PolymerFEM - Constitutive Models

Shift Functions and Reduced Time

shriisall — Tue, 07 Sep 2010 19:31:26 GMT

Hi, .

For thermorehelogically simple materials in viscoelasticity, we know that the use of shift functions to calculate relaxation times (tau) at different temperatures

tau(T) = tau(Tref)A(T) ---- (1)

I am getting confused with the above equation and the reduced time integral which is again used to obtain relaxation times at different temperatures.

I am developing my own FE code for viscoelasticity and not sure how to handle temperature change effects. Can I simple use (1) to calculate the properties at any temperature and use in stress equations

OR

use the reduced time concept which is the integral evaluation and scales the time? Can I use either?

Thanks,

Fortran 11 to Abaqus 6.10

moslempayandeh — Tue, 07 Sep 2010 13:21:29 GMT

Dear

I have problem with Abaqus 6.10 and fortran 11,0,6 on WIN 7 x64 platform

When I run Abaqus verification it passes all C++ Fortran requirement but when it checks for subroutine for standard case or explicit it has problem:

It is std_user.log for error:(

Linking ['std_user.obj'] into user subroutine shared library

Link command: ['cmd', '/c', '"LINK', '/nologo', '/INCREMENTAL:NO', '/subsystem:console', '/machine:AMD64', '/NODEFAULTLIB:LIBC.LIB', '/NODEFAULTLIB:LIBCMT.LIB', '/DEFAULTLIB:OLDNAMES.LIB', '/DEFAULTLIB:LIBIFCOREMD.LIB', '/DEFAULTLIB:LIBIFPORTMD.LIB', '/DEFAULTLIB:LIBMMD.LIB', '/DEFAULTLIB:MSVCRT.LIB', '/DEFAULTLIB:kernel32.lib', '/DEFAULTLIB:user32.lib', '/DEFAULTLIB:advapi32.lib', '/FIXED:NO', '/dll', '/def:export.def', '/out:standardU.dll', 'std_user.obj', 'C:\\SIMULIA\\Abaqus\\6.10-1\\exec\\lbr\\standardU_static.lib', 'C:\\SIMULIA\\Abaqus\\6.10-1\\exec\\lbr\\standardB.lib', 'C:\\SIMULIA\\Abaqus\\6.10-1\\exec\\lbr\\ABQSMABasCoreUtils_import.lib', 'C:\\SIMULIA\\Abaqus\\6.10-1\\exec\\lbr\\ABQSMAAbuLicense_import.lib', 'oldnames.lib', 'user32.lib', 'ws2_32.lib', 'netapi32.lib', 'advapi32.lib', '&&', 'mt', '/manifest', 'standardU.dll.manifest', '/outputresource:standardU.dll;2', '&&', 'del', 'standardU.dll.manifest"']

Creating library standardU.lib and object standardU.exp

std_user.obj : error LNK2001: unresolved external symbol _fltused

standardU_static.lib(dflux.obj) : error LNK2001: unresolved external symbol _fltused

standardU_static.lib(umat_sst.obj) : error LNK2001: unresolved external symbol _fltused

standardU_static.lib(stdu_callallutils.obj) : error LNK2001: unresolved external symbol _fltused

LINK : error LNK2001: unresolved external symbol _DllMainCRTStartup

standardU_static.lib(uanisohyper_inv.obj) : error LNK2019: unresolved external symbol memmove referenced in function UANISOHYPER_INV

standardU_static.lib(uanisohyper_strain.obj) : error LNK2001: unresolved external symbol memmove

standardU_static.lib(umat_sst.obj) : error LNK2001: unresolved external symbol memmove

standardU.dll : fatal error LNK1120: 3 unresolved externals

Abaqus Error: Problem during linking - Abaqus/Standard User Subroutines.

This error may be due to a mismatch in the Abaqus user subroutine arguments.

These arguments sometimes change from release to release, so user subroutines

used with a previous release of Abaqus may need to be adjusted.

