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Pulse-Pressure Forming (PPF) of Lightweight Materials

P.I.: Richard Davies, (509) 375-6474, rich.davies@pnnl.gov Pacific Northwest National Laboratory

May 17, 2012

(Project 60184/Agreement 22422)

2012 DOE Vehicle Technologies Program Review

Project ID: LM033 This presentation does not contain any proprietary, confidential, or otherwise restricted information

Project Overview Project Timeline:

Start – 3Q FY08 Finish – 1Q FY12 100% complete

Budget: Total project funding:

PNNL: $1450k FY08 Funding Received:

$200k FY09 Funding Received:

$450k FY10 Funding Received:

$500k FY11 Funding Received:

$300k

Targets The VTP target for weight reduction of the vehicle and its

subsystems is 50%. Pulse-Pressure Forming (PPF) of aluminum and Advanced High Strength Steels (AHSS) has the potential to achieve 25 to 45% weight savings vs. conventional steels

Barriers Barriers to using PPF of aluminum and AHSS in the

lightweighting of vehicles: Lack of understanding of the formability and strain rates that develop during PPF processing Lack of validated constitutive relations for lightweight materials during PPF processing Lack of validation of finite element simulation of PPF processing

Partners OEM and Industry participants:

Sergey Golovashchenko (Ford) John Bradley (General Motors) Ajit Desai (Chrysler) US Steel

Relevance to Technology Gaps Project Objectives:

Enable broader deployment of automotive lightweighting materials in body-in-white and closure panels through extended formability of aluminum alloys, magnesium alloys, and HSS/AHSS. Enable a broad set of PPF technologies to effectively extend the benefits of high rate sheet metal forming beyond the limitations of electrically conductive metals (aluminum) that are required for electromagnetic forming (EMF) processes. Aluminum and AHSS have limited formability at room temperature and conventional strain rates. High strain rate forming (PPF) can enhance room temperature formability

Extended ductility of most metals Generate greater ductility from lower cost steels Increase formability of Al and Mg alloys Utilize single-sided tooling at lower cost Provide residual stress (springback) management

PPF of Lightweight Materials will address technology gaps Demonstrate and quantify extended ductility in Al, AHSS and Mg using PPF process and high speed camera system Validate high-strain-rate constitutive relations for PPF of lightweight materials Characterize material microstructure and texture evolution at high-strain-rates

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4

Approach/Strategy

Task 1 Formability and Fracture Characterization Design, fabricate, and demonstrate the operation of the PPF system. This includes procuring high-speed cameras for real-time image capture to quantify deformation history using existing PNNL DIC system Perform sheet forming experiments using single-pulse and multi-pulse PPF of Al-5182, DP600, and Mg-AZ31 sheet materials Characterize high-rate formability and extended ductility

Task 2 Microstructure and Mechanical Property Evolution

Develop materials constitutive relations for high-rate forming Characterize microstructural and texture evolution Characterize post-forming mechanical properties

Task 3 Numerical Simulation of PPF Process

PPF sheet forming finite element modeling Sheet-die interaction during PPF

Project Milestones

Milestones Due Status Issues? Demonstrate successful operation of the PPF apparatus

11/08

Complete experimental characterization of PPF process

9/11

Complete constitutive relations for Al, Mg, and AHSS

3/10

Complete evaluation of post-forming properties of materials subject to PPF

6/11

Complete evaluations of numerical simulations

3/11

5

= Complete

= On Track

= At Risk

= Late

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Background

10-5 10-4 10-3 10-2 10-1 100 101 102 103 104 105

Plate tectonics

Creep Forming

Superplastic Forming

Conventional Forming

Automotive Crash

Strain Rate (1/sec)

High Rate Forming

Terminal Ballistics

Cosmic Events

Atomic Fission…

Interior Ballistics

THIS PROJECT

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Introduction High Rate Forming Technologies

Electromagnetic Forming (EMF) Electrohydraulic Forming (EHF) Explosive Forming (classical) Laser Shock Forming (LSF)

