segment to segment contact in marc

SimAcademy webinar, June 6th , 2013

Segment to Segment Contact with Marc

Copyright© 2013 MSC.Software Corporation S1 - 1

Segment to Segment Contact in Marc

Presented by Kiranraj Shetty

June 6th , 2013




• Introduction

• Disadvantages of Node to Segment method

• Segment to Segment Method Description

• Pre processing

• Post processing

• Benefits

• Limitations

• Demo

OVERVIEW




• Segment to Segment contact algorithm provides an easy, efficient and

faster solution to Contact analysis problems

• No Master – Slave concept

• Better stress continuity at Contact interfaces

• Supported in both Mentat & Patran GUI

INTRODUCTION




• Solution depends on selection of master and slave contact body

• Stress continuity is not maintained across the contact interface

• Primary output is Force not Stress

• Conflict with other MPC’s and/or boundary conditions

• Double sided shell contact doesn’t work

DISADVANTAGES NODE TO SEGMENT (N2S) CONTACT




• Fine meshed body has to be the slave

N2S CONTACT MASTER – SLAVE DEFINITION




• With node-segment contact a shell node can only touch another body at

the top or at the bottom, not both.

• Body 2 cannot touch both Body 1 & Body 3

N2S CONTACT AND DOUBLE-SIDED SHELL CONTACT




• auxiliary points per contact segment are introduced to allow for a contact

search

• Each segment (element edge/face) has a fixed number of auxiliary points;

in 2D, we have 3 auxiliary points per segment, in 3D we have 9 auxiliary

points (3x3 grid) per segment

• each auxiliary point can only touch one body at a time; at corners,

multiple auxiliary points will be introduced

SEGMENT TO SEGMENT CONTACT :

PHASE 1 – CONTACT DETECTION

Each contact segment has a

number of auxiliary points, which

are located at fixed positions on

the contact segment and which

are only used during the contact

detection phase.




• Two-pass contact detection is performed for the auxiliary points

• Distance Check: check whether auxiliary point is inside the distance

tolerance

• Direction Check: check whether the angle between the normal vector at

the auxiliary point and the normal vector at the potentially contacted segment

is larger than the threshold value α.The default value of α is 120º

• If both checks are passed, the segments are marked as potentially

contacting

CONTACT DETECTION (CONTD.)




• For each segment-segment combination within contact distance,

polygons (polylines in 2D) will be generated element wise

• Each polygon has a number of polygon points

• These Polyline points does not coincide with the auxiliary points used of

the contact detection before.


PHASE 2 – CONTACT COSTRAINTS




CONTACT CONSTRAINTS (CONTD.)




• In the same way as for the auxiliary points before, a second contact

detection pass is performed for the polygon points (distance + direction

check).

• At the end of this second pass, there is a set of polygon points being in

contact and representing the contact area.

• The polygons can be treated as normal interface elements representing

the contact stiffness.

• The polygon points build the basis for the numerical integration of the

corresponding contact stiffness formulation.

CONTACT CONSTRAINTS (CONTD.)




• For each polygon point in contact a weighted stiffness related to a penalty

factor is added to a normal stiffness matrix. A tangential stiffness induced

by sticking or glued contact is treated in a similar way.

• For each polygon point in contact a weighted contact force related to a

Lagrange multiplier is added to a vector of normal forces. Tangential

forces induced by friction or glued contact are treated in a similar way.


PHASE 3 – ADDING CONTACT CONSTRAINTS TO GLOBAL

EQUATIONS




• The penalty factor can be interpreted as a stiffness per area, applied to the

normal interface elements.

• The default penalty stiffness is based upon the average initial material

stiffness and a characteristic length L of the contacting bodies.

• For solid elements the characteristic length is L= 0.5 L_edge; L_edge =

average edge length of all edges being part of the contact boundary.

• For shell elements L= 0.5 t; t = average thickness of all elements being

part of a contact body.

• This choice gives good results in many application, particularly if the

material stiffness of the contacting bodies is of the same order.

• In cases when a soft material touches a stiff material, or when two thin

shell touch each other and are allowed to bend, the default penalty factor

is possibly too high and may lead to convergence problems

“feature,10201” Can help.

PENALTY FACTOR




• In case that too large penetration occurs, the augmentation procedure

may be used to iteratively adjust the contact normal stress so that the

overlap of the contact bodies will be minimized.

