12/20/2013

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Experimental Testing Of An Off-road Tire In Soft Soil

Corina Sandu, Scott Naranjo,, Saied Taheri, Virginia

Tech

U.S. Army Quad Member: Dr. Paramsothy Jayakumar, TARDEC

Industry Quad Members: Dr. Brant Ross, MotionPort, Mr. Daniel

Christ, Michelin Americas Research Co

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2

Tires on Soft Soil Study

Modeling

Methodology

Tire structure

Tire-soil interaction

Simulations

Experiment

Design of experiment

Terramechanics rig

Instrumentation

Results

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Terramechanics Rig

Single wheel test rig for tire performance on various terrain

• Wheel slip controlled via two separate drive motors

• Measures forces and moments via wheel hub Kistler P 650 sensor

• Various terrain possibilities

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Fluid regulation via flow

• Can control response of system with air pressure

• Response time within 2.8 ms

• PI controller in LaVIEW provides controls

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Toe and Camber Adjustment

Linkages of different lengths adjust camber and toe

• Camber -8 to +80 in steps of 20

• Toe -25 to +250 in steps of 50

Designed for accuracy and robustness

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Additional Measurement Sensors

Fitted ultrasonic sensor to measure relative soil height

Steel Plate

Reference

45o

az

ax

25o

WITS - eight equidistant sensors used to estimate proper speed to maintain a slip ratio value and to estimate max sinkage

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Methods of Soil Measurement

Geotechnical lab tests by Schnabel Engineering

• California Bearing Ratio

• Standard Proctor Test

• Triaxial shear strength test

6.5 kPa/mm

4.4 kPa/mm

Cone Penetrometer Tests

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Silty Sand Preparation

• Versatile soil with a long range of low to high cohesiveness

• 5 stage soil preparation procedure per test run

• Insure soil consistency with Cone Penetrometer CP40 II

and taking samples for moisture content measurement

• Geotechnical lab data for soil

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Determination of Max Sinkage

8

hinitial

Rdeformed

undisturbed

soil surface max sinkage (Δz)

h

Rut

P

M1

M2

ST

W

Δz=(h+Rdeformed )-hinital

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Design of Experiment

• Tire normal load and inflation pressure were chosen to

correlate with full-scale vehicle testing in South Africa

• Soil compaction resistance obtained through the repeatable

soil preparation procedure developed

• Test tire - LT235/85R-16 Michelin LTX A/T 2 E

No. Slip Load Inflation Press.

Soil Comp.

1 All L1 L1 L1

2 All L2 L1 L1

3 All L1 L2 L1

4 All L1 L1 L2

5 All L2 L1 L2

6 All L2 L2 L1

7 All L2 L2 L2

Parameter No. of Levels

Range

L1 L2

Slip % 8 0 – 5 – 10 – 15 –

20 – 40 – 60 - 75 (or 90)

Normal load

2 5000 N 6000 N

Inflation Pressure

2 29 PSI (2 bar)

20 PSI (1.38 bar)

Compaction Resistance

2 4.4 ± 0.4 kPa/mm

6.5 ± 0.9 kPa/mm 9

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Soil Deformation in

Full Range of Slip

0 % 20 %

5 %

40 %

10 %

15 %

60 %

90 %

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Individual Parameter Change

Lower inflation pressure, highest

drawbar pull

Parameter Level

1 Level

2

Normal load (kN) 5 6

Inflation Pressure (psi)

29 20

Cone Index Gradient (kPa/mm)

4.4 6.5

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Several Parameter Changes

Variation result of irregular soil compaction

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Tire Sinkage Results

Lower inflation pressure -> larger sinkage but greater drawbar pull

Higher load -> greater contact patch -> least

sinkage

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Main Effects and Interaction on

Drawbar Pull

• Inflation pressure has main

effect on peak drawbar pull

coefficient

• Interaction of soil compaction is

evident with normal load and

inflation pressure

Peak DP coefficient

High Slip DP coefficient

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Parameter Main Effects and

Interaction on Sinkage

Larger slope indicates a

greater degree of

interaction

Normal load has the

greatest effect on sinkage

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Conclusions

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Tire instrumented with wireless real-time deflection system

Normal load controller hardware installed, and required

software developed

Field scanners installed (used with other sensors for

sinkage measurements)

Various tests from design of experiment performed

Drawbar pull and sinkage data obtained for a large range of

slip ratio values

Interactions of various parameters on the drawbar pull and

sinkage were obtained

Data used to validate tire model developed at AVDL

concurrently with the experimental work