Research & Advanced Engineering
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Horst Lanzerath
Simulation von Kerbeffekten durch
Löcher und Schweißpunkte in
Karosseriebauteilen aus Ultra
Hochfesten Stählen
April 18th, 2012, Bad Nauheim
R&A Europe: H. Lanzerath, Aleksandar Bach, Hueseyin Cakir, Udo Brüx
Research & Advanced Engineering
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Horst Lanzerath
Overview
• Introduction
• Need for Failure Modelling in Crash Simulation
• Summary
• Introduction
• Need for Failure Modelling in Crash Simulation
• Summary
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Introduction – Crash Performance Evaluation
� Increasing Safety Performance Acceptance Criteria
� Increasing Demand for Affordable Light Weight Designs
� Increasing number of derivates on the same, global platform
• ECE 94.01 front offset
• FMVSS 208 front impact Occupant protection
• FMVSS 301 front impactfuel system integrity
• Euro NCAP front offset 64kph
• USNCAP – front impact • IIHS front offset impact
FRONT
REAR
SIDE
ROOF
• ECE 95.01 side impact
• FMVSS214 side impact• IIHS side impact
• Euro NCAP side impact 50kph
• USNCAP side crabbed barrier
• USNCAP side oblique pole
• FMVSS 301 rear impact
fuel system integrity• Rear deformable EU
barrier (70% 80kph 1250kg)
• FMVSS new rule 216 roof strength
• IIHS roof crush assessment (4,2 veh. weight)legal requirement
public domain
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47 % Mild Steel
26 % Conventional HSS
18 % Advanced HSS
9 % Ultra HSS
Introduction – UHSS Applications in Ford Focus
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Introduction – UHSS Applications in Ford Focus
MSW1200 DOCOL1400
Door Beams Rocker Reinforcement
cross member
1.8mm, MSW1200
2.6kg
MSW1200Rear Bumper Beam System
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Weight Save Boron vs. DP600
∆m = 5.2 kg/vehicle
Weight Reduction = 28 %
Implementation – 2006 (CD-Car)
• Standard Boron technologies
• Monolitic hot-formed parts
Implementation – 2011 (Focus)
• Advanced Boron technologies
• Tailor Rolled Blanks / hot-formed
Additional Weight Reduction = 1.4 kg
Introduction – UHSS Applications in Ford Focus
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Horst Lanzerath
Overview
• Introduction
• Need for Failure Modelling in Crash Simulation
• Summary
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Martensitic steels
•cold formed(e.g. DOCOL1400 M)
•hot formed(e.g. BORON1500)
Crash Properties of Steels
IF - SteelIF - Steel
Mild
Steel
Micro Alloyed High Strength Steel
BH and HS IF Steel
Martensitic SteelBoron
Steel
Dual Phase Steel
TRIP Steel
Dual Phase Steel
Complex Steel
Strength
Du
cti
lity
CONVENTIONAL steels
���� Low Strength
���� High Ductility
AHSS/UHSS
���� High Strength
���� Low Ductility
���� Sensitive to notches
� Light weight design ���� use of more AHSS/UHSS (thickness reduction)
� Light weight potential of UHSS cannot be utilised if material failure limits are not known
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Horst Lanzerath
t = 2mm
Crack starts at rectangular hole.
Observations in Prototype Parts
Failure mode and failure strain depend on:
• the local load situation (multiaxiality)
• the local material history• the local strain rate• …
Cracks start at welded areas.Prototype Parts shown
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Failure Modelling - Simulation Approach
Materialcharacterisation
-E, ρ, ν-Flowcurve
-Yield Locus-Fracture Limit Curves
Material Models(User Subroutines)
MF GenYld ®
Elasto-plastizität
CrachFEM ®
Versagensmodell
Commercial Solver
• Radioss• LS-Dyna
(explizit)
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Flow Curve
0.8
1.0
1.2
1.4
1.6
0.0 0.1 0.2 0.3 0.4 0.5 0.6True Strain [-]
Tru
e S
tre
ss
/ σσ σσ
y [
-]
Tensile Test
Layer Compression Test
Swift_Approximation
Strain rate sensitivity
( )( )
)2()1(
)2()1(
ln
ln
εε
σσ
&&=m( ) m
v
n
eqeqa εεεσ &⋅+⋅= 0
Uniform Elongation
Swift - equation Anisotropic behaviour
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Failure Modelling – Material Model
FRACTURE PROPERTIES(failure limit curves)
stress state
pla
stic s
tra
in a
t fr
act
ure
DNF
DSF
INST
DNF ductile normal fracture
DSF ductile shear fracture
INST instability
More testing & material characterisation required !
Shear Fracture
Normal Fracture
Instability
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One Element Tests
Component Tests
Substructure Tests
Full Vehicle Tests
MATERIAL
MODEL
CORRELATION
TEST-SIMULATION ?
