Mech Intro2 14.0 L09 Cont+MeshCon

8/13/2019 Mech Intro2 14.0 L09 Cont+MeshCon

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2011ANSYS,Inc. February13,20121 Release14.0

14.0Release

IntroductiontoANSYS

MechanicalPart2

Lecture9

ContactandMeshConnections


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ChapterOverviewInthischapterextendthediscussionofcontactcontrolbeguninthepart1introductorycourse. Wealsointroducethemeshconnectioncapabilityforuse

withsurfacemodels:

A. ContactReview

B. ContactUtilities

C. AutomaticContactDetection

D.ContactSymmetry

E. ContactControl

F. TheContactPinball

G.SpotWelds

H.ContactResults

I. MeshConnectionsJ. Workshop9,ContactOffsetControl


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A.ContactReview

Part1ofIntroductiontoMechanicaltouchedonthebasicsofcontactelements.

Inpart2wewillexpandonsomeoftheconceptsandbroadenthecoverage.

Keepinmind,however,contactisahighlynonlinearfeatureandiscoveredinits

entiretyintheMechanicalNonlineartrainingcourse.

Contactelementscanbethoughtofasaskincoveringthesurfacesthatareexpected

tointeractwithoneanother.

Onesideofacontactpairisreferredtoasthecontactanditsmateasthetarget.

Mechanicalusesacolorcodingsystemtodifferentiatethecontactandtargetsurfaces.

Target

Contact


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B.ContactUtilitiesWhenimportingassembliescontactregionsareautomaticallycreatedbased

ontheproximityofsurfacestoone

another.

Tolerancecontrols

for

each

contacts

branchallowstheusertospecifythe

rangeofautocontactdetectionviaslider

barorlengthvalue.

WithintheConnectionsbranchindividual

contactgroupscanbeorganizedformore

efficientcontactmanagement.


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...ContactUtilities

Althoughautomaticcontactdetectionisthedefault

(connectionsdetails),itcanbedeactivatedforimporting

andgeneratedlaterbyRMBfromacontactgroup.

Transparencycanbeonoroffbasedonconnectionsbranchdetailssetting:

Withtransparencyonpartsnotassociatedwiththe

highlightedcontactregionaredisplayedas

wireframe.

ON OFF


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C.AutomaticContactDetection

Asmentioned,autodetectioncanbemodifiedusinga

slidercontrol. Theactualtolerancevaluewillbe

reportedbelowtheslider.

AlternativelythetolerancetypecanbesettoValue

andalength

unit

entered

directly.

specify

the

range

of

autocontactdetectionviasliderbarorlengthvalue.

Thecursortargetwillgraphicallyindicatethe

tolerancevaluecurrentlyactive.

AnoptiontoUseRangeallowsautomaticcontactsearchingtobelimitedtoaminimumsearchvalue.

Theminimumisenteredasapercentageofthe

tolerancevalueanditsresultingvalueisreportedas

well.

Tolerance

Display


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D.ContactSymmetry

InMechanicalonesideofacontactpairisreferredtoas

thecontactwhiletheotherisreferredtoasthetarget.

Contactsurfacesarerestrictedfrompenetratingthroughthe

targetsurface.

Whenone

side

is

designated

the

contact

and

the

other

side

the

target,thisiscalledasymmetriccontact.

Ifbothsidesaremadetobecontact&targetthisiscalled

symmetriccontact.

By

default,

Mechanical

uses

auto

asymmetric

contact: Contactbeginsassymmetricbutthesolverretainsthefirstpair

wherecontactisdetectedanddeactivatestheother.

Symmetric

ContactAsymmetric

Contact


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...ContactSymmetry

AsymmetricContactSelection:

Contactdetectionpointsareassociatedwiththetargetface. Untilacontactfaceis

detectedtobepenetratingthetarget,contacthasnotoccurred.

Noticeintheexamplebelow,thechoiceofcontact/targethasamajorimpacton

penetrationwhen

asymmetric

contact

is

used.

