Ansys contact tutorial

Ansys Ansy s Cont Contact act usag usages: es: tips and trick tricks s

Let us talk about convergence

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Ansys Ansy s Cont Contact act usag usages: es: tips and trick tricks s Suggestion One reason for convergence difficulties could be the following: •

FE Model is not modeled correctly in a physical sense 1) If you use a point load to do a plastic analysis, analysis, you will never get get the converged solution. Because of the the singularity at the the node, on which the concentrated concentrated force is applied, applied, the stress is infinite. infinite. The local singularity singularity can destroy the the whole system convergence convergence behavior. behavior. The same thing holds for the contact contact analysis. If you simplify the geometry geometry or use instead of an area contact) you most likely will end up with some problems in convergence. point load

σ

p as c ana ys s

© 2004 ANSYS, Inc.

Geometry

Mesh

con ac ana ys s



FE Model is not modeled correctly in a numerical sense 2) A possible rigid body body motion is quite often the reason which which causes divergence divergence in a . , model the gap size as zero from geometry, it should also be zero in the FE model. But due to the mathematical approximation approximation and discretization, it does not have necessarily to be zero anymore. Exactly, Exactly, this can kill the convergence. If possible, use KEYOPT(5) to close the gap. You can also use KEYOPT(9)=1 to ignore 1% penetration, if it is modeled.

KEYOPT(5)=0 KEYOPT(5)=1 © 2004 ANSYS, Inc.



Numerically bad conditioned FE Model 4) ANSYS uses the penalty method method as a basis to solve solve the contact contact problem and the for the penalty stiffness is used, which usually works fine for a bulky model, but might not be suitable for a bending dominated problem or a sliding problem. A sign for bad conditioning is that the convergence curve runs parallel to the the convergence norm. Choosing a smaller va ue or a ways ma es t e pro em eas er to converge. t e ana ys s s not converging, because of the too much penetration, turn off the Lagrange multiplier. The result is usually not as bad as you would believe.

FKN=1 © 2004 ANSYS, Inc.

FKN=0.01 ANSYS, Inc. Proprietary

Ansys Contact usages: tips and tricks Suggestion •

Numerically bad conditioned FE Model

FKN=.1

FKN=.1 © 2004 ANSYS, Inc.

FKN=0.0001

FKN=0.0001 ANSYS, Inc. Proprietary

Ansys Contact usages: tips and tricks Suggestion One reason for convergence difficulties could be the following: •

Load step is too large

Error in element formulation or element is turned inside out

5) If it is a large deflection problem, you usually need more substeps. 5 to 10 substeps are . , should reduce FKN, because FKN*d produces a large force, which can destroy the element.

NLGEO,ON NSUB,1,1,1

© 2004 ANSYS, Inc.

NLGEO,ON NSUB,10,100,1 ANSYS, Inc. Proprietary


Quads instead of triads Æ Error in element formulation or element is turned inside out 6) If some elements are locally distorted you might get an error in the element formulation or . those problems. You can also use NCNV,0 to continue the analysis and ignore those local problems if they do not effect the global equilibrium. In general, try to use triangular, tetrahedral or hexahedral elements (linear). Do not use quadratic hexahedral elements.

Error in element formulation

Linear quads © 2004 ANSYS, Inc.

Mid-side triads ANSYS, Inc. Proprietary


The parts have no unique minimum potential energy position. 7) If the max. DOF increment is not getting smaller and the force convergence norm keeps , . , friction coefficient is usually better than using a weak spring, not knowing exactly where to place it. Friction can be applied to all contact elements (try MU=0.01 or 0.1)

MU=0

© 2004 ANSYS, Inc.

MU=0.1



Unreasonable defined contact pair 8) Sometimes it is also important to think about possible contact configurations: Which surface influence the convergence behavior as shown below. Tar et Contact

Contact Target

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Unreasonable defined plastic material 11) It is not always a good idea to define the tangential stiffness to be zero using a plastic . , material resistance anymore to carry the load. There will be a plastic hinge and so the solution will never converge. In this case, input the correct tangential stiffness.

Plastic strain

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Stress strain curve with tangential slope zero ANSYS, Inc. Proprietary


Unreasonable defined plastic material

Stress strain curve with tangential slope 10000 Contact region Stress distribution © 2004 ANSYS, Inc.


Ansys Contact usages: tips and tricks Suggestion •

Instable solution 13) Some time, the solution could be instable, if the static analysis type is used, e.g if the . , rid of the instable solution.

© 2004 ANSYS, Inc.



Instable solution

- , before the snap through © 2004 ANSYS, Inc.

- , after the snap through. ANSYS, Inc. Proprietary

Ansys Contact usages: tips and tricks Suggestion TIP

In order to model the contact region reasonably, you should define two contact pairs, one for load step-1 and another for load step-2, and use the node detection = , .

