2.7500
20.1058, 3.0700
22.4502, 3.2600
24.6530, 3.4500
*PLANAR TEST DATA
0.6000, 0.0690
1.6000, 0.1034
2.4000, 0.1724
3.3600, 0.2828
4.2000, 0.4276
6.0000, 0.8483
7.8000, 1.3862
9.6000, 2.0000
11.1200, 2.4897
12.9600, 3.0345
14.8800, 3.4483
16.5800, 3.7793
18.2000, 4.0621
*VOLUMETRIC TEST DATA
60., .9703
118.2,.9412
175.2,.9127
231.1,.8847
*STEP,NLGEOM,INC=20
UNIAXIAL TENSION
*STATIC,DIRECT
1.,20.
*BOUNDARY,OP=NEW
FACE1,3
FACE3,2
FACE6,1
FACE4,1,1,5.
*EL PRINT,F=10
S,
E,
*NODE PRINT,F=10
U,RF
*EL FILE,F=10
S,E
*NODE FILE,F=10
U,RF
*END STEP

St Venant Kirchoff Material in ANSYS

drs261083 — Wed, 08 May 2013 23:26:32 GMT

I am attempting to solve a problem involving biological tissues subjected to static loads and would like to employ a St. Venant Kirchoff model (since it is the simplest non-linear material model). I am not sure that by defining the material model to be linear elastic and turning on the large deformation option, one would be able to model tissue as a StVK material. I am also not familiar whether it would be possible to input this constitutive model using a UMAT option (as is the case with ABAQUS).

weird displacement result using adaptive mesh

Davidz — Wed, 08 May 2013 20:09:38 GMT

Hi all,

I am modeling a indentation test using axisymmetric model, including a rigid body and a deformable body (4x5);

I used dynamic explicit solver with adaptive mesh control because of large deformation will stop simulation.
B.C. : the bottom of the deformable body is fixed, and the rigid body has a velocity along the -y direction.

I have attached stress, displacement results and inp file.

My problem is
the displacement result is weird. but the stress or strain results seems good.
This is the first time for me to use the adaptive mesh technique. I think it caused this weird displacement caused.
Probably this is a bug, because stress results are generated from nodal displacement results. Now the trend of stress and displacement results are not match.

Anyones help will be greatly appreciated!

axisymmetric.zip mesh.jpg sress.jpg u.jpg

Attached Images

mesh.jpg (19.7 KB)
sress.jpg (19.2 KB)
u.jpg (18.8 KB)

Attached Files

axisymmetric.zip (85.0 KB)

reducing computational time in a coated material

mina.pouya — Tue, 07 May 2013 15:37:41 GMT

Hi everybody,

I am trying to simulate a simple elastic fiber coated by NiTi SMA in a cylindrical geometry.
I used the elements C3D8R here for both materials and a tie contact between them.
When I seed hole the geometry by distance 0.15, the simulation takes time like 28 hrs and its okey.
In some reasons but now, I have to seed just the coating NiTi-layer with finer distance like 0.05.
And in this way the simulation is taking too much time like 2 weeks.
Is there any suggestion to make the simulation faster? like using another element types ?

Regards,
Mina

Fluid cavity ball and BC

bubamara — Tue, 07 May 2013 09:47:50 GMT

Dear users,

I would like to compress with a high pressure load a shell deformable ball filled with air . Even I replace the BC there is the same error message and I�d also like to understand that!
The message error is There is zero MOMENT everywhere in the model based on the default criterion.
I attached my INP file

I really appreciate any help
Regards,
B.

Attached Files

fluidcavityball.zip (95.8 KB)

UMAT subroutine for the criterion Hill48

walidnasri — Mon, 06 May 2013 14:29:52 GMT

Hello,
I am a PhD student in Applied Mechanics, I need to mock the anisotropic criterion Hill48 on Abaqus, for that you need this program on a test subroutine UMAT. I am very beginner in the field of programming, so I need to make this simulation as soon as possible.
More about:
1 - How to create a subroutine UMAT to set the anisotropic criterion Hill48.
2 - complete methodology to simulate this subroutine in Abaqus.
I have an answer, Waiting to hear from you, please express my sincere greetings.

Walid Nasri

adhesives and elastomers/rubbers

tuananhppl1 — Mon, 06 May 2013 08:30:04 GMT

I had posted an earlier query. Thanks a lot Dr.Bergstrom for helping in that. I just had a basic question which I am not clear about. I used hyperelastic elements to model rubber/elastomer in abaqus. If I want to model an adhesive whats the exact difference between an elastomer and adhesive? Does one use hyperelastic to model adhsive also or is adhsive simply a low stiffnest elastic material?
Thank you for your help

Mooney model_ clarification

kmgraju — Fri, 03 May 2013 00:24:03 GMT

Dear friends
I am using ANSYS workbench 14.0. I am trying two way FSI problem in a artery. I used Mooney Rivilin 9 parameter for the artery model. For the stabilization control I used Energy method.Energy dissipation ratio( Ratio of the work done by stabilization forces to the
element potential energy) I fixed 0.002 and stabilization force limit I fix default value as 0.2

I have chosen the above values randomly . How I can check this value are correct.

Under damping controls:

I set stiffness coefficient defined by : Direct Input

Stiffness coefficient I set: 0.002 ( randomly). How can I find the stiffness coefficient? or what is the stiffness coefficient for Mooney model?

Thank you

PU seal under dynamic load

Bram V — Thu, 02 May 2013 14:03:51 GMT

Hi,

I got the request to evaluate the sealing capacity of a compressed PU foam under dynamic loads.
In ansys i am limited to linear material models in combination with dynamic input. unless i go transient (not my first choice).

Are there other ways i can proceed and still get a good A to B comparison for 2 seal designs?