finite element modeling of a thermoplastic seal at high … · abaqus standard and explicit...

Finite Element Modeling of aThermoplastic Seal at HighTemperature and Pressure

Jorgen BergstrJorgen Bergstroomm11, Ph.D., Ph.D.

Brun HilbertBrun Hilbert22, Ph.D., P.E., Ph.D., P.E.

22Exponent Inc.Exponent Inc.

Natick, MANatick, MA

11Veryst Engineering, LLCVeryst Engineering, LLC

Needham, MANeedham, MA

Email: [email protected]

Outline of PresentationOutline of Presentation

•• Description of the ProblemDescription of the Problem

•• Mechanical behavior of TeflonMechanical behavior of Teflon

•• New UMAT for TeflonNew UMAT for Teflon

•• Calibration and validation of theCalibration and validation of theUMATUMAT

•• FE simulation of Teflon gasketFE simulation of Teflon gasket

•• ConclusionsConclusions

Threaded Connection SimulationThreaded Connection Simulation

Steel

PipeTeflon

Seal

Steel

Coupling


•• The two steel pipes are threaded togetherThe two steel pipes are threaded together•• The assembled pipe transports gas at highThe assembled pipe transports gas at high

temperature and pressuretemperature and pressure

•• The Teflon seal acts as a secondary sealThe Teflon seal acts as a secondary seal•• How much pressure can the Teflon seal takeHow much pressure can the Teflon seal take

before leaking?before leaking?


•• What is the pressure between the Teflon sealWhat is the pressure between the Teflon sealand the steel pipes at different temperatureand the steel pipes at different temperatureand times?and times?

Finite Element ModelingFinite Element Modeling

Finite Element

Modeling

Geometry and

BC

Material

RepresentationLoading

Specification

• The results from FEA are only as accurate as the input

values

• The most difficult part is typically the material

representation

Geometry and Boundary ConditionsGeometry and Boundary Conditions

•• AxisymmetricAxisymmetricrepresentationrepresentation

•• The model contains 3The model contains 3parts:parts:

–– Lower steel pipeLower steel pipe

–– Upper steel pipeUpper steel pipe

–– Teflon sealTeflon seal

Geometry and Boundary ConditionsGeometry and Boundary Conditions

•• The analysis isThe analysis isperformed usingperformed usingABAQUS/ExplicitABAQUS/Explicit

•• The 3 parts areThe 3 parts areinitially overlappinginitially overlapping

•• No contact activatedNo contact activated

Geometry and Boundary ConditionsGeometry and Boundary Conditions*Expansion, *Expansion, type=orthotype=ortho, zero=,, zero=,

dependencies=1dependencies=1

** alpha11, alpha22, alpha33, T, field** alpha11, alpha22, alpha33, T, field

6.000e-4, 0.000e-5, 6.000e-4, , 1 6.000e-4, 0.000e-5, 6.000e-4, , 1

1.242e-5, 1.242e-5, 1.242e-5, , 2 1.242e-5, 1.242e-5, 1.242e-5, , 2

*Initial conditions, type=temperature*Initial conditions, type=temperature

allNallN, ,

*Initial conditions, type=field,*Initial conditions, type=field, var=1var=1

allN allN, 1, 1

FIRST STEP:FIRST STEP:

*Temperature*Temperature

intPipeintPipe..allNallN,

*Field, op=mod,*Field, op=mod, var=1var=1

allN allN, 1, 1

SECOND STEP:SECOND STEP:

*Temperature*Temperature

intPipeintPipe..allNallN, ,

Apply DIFFERENT TEMPERATURE AND PRESSUREApply DIFFERENT TEMPERATURE AND PRESSURE

HISTORIESHISTORIES

Experimental Data for TeflonExperimental Data for Teflon

T=20°C

Uniaxial Tension

Experimental Data for TeflonExperimental Data for Teflon

Stress Relaxation

Triaxial Compression

Mechanical Behavior of TeflonMechanical Behavior of Teflon

• Creep

• Stress relaxation

• Temperature

dependence

• Yielding

• Large deformations

The Response is Characterized by:

How can the Teflon material be

modeled using ABAQUS?

Constitutive Model DescriptionConstitutive Model Description

*Material, name=Teflon

*User material, constants=17

100, 1, 0, 1.11e-4, , 6.0, 3.5, 600

100, 200, 3.5, 600, 0.0, 1.35, 3.0, 165.0

0.01

*Depvar

18

*Density

2200e-12

Constitutive ModelingConstitutive Modeling

8-chain model

8-chain model

Viscoelastic Flow:

• Modeled with a

reptation based

energy activation

representation

Equilibrium

response

Time-dependent

responseViscoplastic Flow

Chain slippage driven by a

stress driven representation

Response of the EquilibriumResponse of the EquilibriumNetworkNetwork

•• LL-1-1((xx) is the inverse Langevin) is the inverse Langevinfunctionfunction

•• Hyperelastic representationHyperelastic representation•• Micromechanism inspiredMicromechanism inspired•• Accurately predicts large strainAccurately predicts large strain

multiaxial deformationsmultiaxial deformations

8-chain model

( ) ( )( )

1 *0

*

1*

/

dev 11/

ve lock

A ve ve

A lockve

L

JLJ

! !µ "#

!!

