Weight and Cost Reduction of a Vehicle Component by Durability ...

Weight and Cost Reduction of a Vehicle 

Component by Durability Simulation 

Masaru Kabasawa 

Speaker: 

Dr.-Ing. R. Carmine 

Munich 

22.03.2006 

March 06 

- 1 -

Contents: 

• Objectives 

• CAE Approach for Fatigue Life Analysis 

• Modeling Procedure 

• Multi Body Simulation 

• Methodology of Durability Analysis 

• Fatigue Analysis for Road Load Data 

• Conclusion 

March 06 

- 2 -

Objectives: 

CAE based Assessment of the Structural Integrity of 

an Air Suspension System 

Components: 

• Frame 

• CLink 

(Trailing Arm) 

Tasks: 

• Cost and Weight Reduction 

• Stress Recovery and Fatigue Life Analysis for Road Load Data 

March 06 

- 3 -

CAE Approach for Fatigue Life Analysis: 

Virtual Testing 

• CAE Process: 

• What 

Finite Element based Fatigue Simulation 

+ + 

From LMS NEWS (IGEL Test Rig) 

from LMS NEWS (BMW Model) 

March 06 

- 4 -

CAE Approach for Fatigue Life Analysis: 

Work Flow 

• CAE Process: Fatigue Life Analysis 

„Load Model“: Multibody Model of Vehicle 

Input Data: Measured Wheel Loads (Forces + Moments) 

Output Data 

Component Loads 

F 

( t) M ( t) 

i 

, 

i 

„Stress Model“: FE Model Component 

From LMS NEWS (BMW) 

r 

σ ( x, 

t) 

i 

Input Data: Component loads 

Output Data: 

Stress-Time Series 

on Component 

Fatigue Life Prediction (FLP) 

Input Data: Stress-time Series on Component 

With Courtesy of AUDI 

r 

d( x) 

N( r 

x) 

Output Data: 

Life to Crack Initiation 

(Base Material, Welded Joints) 

March 06 

- 5 -

Modeling Procedure: 

Multi Body System of Rear Suspension 

Damper 

Left 

Lateral 

Arms 

Air 

Spring 

Flexible 

Frame 

Rigid 

Axle 

Damper 

Right 

Flexible 

CLink 

Right 

March 06 

- 6 -

Modeling Procedure: Multi Body Modeling: 

Air Spring Characteristics 

Nonlinear Dynamic Spring Rate 

Dependent of Total Weight: 

Laden: 2800 lbf 85 psi 

Unladen: 1000 lbf 32 psi 

Measured Dynamic Spring Rate 

Laden 

Unladen 

Resulting Air Spring Curves 

xxx 

xxx 

xxx 

xxx 

xxx 

xxx 

March 06 

- 7 -


Dampers Characteristic 

Nonsymmetric 

Configuration 

Two Damper Curves: 

Soft: 0-400 

psi 

Firm: 65 psi-up 

March 06 

- 8 -


Bushing Characteristics 

• Bushing 

Locations 

• Axial 

• Radial 

• Conical 

• Torsional 

• Stiffness 

• Damping 

March 06 

- 9 -


Axle as rigid body in Multi Body System 

• Mass Axle = 330 kg 

• Mass one Wheel = 38 kg 

• Total Mass = 406 kg 

4 connection points to Trailing Arm 

1 connection point to Connector Lateral Control Arms 

2 connection points to Air Springs 

2 connection points to Dampers 

2 connection points to the wheels 

March 06 

- 10 -

Modeling Procedure: Finite Element Modeling: 

Frame as flexible body 

• 53000 linear Shell Elements in NASTRAN, 1200 Seamweld Elements 

11 Connection Points 

to suspension components 

and ground: 

10*6 +1*3 = 63 Static modes 

10 normal modes 

67 Craig Bampton modes 

Structural Viscous Damping = 5% 

Mass = xxx 

March 06 

- 11 -


CLink as flexible body (Variant 1) 

• 67000 Tet10 Elements 

• 29000 Tria6 Skinning Elements 

2 Connection Points to axle 

1 connection point to frame 

3*6 = 18 Static modes 

+ 

10 normal modes 

- 

6 rigid body modes 

= 

22 Craig Bampton modes 

Casted Steel 

Mass : 100% 

Cost : 100% 

March 06 

- 12 -


CLink as flexible body (Variant 2) 

• 10000 linear Quad4 Elements 

• 300 linear Seam Weld Elements 

22 Craig Bampton Modes 

Welded Sheet 

Mass : 50% 


March 06 

- 13 -

Methodology of Durability Analysis: 

General Work Flow 

Wheel Forces 

Multi Body Simulation 

Craig Bampton 

Displacement 

Modes 

Craig Bampton 

Load Cases 

Finite Element 

Modal Analysis 

Modal Participation 

Factor Histories 

Craig Bampton 

Stress Modes 

Generation of Local 

Stress Tensor History 

And Damage Evaluation 

Stress Amplitude 

Distribution 

Damage Distribution 

March 06 

- 14 -

Multibody Simulation: 

Input Static Loads: Three Load Cases 

Each Load Case consists of two forces 

at tire contact patch point 

Results: : Hot Spots at Brackets 

Lateral Wheel Forces:xxx N 

Vertical Wheel Forces: 

xxx N 

Longitudinal Wheel Forces: xxx N 

March 06 

- 15 -

Multibody Simulation : 

Input Data: Load Histories Road Load Data 

Drive Fully Laden: Load Histories at Wheel Contact Patch 

Load Weight: xxx lbf xxx N / Wheel 

• Fz left side 

• Fz right side 

March 06 

- 16 -

Fatigue Analysis for Road Load Data: 

