Optimized Steel Solutions for

Roof Strength Using AHSS

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Guofei ChenAutomotive Center

United States Steel Corporation

Outline

• Introduction

• Baseline Model

• Optimization Without Design Change

• Design Change with Steel Inserts

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• Design Change with Steel Inserts

• Optimization With Design Changes

• Design Comparisons

• Summary

Introduction

• In August 2005, NHTSA proposed to increase the roof strength requirement

under FMVSS216 from 1.5 to 2.5 times unloaded vehicle weight (UVW).

• The combination of occupant safety and the new fuel economy standard presents

a challenge to automakers to meet the increased roof load requirements with the

least weight and cost penalties.

• Advanced High Strength Steels are being effectively utilized for vehicle weight

reduction while maintaining or improving safety, durability and NVH

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reduction while maintaining or improving safety, durability and NVH

performance.

• This study focuses on steel only design solutions with the use of AHSS and CAE

optimization technology.

• The target is to achieve a roof strength of 3 times UVW within 4.5 inch (114mm)

load platen travel, 20% safety margin over the new FMVSS 216 requirements.

A/SP MEARS Phase I – With Nylon Inserts

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THK: 1.3mm

MAT: DP590

THK: 0.8mm

MAT: DR210

THK: 0.8mm

MAT: DP980THK: 1.2mm

MAT: DP980

Cab Mass: 500.1kg

Load Factor: 3.05

(Nylon Inserts are located in the A-Pillar and C-Pillar)

A/SP MEARS Phase I – With Nylon Inserts

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THK: 0.9mm

MAT: DQSK

THK: 0.9mm

MAT: DQSK

THK: 1.2mm

MAT: Boron1550

THK: 1.1mm

MAT: DP590

THK: 1.8mm

MAT: DP590THK: 0.8mm

MAT: Boron1550

THK: 0.7mm

MAT: DP780

THK: 0.8mm

MAT: HSLA350

THK: 1.2mm

MAT: HSLA350

MAT: DR210

Baseline Model

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• Built a baseline model from the A/SP MEARS phase 1 model with nylon inserts

• Removed nylon inserts and unnecessary contact definitions

• Increased time step (1.0 1.3 µs) and moving speed (1 3 m/s) of the rigid plate

• Decreased the CPU time from 15 hours to 3 hours with 4 CPUs for each run

Create a Reduced Model for Optimization

A/SP MEARS Phase I Model

Gauge and Material (AHSS) Optimization

w/o Design Change

Methodology Schematic

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Concept Designs

Add Steel Inserts to Improve Crush Load

Update the Model with Optimal Steel Inserts

Gauge and Material (AHSS) Optimization

With Optimal Steel Inserts

AHSS Grades

800

1200

1600

2000

Str

ess (

MP

a)

HSLA350

DP590

DP780

DP980

Boron1550

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0

400

800

0 0.05 0.1 0.15 0.2 0.25

Plastic strain

Str

ess (

MP

a)

Parts for Optimization

Part Name MaterialGauge Range

(mm)

A_Pillar_Inner HSLA350 - Boron1550 0.6 - 2.2

A_Pillar_Rnf HSLA350 - Boron1550 0.6 - 2.2

BSO_Apillar HSLA350 - Boron1550 0.6 - 2.2

BSO_Cpillar HSLA350 - Boron1550 0.6 - 2.2

C_Pillar_Up HSLA350 - Boron1550 0.6 - 2.2

C_Pillar_Low HSLA350 - Boron1550 0.6 - 2.2

Header_Fr_Up HSLA350 - Boron1550 0.6 - 2.2

Header_Fr_Low HSLA350 - Boron1550 0.6 - 2.2

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Header_Fr_Low HSLA350 - Boron1550 0.6 - 2.2

