Dynamic Front Wheel Curb Impact Study

Robert L. GeislerEngineering Group Manager Chassis CAE

General Motors - North American Product Development

Hyung-Joo Hong General Motors NAPD, Chassis CAEJason Kline General Motors NAPD, Chassis CAE

Prasad Kodali General Motors NAPD, Chassis CAE

Study History

1992 Robert Geisler & Prasad Kodali of CLCD invent a method to predict rear suspension curb impact loads and apply it to a vehicle program. Method included elastic-plastic representation of

the rear suspension toe link Correlation to test was very good

1995 Young Kim of LAD applies the above methodology to another suspension topology Correlation is also very good

Study History, cont.

1995 Robert Geisler of CLCD applies methodology to front curb impact simulation. These results did not correlate very well (analysis

loads are much higher than test loads). The theory is that a part of chassis was yielding

significantly. 2002 - Hyung-Joo Hong developed a strategy

to incorporate plasticity into ADAMS to make model more robust. Applied this concept to a vehicle shipping

simulation This study implements the strategy,

benchmarks it, and defines its further development.

Test Procedure

Front Steered Wheel Impact Wheels steered to

full lock, vehicle placed on dollies

Vehicle dragged into Curb

Test Vehicle

Curb

Direction of Vehicle Travel

Test versus Analysis

Test High Impact Force Measurements:

vulnerable to Error Hardware availability

Analysis Requires a very refined model to represent

structural compliance Performed well ahead of Hardware

Analysis: FE versus MBD Approach

FE Approach Better representation of structural

compliance including plastic deformation Requires well-defined FE model and MBD

model, which takes long to get reasonable results

MBD (Multi-Body Dynamics) Approach Very quick to get a result Limitation of Representing Structural

Compliance

Curb Impact ADAMS Model

Full Vehicle ADAMS model, rigid bodies and connections.

Vehicle stationary, tires on ice. Large mass curb moved perpendicularly

into steered wheel vertical plane. Contact Model between Curb and

Tire/Wheel

Standard Model Results

A North American Production Car

TierodF/A Ball Joint

Lateral Ball Joint

Test 12280 17220 26225Original Model 11150 21480 27355

% Difference -9.20% 24.74% 4.31%

Peak force in Newtons

5 mph Peak Force Results

TierodF/A Ball Joint

Lateral Ball Joint

Test 16420 19800 24610Original Model 14400 30690 43720

% Difference -12.30% 55.00% 77.65%

Peak force in Newtons

7 mph Peak Force Results

Opportunities for Improvement

Does not capture local effects Vehicles have experienced plastic

deformation during physical test Predicted loads very high

Need to add local plastic deformation

Force Versus Deflection Curve

Force

Deflection

Bushing Linear RateBushing Linear Rate

Bushing Ground OutBushing Ground Out

Structural FlexibilityStructural Flexibility

PlasticityPlasticity

Rigid Body Analysis

Flex Body Analysis

Elastic Plastic Analysis

Inaccurate Analysis

Plasticity Implementation

Typical Elastic-Plastic load-deflection curves from FE analysis

Force

Deflection

Elastic Limit

Plastic Model Results

TierodF/A Ball Joint

Lateral Ball Joint

Test 12280 17220 26225Baseline (Rigid Cradle) 11150 21480 27355Plasticity Model 11170 18400 22220% Difference Plasticity to Test -9.00% 6.90% -15.30%

Peak Force in Newtons

5 mph Peak Force Results

TierodF/A Ball Joint

Lateral Ball Joint

Test 16420 19800 24610Baseline (Rigid Cradle) 14400 30690 43720Plasticity Model 15100 21700 23800% Difference Plasticity to Test -8.00% 9.60% -3.30%

Peak Force in Newtons

7 mph Peak Force Results

Results Comparison 5 MPH

Results Comparison 5 MPH

Results Comparison 5 MPH

Results Comparison 7 MPH

Results Comparison 7 MPH

Results Comparison 7 MPH

Conclusions

Predicted loads correlate with measured data very well

Less than 5 minute run time for a typical analysis

Accuracy improvement achieved without increasing simulation time (FE analysis)

More design iterations possible in the analysis world

Contact Details

EMEA05-051Dynamic Front Wheel Curb Impact Study

Robert L. GeislerGeneral Motors - North American Product

DevelopmentEngineering Group Manager Chassis CAErobert.l.geisler@gm.com