1. October 2015
Master thesis
Advanced CAE Methodologies for new
AHSS material application in body in
white
Hosting Company:
Centro Ricerche Fiat (CRF)
Academic tutor:
Giovanni Belingardi
Company Tutors:
Rosanna Brun
Alessandro Agnello
Author:
Mohammad Sharif Nategh

2. 2
Contents
1. Introduction ..............................................................................................................................................5
1.2 Development History..........................................................................................................................5
1.3 current projects...................................................................................................................................6
2. Automotive Steel grades overview...........................................................................................................8
2.1 AHSS grades ......................................................................................................................................10
3. Automotive Steel Performance Advantages...........................................................................................11
3.1 Cost ...................................................................................................................................................12
3.2 Safety ................................................................................................................................................13
3.3 Emissions...........................................................................................................................................14
3.4 Life Cycle Assessment (LCA)..............................................................................................................15
4. Crash Performance..................................................................................................................................16
4.1 Crash Performance............................................................................................................................16
4.2 Stiffness.............................................................................................................................................17
5. Metallurgy of AHSS .................................................................................................................................18
5.1 Dual Phase (DP) Steel........................................................................................................................18
5.2 Transformation Induced Plasticity (TRIP) Steel:................................................................................21
5.3 Complex Phase (CP) Steel .................................................................................................................23
5.4 Martensitic (MS) Steel ......................................................................................................................24
5.5 Ferritic-Bainitic (FB) Steel..................................................................................................................26
5.6 Twinning-Induced Plasticity (TWIP) Steel .........................................................................................26
5.7 Hot-Formed (HF) Steel ......................................................................................................................27
5.8 Evolving AHSS Types .........................................................................................................................28
5.9 Conventional Low- and High-Strength Automotive Sheet Steels .....................................................28
5.9.1 Mild Steels..................................................................................................................................28
5.9.2 Interstitial-Free (IF) Steels (Low Strength and High Strength)...................................................29
5.9.3 Bake Hardenable (BH) Steels .....................................................................................................31
5.9.4 High-Strength Low-Alloy (HSLA) Steels......................................................................................32
6. Forming and manufacturing ...................................................................................................................34
6.1 Material Characteristics and AHSS material parameters..................................................................34
6.1.1 Stress-strain Curves (engineering and true) ..............................................................................35
6.1.2 Elastic modulus (E).....................................................................................................................36

3. 3
6.1.3 Yield Strength.............................................................................................................................36
6.1.4 Work hardening exponent (n-values)........................................................................................37
6.1.5 Tensile strength - Uniform Elongation.......................................................................................40
6.1.6 Fracture – Total Elongation........................................................................................................40
6.1.7 Anisotropy ratio – r-value..........................................................................................................42
6.1.8 Forming Limit Curve (FLC or FLD)-Local/Thickness Neck...........................................................44
6.2 Deformation Limits ...........................................................................................................................46
6.2.1 Forming Limit Curves (FLC) ........................................................................................................46
6.2.2 Edge Stretching Limits................................................................................................................51
6.2.3 Stretch bend limits.....................................................................................................................53
6.3 material characteristics of 3rd
generation of DP600 which is nominated DP600HD ........................54
6.3.1 3rd
generation of DP600 (DP600HD) material characteristics ...................................................54
6.3.2 3rd
generation of DP600 (DP600HD) FLD diagram .....................................................................54
6.3.3 3rd
generation of DP600 (DP600HD) Stress-Strain Curve...........................................................55
6.3.4 3rd
generation of DP600 (DP600HD) and common DP600 comparison ....................................56
6.3.5 3rd
generation of DP600 (DP600HD) and Mild steels or low carbon steels ...............................63
6.3.6 3rd
generation of DP600 (DP600HD) and IF (interstitial-Free) steels.........................................65
6.3.7 3rd
generation of DP600 (DP600HD) and Bake-hardening (BH) Steels ......................................67
6.3.8 3rd
generation of DP600 (DP600HD) and High-strength low-alloy Steels (HSLA) ......................70
6.4 Tool requirements.............................................................................................................................74
6.4.1 Tool material..............................................................................................................................75
6.4.2 Tool Design.................................................................................................................................76
7. Simulation ...............................................................................................................................................77
7.1 Advantages for AHSS Forming ..........................................................................................................77
8. Numerical comparison between standard AHSS and new generations.................................................80
8.1 Case study 1 ......................................................................................................................................81
8.2 Case study 2 ......................................................................................................................................89
8.3 Case study 3 ......................................................................................................................................97
8.4 Case study 4 ....................................................................................................................................103
8.5 Case study 5 ....................................................................................................................................109
8.6 Case study 6 ....................................................................................................................................114
8.7 Case study 7 ....................................................................................................................................119

4. 4
9. Conclusion.............................................................................................................................................123
References ................................................................................................................................................129