Simulation von Kerbeffekten durch Löcher und Schweißpunkte ... · Different Failure Mechanisms Research & Advanced Engineering 16 Horst Lanzerath Boron 1900 / N-mode 0 40 80 120

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


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Horst Lanzerath

Overview

• Introduction

• Need for Failure Modelling in Crash Simulation

• Summary

• Introduction


• Summary


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Horst Lanzerath

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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Horst Lanzerath

47 % Mild Steel

26 % Conventional HSS

18 % Advanced HSS

9 % Ultra HSS

Introduction – UHSS Applications in Ford Focus


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Horst Lanzerath


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



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Overview

• Introduction


• Summary


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Horst Lanzerath

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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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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Horst Lanzerath

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



GEOMETRICAL NOTCHES

(holes, cut-outs, …)

cut-outs in B-pillar reinforcement

Ø 10

14



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


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


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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Horst Lanzerath

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



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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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Horst Lanzerath

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

Documents

Simulation von Kerbeffekten durch Löcher und Schweißpunkte ... · Different Failure Mechanisms Research & Advanced Engineering 16 Horst Lanzerath Boron 1900 / N-mode 0 40 80 120