FENET Meeting, WS7, DLE Session Mallorca, 25 March 2004

Creep Simulations with ABAQUS:Super Plastic FormingPRINCIPIA Ingenieros ConsultoresMadrid, SPAINJose L. San Vicentehttp://www.principia.es

FENET Durability and Life Extension“FE Issues Related to Creep and Viscoelasticity”Mallorca, 25 March 2004

FENET Workshop - Finite Element Analysis of Creep and ViscoelasticityMajorca, Spain

25-26 March 2004

CREEP Simulations with ABAQUS

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Table of contents

• Superplastic forming• CREEP models• SPF - FE analysis• Examples• Conclusions

FENET Meeting, WS7, DLE Session Mallorca, 25 March 2004

CREEP Simulations with ABAQUS: Super Plastic Forming

1. Super plastic forming (SPF)

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Super Plastic Forming (SPF) (1)

• Sheet forming process– large elongations are reached in the material– limited to materials with Superplastic properties

• Complex geometries

• Goals – Forming process with no (or little) damage to the components– Reduce the number of components– Reduce the number of joints

• Aerospace applications

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Super Plastic Forming (SPF) (2)

• Aluminium alloys (Al, Ti, V, ...)– Expensive materials

• Superplastic behavior only in a superplastic range– High Temperature: 900 ºC– Low strain rate: 10e-5, 10e-3– Large deformations + low strain rate = long times

• Set-up

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Super Plastic Forming (SPF) (3)

• The industrial production is constrained by:– Productivity: Forming the components as fast as possible– Superplastic behavior only for low strain rates: as slow as possible – Facilities: maximum pressure

• Goals:– Forming as fast as possible, but remaining in the SP range– Find the appropriate load history

FENET Meeting, WS7, DLE Session Mallorca, 25 March 2004

CREEP Simulations with ABAQUS: Super Plastic Forming

2. CREEP models

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CREEP models (1)

• Material behavior

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CREEP models (2)

• Creep modeling

–Primary creep: non-proportional response

–Secondary creep: proportional

–Tertiary creep: hardening

• “Unspecified” Creep: Secondary creep

–Wider range

–Predominant

–Easy to model

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CREEP models (3)

• Modeling of non-proportional creep

– Standard laws

• Time law

• Strain hardening

–More sophisticated laws

• B. Zhang et al.

FENET Meeting, WS7, DLE Session Mallorca, 25 March 2004

CREEP Simulations with ABAQUS: Super Plastic Forming

3. SPF: FE Analysis

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• Finite element modeling of forming– Rigid dies– Mesh of the blank with shell or brick elements– Static analysis

• No inertia forces– Uniform pressure on the sheet surface– Contact: friction, finite sliding– Coupling of models (elasticity, plasticity, …)

SPF: FE Analysis (1)

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SPF: FE Analysis (2)

• Additional features for FE in SPF– Creep governs the response

– Implicit vs Explicit integration• Need of a smooth strain rate• Time stable limitation in explicit

– Too restrictive, even with mass scaling• Implications: deal with contact, large models, … in implicit

– Unknown load history• Solution dependent – need of adaptive loading

– Constraint 1: Strain rate in SP range– Constraint 2: Pressure at the manufacturing facilities

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SPF: FE Analysis (3)

• FE Results

– Formed geometry• Shape• Thickness

– Load history

– Comparison between• Target strain rate • Actual strain rate

•Ciclos de presión

•0.00•1.00•2.00•3.00•4.00•5.00•6.00•7.00•8.00•9.00

•10.00•11.00•12.00•13.00•14.00•15.00

•0.0 •10.0 •20.0 •30.0 •40.0 •50.0 •60.0 •70.0 •80.0 •90.0

•Tiempo (min)

•Pre

sión

(bar

)

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SPF: FE Analysis (4)

• Some difficulties

– Material properties• Owned by the manufacturers• Testing very expensive

– Implicit approach • Large models and small integration time• Contact with finite sliding

– Round-off in the creep equation• Even with double precision

FENET Meeting, WS7, DLE Session Mallorca, 25 March 2004

CREEP Simulations with ABAQUS: Super Plastic Forming

4. Examples

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Case 1

• Calibration example

– Calibration of Inconel 718

– Too complex for library material

– User routine CREEP

– Uniaxial testing

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Case 1

• Validation with actual case: axisymmetric component

– FE-Model

– Testing

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Case 1

• Thickness reduction

• Succesfully used in production

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Case 2

• Slat

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• Analysis of control sections

– Inital package of 4 sheets

– High temperature: Welding of sheets where are in contact• Easy joints: avoids rivets, ... • Welding inhibitor in the rest

Case 2

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• Results

– Pressure-time

– Map of thickness

Case 2

•0

•5

•10

•15

•20

•25

•0.0 •20.0 •40.0 •60.0 •80.0 •100.0

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Case 3 – Study of the nose in the design of one slat

• Last phase of the forming

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• Three dimensional simulation

Case 4 – SPF of a spoiler

FENET Meeting, WS7, DLE Session Mallorca, 25 March 2004

CREEP Simulations with ABAQUS: Super Plastic Forming

5.- Conclusions

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• SPF uses CREEP for manufacturing purposes. Complex geometries with no joints are good candidates in aerospace industry.

• SPF includes all the features in conventional sheet forming, butthe pressure is solution dependent. This requires adaptive load application.

• SPF implicit approach has to face large models and intensive contact. This needs a robust numerical tool.

• Some examples of advanced SPF simulation by PRINCIPIA have been shown. They have been done with ABAQUS/Standard.

Conclusions