Abaqus / polymer simulation

[poucinette]

Hi all,

I'm trying to model a peel T test on a composite material composed of steel and polymer (polypropylen) on Abaqus 6.7. Between these parts, there are cohesive elements COH3D8.
I have a problem with my model and I don't understand it. You can visualize my results in attachs files.
For understand this draw, a few precisions:
The elements in white has just here to guide the materials.
In B (cf attachs files), the nodes are embedded.
In A I applied a velocity.
In C I applied rotation constraints and coupling constraints on all rotations and displacements.
My structure present a strange evolution in the red circle. I don't understand this.

Have you an idea on what is happened in my structure? It is a problem of material? Maybe you have had the same problem...
If you need more precision on the model, the materials or limits conditions, I'll answer it of course.

Excuse my poor english.
Poucinette

[poucinette]

Nobody has an idea??

Below, there is the errors from the file .sta:

***WARNING: In element 124 of instance PELAGE-1 the ratio of deformation speed
to wave speed is 0.31074 at increment 41134. See the message file
for further information.


***ERROR: The ratio of deformation speed to wave speed exceeds 1.0000 in at
least one element. This usually indicates an error with the model
definition. Additional diagnostic information may be found in the
message file.


The following checklist may be helpful in diagnosing the error:

1. Check contact definitions for problems such as excessive initial
overclosure or unrealistic tied definition between contact pairs.
A vector plot of velocities or accelerations will usually help to
identify contact problems.

2. Check stiffness (elastic modulus) and mass (density) definitions for
consistent units and verify that the combination is reasonable.

3. Check for poor mesh definition.

4. Check the boundary conditions for an excessive loading rate. The
*DIAGNOSTICS, DEFORMATION SPEED CHECK=DETAIL option may be used to obtain
detailed diagnostics information.

5. Check the current status of the structure to see if it has
totally failed.

6. A dashpot or a very stiff spring may cause the analysis to go unstable.
The *DYNAMIC, DIRECT option may be used to control the time increment
directly.


***ERROR: The fatal error will generate a new field output in the last
increment. All variables applicable to the current procedure and
material type(s) will be written to the output database.

I verified the points 1 to 5 and the loads are definied by experimentation.

Thanks for any track in advance.

Poucinette

[Jorgen]

It is very difficult to understand your model without more info. I suggest that you:
- use simple material models to make sure things work OK
- try it first without the cohesive elements to make sure your loading and boundary conditions (BC) are OK
- perhaps simplify the geometry to test the model setup.

My guess is that there is something wrong with your BC, loads, or cohesive element definition.

Best of luck,
Jorgen

[poucinette]

To understand the model, I used steel in place of polymer and the problem had disappeared.
I corrected the velocity (with the polymer model) of the test from 100 mm/ minute to 20 mm/ min and the problem doesn't exist.
I saw on other forums this tracks and apparently this velocity imply a very hard load, too much for ABAQUS.

We launch tests at this velocity now to compare results.

Thanks for your help.
Poucinette