12 AUDI Haffner Engl

7/25/2019 12 AUDI Haffner Engl

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P. Haffner N/EL-331.Mai 2001

FatigueFatigue lifelife predictionprediction of MIG -of MIG -WeldedWeldedAluminiumAluminium StructuresStructures

1. Virtual fatigue life prediction in developement of Aluminium Space Frames

5. Summary

Analysis methods and its influence in car frame concept developement

Difficulties in usage of virtual fatigue life prediction methods

3. One step testing in correlation to FEMFAT WELD analysis

T-joint specimen

H-specimen

Peeling-specimen

4. FEMFAT WELD damage analysis in correlation to real car frame testing

Longitudinal Side Vertical testing in relation to the Audi A2

2. Main tasks for fatigue life analysis in the Aluminum Space Frame

Material combinations and joining techniques


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Virtual fatigue life prediction in developement of Aluminium Space Frames

Analysis methods and its influence in car frame concept developement

Prediction poignancy of FE - Methods is improving steadily

Predictions from crash-, dynamics- and stress analysis have become a major influence on the

construction of modern car frames

The bandwidth between optimised function compliance and structural reserves is getting smaller

Predictions of fatigue life for the complete car frame come mostly from real car testings, like actual

driving tests or testing rigs

Aim:Integration of the virtual fatigue life prediction methods into the early developement process


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Difficulties in usage of virtual fatigue life prediction methods:

Bg effort required to create accurate FE - models and the emulation of joining techniques

Emulation of the boundary conditions

- Modelling of the interface areas to the axis system

- Transmission of the load- time dependencies from wheel to frame

- Definition of the load input locations in the Space Frame model

Virtual fatigue life prediction in developement of Aluminium Space Frames

- Definition of the bearing block location in the Space Frame model


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Connection to the longitutinal beam

Example: Shock absorber connection area, Audi A2 (current state)Main tasks for fatigue life analysis in the Aluminium Space Frame

Casting parts

MIG welding


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One step testing in correlation to FEMFAT WELD analysis

Fatigue testing on T-joint-specimen

T - joint


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Profile cross sections used in the testings

One step testing in correlation to FEMFAT WELD analysis T - joint


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F

clamped boundarys

Welding area

a

b

a

b

FE - Model and weld definition

Element edge length 5mm

R = 1 mm

aT-joint weld

bbutt weld

One step testing in correlation to FEMFAT WELD analysis T - joint

Edge Element thickness increased

for profile P2


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0

5

10

15

20

25

30

35

40

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170

Knotennummern

V

onMisesSpannunegen[M

Pa]

.

P2

P3

Profilform : P2

Profilform : P3

Nodal stresses v. Mises

Results of NASTRAN stress analysis

Bending stress amplitude = 40 MPa

T - jointOne step testing in correlation to FEMFAT WELD analysis


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FEMFAT WELD damage plot Crack initiation area in testingOne step testing in correlation to FEMFAT WELD analysis

Bending stress amplitude = 40 MPa

Cycles to Failure = 900

Maximum damage = 1.0

Model : R = 1 mm Profil P3

Standard element edge length 5mm

Stress ratio = -1

T - joint


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Testing results in correlation to FEMFAT WELD Damage analysisOne step testing in correlation to FEMFAT WELD analysis

Aluminium T-Sto Verbindung

1

10

100

1,00E+01 1,00E+02 1,00E+03 1,00E+04 1,00E+05 1,00E+06 1,00E+07

Anrischwingspielzahl Na

Biege

nennspannungsamplitude

s

[MPa]

P3

P2

Versuchsergebnisse P2, P3

FEMFAT-Ergebnisse

testing results P2, P3

FEMFAT WELD results

cycles to failure

bend

ingstressamplitude

[MPa]

Aluminium t-joint specimen

T - joint


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H - specimenOne step testing in correlation to FEMFAT WELD analysis


