IR

AD-A271 546

First International Conference on

Winter Vehicle Mobility

Santa Barbara, California, June 1991

George L. Blaisdell, Editor July 1993

DTIC ELEC

* OCT28B r* j 1-- -

- - 93-25863

I •

ArmrD] Im raf fe
The PAW Infernatlanul Conference on Wkier VeW** Moblitly was fth first

*mcilona .u.n wft y dwoled to Me &kWec of vehicle #avel I cold

eglions. The tschnical sessions Wicsed on predcion and testing meltiods,

pIUd vehile moblWN, moblify enhancemet, cold regions materilds properft, andl mNoe designs for w4rn* mobilly. This report includes 21 papers

preene at the conference.

For conversion of Si metri unts to U.S./Buittsh cus*ornry units of measurement

consuft ASiM Standard E3W80-9, Shondrid PRacice fir Use of the Intemnalional

Sm~w of Uln/, publishe by the American Society for Testin and Materials,

1918 Race St., Philadelphia, Pa. 19103.
Special Report 93-17

U.S. Army Corps

of Engineers Cold Regions Research &

Engineering Laboratory

First International Conference on

Winter Vehicle Mobility

Santa Barbara, California, June 1991

George L. Blaisdell, Editor July 1993

Approved for public release; distribution is unlimited.
FOREWORD

Over the past several years, various researchers and practitioners of winter mobility have

gotten together in small groups in an attempt to solve mutual problems and share information.

No standard forum has been available for this unique topic, however, so each meeting has

been somewhat ad hoc in nature and often occurs as a small part of another larger meeting.

The Engineering Foundation recognized the need for a conference, perhaps leading to s

regularly occurrng meeting, devoted entirely to the subject of vehicle travel in cold regions.

Thus they encouraged and sponsored this international conference. Funding was provided by

the Engineering Foundation and the National Science Foundation. Support for conference

organizers was provided by the Civil and Agricultural Engineering Department of Montana

State University and the Keweenaw Research Center. The Cold Regions Research and

Engineering Laboratory sponsored the conference chairperson and edited and produced the

conference proceedings.

Technical sessions for the conference focused on:

1) Prediction and testing methods,

2) General vehicle mobility,

3) Mobility enhancement,

4) Cold regions materials properties,

5) Novel designs for winter mobility.

A final discussion about the remaining needs of the mobility community and iaeans of

addressing these needs concluded that regular (probably annual) meetings that include field

demonstrations and exercises are very much desired. While no single group or organization

felt compelled to take a lead in organizing future meetings, all attendees seemed eager and

available to help in producing follow-on conferences. Clearly, continued involvement by the

Engineering Foundation, especially in instigating future Winter Mobility conferences, would

be very beneficial.

GEORGE L. BLAISDELL

Chairperson

Q'I

t~lBý !?F

%¶t
FIRST INTERNATIONAL CONFERENCE ON Sture Bernhardsson

WINTER VEHICLE MOBILITY Defense Materiel Administration

Mobility Directorate

Chairperson Transport Vehicles Division

George L. Blaisdell Test Center

Experimental Engineering Division S-645 83 Strangnas

Cold Regions Research and Engineering Laboratory SWEDEN

Hanover, New Hampshire

George L. Blaisdell

Co-Chairpersons Applied Research Branch

Robert Brown Cold Regions Research and Engineering Laboratory

Department of Civil and Agricultural Engineering 72 Lyme Road

Montana State University Hanover, NH 03755

Bozeman, Montana

Robert Brown

Russell Alger Department of Civil and Agricultural Engineering

Institute of Snow Science Montana State University

Keweenaw Research Center Bozeman, MT 59767

Michigan Technological University

Houghton, Michigan Leonard Della-Moretta

1796 Russell Place

Engineering Foundation Pomona, CA 91767

Charles Freiman, Director

Gordon Fisher, Conference Committee Representative Michael Edens

Department of Civil and Agricultural Engineering

Proceedings Editor Montana State University

George L. Blaisdell Bozeman, MT 59717

To obtain a copy of these proceedings write to Michael A. Gillis

CRREL-TL, 72 Lyme Road, Hanover, Navy Support Force Antarctica

New Hampshire 03755-1290, USA. Box 100, Code 50

FPO San Francisco, CA 96601-6010

ATTENDEES Keafur Grimes

Waterways Experiment Station

Russ Alger WES GM-IE

Keweenaw Research Center P.O. Box 631

Michigan Technological University Vicksburg, MS 39180-0631

Houghton, MI 49931

Bill Grusonik

Michael Barber FMC Corp.

