challenges in tire fem simulation - weierstrass · pdf filethe focus for tire fem simulation...

Challenges in Tire FEM Simulation

Dong Zheng, Ph.D.

Commercial Tire TechnologyContinental AG

2 / Dong Zheng / © Continental AG

Tire Components

1. Tread

2. Cap ply

3. Belt

4. Carcass ply

5. Inner liner

6. Side wall

7. Apex

8. Bead

9. Bead reinforcement



History

1970s: FEM tire simulation started at Continental AG=> 2 dimensional simulation for tire inflation, and tire shape change

under high rotational speed.

1980s: Static 3d simulation=> Tire footprint shape can be predicted. Inter-ply shear for tire durability.

Tire vibration model.

1990s: Rolling tire simulation=> Tire footprint under rolling condition. Tire force & moment prediction

for combining tire in to a vehicle model.

2000s: New developments:

More accurate material: Viscoelastic parameter.

More accurate geometry: Tire model with tread pattern; Tire model

combined with rim and air.

More accurate load condition: Tire service matrix used in simulation.



The focus for tire FEM simulation

Durability

Ensure tire will not fail during the life of a tire.

Tread wear

Tire tread should be worn as even as possible and as long as possible.

Environmental concerns

Reduction of tire rolling resistance.

Vehicle handlingTire fitted to vehicle to provide best braking, traction and emergency handling.

Vehicle comfortTire with optimized Noise, Vibration and Harshness (NVH) performance.



Tire simulation steps

Tire Design Data

2D & 3D Tire model

Simulation results

Tire

designModel

building FEM

simulation

Post

processing

Tire Performance



Model Generation

Rubber compounds

• Tread• Inner liner• Side wall• Apex• Coating of cord

Cord material

• Carcass• Belt• Cap ply• Bead• Bead reinforcement

FEM Model

CAD Drawing



Input Data:Rim contactInner pressureCentrifugal loading

Output DataResulting geometry Dynamic contourForce on rim

2D simulation



Tire Simulation

FEM features:

Incompressible non-linear material

Composite material

Contact between tire/rim and tire/road

Large deformation

Rolling dynamic

Investigation parameters:

Tire construction

Material parameters

Inner pressure

Tire speed and load

Tire camber and slip angles



Tire footprint results

Static Simulation

Rolling Simulation

Contact Pressure Longitudinal frictional Stress



Temperature inside a tire due to energy dissipation

75 km/h

42.7°

150 km/h

55.8°

190 km/h

80.8°

200 km/h

106.8°

0.0

10.0

20.0

30.0

40.0

50.0

60.0

70.0

80.0

90.0

100.0

0 50 100 150 200 250

Rolling speed (km/h)

Ro

llin

g r

es

ista

nc

e (

N)

2.6bar 1.3bar



We are able to predict

frictional energy

of block patterns

Prognosis for

heel & toe wear

(Sägezahnabrieb)

Tread pattern irregular wear



Tire lateral force vs. slip angle

-4000

-3500

-3000

-2500

-2000

-1500

-1000

-500

0

500

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5

Slip angle [°]

La

tera

l fo

rce

[N

]

Test Simulation, mue=const Simulation, mue=f(p,v)



Tire Vibration – modal analysis

Tire noise and vehicle comfort is affected by tire construction.

Vibrations can be predicted by FEM.

Torsion mode

Bending modes

Radial Modes



Challenge: Better Rubber Material model

Rubber Characteristics:

Incompressible

Non-linear

Viscoelasticity

Loading history dependency

Ageing

Dumbbell Test for Simulation Parameter

-2.5

-2

-1.5

-1

-0.5

0

0.5

1

1.5

2

2.5

-40 -20 0 20 40 60 80

Elongation [%]

Str

es

s [

N/m

m²]

T4565

Can we find a material model to represent behavior of rubber?



Challenge: Modeling of belt and cord

Tire belt and ply is made of tire cord embedded in rubber matrix specific

end count.

The cord is made of two or more steel or polymer cord twisted

according to specific design.

How to model the belt so we not only how the average stress but also the

true stress between cord?

How to model the cord, especially when it is under compression?

Can multi-scale simulation help?



Challenge: Rubber abrasion model

Abrasion rate dependent on

contact pressure, sliding velocity,

temperature, etc.

Rubber slide for a very short time for each tire revolution where none of above parameters are easily

determined by measurement.

Time

Time

Wear

Sliding velocityContact Pressure

Time

Frictional energy dissipation rate

Can we find an abrasion model and define test method to measure its parameters?



Challenge: Rolling tire vibration

Rolling tire and standing tire show clearly difference in vibration.

Gyroscopic effect for rolling tire cannot be represented in standing tire model.

How to model the boundary condition on the contact area?

-55

-50

-45

-40

-35

-30

-25

-20

-15

90 100 110 120 130

Frequency [Hz]

Ac

ce

l./F

orc

e [

dB

re

f 1

(m

/s^

2/N

)^2

]

0km/h

50km/h, Leading Edge

50km/h, Trailing Edge

Tire on SSF

ΩΩΩΩ

Spindle Acceleration

Response

Spindle Force Excitation

Trailing Edge

Leading Edge

( ) ( ) Ffifdi ∆uMuCCCuKKKK =+++++++ &&& δδδ



Challenge: Modeling of Tread Pattern

Tire tread pattern is important for many tire performances such as traction, wear, hydroplaning, noise and

vibration.

Tire tread pattern has strong interaction with the road, and water,

snow, mud, etc on the road.

Full transient dynamic simulation coupled with water/snow/mud will be economically impossible to do.

How to simplify the model/simulation procedure to save time yet still produce meaningful results?



Challenge: What is really inside a tire

Rubber curing state differs from location to location. Rubber property depends on curing

state.

Pre-strain exists inside tire due to tire building, lifting of belt, and curing. The pre-strain

influences the tire performance.

Will simulation of tire building/curing help?

How rubber property changes from uncured to cured?

What about the chemical reaction during tire curing?



Challenge: Prediction of real life performance

Vehicle runs at cruise condition for

around 95% of time.

However, tire load is much higher

when vehicle accelerates, brakes, or turns.

The combined effects are needed to

predict tire performances, such as

durability, tread wear, in the real

usage.

-0.6-0.4

-0.20

0.20.4

0.6

-0.6

-0.2

0.2

0.6

1.0E+00

1.0E+01

1.0E+02

1.0E+03

1.0E+04

1.0E+05

1.0E+06

Lat. Acc. (g)

Fo

re-a

ft

Acc. (g

)

Vehicle acceleration histogram

Tire responses for all type of loading has to be predicted. Can we develop a model to combine the effect from different loading together?



Summary

Continental AG has a long history of tire FEM simulation and is actively

improving and expanding the simulation

The simulation is helping Continental on all key areas of tire performance

including:

Tire durability

Tread wear

Rolling resistance

Vehicle handling

NVH

Many challenges remain for us to overcome.

challenges in tire fem simulation - weierstrass · pdf filethe focus for tire fem simulation...

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