$

$% & % &= + $' ( ' (T B 1

detve veJ ! "= # $F

( ) ( )2/3

*T

ve ve ve veJ

!

=B F F

( )* *tr / 3ve ve! = B

( )0 0expA Abase

! !µ ! µ

!

" #$= % &

' (


•• The details of theThe details of thematerial model arematerial model areavailable in:available in:

–– ““A Constitutive ModelA Constitutive Modelfor Predicting thefor Predicting theLarge DeformationLarge DeformationThermomechanicalThermomechanicalBehavior ofBehavior ofFluoropolymersFluoropolymers””, J.S., J.S.Bergstrom, L.B.Bergstrom, L.B.Hilbert, Mechanics ofHilbert, Mechanics ofMaterials, Materials, vol vol 37, pp.37, pp.899-913, 2005.899-913, 2005.


•• Available for bothAvailable for bothABAQUS standardABAQUS standardand explicitand explicit

•• Physically motivatedPhysically motivated

•• Incorporates:Incorporates:–– Rate effectsRate effects

–– ViscoelasticityViscoelasticity

–– ViscoplasticityViscoplasticity

–– PermanentPermanentdeformationdeformation

–– Temperature effectsTemperature effects

–– Volumetric creepVolumetric creep

Determination of MaterialDetermination of MaterialParametersParameters

1)1) Calibrate model toCalibrate model toavailable uniaxial dataavailable uniaxial data(different strain rates,(different strain rates,temperatures, and straintemperatures, and strainhistories)histories)

2)2) Simulate multiaxial testsSimulate multiaxial testsusing the calibratedusing the calibratedmodelmodel

3)3) Evaluate performance ofEvaluate performance ofthe modelthe model

Calibration

Verification

Evaluation

Material Parameters for PTFEMaterial Parameters for PTFE

8.52 MPa

71.2 C

5.0

500 MPa

A

base

lock

µ

!

"

#

=

=

=

=

o

Network A

12.97Bs =

1

9.11

28.9

19.0 MPa

152 GPa

base

vol

C

m

n

!

"

= #

=

=

=

=

0

0.046

1.0

19.0 MPa

a

b

!

=

=

=

Network B

Viscoelastic flow

Plastic flow

Glass Fiber Filled PTFEGlass Fiber Filled PTFE

PTFEPTFE

PTFEPTFE

Triaxial Compression

(T=20°C)

Limit of applicationLimit of application

•• DeformationDeformation–– The model works for arbitrary multiaxialThe model works for arbitrary multiaxial

deformation statesdeformation states

–– The model has been tested forThe model has been tested fordeformation rates between 10deformation rates between 10-5-5/s to 1/s/s to 1/s

•• Temperature rangesTemperature ranges–– The model has been tested forThe model has been tested for

temperatures between 20temperatures between 20°°C and 200C and 200°°CC

•• Software implementationsSoftware implementations–– Implemented and tested for ABAQUSImplemented and tested for ABAQUS

(both Explicit and Implicit)(both Explicit and Implicit)

•• Uniaxial testing onlyUniaxial testing onlyprobes one aspect of theprobes one aspect of thematerial modelsmaterial models

•• Many models can predictMany models can predictuniaxial deformation,uniaxial deformation,only a few can predictonly a few can predictmultiaxial loadingmultiaxial loading

•• In many importantIn many importantapplications the appliedapplications the appliedload is multiaxialload is multiaxial

The Need for Multiaxial TestingThe Need for Multiaxial Testing

Verification: Punch testingVerification: Punch testing

Specimen geometry:Specimen geometry:

•• Diameter=6.4 mmDiameter=6.4 mm

•• Thickness=0.5 mmThickness=0.5 mm

Experimental DataExperimental Data

Model PredictionsModel Predictions

Threaded ConnectionThreaded ConnectionSimulationsSimulations

Threaded ConnectionThreaded ConnectionSimulationSimulation

ConclusionsConclusions

•• FE analysis generally requires 3FE analysis generally requires 3parts:parts:

–– Geometry specificationGeometry specification

–– Load and boundary conditionsLoad and boundary conditions

–– Material modelsMaterial models

•• The specification of the materialThe specification of the materialmodel is often the most difficult partmodel is often the most difficult part

ConclusionsConclusions

•• Accurate FE analysis of polymersAccurate FE analysis of polymersrequires:requires:

–– Careful experimental testingCareful experimental testing

–– Material model calibrationMaterial model calibration

–– Material model validationMaterial model validation

–– Specialized user material modelsSpecialized user material models((UMATsUMATs) can provide accurate) can provide accuratepredictions for many predictions for many ““toughtough”” problems problems

Exponent UMAT models forExponent UMAT models for

•• ElastomersElastomers–– Filled or unfilledFilled or unfilled

•• Semi-crystalline glassy polymersSemi-crystalline glassy polymers–– PolyethylenePolyethylene

–– FluoropolymersFluoropolymers

•• FoamsFoams–– Silastic foamSilastic foam

Special Thanks:Special Thanks:

Shell Exploration and Production CompanyShell Exploration and Production Company

Sina Ebnesajjad Sina Ebnesajjad at DuPont at DuPont FluoroproductsFluoroproducts

Pradip Kaladkhar Pradip Kaladkhar at DuPont at DuPont FluoroproductsFluoroproducts

finite element modeling of a thermoplastic seal at high … · abaqus standard and explicit...

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