Department of Civil and Agricultural Engineering 2890 Della Cruz

Montana State University Box 58123 (MD-P73)

Bozeman, MT 59717 Santa Clara, CA 95052

Joseph Barthelemy Doug Hanna

Naval Civil Engineering Laboratory DOD Canada

Code L66 P.O. Box 4000

Port Hueneme, CA 93043-5003 Medicine Hat

Alberta, CANADA TIA 8K6

Illoi
Andrew Hansen Northern Terrain Vehicles

Mechanical Engineering Department CLDO Branch/PD-NTV, NDHQ

University of Wyoming G. Pearkes Bldg.

Box 3295, University Street Ottawa, Ontario, CANADA KIA 0K2

Laramie, WY 82071

Mark Osborne

Henry Hodges Keweenaw Research Center

Nevada Automotive Test Center Michigan Technological University

P.O. Box 234 Houghton, MI 49931

Carson City, NV 89701 James Poplin

Glen Isnor Esso Resources Canada, Ltd Lete 3535 Research Road,NW National Defense Department Calgary, Alberta, CANADA T2L 2K8

Ottawa, Ontario, CANADA KIA 0K2 Rick Schenck

Tank-Automotive Command

Roger Jacobson AMSTA-WS

Imagineering Warren, MI 48397-5000

3236 16th Avenue, SW

Seattle, WA 98134 Tom Schmidt

Navy Support Force Antarctica

Michael Kriz Box 100, Code 50

Tank-Automotive Command FPO San Francisco, CA 96601-6010

AMSTA-ZDM

Warren, MI 48397-5000 Sally Shoop

Applied Research Branch

Ronald Liston Cold Regions Research and Engineering Laboratory

Applied Research Branch 72 Lyme Road

Cold Regions Research and Engineering Lalbo.ratory Hanover, NH 03755

72 Lyme Road

Hanover, NH 03755 Dale Steinke

Defense Products, JB7

Urban Lundberg Caterpillar, Inc.

Hagglunds Peoria, IL 61629

35414 Mound Road Sterling Heights, M1 48310 M. R. Surendran

U.S. Army Tank Automotive Command

AMSTA-WS

Michael Moggridge Warren, MI 48397-5000

Canadian Armed Forces

MRCV Project Calude Thomas

NDHQ/CLDO/DLR Naval Civil Engineering Laboratory

G. Pearkes Bldg. Code L66

Ottawa, Ontario, CANADA KIA 0K2 Port Hueneme, CA 93043-5003

Marc Moosang

Jeffrey Weaver

Esso Resources Canada, Ltd

3535 Research Road, NW

Calgary, Alberta, CANADA T2L 2K8

iv
CONTENTS

Forew ord ................................................................................................................ ii

A ttendees ................................................................................................................ iii

1. Introduction ....................................................................................................... I

Mobility research: where we have been and where we are going

Ronald A . Liston .......................................................................................... ..

2. Prediction and testing methods ........................................................................ 19

Predicting vehicle mobility on snow-covered slopes

Paul W. Richmond ................................... 20

An experimental method for vehicle mobility research on freezing/

thawing soil

Sally Shoop, E. Berliner and S. Decato ...................................................... 29

Ice cleat design and testing for tracked military vehicles

Mark D. Osborne ......................................................................................... 38

3. V ehicle m obility ................................................................................................ . 47

BV 206: A proven concept in winter mobility

Jan Ljunggren ............................................................................................. 48

Operability: The first step to mobility

Deborah Diemand ...................................................................................... 59

Wheeled vehicle mobility evaluation in deep snowpack

D.M. Xu, A.M.O. Mohamed, R.N. Young, and G.J. Irwin ........................... 67

The Army MANPRINT program and its relationship to industry

David A. Sloss and Michael A. Kriz ........................................................... 85

4. Mobility enhancement ....................................................................................... 93

Cross-country mobility of tracked vehicles

Bjorn Andersson .......................................................................................... 94

Investigation of forces incurred during snow plowing

Wade Steiger, Andrew Hansen and Kynric Pell .......................................... 103

