Cylindrica Connector Elasticity Not Working

[donaldhume]

Hello all,

(first post)!

I am trying to use a CONN3D2 cylindrical connector and adding a simple linear elasticity to DOF1, lengthening. Unfortunately I don't think that the elasticity is working how I expect & want it to. The connector is lengthening up to 12mm, when i just want it to be incredibly stiff so I know it's working. Despite changing the F/dx curve it doesn't affect it. Here's the spring file, I'm pulling the connector outputs.

Any help would be greatly appreciated.

[pre]
**RESTRAINT SPRING FILE
*NODE
5499, 0.00, -430.00, -60.00
5498, 0.00, -430.00, 0.00
**
**
*MPC
BEAM, 5498, 690000
**
*ELEMENT,TYPE=CONN3D2,ELSET=EXT_RESIST
59999, 5499, 5498
*CONNECTOR BEHAVIOR, NAME=EXT_RESIST_behavior
*CONNECTOR ELASTICITY, COMPONENT=1, NONLINEAR
0.0 , 0.0
100000 , 0.01
*CONNECTOR DAMPING, COMPONENT=1
0.05
*CONNECTOR SECTION, ELSET=EXT_RESIST, BEHAVIOR=EXT_RESIST_behavior
CYLINDRICAL,
axis_ORI
*ORIENTATION, NAME=axis_ORI, DEFINITION=NODES
5499, 690000, 5498
*MASS, ELSET=ext_resist_mass
1E-6
*ROTARY INERTIA, ELSET=ext_resist_rot
0.001,0.001,0.001
*element, type=mass, elset=ext_resist_mass
59998, 5499
59997, 5498
*element, type=rotaryi, elset=ext_resist_rot
59996, 5499
59995, 5498
**[/pre]

 

[akabarten]

Hi,

Perhaps your deformation is in compression not in tension.
What values you have for CU1 output? Are they negative?

Displacement output (CU1) used to calculate force in connector is measured in local coordinate system.
In some situation element in global coordinate system is under tension but the same deformation measured in local coordinate system is in compression.

You can get this behaviour in your model as well:
Fix node 5499 and apply positive z global displacement for node 5498.
Animation shows the connector is in tension but CU1 output is always negative (in compression).

Your definition of elasticity cover only positive displacement.
By default Abaqus use constant extrapolation and it means for all negative CU1 you have zero force.

You can extend your characteristic for compression domain:

**
*CONNECTOR ELASTICITY, COMPONENT=1, NONLINEAR
-100000 , -0.01
0.0 , 0.0
100000 , 0.01
**

or use linear extrapolation:

**
*CONNECTOR ELASTICITY, COMPONENT=1, NONLINEAR, EXTRAPOLATION=LINEAR
0.0 , 0.0
100000 , 0.01
**

Regards,
Bartosz

 

[donaldhume]

Bartosz,

That was my issue. While the spring was in fact in tension the coordinate system dictated a negative displacement. Thank you for your help.

Don