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MSC.Software Confidential

Contact Analysis and Its Parameter Settings

Pei Gu




Contact Analysis and Its Parameter

Settings

Mentat: contact/contact bodies;

Patran: LBCs/contact




A group of elements orgeometric entities maycontact.

Types of contactbodies:Deformable: a group ofelementsRigid: a group ofgeometric entities

Analytical contactdefinition to smoothcontact surface

Rigid contact bodies arespecified bydisplacement or forceapplied to them

Contact Definition




Contact bodies:groups ofelements or

geometric entities

Rigid bodies-geometric entitiesor heat transferelements

This rigid body is

controlled byposition in ydirection, x and zare withoutmotion




Manually orautomaticallydefine thediscontinuousnodes oredges

Analytical Contact:deformable




Rigid Body BC andLoad:

(a) Prescribe

translational androtation velocity andposition;

(b) Prescribe forcethrough extra nodes




Symmetry rigid bodies

Provide easy way toapply symmetryboundary conditions

In rigid bodydefinition in Patran:

LBCs/contact

contact/contactbodies in Mentat




Contact Detection

nuΔA•

MSC S ft C fid ti l




D

D

Default

D (1-B)

D (1+B)

Bias factor

Distance tolerance and Bias factor

Contacted surface

Contactedbody

node not in contactnode in contact

node

penetrated

node not

penetrated

default contact distance tolerancecan be founded in out file

MSC Soft are Confidential




MSC Software Confidential




• Use of the Contact Table is to describe the specific interaction betweencontact pairs (i.e. contact checking is defined by contact interfaces).

• If no contact table is specified, each contact body is assumed to be able totouch the other including self-contact.

• An additional benefit can be in reducing the solution cost by specifyingonly those bodies that can contact.

• Contact tables must be turned on for the loadcase or loadstep duringwhich it is active

34 1

2

Contact Tables





Contact Tablesanalysis/loadstep creation/solution parameters

contact/contact tables





wrong bodynumbering

body 1 body 2

1

72

6

5

4

3

●

Check Body 2:u4 = u4(u1, u3)

u5 = u5(u1, u3)

u6 = u6(u3, u2)

u7 = u7(u3, u2)

Skipped, since node 3 has alreadybeen used as a tied node.

Contact Checking





Double-sided contact:

jobs/mechanic

al/control

control/advanc

ed contact

control

analysis/job

parameters/contact

parameters

Double-sided and

single-sided are turned

on in:




SC So t a e Co de t a

Using contact table todefine contact checkingorder:

First->second;Second->first;Double-sided;Default;Automatic.




Glue Option In Contact Table:

Complex body can be split up into part which can be meshed easy:

(1)Define each part as a contact body;

(2)Invoke the glue option in contact table to make a physical body.




δ δ

• A positive value is interferenceclosure.

• A negative value is a gap .• Alternatively, include the

interference into the geometry andlet Marc automatically return thesurfaces.

Important: requires the distance toleranceto be larger than the interference.

Interference Fit

gap overlap




Contact Areas and Exclude Segments

Define nodes that are on contact bodies thatpotentially enter contact. Save contact checking.

Exclude edges (faces) that are oncontact bodies that do not entercontact. Save contact checking.

in contact definition inboth Mentat andPatran




Friction Model

friction models :

• Coulomb friction

• “Stick-slip” model

• Bilinear

analysis/job

parameters/contactparameters/frictionparameters

jobs/mechanical/ contact control




A reasonable choice for constant C

(relative sliding threshold) is 1 to 10

percent of the actual sliding velocity.

C very small causes large friction andnumerical convergence. C very large maycause less friction than physically

expected.

F t

vr

1

-1

C = 0.1

C = 1

C = 10

Conventional Coulomb Friction ModelAll friction models in Marc canbe based on either nodal forceor nodal stress




• ∆u t = incremental tangential displacement

• α= friction coefficient multiplier

• β= slip to stick transition region

• ε= small number (εβ » 0)

F t

∆u t

2β

2εβαµ

F n

µ F

n

Stick-Slip Coulomb FrictionModel

nt f f αµ ≤Stick:

Slip: nt f f αµ >




Bilinear Coulomb FrictionModel

Displacement slipthreshold:

δ

Friction force tolerance is for convergence. Donot change, in general.

This model is the

newest, and isrecommended.




Setting the separation force: – Can be done in the contact

table. – OR

jobs/mechanical/contactcontrol/advanced contactcontrol (Mentat);

analysis/jobparameters/contact

parameters/separation(Patran)

Separation Control

The default critical separationforce/stress is given by:10% of the maximum

reaction force.10% of the maximum

contact body normalstress.




• Chattering:

– Suppressed: A node whichcomes into contact may notseparate again in the sameincrement. In general, NotRecommended.

– By default, chattering is

allowed.• Increment:

– Next: A node which shouldseparate can be forced notto separate in the currentincrement but at the

beginning of the nextincrement. In general, NotRecommended.

– By default, it separates inthe current increment.

Additional Separation Parameters forSeparation

analysis/job parameters/contactparameters/separation




Marc Input Deck

Three portions:

(1) Parameters section: before the ‘end’card

-job controls

(1) Model definition section: before the‘end option’ card

-nodes, elements, contactdefinition, BCs and loadsdefinition, tables,materials

(1) History section: after the ‘end option’card

-loadsteps (loading controls)




Contact Definition in Marc Input Deck

Contact Table




Contact works with nearly 100% elementsin Marc, i.e. quad, hex, tet, shell, beam…

Contact works with every material models inMarc, i.e. elastic, isotropic, anisotropic,

orthotropic, plasticity, creep, elastomer,fracture mechanics…

Contact works with coupled thermal-mechanical analysis.

Contact works with remesh (auto-remesh). Post-processing is the same as models

without contact.

Vol A: Theory Manual (Chapter 8 for

Contact)Vol B: Element LibraryVol C: Input Deck, including contactrelated cards in input deck

Where to find contact topics: MarcDocumentations:

Rigid body

Rigid body




Few Tips for Running Marc Contact Jobs

(1) Set contact parameters as default at the initialtry, except in the case that you know thephysical problem. For example, set distancetolerance, bias factor, separation force, etc., asdefault.

(2) If many contact bodies in a model, try to run themodel with fewer contact bodies as the initialtry. This gives insight.

(3) In general, increasing the separation forcestabilize the structure and makes the contact tobe easier to converge.

(4) Glue option stabilizes the structure and makescontact easier to converge. But, whether it canbe used depends on the physical condition

(5) Use contact table to define contact pairs. If youknow the two bodies do not touch, do not definethem contact in the contact table.

(6) Use the card ‘print,5’ in the input deck to debugcontact.




Modeling Contact

Geometrical entities (circular arc andstraight lines)

MSC Marc element 10(full integration axisymmetric)

• Rigid body for channel

– No stress distribution

channel

billet




MSC Marc element 10(full integrationaxisymmetric)

MSC Marc element 40(full integration axisymmetric

thermal)



Modeling Contact (continued)

Channel is defined as the contactbody of Rigid with Transfer

Channel is defined asdeformable contact body

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