Theoretical and experimental results of using binders for snow

roads and runways in Antarctica

Michael Barber and Robert L Brown ......................................................... 113

v
The influences of adjustable tire pressure (CTIS) and antiskid

devices when driving in snow

Sture Bernhardsson ..................................................................................... 125

The negatively buoyant jet/plume with applications to snow

plow exit flow behavior

William R. Lindberg and Joseph D. Petersen .............................................. 135

5. M aterials Properties .......................................................................................... 155

Viscosity measurements on very wet soils

Sally Shoop .................................................................................................. 156

The relationship between the microstructure and mechanical properties

of snow

Michael Q. Edens and Robert L Brown ...................................................... 164

Short term settlement of footing on snow foundation

Puneet Mahajan and R.L Brown ................................................................ 174

Snow characterization for traction testing: A survey of techniques used .............

Sally Shoop and Russ Alger ......................................................................... 186

6. N ovel D esigns ..................................................................................................... 191

Caterpillar mobil-trac system's application to cold regions mobiliy

problems

D ale Steinke ................................................................................................. 192

Ultra-track: The ultimate all-terrain attachable tracks

RogerJacobson ........................................................................................... 198

The U.S. Army's Bv 206 oversnow vehicle

U rban Lundberg .......................................................................................... 201

The Flextrac MPV: A novel concept in a personal all-terrain vehicle

Mark D. Osborne ......................................................................................... 203

vi
A.A

1. INTRODUCTION
Mobility Research: Where We Have Been and Where We Are Going

RONALD A. LISTON

U.S. Army Cold Regions Research and Engineering Laboratory

Hanover, New Hampshire 03755-1290

The request to give an hour's talk on mobility re- of knowledge that we have developed about vehicles

search seemed an innocuous one when it was made to has not resulted in dramatic changes in form and performe. But as I began to think about how I would cover the mance.

topic, things became more and more complicated. My The first reason that comes to mind is that dramatic

first thought was to prepare a list of the people whose improvements do not come from modest changes. For

contributions should be highlighted and I was inun- example, the difference between a high-speed catamadated with a flood of names: Uffelmann, lanosi, Mick- ran and a conventional sailboat is clearly major. The

lethwaite, Bekker, Van Duesen, Knight, Turnbull, more than doubling in speed of wind-powered craft

Grabau, Murphy, Green, Shockely, Ehrlich, Nuttall, the could only be achieved by making a clear departure

Hodges clan, Reece, Leger, Dixon, Sela, Soehne, from conventional designs. In general, I think that a

Areskoug, Kitano, and on and on until I realized that I drive created by competition between teams of men and

was going to have to cover the complete roster of the their machines creates an attitude that anything new and

ISTVS and all of its associates-an impossible task for different will not only be accepted but sought out if there

60 minutes. is the possibility of gaining a slight advantage. InnovaMy next thought was to cover the major groups of tion is vital to competition. The users of automotive

research organizations that have been active over the equipment simply will not accept radical changes repast half century. The list quickly became unmanageable: quired to give them vehicles that can operate either at

Valcartier, TACOM and all its variants, WES, SIPRE, high speed off the road or in terrain conditions that

CRREL, NIAE, FVRE, Stevens, U. of M., Michigan prevent operation of conventional vehicles because

Tech., U. Cal. Davis, Tulane, McGill, Carlton, U. of their agendas, forreasons thataren't immediately clear,

Miss., DRES, NATC, and this list also went on and on. don't have an element of desperately seeking for the

My conclusion was that I would be lucky in one hour competitive edge. For example, the Twister (Fig. I),

to cover what has happened in the U.S. Government- developed by Steve Hodges at Lockheed, was an amazsupported mobility research program during its lifetime ing machine that allowed highway speeds to be achieved

(which happens to fit nicely into the half century men- in rough terrain that would normally limit vehicles to

tioned above). I proposed that my historical review be four or five miles pcr hour. It was offered in a var-ctý of

anecdotal in nature, so that what is presented is not configurations that ranged from an ambulance to a fullsupported by references, making some details open to fledged fighting vehicle. The concept was discarded

challenge. I hope that, in general, my review captures partly because its form was as unconventional as was its

the essence of what has transpired. performance: two engines, multiple walking beam susBefore discussing the mobility programs and vari- pension, articulation with three degrees of freedom.

