CHS Theme Day at Volvo Cars, 170906

Simulation models for development of components with tailored material properties

Professor Mats OldenburgLuleå University of Technology

Presentation outline:- The press hardening process- Process modelling- Components with tailored material properties- Challenges and opportunities

Press hardening – from innovation and research in Luleå toa global technology

Background • Manufacturing of ultra-highstrength steel components

• Thermo-mechanical process

• Boron alloyed steel

• Simultaneous forming andquenching

• Innovation from Luleå, Sweden, 40 years ago.

• Cooperation between the university and the iron works NJA (nowSSAB)

• Industrialized by Plannja Hardtech (now Gestamp Hardtech)

• Today the globally dominant technology for weight reduction ofvehicle structures

Interactions involved in the thermo-mechanical formingprocess

1 - Deformation dependent thermal boundary conditions

2a - Mechanical properties depend on temperature

2b - Thermal expansion

3a - Latent heat due to phase transformations

3b - Thermal properties depend on microstructure

4 – Microstructure evolution depend on temperature

5a - Mechanical properties depend on microstructure evolution

5b - Volume change due to phase transformations

5c - Transformation plasticity

6 - Phase transformations depend on stress and strain

Research: Process modelling

Advanced automotiveapplications

Structural components withdistributed tailored mechanicalproperties

• Side rails

• B-pillar

• Other structural components

Research: Process modelling

Results – final component

Measured and calculatedforming force

Maximum springback = 0.29 mm (negative, scaled 20 times)

Martensite

(Åkerström, Oldenburg: Numerical simulation of a thermo-mechanical sheet forming experiment, Numisheet 2008, Interlaken)

Tailored properties - process modelling

Formation of ferriteFormation of martensite

Tool model for studies of pressing sequence Steady state condition - temperature histories

Industrial application example, Gestamp Hardtech

Tooling compensation for cooling deformation of a tailored property component- Volvo XC90 A-pillar inner reinforcement

- Initial deformation range -2.4 to 3.3 mm

- Cooling deformation compensation in one step

- Production tool design based on simulation results

- Component within tolerances (+/- 1 mm) with only minor further adjustments of the production tool

Range -2.4 mm (blue) to 3.3 mm (red)

Out of plane cooling deformation Martensite content

Range 0.0% (blue) to 99.9% (red)

Paradigm shift

- Component and structure design include design of material properties that govern final performance

- The complete process chain is taken into account during technology development

- Technology developments creates new demands on accuracy in material and process modelling

- New demands on material and process modelling when performance simulations are directly linked to process simulation results

Challenges and opportunities

- Short term:

- Improved microstructure models that takesdifferent types of ferrite, bainite and martensiteinto account => better prediction of materialproperties and performance

- Model development for new steel grades andmanufacturing processes

- Accurate prediction of strength, deformation andfailure properties based on process simulations

- Long term:

- Accurate prediction of fatigue properties based onprocess simulations

- Material development based on simulationmodels, taking the complete process chain intoaccount

Example of cooperation between research and industrial development

Industrial partner

LTU, Solid Mechanics

Component function analysis

Analysis of hot stamping

Process simulation

Crash simulation and test

IMCOR DYNSYS

LOWHIPS

TiFORM I, II

20171996

OPTUS

PROCSIM II PROCSIM III

Tailored material properties

CHS Failure modelling

PROCSIM IV

OPTUS Hot

OPTUS II

Failure modelling and simulation

Wear modelling and simulation

OPTUS III

FFI Tool Wear Diecond

From quasi-static to high-speed (VHS) (20 m / s).

