Strengths and Weaknesses of the different contact formulations available in explicit software

Innovation Intelligence®

Gérard WINKELMULLER, Chief Scientist Finite Element Analysis, Altair dev. France

Régis LATRILLE-SEIGNEUR, Support Technical Specialist, Altair dev. France

Altair Technical Conference Torino April 2013

Strengths and Weaknesses

of the different contact formulations

available in explicit software

Copyright © 2012 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved.

Summary

• New contact formulation

• Numerical Robustness

• Numerical Sensitivity

• Contact and Advanced Mass Scaling

• Conclusion

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Mains contact formulation

• Kinematic contact treatment

• Perfect contact treatment

• Lagrange multiplier

• Lagrange multiplier matrix has to be

inverted at each cycle

• Not well adapted for explicit code

• expensive

• Penalty contact treatment

• Linear penalty (type 24)

• Approximate contact treatment

• Large penetration can be observed locally

• Limited time step effect

• Non linear penalty (type 7)

• contact treatment with small

approximation

• penetration bounded by the gap

• Large time step decrease in some cases

• or large mass increase with mass scaling

shell

shell

shell

solid

solid

solid


New contact formulation type 24

• Why a new contact formulation

• Interface type 7 is well adapted for shell to shell or

shell to solid

• Interface type 7 can only work with non zero gap

value giving some limitations for solid to solid contact

• Electronic component drop test

• A mobile phone is very complex, involving many parts

and often with initial penetrations

• Zero gap treatment become critical here

• New interface type 24 was develop to answer to

these requests and will also provide a contact

formulation similar to competitor approach

Front cover

Window and

Touch sensor

Gasket

Buttons

LCD module

Carrier

PCB

Battery

Frame

Screws

Back cover

Special thanks to

Fredrik Nordgren

Altair Sweden


Numerical Robustness Analysis

• Robustness analysis is done on a simple Crash

Box collapsed between 2 rigid walls

• Medium mesh quality is used to increase potential

robustness issues

• Simulation is pushed as far as possible

• Up to complete box flattening t= 15.4ms (an still more)

• 3 contact formulations are compared

• Kinematic with Lagrange multiplier

• Type 7 non linear penalty

• Type 24 linear penalty

• 3 time step control are compared

• Free time step (no time step control)

• /DT/SHELL/CST

• Small strain after 15% time step decrease (about

15% strain)

• /DT/NODA/CST

• Mass scaling



T=6ms T=11.4ms T=14.6ms T=15.1ms T=16ms

Lagrange multipliers

Int7 non linear penalty

Int24 linear penalty

Impossible to invert

Lagrange Multiplier Matrix

After 14.6 ms

Time step

decline to zero

after 15.2 ms



T=6ms T=11.4ms T=14.6ms T=15.1ms T=16ms

Int7 non linear penalty

Int24 linear penalty


Numerical Robustness Analysis & time step control

Interface type 7 Interface type 24

Free time step •Final time 15.2 (dt too small)

•Dt: 4.6e-4 (t=0) -> 0 (t=15.2)

•338000 cycles

•105000 cycles at t= 14.9

•Final time >16

•Dt: 4.6e-4(t=0) -> 2.9e-5 (t=16)

•232000 cycles

•179400 cycles at t= 14.9

/DT/SHELL/CST

Dt = 4.e-4

Small strain after about 15%

deformation

•Final time 15.3 (dt too small)

•Dt: 4.6e-4 (t=0) -> 0 (t=15.3)

•143400 cycles

•43100 cycles at t= 14.9

•Final time >16

•Dt: 4.6e-4(t=0) -> 2.6e-4 (t=16)

•45100 cycles

•40900 cycles at t= 14.9

/DT/NODA/CST

DT = 4. e-4

Mass scaling

•Final time 15. (energy error)

•Dt: 4. e-4(t=0) -> 3.8e-4 (t=15)

•37700 cycles

•37300 cycles at t= 14.9

•Final time 14.9 (mass error)

•Dt: 4. e-4(t=0) -> 3.9e-4 (t=14.9)

•37300 cycles

•37300 cycles at t= 14.9


CRASH_BOX Numerical Sensitivity Analysis

8912 shells

Initial velocity : 5 mm/ms on

RBody with free rotation

around Y

Used a free time step

Interface:

1 TYPE7 or TYPE24

RADIOSS_DP SMP SPMD CPU time Nb_Cycles Time/Cycles

TYPE7 8 1 925 226762 0.004

TYPE24 8 1 771 187663 0.004

• Sensitivity analysis is done on a Crash Box

connected to an articulated rigid body and fixed

at the other end

• 10 runs with random noise on nodal

coordinates

• maximum noise 10-6 mm

• Variable seed



TYPE7



TYPE24



TYPE24 TYPE7

• Interface type 24 is much more sensitive than Interface type 7


Numerical Robustness Analysis & time step control

Lagrange multiplier Interface type 7

Non linear penalty

Interface 24

Linear penalty

Contact

Quality ***** **** *** Numerical

Robustness * *** ***** Numerical

sensitivity

?

**** ***


Contact formulation and Advance Mass Scaling

• NEON1M14 (80ms)

• 1M elements

• Rigid Wall

• Interface formulation

• interface TYPE7 with variable gap

• Interface TYPE24 (use variable gap by default)

• Time step control

• /DTNODA/CST dt=0.5µs (mass scaling)

• AMS DT=10µs

• AMS DT=20µs


Constant nodal time step dt=0,5 µs

NEON1M14 (80ms)

1M elements

Rigid Wall

19 numbers of interface

TYPE24

RADIOSS Objective (µs) Mean time step (µs) Nb of cycles

TYPE7_Igap1 0.5 0.495 161802

TYPE24 0.5 0.496 161230


Advanced Mass Scaling dt=10 µs

NEON1M14 (80ms)

1M elements

Rigid Wall

19 numbers of interface TYPE24


TYPE7_Igap1_AMS 10 5.43 14707

TYPE24_AMS 10 9.99 8001


Advanced Mass Scaling dt=20 µs

NEON1M14 (80ms)

1M elements

Rigid Wall

19 numbers of interface TYPE24


TYPE7_Igap1_AMS 20 8.88 9002

TYPE24_AMS 20 19.99 4001


Conclusion

Lagrange multiplier Interface type 7

Non linear penalty

Interface 24

Linear penalty

PROS •Contact quality

•Perfect kinematic

continuity

•Contact quality

•Limited contact penetration

•Low numerical sensitivity

•Allow zero gap

•Allow small initial

penetration

•Robust formulation

•Efficient with element time

step control

CONS •Too expensive

•Not robust for crash (shell

to shell contact)

•Smaller time step

•Not efficient with element

time step control

•Not adapted for solid to

solid contact

•Possible large penetration

•Possible topology contact

errors for complex mesh

folding and large penetration

•More numerical sensitivity

OVERALL •Not recommended for

explicit

•Recommended for high

quality car crash simulation

•Recommended for

sensitivity analysis

•Recommended for

electronic components drop

test

•Can be used for car crash

simulation (especially if AMS

is used)


Thanks You

Strengths and Weaknesses of the different contact formulations available in explicit software

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