• augmentation means that a gap function g defined by the contact gap (g=0

when gap is closed) will be minimized iteratively by adjusting the contact

normal stresses p

• The augmentation procedure (adjustment of the spring base) forces

additional recycles in the global Newton-Raphson algorithm.

AUGMENTATION




• No augmentation. Recommended in most cases since it gives

reasonable accurate results without additional recycles.

• Augmentation based on constant penetration field. Recommended for

linear finite elements

• Augmentation based on (bi-)linear penetration field. Should be only

used for quadratic elements.

• Automatic detection: choice is made based on the combination of

elements corresponding to the contacting segments.

AUGMENTATION (CONTD.)




• An exact fulfillment of a zero gap is hardly achievable, therefore a

threshold called “penetration distance” has been introduced to control

the augmentation based iterations. If a gap exceeds the penetration

distance, an additional recycle will be forced to reduce it.

• The default penetration distance beyond which an augmentation will be

applied is defined as 0.001 L; L = characteristic length of the contact pair.

• Users may redefine the penetration distance, either globally or

individually per contact body pair.

• In the same way the augmentation method is applicable to adjust the

tangential displacements under sticking conditions.

• Equivalent to the penetration distance, a slip distance is defined for the

tangential augmentation procedure.

AUGMENTATION (CONTD.)




• Marc continuously monitors the relative displacements of the polygon

points.

• Once a threshold value is exceeded, new polygon points will be created.

• The default value of the recreation threshold for the polygon points equals

five times the contact tolerance. This value can be redefined by the user.

• As soon as new polygon points have been created, significant contact

data like the contact stresses is mapped from the old to the new polygon

points and used as a starting point to continue the analysis.

FINITE SLIDING




• Friction

Only the bilinear coulomb and bilinear shear friction model based on

stresses are available for S2S contact

• Separation control

Separation is always based on absolute nodal stresses.

If the contact normal stress is in tension, then the corresponding polygon

point will separate, which implies that this point will no longer contribute to

the global stiffness matrix and force vector.

FRICTION & SEPARATION CONTROL




• Contact Detection

– Auxiliary points located on each contact segment are used to detect

contact between potential contact segments.

– A two-pass contact detection including a distance and a direction

check is performed to check segments on contact.

• Contact Constraints

– Based on a projection from a contacting segment to a contacted

segment, polygons representing the contact stiffness are built.

– Each polygon consists of a couple of polygon points building the

basis for the numerical integration of the contact stiffness.

– The penalty factor represents the contact stiffness. It may be

determined by Marc or defined by the user.

– Penetration may be limited by a correction procedure - augmentation.

SUMMARY S2S CONTACT ALGORITHM




PRE PROCESSING – MENTAT GUI




PRE PROCESSING – MENTAT GUI (CONTD.)




PRE PROCESSING – PATRAN GUI




PRE PROCESSING – PATRAN GUI (CONTD.)




PRE PROCESSING (CONTD.)

0 - N2S contact

1 - S2S contact

1- Poly point info is

written in con.t19 file




• Contact status: set to 1 as soon as contact has been detected in at least

one polygon point on a contact segment to which the node belongs. So

the contact status is shown on both contact bodies of a contact body pair.

• Contact normal force: computed by integration of the contact normal

stresses in the polygon points.

• Contact friction force: computed by integration of the contact friction

stresses in the polygon points.

• Contact normal stress: nodal vector representing the normal stresses in

the polygon points based on a constant field approximation per contact

segment of the polygon values.

• Contact friction stress: nodal vector representing the friction stresses in

the polygon points based on a constant field approximation per contact

segment of the polygon values.

POST PROCESSING




• Easy job setup

• Better stress continuity

• Better contact normal stress distribution

• Contact status shown in both bodies

• Faster solution time

Run time comparison for Aerospace Buckling Application

BENEFITS

Contact Type Displacement # increments # iterations Wall Time

(Sec)

N 2 S 2.183 17 339 111939.00

S 2 S 2.197 38 156 41702.00

S2S 62% Faster




• Anisotropic friction

• Deactivation of glued contact

• Breaking glue

• Brake squeal

• Pore pressure, fluid-solid and piezo-electric analyses

• Wear

• Domain Decomposition Method (DDM)

LIMITATIONS AS OF MARC 2013




DEMO




Q & A




THANK YOU

segment to segment contact in marc

Documents