Target Surface Contact Surface

Target SurfaceContact Surface


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Thefollowingguidelinescanbebeneficialforpropermanualselectionofcontact

surfacesforAsymmetricbehavior:

Ifaconvexsurfacecomesintocontactwithaflatorconcavesurface,theflatorconcave

surfaceshouldbetheTargetsurface.

Ifonesurfacehasacoarsemeshandtheotherafinemesh, thesurfacewiththecoarse

meshshouldbetheTargetsurface.

Ifonesurfaceisstifferthantheother,thestiffersurfaceshouldbetheTargetsurface.

If

one

surface

is

higher

order

and

the

other

is

lower

order,

the

lower

order

surface

shouldbetheTargetsurface.

Ifonesurfaceislargerthantheother,thelargersurfaceshouldbetheTargetsurface.

Asnotedearlier,ANSYSMechanicaldefaultcontactisautoasymmetric.

...ContactSymmetry


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E.ContactControlFivecontacttypesareavailable:

BondedandNoSeparationcontactarelinearandrequireonly1

iteration.

Frictionless, Rough

and

Frictionalcontact

are

nonlinear

and

requiremultipleiterations.

Nonlinearcontacttypesallowaninterfacetreatmentoption:

AddOffset:

input

zero

or

non

zero

value

for

initial

adjustment.

AdjustedtoTouch:ANSYSclosesanygaptoajusttouching

position.

Contact Type Iterations Normal Behavior (Separation) Tangential Behavior (Sliding)

Bonded 1 No Gaps No Sliding

No Separation 1 No Gaps Sliding Allowed

Frictionless Multiple Gaps Allowed Sliding Allowed

Rough Multiple Gaps Allowed No SlidingFrictional Multiple Gaps Allowed Sliding Allowed


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...ContactControlInterfacetreatmentoptions:

Add offset: contact surface is

numerically offset a given amount

in positive or negative direction

(offset can be ramped on).

Adjusted to touch: offsets contact

surface to provide initial contact

with target regardless of actual

gap/penetration.

TCC T


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...ContactControlInterfacetreatmentexamplemodelingapressfit:

Thegeometrymodelcontainsapininaholewhichareofthesamediameter.

Contactoffsetisusedtosimulateapressfitofanoversizedpin. Theresulting

stressplotisshown.


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F.TheContactPinball

ThePinballRegionisacontactsettingthatdifferentiatesbetweenfarfieldopen

andnearfieldopenstatus.Itcanbethoughtofasasphericalboundary

surroundingeachcontactdetectionpoint.

ContactStatus:

Insidepinball= nearfieldcontact

Outsidepinball=farfieldcontact

Allowsthesolverto moreefficientlyprocesscontactcalculations.

Pinball radius


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...TheContactPinball

PinballSize:

ProgramControlled(default)calculatedbasedonunderlyingelementtypeandsize.

AutoDetectionValueequaltotheToleranceValue

asset

on

the

Global

Contact

Settings.

Radiusmanuallyspecifiedinthedetails.

Auto Detection Value or a

user defined PinballRadius will appear as a

sphere on the ContactRegion for easy verification.


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...TheContactPinball

ThereareseveralusesforthePinballRegion:

Providescomputationalefficiencyincontactcalculations,bydifferentiatingnear

andfaropencontactwhensearchingforwhichpossibleelementscancontacteach

other. Allowsbondedandnoseparationcontacttobeactivewhengapsarepresent

(withinthepinballradius).

AffectshowmanynodeswillbeincludedintheMPCequations.


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G.SpotWeldsSpot

welds

provide

ameans

of

connecting

shell

assemblies

at

discrete

points:

SpotwelddefinitionisdoneintheCADsoftware. Currently,onlyDesignModelerand

Unigraphicsdefinesupportedspotwelddefinitions.