Project Plan - Subject Materials Aluminum Alloys

Initial focus on AA5182-O (1 mm and 2 mm) AHSS (and HSS)

Initial focus on DP600 (1 mm and 0.6 mm) [ Provided by US Steel] Magnesium Alloys

Initial focus on AZ31-O (1 mm)

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Technical Progress Task 1.1 - Fabrication, Assembly, and Testing of PPF Apparatus

PNNL’s PPF Setup For Free-Forming Dome

Test sheet with speckle pattern for strain evaluation

Clamping ring

Conical Die

φ=6”

5182-O 1 mm 7500 V

Free-Forming

hmax~2” “Just” cracked

PNNL Test T-15

5182-O 1 mm 7500 V

“Petaling” failure hmax>2.5”

Conical Die PNNL

Test T-22

- +

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Technical Progress Task 1.1 - Fabrication, Assembly, and Testing of PPF

Top View: Free-Forming

Side View: Cone Die

Close-up of Cameras

Looking Inside Conical Die

Test Sheet

Imaging Setup

• Imaging at ~75000 frames/second (~13 microseconds per frame)

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Technical Progress (PPF Deformation Evolution) Task 1.2 - Single-pulse PPF

Deformation history obtained at any location on the sheet

High-speed Cameras +

Digital Image Correlation

Duration < 1 ms

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Technical Progress (Free-Forming of Mg, Al, DP600) Task 1.2 – Single-pulse PPF

Room temperature forming of AZ31B needs experimental re-designs to

prevent failure at tool-radius

5182-O 1 mm 7500 V

PNNL Test T-15

Formable

ALUMINUM

DP600 1 mm 9500 V

PNNL Test DP6-3

Formable

DP600

Almost No Formability

AZ31B-O 1 mm 5500 V

PNNL Test AZ-1

FAILURE AT RADIUS

MAGNESIUM

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Technical Progress (Determination of FLDo) Task 1.3 – Characterize High-Rate Formability

True eq. plastic strain

Model 1 5182-O

1 mm 8500 V

PNNL Test T-71

True eq. plastic strain

Model 2

PNNL Test T-74

PNNL Test T-74

5182-O 1 mm

8500 V

Novel specimen geometries developed to determine plane-strain formability during PPF

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Technical Progress FLD at High-Strain-Rates during PPF

•Enhanced formability is observed in Al during PPF: •FREE-FORMING () and CONICAL-DIE() •Strain-rates ~4000/s and up

•DEFORMATION HISTORY QUANTIFIED

PPF high-rate forming vs.

quasi-static forming (Reynold’s data)

All data in engineering units

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

-0.5 -0.4 -0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4 0.5

Maj

or S

trai

n

Minor Strain

T-30 - 6500V Conical Die

T-64 - 9900V Conical Die

T-74 - 8500V Free-forming

T-74 - 8500V Free-forming

Safe,Conical Die(est. ~1700/s

at apex)

Incipient

Safe, Conical Die

(~740/s)

Safe

Free-form(~3900/s)

Forming Limit Diagram for 5182-O Al•Strain-rate amplification at non-apex locations, strain-rate in die-interior ~ 5000/s (estimated)

PNNL Test T-74

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Technical Progress (Mechanical Characterization) Task 2.1 – Constitutive Relations

• Tensile behavior quantified at quasi-static and high-strain-rates • Constitutive equations are used to model sheet behavior

during pulse-pressure forming

0

100

200

300

400

500

0 5 10 15 20 25 30 35 40

0.001/s0.01/s0.1/s1000/s2000/s2400/s

Eng

inee

ring

Stre

ss (M

Pa)

Engineering Strain (%)

AZ31B-O, Rolling DirectionTension, Room Temperature

AZ31B

Test data from Prof. K.S. Vecchio, UC San Diego

0

100

200

300

400

500

0 5 10 15 20 25 30 35 40

0.001/s0.01/s0.1/s1000/s2000/s2400/s

Eng

inee

ring

Stre

ss (M

Pa)