Exception: (, LinkError('Abaqus/Standard User Subroutines',), )

Traceback (most recent call last):

File "Python/driver/driverAnalysis.py", line 181, in run

File "Python/driver/driverStandard.py", line 63, in analyze

File "Python/driver/driverSharedLibrary.py", line 174, in run

File "Python/driver/driverSharedLibrary.py", line 319, in link

LinkError: Abaqus/Standard User Subroutines

Abaqus/Analysis exited with errors

Also Explicit has the same problem with many error

Please give me some advice to solve my problem

System Error 2 in run UMAT

koohsari — Mon, 06 Sep 2010 03:01:37 GMT

Hi every body
I write a Constitutive Rock model (Hoek-Brown) in Fortran For Abaqus, But When I run my model this error I see:
"System error 2 in std_OperatorWorkSpaceManager::DeAllocate: An offset overwrite was detected for Element operator workspace ID = 13, Element operator workspace name = idEO_MaterialStiffness, Offset = -1.)"
Can any one help me about solve this error?

Stress-strain curve using FEM software

mechanicaldesign — Sat, 04 Sep 2010 12:29:38 GMT

Good afternoon,

How I observed on some articles which develop subject of stress-strain curve, appear some FEM results and with FEM results is compare analytical calculus and experimental calculus.

My question is how can be construct curve stress-strain for material using material data like :modulus of elasticity, Poisson coef., density of material.

Can be combined FEM power with analytical calculus in a manner in which values obtain from FEM is entered in analytical calculus and the results from analytical calculus is entered in FEM, in an iterative manner ?

Thank you for understanding and best regards.

P.S. I�m ANSYS user.

Stress-strain curve for Grey Cast Iron

mechanicaldesign — Sat, 04 Sep 2010 08:11:59 GMT

Good morning,

I am interesting about construction of curve stress-strain for cast iron. From my knowledge cast iron have only ultimate strength and after that appear fracture. Beside of this, have different ultimate strength in tension comparison with compression. My scope is to establish this curve from the analytical point of view, like curve stress strain for steel.

I�m using ANSYS software to made FEM study.

Best regards.

Young's modulus iteration using Abaqus umat

aeroall — Wed, 01 Sep 2010 21:21:01 GMT

Hello

I'm a new commer in Abaqus and working on topology shape optimization for dental implantation.I have two user-defined materials for Jaw bone area, and using the stress-increment-controlled method, Young's modulus of an element is changed according to the following equation (1) with two constraints (2)
E(i+1) = E(i) + k(sigma(i) - sigma_ref) --- (1)
where k and sigma_ref are constants
E(i+1) = E_min if E(i+1)E_max (2)
If my Young's modulus is changing with two different user-defined materials, is it possible for this process to work through Abaqus UMAT?
I've already created the simple input file before I go through the final analysis, but kind of stucked with how to define materials in UMATand how to implement the above equation if I need some iterations.
For example, I can say E = STATEV(1)

if E > E_min
E = E + k(sig - sig_ref)
elseif E < E_min
E = E_min
elseif E > E_max
E = E_max
end
But do I still need to define the E in the DO-loop?

Simulation of PP and ABS by using Ansys

Daimrizvi — Wed, 01 Sep 2010 13:29:20 GMT

Hi everyone,

Firs of all I am happy to have membership in this forum.
Now a days, I am selecting the material model for PP and ABS to ultrasonically weld them. I have studied a lot of literature on this topic. And I finally selected some of them that need to be in ansys by writing subroutines.

I want your guidance in three issues,

1. What is the best programming language for writing subroutine in ansys, C or FORTRAN?
2. Can you please suggest me any precise model for above two plastics?
3. I also want to simulate with Maxwell model (easiest)about which I know little, I want your guidance in implementing the Maxwell model for PP and ABS.

PVC based sealing

oflu72 — Sun, 29 Aug 2010 13:34:01 GMT

Hi,
I have to model the closing of a refrigerator door and here PVC based gasket is being used. gasket web page -http://na.rehau.com/industry/appliance/commercial.refrigeration/gaskets.shtml. Can anybody provide material properties for this type of gasket (Pvc based with plasticizier? Compression ratio of the gasket is about %70.
Regards,

Dursun

Apply compressive load in [110] direction

pshukti — Thu, 26 Aug 2010 20:29:23 GMT

Hi everybody

I am trying to apply compressive load along [110] direction in a single crystal. I created a datum plane along that direction and then tried to apply load but it is not working. Is there anyway I can do it in cae file or should I try to do that in inp file? Any suggestion will be really helpful.

