Page 1 Introduction to Lagrange Chapter 12 - ContactMSC.Dytran Seminar Notes CHAPTER 12 - CONTACT.

Introduction to Lagrange

Chapter 12 - Contact MSC.Dytran Seminar Notes

CHAPTER 12 - CONTACTCHAPTER 12 - CONTACT



CONTENTS

• Contact definition

• Master Slave Surface Contact

• Single Surface Contact

• Adaptive Contact

• Penalty Method in Contact

• Contact Force

• Contact Search

• Contact Options

• Contact Output



CONTACT DEFINITION

Defines interaction between Lagrangian gridpoints and elements

Three types of contact exist

• Master Slave Contact

• Single Surface or Self Contact

• Adaptive or Eroding Contact



SlaveSurface

MasterSurface

MASTER-SLAVE CONTACT

Prevents two surfaces from penetrating each other

Fast and efficient contact algorithm

Example: Contact between surfaces 202 and 102

CONTACT,1,SURF,SURF,202,102SURFACE, 102, , PROP, 103SURFACE, 202, , MAT, 203



SINGLE SURFACE CONTACT

Prevents a surface penetrating itself

Useful for modeling buckling problems where the points of contact can not be determined before the analysis

In case it is not known beforehand where contact will occur or which parts of a structure will be in contact all the different parts of that structure can be put into a single contact surface definition.

Expensive to use, but very powerful

Easy to use

Example: Self contact of surface 204

CONTACT, 1, SURF, , 204SURFACE, 204, , ELEM, 204



ADAPTIVE CONTACT

Defines interaction between Lagrangian objects that can fail

Upon element failure the element is removed from the calculation and the contact surface is automatically updated

Automatic generation of initial contact surface

Example: Contact between objects with properties 202 and 102

CONTACT, 1, PROP, PROP, 202, 102, , , , ++, , , , YES



CONTACT METHOD OF MSC.Dytran

• Contact uses Penalty Method

Allowed penetration of nodes

Forces perpendicular to face normals to push slave node back

Conservation of momentum

• Contact is based upon the Master Face - Slave Node Algorithm

Slave nodes will look for contact with master faces

Therefore contact in MSC.Dytran is not symmetrical!!!

Exception is Single Surface Contact



CONTACT SEARCH ALGORITM

Four regions:

• Do nothing if free grid point

• Check for penetration if inside monitoring region

• If penetrated apply force to bring slave point to surface

• If penetrated to deeply do not apply any force (missed contact)

Monitoring Region

Slave

Master Segment

Penetration Region

Slave Node:

free

penetrated too deeply

monitoring

penetrated



dp dm

n

• Penetration region depth, dp, can be user defined

Use to maintain stability of structure

• Monitoring region width, dm, can be user defined

Monitoring region is dynamic: it will be increased automatically when slave nodes have high velocity

CONTACT SEARCH ALGORITM(Continued)



Contact can occur from different sides

- TOP side: slave nodes will stay above the master faces

CONTACT, 1, SURF, SURF, 202, 102, , , , ++, , TOP

- BOTTOM side: slave nodes will stay beneath the master face

CONTACT, 1, SURF, SURF, 202, 102, , , , ++, , BOTTOM

Automatic initialization of contact side when side is set to option BOTH.MSC.Dytran will set option for each node to either TOP or BOTTOM and option can change during simulation

• Use only when initially a gap exists between master and slave surface

• Required to use BOTH option for self surface contact

CONTACT, 1, SURF, SURF, 202, 102, , , , ++, , BOTH

G1

G4 G3

G2

TOP

BOTTOM

Xseg

Yseg

Zseg




To determine TOPor BOTTOM contact uniquely the normal of the faces of the contact surfaces must all point in the same direction

Example of top side contact:

Initial penetration would occur when BOTTOM option was defined

No initial penetration would occur when BOTH was defined:the initial geometrical layout determines from which direction the contact occurs