Result: Multi Body Simulation 

March 06 

- 17 -



Wheel Forces 


Craig Bampton 

Displacement 

Modes 

Craig Bampton 

Load Cases 



Modal Contribution 


Craig Bampton 

Stress Modes 





Distribution 


March 06 

- 18 -


Step 1: Stress Recovery for Transient Loads 

(stress) mode shapes 

… 

β 1 (t) 

modal contribution 

factor histories 

[ c ij ] 1 

[ c ij ] m 

modal influence 

coefficients: 

β m (t) 

time, t 

e σ ij (t) = ∑ m [ c ij • β(t) 

] m 

March 06 

- 19 -


Fatigue Life Prediction for Sheet Material 

Stress-Life Approach: 

e σ x 

e τ xy 

e σ ξ 

e τ ξη 

e σ y 

α 

FE-result 

result: Elastic Stresses 

• initiation and growth of 

small cracks 

analyze potentially critical 

(crack) planes 

evaluate uni-axial pseudo- 

stress history in each plane 

simultaneous treatment of 

all planes to find most 

severe damage 

maximum damage defines 

critical plane 

March 06 

- 20 -


Fatigue Life Prediction for Sheet Material 

Critical Plane Approach: 

e 

σ x 

S 

e 

τ xy 

e 

σ ξ 

e 

τ ξη 

March 06 

e 

σ y 

N 

α 

e 

σ ξ 

e 

τ ξη 

e 

σ x 

e 

σ y 

e 

τ xy 

ξη 

α = 0 o 

- 21 - 

time 

damage accumulation 

10 o ... 160 o 

... 

... 

... 

time 

e 

σ ξ 

e 

τ ξη 

170 o 

time 

damage accumulation 

D(α=0 o ) D(α=170 o ) 

D = max[ D(α) ]


Fatigue Life Prediction for Seam Welds: 

RxMS Approach: 

• LMS Virtual.Lab combines a 

shell based FE model and a 3D 

fine model to simulate the 

stress tensor histories in the 

weld toe and root. 

• RxMS SN-curve 

log(S) 

Seam Weld SN curve 

log(N) 

F 

M 

Coarse 

Model 

Transition 

Matrix 

Fine 

Model 

σ 

s 

s 

F M 

All stress 

concentration 

factors 

K t 

R03MS 

R = 0.3 mm for weld toes and root 

March 06 

- 22 -


Fatigue Life Prediction for Seam Weld: 

LMS Virtual.Lab Seam Weld Analysis: 

• Automates the well accepted 

RxMS approach. 

• No FE mesh adaptations 

required 

• Automatic detecting of seam 

welds – location and type 

• High Amount of accurate 

solid models for seam welds 

in open database 

Subframe Mercedes Benz 

March 06 

- 23 -


Fatigue Life Prediction for Seam Weld: 

Seam Weld Modelling: 

Congruent mesh for two welded sheets 

shell elements 

March 06 

- 24 -


Fatigue Life Prediction for Seam Weld 

Automated Seam Welds Recognition 

March 06 

- 25 -



Wheel Forces 


Craig Bampton 

Displacement 

Modes 

Craig Bampton 

Load Cases 



Modal Participation 


Craig Bampton 

Stress Modes 





Distribution 


March 06 

- 26 -


Input Data: Stress Tensor Histories 

• Multi Body Simulation creates 22 Modal Contribution Factor 

Histories assigned to the 22 Craig Bampton Modes 

MPFH 

CB Modes 

e σ ij (t) = ∑ m [ c ij • β(t) 

] m 

March 06 

- 27 -


Input Parameters: Seam Welds 

• The seam weld type is recognized automatically 

• For the seam weld type there is assigned the right micro 

model of the seam weld shape automatically 

SN-curve 

selected: 

R03MS Steel (R=-1) 

Slope: : 3.75 

Endurance Limit: 

• 331 MPa 

• 5*10 6 cycles 

March 06 

- 28 -


Input Data: Casted Steel & Sheet Material 

• Materials Data 

Stress – Cycles to crack initiation curve 

• Critical Plane Approach (Mode 1) 

March 06 

- 29 -


Stress Analysis for C-Links (Variant 1) 

• Max. Stress Amplitude far below endurance limit 

• Safety Factor to Endurance Limit is 4.6 

• Damage Value is zero all over the structure 

Casted Steel 

Mass : 100% 


March 06 

- 30 -


Stress Analysis for C-Links (Variant 2) 

• Max. Stress Amplitude far below endurance limit 

• Safety Factor to Endurance Limit is 4.3 

• Damage Value is zero all over the structure 

Welded Sheets 

Mass : 50% 


March 06 

- 31 -


Seam Weld Analysis for C-Links (Variant 2) 

• Hot Spot 1 is at overlap joint of additional sheet 

• Hot Spot 2 is at seam weld end of overlap joint 

• 2.000.000 repeats of the simulated block until crack initiation 

HS2: 

HS1: 

March 06 

- 32 -

Conclusion of Fatigue Life Analysis : 

• Results of Fatigue Life Analysis for C-Links 

(Trailing 

Arms): 

• Stress Amplitudes for both Variants are far below Endurance 

Limit, Safety Factors are near to each other 

• There were identified two Hotspots for the Seamwelds 

• The casted steel CLink can be substituted by the welded sheet 

construction 

• Further Tasks: 

• Compare Strain Gage Measurement results at Test Rig with 

Simulation Results 

• Compare Crack Initiation Locations (Hot Spots) 

Test Rig - Simulation : Location + Life Time 

March 06 

- 33 -

Weight and Cost Reduction of a Vehicle Component by Durability ...

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