abaqus interaction module

of 10IIT Madras Student Satellite Project

Indian Institute of Technology Madras

Interaction module experiments in Abaqus Standardby Rakesh Ramakrishnan, Ajayraj, Lokaditya, Ananth Saran

iitmsat-H-CRR,RA, RL, ASY-2-Feb-13 3 Feb 2013

1 Background: Any 3-D model in real life contains various individual surfaces in contact with each other during its assembly. The property displayed by such a model depends on how the various surfaces interact with each other. For example, in a rotating fan: the blades are rigidly fixed (tied) to the main rotating body, The rotor is fixed rigidly to the motor but also has low friction in the tangential direction to avoid high damping. Abaqus/Standard provides us with a plethora of interaction properties which can be used to model various kinds of interactions. In addition to this, different methods of enforcing such interactions are present which yield different results each time. In this we use a dummy model to model and understand the effect of various constraints and hence understand which to use

2 Model used:

These 2 plates are given different interaction properties. The sides are "clenched" so as to form a realistic version which can even be experimented with. Just having two blocks introduces possibility of them flying apart which makes the simulation exit with an error.

The red and blue dots indicate locations of boundary conditions which are the regions which are rigidly fixed throughout the simulation. The square region on top is where the load is applied and the direction of load is shown by the arrows. In the above shown case, the pressure load is downward-into.



3 Experiments:

Experiment 1:

Interaction Pressure OverclosureConstraint Enforcement

MethodStiffness (if any)

Interaction Hard Contact Penalty - Linear 10

Allow separation after contact?

Master Surface Slave surfaceRelative meshing

Yes - ticked Top Bottom Slave finer mesh

Load Pressure Direction

ResultInference / Additional

RemarksShould we use it for our model?

Downward - IntoPenetration into Slave,

Umax = 1.123x10-3m

Distinct Penetration observed even with slave having a finer

meshNo

Figure 1

Experiment 2:






Yes - ticked Top Bottom Equal meshing





Umax = 1.121x10-3m

Slightly lesser penetration than expt 1 contradicting previous

knowledgeNo



Figure 2

Experiment 3:






Yes - ticked Top BottomMaster finer mesh

- ratio = 20





Umax = 1.805x10-3mMore penetration than expt 1 -

Follows previous knowledgeNo

Figure 3



Experiment 4:



Interaction Hard Contact Penalty - Linear 1 x 1010



No - Unticked Top Bottom Equal Meshing




Up - OutwardNo Upward displacement

where no load is applied, sides warped; Umax = 1.2x10-6m

Does strict enforcement of no separation mean more stiffness?

Yes

Figure 4

Experiment 5:










Up - OutwardUpward displacement like a an

arch, Umax = 1.121x10-3mExtent to which separation allowed dependent on k??

Maybe - dependence on k

unexpected



Figure 5

Experiment 6:






Yes - Ticked Top Bottom Equal Meshing





arch, Umax = 1.121x10-3m

When there is separation, there is NO FORCE indicating non-

linearity in systemNo

Figure 6



Experiment 7:



Interaction Hard Contact Default N/A







Up - OutwardNo Upward displacement

where no load is applied, sides warped; Umax = 5.2x10-6m

Umax higher than expt 4 expected since linear

enforcement more strict than default enforcement

Yes - 4 is better

Output similar to figure 4

Experiment 8:






Yes - Ticked Top Bottom Equal Meshing





arch, Umax = 1.120x10-3mSimilar to expt 6 - expected No

Output similar to figure 6Experiment 9:










Downward - IntoVery minimal Penetration.

Extra force transmitted to sides which warped outward

Exact result we were looking for - Confirms that not allowing

separation removes penetration issues

Yes



Figure 9

Experiment 10:



Interaction Linear Default 1 x 1010



N/A Top Bottom Equal Meshing





arch, Umax = 1.121x10-3mSame as expt 6 - Introduces non

linearityNo - Never use

linear

Output same as figure 6

Experiment 11:



Interaction Linear Default 1 x 1010







Downward - IntoPenetration observed in the

load bearing regions, Umax = 5.9x10-6. Sideswarped upwards!

Different result! Unexplained behaviour

No - Never use linear



Figure 11

Experiment 12:



Axial Connectors, Linear Uncoupled, F1 ticked 1 x 1010







Downward - Into

Penetration present only in circular region bounded by

connectors, Umax = 8.949x10-

4m

Connectors are working - Absence of interaction caused

penetration

Yes, try with interaction

Figure 12

Experiment 13:Interaction Pressure Overclosure Constraint Enforcement Stiffness (if any)



Method

Axial Connectors, Linear Uncoupled, F1 ticked 10







Downward - Into

Penetration present only in circular region bounded by

connectors, Umax = 1.149x10-

3m

More penetration than expt 12 - expected

Yes, try with interaction

Figure 13Experiment 14:

Used a non constrained primitive model comprising only of 2 plates










Downward - Into Each plate rotates Unexplainable result No



Figure 14

4 Conclusions: The linear type of interaction is never to be used. We now use a hard type of pressure overclosure with penalty type of enforcement method and use a stiffness of 1010 N/m2 for simulating hard contacts and a stiffness of 106 N/m2 for simulating rubber like soft normal interactions.

Also, the finer mesh surface is assigned the slave surface to minimise any possible penetration as penetration is not at all avoidable due to the approximate nature of the solutions.

abaqus interaction module

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