CONTACT FORCE

Slave node penetrates master segment from time n to n + 1 over a distance

Slave Node

Penetration Region

n (normal)

n

n + 1

Contact force computed from penetration

nt

WFACTF mass **

*2

w h e r e

slavemaster

slavemastermass MM

MMW

*

F A C T = S c a l e F a c t o r

timestept

FACT = .1 by default to avoid instabilities

A factor of 1.0 would result in the Lagrange multiplier method



CONTACT FORCE (continued)

Conservation of impulse

The computed contact force is put on the slave node in order to bring it back to the master surface

The same, but reversed force will be distributed to the nodes of the master surface



CONTACT OPTIONS - THICK

Shell thickness can be taken into account for contact

• The penetration region is increased with half of a user defined factor of the master element thickness.

• The position of the slave node used in the penetration calculation is update with half of a user defined factor of the slave element thickness.

penetration

m2

s



CONTACT OPTIONS - GAP

A gap can be taken into account for contact

• The penetration region is increased with the value of GAP

penetration

g



CONTACT OPTIONS - FRICTION

Friction may be included in the contact

The coefficient of friction at low and high speed may be different:

By default no friction

Example: Master-Slave contact between surface 3 and 7 with a static friction coefficient 0.3

CONTACT, 1, SURF, SURF, 3, 7, 0.3

k

s

k– e –

+=



CONTACT OPTIONS - (DE)ACTIVATION

Contact can be activated or deactivated to save calculation time

- TSTART Time at which contact is activated (default t = 0.)

- TEND Time at which contact is deactivated (default ENDTIME)

Example: Contact active between 0.1 and .5 of a Master-Slave contact between surfaces 3 and 7

CONTACT, 1, SURF, SURF, 3, 7, , , ,++, , , , , , , , , ++, 0.1, 0.5



CONTACT OUTPUT

Output is presently only available for timehistory and is specified using the following Case Control commands:

CONTOUT - indicates variables to be output

CONT - indicates a SET containing contact surface

ID’s for which output is requested

STEPS/TIMES - Time-interval at which output is requested

TYPE - indicates time-history format (only TIMEHIS)

SAVE - interval at which a new output file is to be created

Example:

TYPE (Contact_File) = TIMEHIS

CONTOUT (Contact_File) = XFORCE, YFORCE, ZFORCE,

FMAGN, AMAGN

CONTS (Contact_File) = 10

SET 10 = 111

TIMES (Contact_File) = 0.0 THRU END BY 1.0e-4

SAVE (Contact_File) = 1000000



CONTACT VERSIONS

•DRAWBEAD

• Suited for modeling a drawbead



APPLICATION OF DRAWBEAD IN CONTACT

A drawbead model is implemented in the CONTACT algorithm for sheet metal stamping. A list of grid points must be created to define the location of the drawbead line. The grid points are then used to define a row of dummy rod elements representing the drawbead. An RCONN rigid connection is used to couple the drawbead grid points and the tool. The user need to define restraining force/unit of drawbead length on the contact card (“DRAWBEADF” entry ) and use “DRAWBEAD” flag as “VERSION” on the CONTACT card.

Example:

CROD,501, 5 , 5001 , 5002SET1, 51 , 5001, 5002 $ List of grid points at drawbead locationPROD, 1, 5 , 1.0E-20$ Dummy properties for rod doesn’t add mass or inertia effectsMAT1, 5, 1.0E-20, , 0.3, 1.E-10 $ Define a rigid connection between drawbead grid points (GRID Set =51) and the tol (SURFACE ID=11).$RCONN,1,GRID,SURF, 51, 11, , , , ++, , , , , , , , , ++, YES$ Define the drawbead restraining force per unit length on the CONTACT Card. The force is applied via GRID SET = 51 on the blank (SURFACE ID=1)$CONTACT,1, GRID, SURF, 51, 1, , , ,++,DRAWBEAD, , , ,1.0, , , ,++, , , , , , , , , ++, , , , , , , , , ++,drawbeadf = force/length

Page 1 Introduction to Lagrange Chapter 12 - ContactMSC.Dytran Seminar Notes CHAPTER 12 - CONTACT.

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