ous approaches taken to studying vehicle/terrain inter- Except for a handful of people who become overactions, let us take a quick look at what our research whelmed by radically new off-road machines, the revoefforts have produced. Unhappily we have worked lutionary potential of this machine was overlooked

diligently and, usually, well but have had little impact because it was so different that it demanded rejection.

on the performance of machines in use, whether they be A second example is the series of vehicles developed

military, agricultural, forestry, construction or high- in response to Bob Phillipe's desire to show that highly

way. One is forced to wonder why the significant body mobile vehicles designed to operate in very weak soils

2
All.K

"ItIi 0I)ClAte cqlualll \%Cll on thle load ()I filtte load, Jre \iLI iLitlew t"' t toeniiltiil It I

)nc tiakckd \ i VIL i. 21 mid t\w %i heeled ctrlioný iiker\atlion that th iilt\el'ir iilfhli\and

a.ý' nk I~ I) ckrc dc,,iiLned toiiperatc inI Nill c( ndtridi tin'ý thc UýCr CoIIIIlIulltI I\ee ti I lia CIle Ih it I PI C~Io[ thI IlI 

mt %%Cak that iril the hliehtc~t %ehiele\ a\ .naiile Lit tlic \o in Ne the rielit tire or track wo,,n Lom ciiihroit

time ~ ii eiar ~ ~ iihl.IeChicle\, ~ i ý \kvrckdecswned kii\ \k here. 0ir 111.1\ he thalt thicC 1, d 111ti'Cial tra1l1NIl\1

I') operate III oilk %% itli a \(I ot 71 ilicit imipact oft thc 'ion that ý% III let \OIJ dri\ e (iii % itci. We in the iiiihihll\

worldl it ott-road riiachincr\ ~ ~III]. A \crN 'enior .otflifltlliit% lIMC(t2 detlRVIJtratLI thle alue of artýiclai

TA\(( All nwianager srepIion,,e ý% as "What InI [lie wdird nion. if a I ,per- flex Ihie framec of liiihl\ compttlianit

Figuire' 2. Traicked visitof o] the MEAI•, ve/ll /ivs
suspens~ion,,. of controllable pitch joi nts. and of a wide I will point out later, the mobil it\ conlnunit\ maý tic

collection of thing-s that can be dcae to provide mia- more at fault than the user community becausec %%c

chines that are at ease in the off-road environment. But probably tried to solve the wrong problem w ith i11iosI Of

it has taken us 5() years to convince the Amly customner the new vehicle concepts that w ere proposed. With that

that radial tires in the sin&gk configuration, locking happy note. I Will turn to ý%.ho did wrhat to \\honi.

differentials and central inflation systemns are reliable. In the beginning. God created mud. and the Bureauine\pensive. not really exotic and can provide signifi- cracy created the NIUdI Nobility, Committee. 11wc formacant. if not dramatic. improvements in performnance. As tion of the committee formnalized mobility as a problem

Figure 4. 8>6 ver-sion of the MEXA vehles.

4
and eventually led to mobility research efforts and development of the Weasel was remarkable in that it

organizations having the goal of solving the Army's was designed at the newly formed Detroit Arsenal in a

mobility problems. period of six weeks; compare this to the 14 years

The period between the two World Wars saw virtu- expended on the disastrous M 114 personnel carrier.

ally no research or development of military vehicles. It is difi :,,lt to be precise in tracking the dates at

The Quartermaster Corps had responsibility for the which various people began their work; most of the

development, procurement and maintenance of the early researchers a.'e dead and those who aren't have

modest collection of vehicles that the Army had. Prob- flexible memories. The Mud Mobility Committee had

ably the most ambitious piece of vehicle development joint U.S./U.K. membership, and its name implied that

was done by Walter Christie, who thought that he had a mud was the primary problem to be addressed. The

contract with the War Department to build a new tank. Committee advised Board #2 at Ft. Knox relative to

He devised a highly efficient suspension system that their test procedures, and a reference mud course was

relied on large-diameter road wheels that provided a established there. The board, which later became the

ground pressure that was fairly uniform and resulted in Armor Board, was responsible for all tire, track and tire

a low rolling resistance. The vehicle was capableofvery chain testing for the Army but had no research role.