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Load application

Overlap weldMIG 3x50 mm


clamped boundary on bottom side


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H-Specimen: Overlap MIG Weld 3x50mm

Material: A6009

Comparison of Mean Stress infuence

1,00E+04

1,00E+05

1,00E+02 1,00E+03 1,00E+04 1,00E+05 1,00E+06

Cycles

LoadAmplitude

(N)

r = -1

r = 0.1

testing (r = 0.1)

k = 4.06

k = 4.00

k = 4.04

cycles to failure

loadamplitude

[N]

Testing results in correlation to FEMFAT WELD damage analysis


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Overlap weld

Load application

clamped boundary

Peeling - specimenOne step testing in FEMFAT WELD analysis


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Peeling - specimenOne step testing in FEMFAT WELD analysis

Peeling specimen: Overlap MIG Weld

Material: AlMgSiMn

Comparison of Mean Stress influence

1,00E+02

1,00E+03

1,00E+04

1,00E+02 1,00E+03 1,00E+04 1,00E+05 1,00E+06

Cycles

LoadAmplitude

(N)

r = -1

r = 0.1

k = 4.62

k = 4.45

loadamplitude

[N]

cycles to failure

Results from FEMFAT WELD damage analysis


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6 Hydrolic cylinders

Car frame clamped

Springs/damper as

rigid beams

Testing VA, HA

Driving measurement

Forces, Moments on the wheel

Fk(t), M k (t), k=x,y,z

Testing rig configuration

Longitudinal Side Vertical testing (LSV)

Car frame testing


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Overlap weld

T-joint weld

Car frame interface

areas

FZ, MZ

FX, MX

FY, MY

Load- time

dependencies

in wheel mid-point

FEMFAT WELD damage analysis in correlation to real car frame testing Audi A2(early state of

developement)


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Overlap weld

T-joint weld

Car frame interface

areas

FZ, MZ

FX, MX

FY, MY

Load- time

dependencies

in wheel mid-pointCrack prediction from FEMFAT WELD

FEMFAT WELD damage analysis in correlation to real car frame testing Audi A2(early state of

developement)


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Crack predicton from FEMFAT WELD

FEMFAT WELDFEMFAT WELD damagedamagePlotPlot

Fatigue life prediction < 200 km EVP

ca. 4000 km normal driving

FEMFAT WELD damage analysis in correlation to testing reults

FEMFAT WELD damage analysis in correlation to real car frame testing

cracks on MIG- welds

Testing resultsTesting results

Fatigue life ca. 8000 km EVP

ca. 160000 km normal driving

Audi A2(early state of

developement)

F iF ti liflif di idi ti f MIGf MIG W ld dW ld d Al i iAl i i SSt t


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Shock absorber connection area optimised for fatigue Audi A2(current state)

The optimisation in the welding areas is done by the classic stress analysis

Real testings were nessecary for cross validation

The FEMFAT WELD prediction poingnancy was comparable to a vertical load stressanalysis at the shock absorber connection

F tiF ti liflif di tidi ti f MIGf MIG W ld dW ld d Al i iAl i i St tSt t


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Summary

One step testing

Damage locations are correctly identified

Fatigue life prediction until crack initiation is on the conservative side

Predictions with mean stress influence lead, in some cases, to disproportional results

This effect is more noticable under peeling conditions than under shear tension

Car frame testing

The location of first crack initiation can be identified with relatively high confidence

Other real crack locations are also able to be predicted using FEMFAT WELD

However, not all cracks can be identified

There are also cracks identified with FEMFAT WELD, that are not problematic in real testings

Absolute fatigue life predictions with FEMFAT WELD for particular weldings are extremly conservative

F tiFatig e liflife di tiprediction f MIGof MIG W ld dWelded Al i iAl mini m St tStr ct res


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For the FEMFAT WELD tool to be as powerful as crash simulation

in the Space frame concept developement, it is required to get the

prediction much closer to the real fatigue life time

12 AUDI Haffner Engl

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