Header_Rr_Up/C_Jt_Rnf HSLA350 - Boron1550 0.6 - 2.2

Header_Rr_Low HSLA350 - Boron1550 0.6 - 2.2

Roof_Bow HSLA350 - Boron1550 0.6 - 2.2

Roof_Rail_Inner HSLA350 - Boron1550 0.6 - 2.2

Roof_Rail_Outer HSLA350 - Boron1550 0.6 - 2.2

• 13 parts for material and gauge optimization w/o design changes

• Optimization software: HyperStudy and LS-Dyna

• Optimization objective: minimum mass

Constraints: roof crush load factor > 3.0

495

500

505

510

Ma

ss

(k

g)

1.5

2

2.5

3

3.5

Cru

sh

Lo

ad

Fa

cto

r

Cab Mass

Crush Load Factor

Optimization Results – With Boron1550

Best

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490

0 5 10 15 20 25 30 35 40

Iteration Number

1

Optimization Results – With Boron1550

THK: 1.54mm

MAT: Boron1550

THK: 1.0mm

MAT: DP590

THK: 0.7mm

MAT: DP980THK: 0.8mm

MAT: DP980

Cab Mass: 501.6kg

Load Factor: 3.00

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THK: 0.69mm

MAT: TRIP780

THK: 1.61mm

MAT: TRIP780THK: 1.24mm

MAT: Boron1550

THK: 1.32mm

MAT: Boron1550

THK: 0.97mm

MAT: Boron1550THK: 1.29mm

MAT: Boron1550

THK: 0.79mm

MAT: DP780

THK: 1.0mm

MAT: DP590

THK: 0.9mm

MAT: DP590

Optimization Results – No Boron1550

THK: 2.2mm

MAT: DP590

THK: 1.02mm

MAT: DP590

THK: 0.71mm

MAT: DP980THK: 0.82mm

MAT: DP980

Cab Mass: 505.6kg

Load Factor: 2.98

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THK: 0.74mm

MAT: TRIP780

THK: 1.78mm

MAT: TRIP780THK: 1.49mm

MAT: DP980

THK: 1.45mm

MAT: DP780

THK: 1.08mm

MAT: DP780THK: 1.36mm

MAT: DP980

THK: 0.8mm

MAT: DP780

THK: 0.96mm

MAT: DP590

THK: 1.02mm

MAT: DP590

Plastic Strains on Roof Structures

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Steel Inserts In Roof Rails

Insert Case #1 Insert Case #2

Section Cut Section Cut

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Roof Bow Location

Original Location 90mm Forward

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Reinforcement at C-Pillar

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Reinforcement

DP980 or Boron1550

Tube at C-Pillar

Tube

1.5mm DP590

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1.5mm DP590

Reinforcement Tube at A-Pillar

Reinforcement - Tube

DP780

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A-Pillar Extended

ExtendedExtended

Extended

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Flange Added

Extended

Flange Added

A-Pillar Extended

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After Extension

Roof Crush Performance With Steel Inserts

�Add C-Pillar Reinforcement

� Remove Rear Header Upper

�Add A-Pillar Reinforcement Tube

� Extend A-Pillar

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Optimization Results –

With Boron1550 & Steel Inserts

495

500

505

Ca

b M

as

s (

kg

)

1.5

2

2.5

3

3.5

Cru

sh

Lo

ad

Fa

tco

r

Cab Mass (kg)