Engineering Strain (%)

Al 5182-O, Rolling DirectionTension, Room Temperature

5182-O Al

0

200

400

600

800

1000

0 5 10 15 20 25 30 35 40

0.001/s0.01/s0.1/s1000/s2000/s2400/s

Eng

inee

ring

Stre

ss (M

Pa)

Engineering Strain (%)

DP600, Rolling DirectionTension, Room Temperature

DP600

Technical Progress Constitutive Model w/ Variable Strain Rate Sensitivity

150

200

250

300

350

400

450

0.001 0.01 0.1 1 10 100 1000 10000

Flow

Stre

ss (M

Pa)

Strain Rate (1/sec)

Comparison of Higashi Experiments Results with Model Predicted Flow Stress

Experiment @ Strain = 0.05 Experiment @ Strain = 0.1Experiment @ Strain = 0.15 Experiment @ Strain = 0.2Model @ Strain=0.05 Model @ Strain=0.1Model @ Strain= 0.15 Model @ Strain=0.2

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K = 538 n = 0.292 A = 2.47x10-5

mquasistatic = -0.0227

Constitutive Model Adapt Hollomon Equation to capture variable strain rate sensitivity (m)

Higashi, K., et al., The Microstructural Evolution During Deformation under Serveral Strain Rates in Commercial 5182 Aluminum Alloy. Journal De Physique IV, Colloque C3, October 1991. p. C3-347.

Technical Progress M-K Method Predictions of Forming Limits

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

-0.6 -0.5 -0.4 -0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4 0.5

Maj

or St

rain

(Tru

e)

Minor Strain (True)

Theoretical Forming Limit Diagrams - Influence of m-value

ρ=1

ρ=0.5

ρ=0.01

m=0

m=0.02

m=0.04

m=0.06

Hosford Yield Criteria Constantsa=8R=0.7

Constitutive Model Constantsn=0.25m =0, 0.02, 0.04, and 0.06

M-K Constantsf=0.99

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Use a classical M-K method imperfection model using

Anisotropic yield locus High rate constitutive model

M-K method capture the influence of the strain rate sensitivity of the materials

Technical Progress – Model Validation Comparing Formability Model to Experiments

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0.5

-0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4

Maj

or S

trai

n (T

rue)

Minor Strain (True)

Incipent Neck

Safe

Theoretical FLD

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K = 560 n = 0.303 A = 6.73x10-6

mquasistatic = -0.0022 f = 0.995

y = -2E+07x6 + 2E+07x5 - 7E+06x4 + 1E+06x3 - 74445x2 + 1850.7x

0

200

400

600

800

1000

1200

1400

1600

1800

2000

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7

Effe

ctiv

e Pl

astic

Str

ain

Rate

Effective Plastic Strain

Effective Plastic Strain and Strain Rate for T74 Apex

Experimental Results Free Forming with plane strain specimen. Polynomial

Curve Fit.

Approximate the experimental data using a polynomial curve fit to describe the relation between effective plastic strain rate and effective plastic strain

Formability model accuracy is validated through experiments

M-K method approach Modified Hollomon relation Polynomial fit above

Technical Progress Parametric Investigation of Formability

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

-0.6 -0.5 -0.4 -0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4 0.5

Maj

or S

trai

n (T

rue)

Minor Strain (True)

Theoretical Forming Limit Diagrams: Cases 1 Through 5

Case 1

Case 5

Case 4

Case 3

Case 2

ρ=1

ρ=0.5

ρ=0.01

Quasistatic Case

AA5182

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0

2000

4000

6000

8000

10000

12000

0 0.2 0.4 0.6 0.8 1

Effe

ctiv

e Pl

astic

Str

ain

Rate

(1/s

ec)

Effective Plastic Strain (True)

Ideal Sinusoidal Waveforms

Case 5

Case 2

Case 3

Case 4

Case 1

Five parametric cases studied where the maximum strain rate was modeled between quasistatic and 10,000/sec

Parametric analysis shows the importance of the peak strain rate on the formability of the AA5182 materials.

