Experimental Study of Lightweight Tracked Vehicle Performance on Dry Granular Materials.Paper81662

12/20/2013

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Experimental Study Of Lightweight Tracked

Vehicle Performance On Dry Granular Materials.

Carmine Senatore*, Paramsothy Jayakumar†, and Karl Iagnemma*

* Massachusetts Institute of Technology, Cambridge, MA, USA †U.S. Army TARDEC Warren, MI, USA

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2

Motivation

• Evaluate the performance

of lightweight tracked

vehicles on granular media

• Understand modeling

shortcomings

• Highlight future directions in

track modeling

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Outline

• Experimental Setup

– Terramechanics test rig

– Single track device

• Experimental Plan Overview

• Experimental results

• Semi-Empirical Modeling

• Experiments vs. Models

• Conclusions

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Terramechanics Test Rig

4

Vertical

load

control

6-axis

F/T

Sensor

Mojave Mars

Simulant

Torque

sensor

Draw-wire encoder

for sinkage

measurement

A motor drives

the horizontal

carriage.

A motor

drives the

track

Quikrete

Medium Sand

Quikrete

All Purpose Gravel

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Single Track

5

Road Wheels

92 shore A durometer toothed belt

250 mm

Tensioner

33 mm

5.5 mm

Trailing arms

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Single Track

6

DC Motor Torque

Sensor

Flexible

Coupling Bevel

Gears

Drive

Pulleys

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Experimental Plan Overview

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125 N

155 N

190 N

Fz Range Slip Levels Terrains

Gravel

Medium Sand

Mars Simulant

± 50 %

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8

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Mars

Sand

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-0.6 -0.4 -0.2 0 0.2 0.4

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

Slip

Tra

ctio

n C

oe

ffic

ien

t -

F

x/Fz

Fz = 125 N

Fz = 155 N

Fz = 190 N

-0.6 -0.4 -0.2 0 0.2 0.4-2

0

2

4

6

8

10

Slip

To

rqu

e -

T [N

m]

-0.6 -0.4 -0.2 0 0.2 0.4

15

20

25

30

Slip

Sin

ka

ge

[m

m]

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10

10

Medium

Sand

-0.5 0 0.5-0.6

-0.4

-0.2

0

0.2

0.4

Slip

Tra

ctio

n C

oe

ffic

ien

t -

Fx/F

z

Fz = 125 N

Fz = 155 N

Fz = 190 N

-0.5 0 0.5

-2

0

2

4

6

8

Slip

To

rqu

e -

T [N

m]

-0.4 -0.2 0 0.2 0.4 0.6

10

15

20

25

30

35

40

45

Slip

Sin

ka

ge

[m

m]

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11

Gravel

-0.5 0 0.5

-0.6

-0.4

-0.2

0

0.2

0.4

Slip

Tra

ctio

n C

oe

ffic

ien

t -

Fx/F

z

Fz = 125 N

Fz = 155 N

Fz = 190 N

-0.5 0 0.5

-2

0

2

4

6

8

10

Slip

To

rqu

e -

T [N

m]

-0.5 0 0.5

0

5

10

15

20

25

30

35

Slip

Sin

ka

ge

[m

m]

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Comparison for Fz = 125 N

12 -0.6 -0.4 -0.2 0 0.2 0.4 0.6

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

Slip

Tra

ctio

n C

oe

ffic

ien

t -

Fx/F

z

Mars

Medium Sand

Gravel

Mars Medium Sand Gravel

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Modeling

• Excluding numerical-intensive approaches (DEM/FEA)

the vast majority of models for tracked vehicles are

based on Bekker, Wong, and Muri’s work.

• Sinkage is calculated through Bekker’s pressure-sinkage

equation:

• Maximum traction is deduced from Mohr-Coulomb failure

criterion

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Modeling

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• For frictional materials

cohesion is zero and

friction dominates trust.

0

Material

Mars 1.4 846 6708 600 35 0.0006

Medium Sand 1.0 -20 3130 1500 34 0.0006

Gravel n/a n/a n/a n/a 30 n/a

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Modeling

• Basic Wong Model (BWM) over estimates drawbar

mostly because it does not predict sinkage correctly

• Model Assumptions:

– Track is rigid

– Uniform ground pressure

– Continuous shear stress representation

15 -0.6 -0.4 -0.2 0 0.2 0.4

-150

-100

-50

0

50

100

150

Slip

Dra

wb

ar

- F

x [N

]

BWM @ Fz = 190 N

BWM @ Fz = 125 N

-0.6 -0.4 -0.2 0 0.2 0.4

5

10

15

20

25

Slip

Sin

ka

ge

[m

m]

BWM @ Fz = 190 N

BWM @ Fz = 125 N

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Modeling

• Advanced Wong Model (AWM) assumptions:

– Track is a flexible belt

– Belt tension between road wheels is function of shear stress

– Terrain reaction force follows Bekker pressure-sinkage equation

– Shear Stress resets when normal load decreases

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0.05 0.1 0.15 0.2 0.25

-0.2

0

0.2

0.4

Length [m]

Sin

ka

ge

[m

]

0.05 0.1 0.15 0.2 0.25

-10

-5

0

Length [m]

Str

ess [kP

a]

Fz

Fx

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0 0.1 0.2 0.3 0.4 0.5

-40

-20

0

20

40

60

80

100

120

Slip

Dra

wb

ar

- F

x [N

]

0 0.1 0.2 0.3 0.4

-20

0

20

40

60

80

100

120

Slip

Dra

wb

ar

- F

x [N

]

AWM @ Fz = 190 N

AWM @ Fz = 125 N

Modeling

• AWM produces results closer to the measured data.

• AWM does not incorporate slip-sinkage effects (i.e,

sinkage response is flat)

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Mars Medium Sand

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Conclusions

• The experiments highlighted that track performances are

mildly sensitive to the three granular materials under

investigation.

• Basic Wong Model showed to be inappropriate for

detailed analysis.

• Advanced Wong Model produced better predictions of

track performance.

• Both models showed to be sensitive to pressure-sinkage

parameters while the experiments showed that track

performances are not influenced by pressure-sinkage

behaviour.

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