/prep7 et,1,182,2 , , et,3,171,,1,,1 mp,ex,1,2e5 mp,mu,1,.1 mp,prxy,1,.3 r,1,,,.001,,,-2 r,2,,,.001,,,-2 rect,0,1,0,3 wpof,1,3 w rot -20 rect,-.2,3,0,.2 esize,.2 amesh,1 esize,.1 ,

lsel,s,,,5 nsll,s,1 type,2 esurf lsel,s,,,2,3 nsll,s,1

/solu

, nsub,100,100,1 outres,all,all nsel,s,loc,y,0 d,all,all se ,s,,, ,,, esurf d,all,ux lsel,s,,,2 d,all,uy,-.5 nsll,s,1 alls type,2 solv , /COM Load step-2 esurf lsel,s,,,6,,,1 lsel,s,,,5,8,3 d,all,ux nsll,s,1 d,all,uy,-1 type,3 esurf nsub,10,10,1 solv

Status-1 Contact-1

Target-1

Status-2 Target-2

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Contact-2 ANSYS, Inc. Proprietary

Ansys Contact usages: tips and tricks Suggestion Good mesh will generally make problem easier to converge. •

The fine mesh and similar are always good the contact simulation:

Geometry

Contact region

Contact mesh © 2004 ANSYS, Inc.


Ansys Contact usages: tips and tricks

How can I make the problem converge? • Tru t

ur

lf: I’m bl t m k it

nv r

!

• Consider the problem as idealized real world problem: - ec an cs exper se, 30%- FEA expertise,

- ng neer exper se 30%- Software expertise

• Use the magic KEYOPTIONS = :

o e m na e

erg

o y mo on

KEYOPT 10 =2: To make ANSYS think

© 2004 ANSYS, Inc.


Ansys Contact usages: tips and tricks Table of Contents

1. Introduction 2. MPC connection for SOLID-SOLID SHELL-SHELL 3. MPC connection for SOLID-SHELL 4. MPC connection SOLID-BEAM and SHELL-BEAM 5. MPC connection between the FE model and loading point

© 2004 ANSYS, Inc.


Ansys Contact usages: tips and tricks 1. Introduction, What is MPC? L

ui

j

u j =

4 (1) ( 2)

( 3)

− UY

2

3

( 3)

L

Beam 1

0

j =1

= Sin( ROTZ ) • L

L (2)

L (1)

0 = UY

Solid

(1)

UY

( 3)

− 2 L • Sin( ROTZ )

For small rotation:

ROTZ (3)

0 = UY ( 2)

UY

© 2004 ANSYS, Inc.

( 2)

− UY

(1 )

− UY

(2)

− 2 L • ROTZ

( 3)

CE ,2,0,1,UY ,1,2,UY ,−1,3, ROTZ ,−2


Ansys Contact usages: tips and tricks 1. Introduction, What do you need MPC? • To connect the dissimilar mesh: – If the geometries are not topologically connected, you can mesh the geometry independently and connect the FE model via MPC.

Geometry

© 2004 ANSYS, Inc.

Dissimilar mesh

Stress distribution


Ansys Contact usages: tips and tricks 1. Introduction, What do you need MPC? • To connect the different element types: – If the different element types are used on the connection region, because of the different DOFs, the connectivity is not consistent. The consistence can be achieved in the FE model via MPC.

Geometry

© 2004 ANSYS, Inc.

Solids and Shells

Deformation


Ansys Contact usages: tips and tricks 1. Introduction, What do you need MPC? • To a

l the remote load:

– If the loading point is not connected to the FE model, the connection can be achieved in the FE model via MPC.

Loading point and FE model Connected via MPC

© 2004 ANSYS, Inc.

Stress distributions


Ansys Contact usages: tips and tricks 1. Introduction, Why the existing contact algorithm is not used? . – The existing bonded contact algorithm using the penalty method, because of contact stiffness(cause the ill-conditioning) and the penetration, it might .

• Multiple iterations are required to adjust penetration in order to . – This will cause the iteration, even for linear problem.

. – This is because of the contact stiffness used.

•

. – This will cause the accuracy problem, if the distance between the contact and target is not zero. – e eam assem y can no e an e .

© 2004 ANSYS, Inc.


Ansys Contact usages: tips and tricks 1. Introduction, Why the existing contact algorithm is not used? •

s on y su a e or sma s ra n. – Because the existing CE method always uses the original nodal orientation.

• The RBE3 constraint can only support low order elements. – 10 nodes tetrahedron element are most commonly used element.

• It is not allowed to apply displacement constraints on the master node of RBE3

© 2004 ANSYS, Inc.