Project Plan Technology Transition including Industry Partners

Industrial partners: GM, Ford, and Chrysler: Review project progress Guidance on material and process priorities Results available for internal process development Review commercialization opportunities

PNNL has partnered with OEM and materials suppliers who have active development programs in this topic area. The research plans and results are actively shared with those collaborative partners

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Future Work (FY12-FY14)

Follow-on work Enhanced Room-Temperature Formability in High-Strength Aluminum Alloys through Pulse-Pressure Forming

Evaluating the formability and demonstration of forming for 6000 series and 7000 series heat treatable Al alloys

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Summary Unique Experimental Capability Yields Unique Results

Time-resolved measurements of full-field deformation during PPF High-rate forming behavior quantified for Al Safe plane-strains as high as ~50% at ~3900/s peak strain-rate observed in free-forming of aluminum Safe plane-strains of ~65% at ~2000/s peak strain-rate (apex) measured when aluminum is formed in a conical die

Mechanical Properties Characterized the mechanical properties of AA5182, AZ31, and DP600 sheet materials from quasistatic to 2.5x10^3/sec Developed a modified power law model that accurately described the properites

Formability Modeling Applied the M-K method model along with the newly develop constitutive model to accurately predict experimentally observed formability results Conducted a parametric analysis show the effect of strain rate on formability

Publications 7 journal and conference articles published, submitted, and in preparation

Technical Back-up Slides

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Introduction - Technical Barriers

lack of understanding of the formability and strain rates that develop during PPF processing lack of validated constitutive relations for lightweight materials during PPF processing lack of validation of finite element simulation of PPF processing

Tamhane, A; Altynnova, M; Daehn, G.; 1996. Effect of Sample Size on the Ductility in Electromagnetic Ring Expansion; Scripta Materialia, Vol. 34, No.8, pp1345-1350.

Golovashchenko, S; and Mamutov, V.; 2005. Electrohydraulic Forming of Automotive Panels; Symposium on Global Innovations in Materials Processing & Manufacturing, TMS.

Project Plan Detailed Gap Analysis

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Technical challenges Today Tomorrow

how to get

there

Task 1 Formability and Fracture of Metals during PPF

1A lack of method to characterize strain rate during PPF

No detailed understanding of strain rates during PPF processes Apparatus to measure strain rates during PPF 1.1

1B

lack of understanding of the strain rates and strain rate variability developed during PPF

Estimates of strain rate based on total deformation in final parts/specimens and estimated process time process

A detailed understanding of the variable strain rate developed during single pulse PPF 1.2

1C

Lack of understanding of the influence of incremental PPF on sheet metal formability.

Some experience suggest incremental PPF may be more favorable than single pulse PPF from an overall material formability and properties standpoint.

A detailed understanding of how incremental forming influences sheet metal formability and properties 1.3-1.4

Task 2

Microstructure and mechanical property evolution during PPF

2A

Lack of validated constitutive relations for automotive materials during PPF processing

Understanding of the detailed strain rate and strain rate variability during PPF processes is unknown

PPF laboratory experiments that detail strain rates, and a set of validated constituent relations for relevant automotive materials 2.1

2B

Lack of understanding of the microstructure and post-forming properties of materials subject to PPF

Most R&D limited to formability investigations, with limited research on the microstructure evolution and post-forming properties

Complete investigation of the microstructure and crystallographic texture evolution during PPF, and a detailed characterization of the post-forming properties of automotive lightweight materials. 2.2-2.3

Task 3 Numerical simulation of PPF process

3A

Limited constitutive relations and detailed experimentation to validate FEA of PPF

PPF is a process that has a duration of microseconds, and little or no detailed strain data is available for validation

Detailed characterization of the strain rate coupled with numerical simulation comparisons to validate FEA predictions of PPF 3.1-3.2