Laboratory resources Materials testing machines and Split-Hopkinson pressure bar

High Speed Test (VHS) of car structure component

15 m/s (54 km/h)15 m/s (54 km/h), max. velocity = 20 m/s, max. force = 100 kN

Laboratory resources

15 m/s (54 km/h), max. velocity = 20 m/s, max. force = 100 kN

Laboratory resources High Speed Test (VHS) of car structure component

Measured force

Measured velocity

Fast video camera, 50000 frames/sec, at 512x512 resolution

Laboratory resources High speed, high temperature strain field measurements using Digital

Speckle Photography, notched specimen

Boron steel sheet, heated to 900 DegC, fast cooling to 800 DegC, initial strain rate 200 /sec

Impact mechanics– Tensile testing of Inconel 718 at high temperatures and strain rates– High temperature compressive testing in Split Hopkinson Pressure Bar

0 0.1 0.2 0.3 0.4 0.5 0.6 0.70

100

200

300

400

500

600

700

True strain

True

stre

ss [M

Pa]

Strain rate ~4400 1/s

900oC1000oC1100oC

0 0.05 0.1 0.15 0.2 0.25 0.3 0.350

50

100

150

200

250

300

350

400

450

True strain

True

stre

ss [M

Pa]

Strain rate ~900 1/s

900oC1000oC1100oC

Laboratory resources

Hot tensile test at 800 DegC – austenite phaseAustenitisation at 900 DegC for 3 minutes, fast cooling to 800 DegC, strain rates = 1, 10, 50 and 200/sec

Engineering stress–strain curves

Laboratory resources

• The sixth international conference on hot forming and press hardeningwhere arranged by Luleå University of Technology, University of Kasseland AIST in Atlanta, Georgia, USA, 4 - 7 June, 2017.

6th International Conference on Hot Sheet Metal Forming of High-Performance Steel, CHS2 - 2017

• The seventh international conference on hot forming and presshardening where arranged by Luleå University of Technology in Luleå,Sweden, 2 - 5 June, 2019.

7th International Conference on Hot Sheet Metal Forming of High-Performance Steel, CHS2 - 2019

© Gestamp 2017

CHS Temadag

© Gestamp 2017 2

• Development of the OPTUS model started in 2005

• Cooperation with Ford Forschungszentrum Aachen (FFA), Volvo cars & Luleå university of technology

• Features that were considered lacking in models available in commercial software• Mesh size regularization • Capturing thickness dependent fracture elongation for shells

Background Failure prediction at Gestamp

© Gestamp 2017 3

The OPTUS model

𝐷𝐷 = 𝐴𝐴𝑙𝑙𝑡𝑡

2

𝑒𝑒𝐵𝐵 𝜀𝜀𝑝𝑝 −𝜀𝜀0 − 1 , 𝜀𝜀𝑝𝑝 ≥ 𝜀𝜀0, �𝝈𝝈 = 𝝈𝝈(1 − 𝐷𝐷)

• A = Material parameter

• B = Material parameter

• l = Characteristic element size

• t = sheet thickness

• 𝜀𝜀0 = localization threshold strain

© Gestamp 2017 4

The OPTUS model

Longitudinal coordinate

0

0,05

0,1

0,15

-2,5-1,5

-0,50,5

1,52,5

L0

x/t

a)

𝜀𝜀𝑝𝑝

Summary

• The predicted fracture strain is a function of stress state, mesh size and sheet thickness.

• Overall behavior is regularized with respect to mesh size

• Handles several sheet thicknesses without modification of input data

© Gestamp 2017 5

Failure prediction with reference to manufacturing history

Thermo-mechanical forming analysis

• Air cooling during transfer

• Forming and quenching

• Post cooling to obtain final shape, thickness and microstructure

Mapping

• Field variables

• Material properties / phase content

• Failure parameters

• geometry/ thickness

Crash analysis

• Force-displacement response

• Deformed geometry

• Area with failure

© Gestamp 2017 6

Failure prediction with reference to manufacturing history

• Approach based on mean-field homogenization

© Gestamp 2017 8

Rear side rail example

Rear side rail example

• Mesh division into property groups

• Flow curves and fracture properties of each group estimated with the MFH method

© Gestamp 2017 9

Rear side rail example

© Gestamp 2017

www.gestamp.com

© Gestamp 2017

Working for a Safer and Lighter Car