Mechanical Nonlin 13.0 WS 09A Diagnostics

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ANSYS Mechanical Structural Nonlinearities

Customer Training Material Workshop 9A: Diagnostics

• Goal

Diagnose convergence trouble with surface body contact model

• Model Description

– 3D Spring plate –Surface Body

– 3D Rigid Target Body

– Linear steel material

– Meshed with 3D SHELL elements

– Spring Fixed support at one end, A

– Rigid Body displaced into Spring 19mm

WS9A-2 ANSYS, Inc. Proprietary

© 2010 ANSYS, Inc. All rights reserved.Release 13.0

December 2010




Customer Training Material …Workshop 9A: Diagnostics

Steps to Follow:

• Restore Archive… browse for file “W9a-diagnostics.wbpz”

• Save as

– File name: “W9a-diagnostics”

– *



December 2010




Customer Training Material … Workshop 9A: Diagnostics

The project Schematic should look like the

picture to the right.

– From this Schematic, you can see that the

Engineering (material) Data and Geometry have

already been defined (green check marks).

– It remains to set up and run the FE model in

ec an ca

– Highlight the Engineering Data Cell and open by

(RMB)=>Edit to verify the linear material

properties.

– Verif that the units are in Metric Tonne mm ..

system. If not, fix this by clicking on…

• Utility Menu=>Units=>Metric(Tonne, mm,..)



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• Return to Project Schematic

– Utility Menu > Return to Project

• ou e c c on e o e e o open e o e ec an ca

Session) (or RMB=>Edit…)



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• Once inside the Mechanical application, verify the working unit system

– “Unit > Metric (mm,kg,N,s,mV,mA)”

• The spring assembly is already set up with frictionless contact pairs, a fixed

.

• Highlight the entities beneath each folder to become familiar with the modeland to confirm that it is properly supported and loaded and ready to solve.



December 2010





• After solution run is complete, highlight the Solution Information folder

and scroll to near the bottom of the output.

– The model solves without error.



December 2010





• Review the Total Deformation results.

– Something is wrong. The contact relationship between the two parts has

obviously failed.



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With 25 initial substeps and Auto Time Stepping turned On, the contact should

have engaged. In an effort to determine the problem, we will evaluate what the

initial condition of the contact pairs are.

• Highlight the Connections Folder: RMB> Insert> Contact Tool

• Highlight the Contact Tool: RMB>Initial Information>Generate Initial Contact

Results. This will run a partial solve to establish initial contact parameters

(i,e. Initial status, gap, penetration, etc…).



December 2010





• Review the Initial Contact Information.

• Note the following:

– The two active pairs both have an initial status of “Far Open”

– ot pa rs ave a p n a ra us o mm. s mm enoug



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• By studying a profile of the undeformed geometry we can see that the

initial gap is less then 1.50mm. Hence, the Pinball Radius of 4mm should

be sufficient for this contact pair to be in an initial status of ‘near-open’.

Rigid Target



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• g g e con ac reg on represen ng e con ac e ween e spr ng

and target.

– In order for contact to work properly, the contact element normals must be facing

the tar et element normals.

– Recall that surface bodies are meshed with shell elements that have a ‘top’ and a

‘bottom’ face. The reason this contact pair is not working is because the contact

normals are on the wrong side of the surface body with normals that face away

. .

Contact element

normal direction

Target element

normal direction



December 2010





• From the details window of the contact region, switch the ‘contact shell face’

from Bottom to Top . The red color highlighting the contact side should

switch.



December 2010





• Highlight the Solution Information Branch

– Set Newton-Raphson Residuals = 3

– This will save force imbalance data for the last

‘ ’ - .

especially helpful information for

troubleshooting troubling contact convergence

problems.

• Rerun the solution



December 2010





• From the Solution Information Branch, the contact is now engaging, but

the solution fails to converge after several iterations.



December 2010





These first two converged substeps likely represent the trivial solutions

that occur as the small gap between the two parts is being closed and no

contact has been made yet.

s rs sp e n e ew on- ap son res ua measure

of imbalance) likely occurs at the point when contact firstengages. From there on out, the solution struggles and

fails after two bisections and man iterations to find a

balance.



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A plot of Newton-Raphson Residual (measure of force imbalance in the model)

confirms that the point where contact is engaged is the source of the highest

imbalance .



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• Highlight both Contact Regions and change the

contact specifications in the details window.

Augmented Lagrange is

recommended for general

contact

Reducing the contact

stiffness factor will reduce

the calculated force

generated at the contact

the imbalance



December 2010

• Re-run the solution





The solution now converges very nicely with no bisections



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• ev ew e o a e orma on resu s. – Although this solution is now converged, notice the excessive penetration.

This is because, by default the shell contact detection points are at themidplane of the shells.

– This can be remedied by adding a command object to the contact elementswith the following command: KEYOPT,cid,11,1 (refer to Element manualdocumentation on CONTA174 and the KEYOPT command)



December 2010

– This command will include an adjustment for the shell thickness.





EXTRA CREDIT !!

• Highlight each Contact Region

an nser omman s

– Inside the command object andtype the command as shown

*

* Refer to Element Reference documentation onCONTA174 along with Command Manual

documentation on ‘KEYOPT ’



December 2010

• Re-run the solution





• Review the Total Deformation results as before.

– Shell thickness is now properly accounted for.



December 2010

Mechanical Nonlin 13.0 WS 09A Diagnostics

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