CORRELATION
TEST-SIMULATION ?
yes
yes
yes
no
no no no
• Robustness
F •V=const= 2.5mm/s•s
m ax= 500mm
0 DGOF
0 DGOF
Failure Modelling – Systematic Validation
Systematic Validation Procedure
& Version Checker
CAE vs. Test
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MAT_1
MAT_2
CAE without failure modeling
MAT_1
MAT_2
CAE with failure modeling
Failure Modelling: Tool for Material Selection
Example:• Component tests on bumper beams• 2 different material grades investigated:
• MAT_1• MAT_2
Without failure modeling: MAT_1 would be the initially selected material
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1. Pure Material Failure
2. Geometrical Notches (Holes, Cut-edges, Rivets, …)
3. Metallurgical Notches (RSW, MIG-Welds, Laser-Welds, …)
Different Failure Mechanisms
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Boron 1900 / N-mode
0 40 80 120
Displacement [mm]
TEST_1
TEST_2
CAE
3Point Bending
of a Boron
Beam
CAE
TEST
Boron 1500
Different Failure Mechanisms - Pure Material Failure
Tests on Prototype Parts
F/2
F/2
Fo
rce
F
F
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A A
HAZ (heat affected zone)
section A-A
METALLURGICAL NOTCHES
heat affected zones (HAZ) of spot welds in UHSS
METALLURGICAL NOTCHES
heat affected zones (HAZ) of spot welds in UHSS
GEOMETRICAL NOTCHES
(holes, cut-outs, …)
cut-outs in B-pillar reinforcement
Ø 10
14
METALLURGICAL NOTCHES
heat affected zones (HAZ) of spot welds in UHSS
GEOMETRICAL NOTCHES
(holes, cut-outs, …)
FAILURE MODELLING
of NOTCHES
Ø 10
14
CAE methodology to predict material
failure due to notches
Different Failure Mechanisms - Notches
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0 10 20 30 40 50 60
Displacement [ mm ]
NO NOTCH
HOLE
SPOT WELD
3PB of Boron beam(with & without notches)
HOLE SPOT WELDNO NOTCH
Significantly reduced energy absorption and sudden failure !
Different Failure Mechanisms - Notches
Fo
rce
F
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epsPL
high
low
Discplacement [mm]
Imp
acto
r F
orc
e
CAE_STANDARD
CAE_REFINED
TEST
Refined mesh …
���� more accurate prediction of deflection behaviour including fracture
���� increase of CPU time
CAE_Standard CAE_Refined
Geometrical Notches – Holes
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Direction 0°
Direction 45°
Direction 90°
Hardness HV
Section A-A
Metallurgical Notches
AA
Base BaseHAZ HAZNugget
� HAZ = Heat Affect Zone
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Metallurgical Notches – Conventional Modelling
Spring-Element
Typical Crash-Modell:- ~ 2 Mio. Finite Elements
- Edge Length 5 - 10 mm- ~ 3500 Spot Welds
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Metallurgical Notches – Validation on Component Level
Conventional Modelling – Test vs. Simulation
Tests on Prototype Parts
Impactor: Force over Displacement
Conventional model for RSW not applicable to predict HAZ effects!
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Metallurgical Notches – Micro-Modelling
Properties:
- detailled geometrical representation
- local material properties- Mesh dependency
BaseHAZ
Weld-Nugget
A A
Section A-A� HAZ = Heat Affect Zone
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Micro-Modelling – Test vs. Simulation
Metallurgical Notches – Validation on Component Level
Tests on Prototype Parts
Impactor: Force over Displacement
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Comparison of CPU Time – Full Car SimulationS
imula
tio
n T
ime in h
Conventional Micro
1. Accurate,
2. Efficient.
New CAE Methods are required, which are
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What is “Multi-Domain” for Crash Simulation ?
source: Maciek Wronski (Altair), HTC Conference, 2010
� Arbitrary number of domains can be
specified within a Full Car Crash Model
� E.g. non-crash relevant parts can be
modelled with coarse meshes, while
safety critical components are
modelled in detail
� Each domain can have own time step
(element size)
� Optimized CPU usage
� Improved Failure Prediciton
RAD2RAD
DOMAIN A DOMAIN B DOMAIN C
Model 1
Model 2
� Increased computation accuracy at low CPU time increase
Model 1
Model 2
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STANDARD CAE
� no prediction of failure
Multi-Domain CAE
� accurate failure prediction
Side Pole Impact
Multi-Domain CAE: Validation on Full Vehicle Level
Standard CAE
Refined Mesh CAE
Multi-Domain CAE
Computational Time
Tests on Prototype Parts
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Design Solutions
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Reduce Notch Effects – Tailored Tempering
Source: TKSE
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Reduce Notch Effects – Tailored Properties
Source: GESTAMP
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Cut-edge moved in
less critical area
Reduce Notch Effects – Redesign
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Further Challenges for CAE
• New Boron Technologies (1900 MPa, Tailored Properties,
Softzones, …)
• New Manufacturing Processes (e.g. Form Blow Technology, …)
• Mechanical joining technologies (e.g. RIVTAC, SPR, FDS,
laser-welding,friction-element welding,…)
Source: Böllhoff Source: EJOT Source: EJOT
RIVTAC EJOT-Weld FDS
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Summary
• The trend in body structure design is to use more and more
materials that offer lightweight potential at affordable costs.
• UHSS offer significant weight saving potential
• In order to utilize UHSS in the best way
• Design guidelines need to be followed
• CAE optimization including the capability to predict failure
modes is required
• The consideration of these aspects
• Supports proper material selection
• Enables robust designs and efficient d’pment processes
• Avoids bad surprises at first prototypes
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