Crush Load Factor

Best

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490

0 5 10 15 20 25 30 35

Iteration Number

1

Crush Load Factor

THK: 1.31mm

MAT: Boron1550

THK: 0.61mm

MAT: DP590

THK: 1.09mm

MAT: Boron1550THK: 0.99mm

MAT: Boron1550

Cab Mass: 496.6kg

Load Factor: 3.00

Optimization Results –

With Boron1550 & Steel Inserts

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THK: 0.63mm

MAT: TRIP780

THK: 1.34mm

MAT: TRIP780

THK: 1.53mm

MAT: Boron1550

THK: 0.96mm

MAT: Boron1550

THK: 0.80mm

MAT: Boron1550

THK: 0.60mm

MAT: Boron1550

THK: 0.60mm

MAT: DP780

THK: 0.62mm

MAT: DP590

THK: 0.64mm

MAT: DP590

Optimization Results –

With Steel Inserts, No Boron1550

THK: 1.41mm

MAT: DP590

THK: 0.86mm

MAT: DP590

THK: 1.23mm

MAT: DP980THK: 1.22mm

MAT: DP980

Cab Mass: 501.3kg

Load Factor: 3.00

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THK: 0.76mm

MAT: TRIP780

THK: 1.65mm

MAT: TRIP780

THK: 1.60mm

MAT: DP980

THK: 1.26mm

MAT: DP780

THK: 0.90mm

MAT: DP780

THK: 0.71mm

MAT: DP980

THK: 0.60mm

MAT: DP780

THK: 0.60mm

MAT: DP590

THK: 0.60mm

MAT: DP590

Design Comparisons

Components

A/SP Phase I Nylon Inserts

Optimized

Optimized To DP980

Optimized To Boron1550

Steel Inserts and Optimized To

DP980

Steel Inserts and

Optimized To Boron1550

Mass: 500.1kg Mass: 505.6kg Mass: 501.6kg Mass: 501.3kg Mass: 496.6kg

Load: 3.0 Load: 3.0 Load: 3.0 Load: 3.0 Load: 3.0

MAT THK(mm) MAT THK(mm) MAT THK(mm) MAT THK(mm) MAT THK(mm)

A_Pillar_Inner DP590 1.1 DP780 1.45 Boron1550 1.32 DP780 1.26 Boron1550 0.96

A_Pillar_Rnf Boron1550 1.2 DP980 1.49 Boron1550 1.24 DP980 1.6 Boron1550 1.53

BSO_Apillar DQSK 0.9 TRIP780 0.74 TRIP780 0.69 TRIP780 0.76 TRIP780 0.63

BSO_Cpillar DQSK 0.9 TRIP780 1.78 TRIP780 1.61 TRIP780 1.65 TRIP780 1.34

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BSO_Cpillar DQSK 0.9 TRIP780 1.78 TRIP780 1.61 TRIP780 1.65 TRIP780 1.34

C_Pillar_Up DP590 1.3 DP590 2.2 Boron1550 1.54 DP590 1.41 Boron1550 1.31

C_Pillar_Low DP590 1.8/.8 DP780 1.08 Boron1550 0.97 DP780 0.9 Boron1550 0.8

Header_Fr_Up HSLA350 0.8 DP590 0.96 DP590 1 DP590 0.6 DP590 0.62

Header_Fr_Low HSLA350 1.2 DP590 1.02 DP590 0.9 DP780 0.6 DP590 0.64

Header_Rr_Up/C_Rnf DP980 1.2 DP980 0.82 DP980 0.8 DP980 1.22 Boron1550 0.99

Header_Rr_Low DP980 0.8 DP980 0.71 DP980 0.7 DP980 1.23 DP980 1.09

Roof_Bow DR210 0.8 DP590 1.02 DP590 1 DP590 0.86 DP590 0.61

Roof_Rail_Inner DP780 0.7 DP780 0.8 DP780 0.79 DP780 0.6 DP780 0.6

Roof_Rail_Outer Boron1550 0.8 DP980 1.36 Boron1550 1.29 DP980 0.71 Boron1550 0.6

Summary

• Steel inserts at A-pillar lower and C-pillar upper are effective to

improve roof crush performance for the B-pillarless pickup truck.

• The optimized steel only design meets the new roof strength

regulation with 3.5kg mass savings compared to the A/SP phase I

nylon insert design, and potential cost savings can also be achieved.

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• Using hot-stamped boron steel for A-pillar, C-pillar and roof rail for

roof crush offers about 4kg more mass savings than using DP steels.