high speeds but was rejected, partlybecauseofthebattle However, the earliest studies seemed more heavily

between Christie and the War Department (which alleg- involved with sand than mud. Colonel Karl Eklund,

edly included a dramatic trip up the stairs of the Trea- who was responsible for an Engineer Reseaich and

sury Department with an angry Christie dismounting Development Laboratory study, was one of the first

the vehicle and storming away) and partly because there investigators to attempt to develop an understanding of

was not a clearly stated need for new vehicles and no the interaction between tires and soil. He conducted a

money to buy them even if there were a need. Mr. series of tests in the Mojave desert in the 1943-44 time

Christie took his suspension to Europe, where it became frame, and the analysis of the results of these tests

the mainstay of the German Panzer fleet. produced an equation that was known widely as the

With the entry of the U.S. into WWII, responsibility Eklund formula, which related tire pressure and several

for automotive equipment was transferred to the Ord- other tire parameters to performance. The formula was

nance Corps, and their frantic activities to get an ad- elegant in its simplicity; only apiece of paper and pencil

equate vehicle inventory produced some very good or a slide rule was needed to estimate vehicle perforvehicles: the jeep (Fig. 5) (or peep, if your memory goes mance. Whenever mobility grey heads meet, Karl's

back farther than you like to admit); the 2-1/2 ton name is sure to come up with a certain air of nostalgia:

Jimmie; the Weasel (Fig. 6) and the M4 tank series. The "If good old Karl were still around, life would surely be

r -

AmW - nl• rii a rkl mt 9f

Figure 5. The original "Jeep."

5
Figure 6. The WWII "Weasel." the miracle machine.

simpler without all this computer nonsense." was made to back up when forward motion had been

At about the same time that Eklund was working in lost. The key point to the careers of Kerr and England

the Mojave, Dick Kerr, Bill England and J.W. Shields was that they had an in-depth understanding of how tires

were conducting an extensive series of tests with the behaved; this understanding was gained by years of

objective of selecting a tread for the tires to be used on observing vehicles in the field rather than by research in

all wheeled vehicles. If tenacity is a virtue, the length of the laboratory that could provide an understanding of

time that the selected treads stayed around would imply the fundamentals of tire performance.

that the series of tires was faultless. There were four Camp Bullis became the first "center" for tire testNDCC treads that were agreed upon. As time passed, ing. It was first operated by the Copolymer Company,

the identity of the different treads seemed to disappear, which was tasked with determining the performance of

but the sand version, if findable, is still considered to be tires using the new synthetic rubbers. Bullis operations

as good in sand as any of th6 current tires. The tests by began in 1942, and Copolymer was replaced by Hodges

Kerr and company reflected the early wartime approach Transportation in 1951, who ran the operation until

to R&D: get out in the field and test everything that you 1957 when it was closed down.

can find and come up with the best that is available. The first real Army mobility research began in 1944

There simply wasn't time to study why the best was at the Waterways Experiment Station in preparation for

best; results were needed immediately and work was a the invasion of Japan. The landing at Iwo Jima was a

seven-day-a-week routine. In later years Dick Kerr disaster, when most of the automotive equipment got

joined ARAMCO in Saudi Arabia and trained operators stuck on the beach, which consisted of powdered coral

for heavy, expensive equipment to solve transportation rather than sand as assumed, and the vehicles were easy

problems in the desert. He solved both people and prey for the Japanese defenders. WES began what was

vehicle problems so well that his name was known a long series of studies that relied on the cone penefromthroughout the truck/trailer world. After solving eter in order to assure that the Iwo Jima disaster would

ARAMCO's problems, Dick became the Chief Scien- not be repeated. Keith Boyd, Chief of the Flexible

tist of the Transportation Corps. Bill England took over Pavements Branch, selected 14 vehicles that reprethe tire group at TACOM and defended the NDCC until sented the Army vehicle fleet and began a series of tests

his retirement. One of his arguments for the NDCC tire to relate soil strength as measured by the cone penwas that it developed the same traction whether going etrometer to the ability of a vehicle to negotiate a given

forward or backward: if forward traction wasbetterthan area. They ran tests both at WES and at Yuma Proving

rearward traction, he reasoned that in marginal condi- Ground; these tests consisted of progressively weakentions a vehicle could become immobilized if an attempt ing the soil by adding water until the test vehicle became