Ansys Contact usages: tips and tricks 1. Introduction, Advantages of new MPC approach •

. – It is not necessary to define the equations by hand, the user treats the connection as bonded contact, ANSYS will generate automatically the MPC.

• Degrees of freedom of the contact surface nodes are eliminated. – This will improve solution efficiency. • No contact stiffness is required as an input. – The accuracy of the solution is not dependent on try-and-error anymore.

• or sma e ormat on pro em, t represents true near contact behavior. – No iteration is needed in solving system equations. • For large deformation problems, the MPC equations are updated during each iteration.

© 2004 ANSYS, Inc.


Ansys Contact usages: tips and tricks 1. Introduction, Advantages of new MPC approach •

o on y rans a ona constrained.

u ro a ona

egrees o ree om can a so e

– It will improve the solution accuracy, and makes the connection between solid, , .

• The generation of internal MPC is also very easy thanks to contact pa r e n t on. – For the users, it is nothing new, if you know how to define the contact.

• It is not like MSC/Nastran (RBE3 type) – Sha e functions are taken into account automaticall ; no wei ht factor is needed. – not only forces but also displacements can be applied.

© 2004 ANSYS, Inc.


Ansys Contact usages: tips and tricks 2. MPC connection for SOLID-SOLID, SHELL-SHELL

Model-1: mesh is pretty similar SMAX=1.71 © 2004 ANSYS, Inc.

Model-2: mesh is uite different SMAX=1.71

Model-2: consistent mesh SMAX=1.71 ANSYS, Inc. Proprietary

Ansys Contact usages: tips and tricks 2. MPC connection for SOLID-SOLID, SHELL-SHELL KEYOPT(9)=0

If you have the geometry penetration: 1) Set the PINBALL to catch the contact 2 Use KEYOPT 9 =1 to i nore the pentration © 2004 ANSYS, Inc.

KEYOPT(9)=1

Model-2: Penetration and KEYOPT(9)=1 SMAX=1.71


Ansys Contact usages: tips and tricks 2. MPC connection for SOLID-SOLID, SHELL-SHELL KEYOPT(9)=0

If you have the geometry gap: 1) Set the PINBALL to catch the contact

KEYOPT(9)=1

Model-2: Gap and KEYOPT(9)=1 SMAX=1.73

pentration © 2004 ANSYS, Inc.


Ansys Contact usages: tips and tricks 2. MPC connection for SOLID-SOLID, SHELL-SHELL MPC connection for SHELL-SHELL(Edge-to-Edge)

Contact175

© 2004 ANSYS, Inc.


Ansys Contact usages: tips and tricks 2. MPC connection for SOLID--SHELL Summary: For most applications, default KEYOPT(5)=0 or 3 can be used. Many test = . New

New shell elements

elements CONTA175

shell elements

SHELL18 1 MPC equations

MPC equations

(translation DOF only) Virtual shell - solid surface

KEYOPT(5)=1 SHSD,ID 1st Approach: solid-solid constraint © 2004 ANSYS, Inc.

Shell thickness

MPC equations

(translation + Rotation DOF)

FTOLN

shell edge - virtual shell

Influence distance

KEYOPT(5)=2 , 2nd A roach: shell-shell constraint

shell edge – solid surface

FTOLN Influence s ance

KEYOPT(5)=0,3

3rd A roach: shell-solid constraint ANSYS, Inc. Proprietary

Ansys Contact usages: tips and tricks 3. MPC connection SOLID-BEAM and SHELL-BEAM roce ure: 1)

3)

Treat the solid surface and/or shell edge as contact surface, treat the beam node as target pilot node. No additional target is needed. e e con ac e emen eyop ons: KEYOPT(2)=2 this will activate the MPC method KEYOPT(12)=5 or 6 Set the bonded contact key KEYOPT(4)=1 Force-distributed surface KEYOPT(4)=2 Rigid constraint surface Run the analysis

© 2004 ANSYS, Inc.


Ansys Contact usages: tips and tricks 3. MPC connection SOLID-BEAM and SHELL-BEAM /prep7 et,1,45 et,2,188 et,3,173,,2 !KEYOPT(2)=2 Keyopt,3,4,1 !KEYOPT(4)=1 keyopt,3,12,5 !KEYOPT(12)=5 et,4,170 mp,ex,1,2e5 mp,prxy,1,0.3 SECTYPE, 1,BEAM, CTUBE SECOFFSET, CENT SECDATA,10,11 pcir,10,11,0,90 pcir,10,11,90,180 pcir,10,11,180,270 pcir,10,11,270,360 numm,kp lesi,4,,,2 es z,, et,10,42 esha,2 type,10 ames,a esiz,,20 type,1 © 2004 ANSYS, Inc.