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...SpotWeldsAs

said,

spot

welds

are

created

as

point

pairs

on

opposing

surfaces

in

the

geometrymodeler:

Noticetheactualconnectionisaccomplishedusingabeamconnectionbetweenthe

points.

A

spider

web

of

beams

is

radiated

from

each

point

to

distribute

the

load.


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...ContactResultsSelect

the

contact

region(s)

for

the

Contact

Tool

(2

methods):

1. Worksheetview(details):selectcontactregionsfromthelist.

Contact,targetorbothsidescanbeselected.

2. Geometry:selectcontactregionsonthegraphicsscreen.


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...ContactResults

Contactresultsareassociatedwiththecontactsideonly. Withautoasymmetric

contact,sincethesolverchooseswhichsideisdesignatedcontactitmaynotbe

obviousattheoutsetwhichsidewillshowresults.

Example:

in

this

case

we

see

the

larger

of

the

2

blocks

below

has

been

designated

contactbytheautomaticcontactdetection. Referringtoslide9showsthe

choice,basedonsize,isreversed(assumingmesh,materials,etc.aresimilar).


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...ContactResults

Aftersolving,thecontacttoolworksheetisusedtorequest resultsforboth

sidesofthecontactpair.

Noticeintheupperfigure(viewingthe

contactface),theresult showsfarfield

whichisnotmeaningfulsincethecontact

isbondedtogether.

Only whenweviewthesmallerblock

frombelowcanweseethetrueresult,

sticking.


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...ContactResults

Againthelowershows theviewofthe

contactside. Since

it

ultimately was

declaredthetargetbythesolverhowever,

noresultsaredisplayed.

Similarly,wecanrequestresultsfromoneortheothersidesofacontactpair.

Whenasymmetryisusedhowever,resultswillonlyappearonthesidethatis

finallydesignatedasthecontact. Recallthetargetsidewasthesmallerblockbut,

duetoautoasymmetry,itbecamethecontactside.


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ContactResults

Hereasymmetriccontactpairshowsresults

onbothsurfaces.

Incasesofsymmetriccontact,resultswillbedisplayedonbothsideshoweverthe

actualresultistheaverageofthecontactandtargetresults.


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I.MeshConnectionsThe

mesh

connection

feature

allows

you

to

join

the

meshes

of

topologically

disconnectedsurfacebodies:

Previouslyconnectionssuchasthisrequiredageometryapplicationtorepair

gaps(e.g. DesignModelerorCAD).

Mesh

connections

are

made

at

the

mesh

level

using

either

edge

to

edge

or

edge

tofaceconfigurations.

Unlikegeometrysolutions,amultibody partisnotrequired.

MeshConnectionExample


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...MeshConnectionsMesh

connections

use

the

concept

of

master

and

slave

geometry

to

control

howtheconnectionismade:

Master:indicatesthegeometry/topologyontowhichothergeometryis

projected.

Slave:

indicates

the

geometry

that

will

be

projected

onto

the

master

geometry.

Mastergeometrycanbefacesoredgeswhereasslavegeometrycanonlybe

edges.

Slave

MasterProjection


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...MeshConnectionsManual

Mesh

Connection:

Scopemaster/slavegeometry.

Entertolerancevalue,sliderorusesheetthickness.

UseSheetThickness:allowssettingascalefactorwhichwillresultina

tolerancevalue

based

on

the

thickest

surface

geometry

involved

in

the

mesh

connection.

Snaptoboundary=No:resultsinstraightprojectionoftheslaveontothemaster.


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...MeshConnectionsManual

Mesh

Connection:

Snaptoboundary=Yes:SearchesforboundaryonthemasterwithintheSnap

ToleranceorElementSizeFactor.

Elementsizefactorisbasedontheelementsizeslocatedonthemaster

geometry. Notethekinkedsurfaceintheexamplebelow.Thesnaptoboundaryfeaturewasused

withexaggeratedtolerancestoillustratepotentialproblems.


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