Thanks

pshukti

Abaqus randomly crashes when trying to create XY-report from field output in Abaqus

jimstian — Thu, 26 Aug 2010 12:55:45 GMT

Hi,
I am having a problem when I try to generate a XY-report from field output in Abaqus 6.9-2: Abaqus randomly crashes when I try to generate the report. By random I mean that working with some odb-files are ok, while others makes the program crash.

I tried both manually in CAE and by python scripting.

Does anybody have any ideas what the problem might be?

I am running on a Windows7 64x computer.

Jim

Dstran

pshukti — Thu, 26 Aug 2010 00:02:44 GMT

Hi

So if I set stran = Green strain (using equation in terms of deformation gradient tensor), that case for 'dstran' is ABAQUS going to use defined strain value to get that or it will still use logrithmic strain?

Can anybody clarify this for me please?

Thanks

pshukti

Surface load pressure disappears after contact

fred1980 — Wed, 25 Aug 2010 15:37:52 GMT

Hi
I'm using Abaqus Explicit. My model includes a rigid body that contacts and indents into a deformable body. Before the contact happens I applied a pressure load on the contact surface of the deformable body at the first step. In the second step I moved the rigid body toward the deformable body so contact happens. My problem is the surface elements at the beginning of this second step are in equilibrium with the pressure load that I have applied but when I move away the rigid body from the deformable elements (you may see it as unloading), their pressure values would become around zero as if the surface pressure has never existed! Is there something I'm missing here? I would appreciate if anyone gives me some hint in case they have already faced such situation.

Thanks
Fred

periodic boundary conditions

LOUKIL — Wed, 25 Aug 2010 13:16:38 GMT

Hello!

I want to model a unit cell (RVE) with periodic boundary conditions.

Otherwise, X is the displacement application direction, Y is the width direction and Z is the thickness direction. On the front edge (y=0) and the far-away edge (y=w) I want to apply coupling conditions (Uy= unknown constant) which is equal to infinite dimensions in the width direction.

I am working with composite materials, then for cross ply laminate, I used Constraints-Equation. For example on y=0, i have to define two sets: a plane (without a corner node) as one set and a corner node as another set. And then create Equation, 1*plane.DOF2 -1*point.DOF2=0

Which means that DOF2 for all nodes in plane set will be the same as DOF2 of a corner node (point set)

But, when I use Quasi-isotropic laminate (45/-45) for example, this method does not work!

Please, can you help me?

I want to know how I can apply the coupling conditions correctly using ABAQUS.

Thank you!

Looking for progrem that will allow 11 degrees of freedom for a node

eladkatriel — Mon, 23 Aug 2010 22:06:03 GMT

Hello,
My name is Elad Katriel and I am a fourth year student for MSC in civil engineering in the Technion - Israel Instute of Technology.
I hope I can help your project and myself at the same time.
During my studies I try to solve a laminate shell problem by defining a new elemnt. That element will include 11 degrees of freedom at each node, and will have 4 nodes at total. The degrees of freedom will be the movments and rotations of diffrent parts of the laminate. Hopefully I will have better results than I get in usual elements.
Does anyone has idea which program is open enough to allow me to do it?

Thank you in advance
Elad Katriel

Shape of PNM-model prediction curves

Bigal-85 — Mon, 23 Aug 2010 12:16:05 GMT

Hi, I am currently trying to obtain parameters for a filled polybutadiene rubber for use in finite element analysis. I am using a PNM with eight-chain and Yeoh hyperelastic models and the Bergstrom-Boyce flow model. The general fit is pretty good and the peak force looks great but the problem lies with the initial gradient. Here is a picture to help you understand my point:

You can see that the loading curve shape, especially the initial section isn't quite right. Is this due to my selection of material models or is there a parameter which controls the loading shape??

Any help you be greatly appreciated. Thanks.