vext,all,,,,,150 k,100,0,0,150 k,101,0,0,300 k,102,1,1,150 lsel,s,,,33 LATT,1,,2,,102,,1 lmes,33 real 10 type,4 tshap,pilo !Pilot node on beam e,2017 !Pilot node on beam nsel s loc z 150 nsel,u,,,2017 esel,s,type,,1 type,3 Esurf !Contact on solid /solu nsel,s,loc,z,0 d,all,all nsel s loc z 300 f,2018,fx,1000 alls

SOLID-BEAM


Ansys Contact usages: tips and tricks 3. MPC connection SOLID-BEAM and SHELL-BEAM Example

Solid solution

© 2004 ANSYS, Inc.

Solid-Beam via MPC


Ansys Contact usages: tips and tricks 3. MPC connection SOLID-BEAM and SHELL-BEAM /prep7 et,2,188 et,3,175,,2,,2 Keyopt,3,4,2

!KEYOPT(2)=2 !KEYOPT(2)=2 =

et,4,170 mp,ex,1,2e5 mp,prxy,1,0.3 SECTYPE, 2, BEAM, CTUBE SECOFFSET, CENT SECDATA,10,11 cir 0 10.5 0 90 pcir,0,10.5,90,180 pcir,0,10.5,180,270 pcir,0,10.5,270,360 numm k lsel,s,,,1,10,3 lesi,all,,,8 esha,2 esiz 20 k,50 k,51,0,0,150 l,50,51 © 2004 ANSYS, Inc.

adra,1,4,7,10,,,6 , ames,5,8 k,100,0,0,150 k,101,0,0,300 , , , , l,100,101 lsel,s,,,18 LATT,1,,2,,102,,2 , real,10 type,4 tshap,pilo

SHELL-BEAM

nsel,s,loc,z,150 nsel,u,,,673 esel,s,type,,1 esurf /solu nsel,s,loc,z,0 nsel,s,loc,z,300 f,674,fx,1000 alls ANSYS, Inc. Proprietary

Ansys Contact usages: tips and tricks 4. MPC connection between the FE model and loading point roce ure: 1)

3)

Treat the FE surface and/or edge as contact surface, treat the loading node as target pilot node. No additional target is needed. e e con ac e emen eyop ons: KEYOPT(2)=2 this will activate the MPC method KEYOPT(12)=5 or 6 Set the bonded contact key KEYOPT(4)=1 Force-distributed surface KEYOPT(4)=2 Rigid constraint surface Run the analysis

© 2004 ANSYS, Inc.


Ansys Contact usages: tips and tricks 4. MPC connection between the FE model and loading point /prep7 et 1 42 et,2,169 et,3,171,,2,,11 keyopt,3,12,5 m ex 1 2e5 mp,prxy,1,.3 rect,0,10,0,2 esiz,1 ames 1 n,100,5,5 lsel,s,,,2 nsll,s,1 t e3 real,3 esurf alls t e2 tshape,pilot e,100 nsel,s,loc,x,0 d all all alls f,100,fy,-100 © 2004 ANSYS, Inc.

!KEYOPT(2)=2 !KEYOPT(12)=5

!KEYOPT(4)=1


Ansys Contact usages: tips and tricks 4. MPC connection between the FE model and loading point

= Force-distributed surface

KEYOPT(4)=2 Rigid constraint surface © 2004 ANSYS, Inc.



/prep7 et 1 42 et,2,169 et,3,171,,2,,1 keyopt,3,12,5 m ex 1 2e5 mp,prxy,1,.3 rect,-10,10,-5,5 pcir,3 asba 1 2 smrt,4 ames,all © 2004 ANSYS, Inc.

n,1000,0,0 lsel s 5 8 nsll,s,1 type,3 real,3 esurf alls type,2 tshape,pilot e 1000

KEYOPT(4)=2 Rigid constraint surface

KEYOPT(4)=1 Force-distributed surface

/solu nsel,s,loc,x,-10 d,all,all a s f,1000,mz,-.7e6 nlgeo,on solv



/prep7 et,1,45 et,2,170 et,3,173,,2,,1 keyopt,3,12,5 mp,ex,1,2e5 mp,prxy,1,.3 © 2004 ANSYS, Inc.

cylin,10,20,0,100,0,90 *rep,4,,,,,90,90 numm,kp esiz,3 vmes,all n,10000,0,0,100 asel,s,,,2,20,6 nsla,s,1

type,3 real,3 esurf alls type,2 tshape,pilot e,10000

/solu nsel,s,loc,z d,all,all alls f,10000,mx,4.766e3 alls solv ANSYS, Inc. Proprietary

Ansys contact tutorial

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