6
immobilized. The soil strength, or lack of it, that pro- approach is that it was assumed that to be able to operate

duced immobilization became the vehicle cone index, in very soft soil was a virtue, and that was the controlling

The concept was that when Japan was invaded, scouts criterion for "good." The concentration on soft soil as

would be sent forward to measure the soil strength of the the primary vehicle problem is fully understandable in

rice paddies to determine which vehicles could be light of the horror stories about seas of mud that came

moved off-road. out of WWII from Europe and the Pacific theaters, and

The idea was interesting, but studies conducted it took many years for the development of a realization

many years later showed that weak soil was not a rice that soft soil operations play a very small role in the life

paddy problem: to have a rice paddy it is necessary to of a vehicle. When soft soil is a problem, it may well be

have an impervious base or else the water will drain out. critical, as demonstrated in Figure 7, but soft soil perforThe problem posed by rice paddies to vehicles is one of mance must be viewed as one of many criteria used to

geometry, because there must be berms to keep the evaluate a vehicle. The WES studies concentrating on

water in the paddy and the berms are severe obstacles to granular and fine-grained soils were designed to estabany wheeled vehicle and to many tracked vehicles. One lish the one-pass cone index and the fifty-pass cone

outcome of the initial WES study was the development index. Essentially these numbers were taken as a meaof two concepts that plagued the mobility research sure of quality: if one vehicle had lower indexes, it was

community and was the source of confusion and bick- better than the other vehicle. They also did some work

ering. These two concepts were trafficability and mo- in snow in Greenland and at Ft. Churchill and

bility: trafficability referred to the ability of soil to Kapuskasing in Canada. They made the same error in

support traffic and was a function of soil strength; approaching snow that TACOM did in its snow studies

mobility, on the other hand, was the ability of a vehicle and as did CRREL, which had little excuse for sharing

to operate on soft soiland wasafunctionofsoil strength their sister lab's views that snow is similar to soil and

plus some vehicle characteristics. Although the distinc- that soil mechanics and snow mechanics are closely

tion between the roles of these two ideas seems modest, enough related that what works for soil should work for

many of the discussions of these concepts were con- snow and that therefore the equations relating vehicle/

ducted with the dignity of a hair pulling contest and soil interactions can be applied freely to either snow or

created much heat but little light and absolutely no soil.

mutual understanding. The WES approach for the description of soil/vehicle

Prior to 1962 the majority of mobility research was interactions worked well and still does in most situadone for the Army at three facilities: the Transportation tions because their equations are based on an incredible

Corps' Transportation Research Engineering Command number of tests and those equations are almost exclu-

(TRECOM), WES and the Ordnance Tank Automotive sively applied to the kinds of vehicles used to establish

Command, the predecessor of TACOM. The Snow, Ice the equations. The truck/tank of WWII is hardly distinand Permafrost Research Establishment, later CRREL, guishable from the vehicles of today; the wheeled veconcentrated on oversnow mobility, but they tended to hicles are conventional, and the tracked vehicles are

be more concerned with evaluating and developing conventional so that the equations used to predict yeequipment for operations in deep snow that could be hicle performance, which are based on data gathered on

used to support their science programs. Because each conventional vehicles for decades, should work nicely.

technical service was a completely separate agency, the When WES established the Mobility Systems Diviprograms of the three major groups went their indi- sion in the early sixties, Warren Grabau began forcing a

vidual ways, since there was no strong hand monitoring change in their conception of off-road mobility by

what was going on. I will cover their approaches and including many other parameters in the analysis of the

histories reasonably briefly. vehicle/terrain problem. Such things as vegetation, tree

WES: The WES approach essentially followed the spacing and the use of terrain analysis to prepare going

lead established by Keith Boyd (who later became the maps based on the total terrain environment began to be

Chief Engineer of CRREL) and was based on the cone introduced, and a more sophisticated outlook develpenetrometer. They conducted a great many tests and oped. In addition, Grabau proposed the concept of linear

gradually developed empirical relationships that re- obstacles, such as rivers, streams or cliffs, to highlight

lated the vehicle cone index to such things as transmis- the fact that some obstacles extend well to the right and

sion type, number of wheels, wheel size, engine power, left of a vehicle's path.

number of powered wheels, track contact area, nominal Although much of WES's work involved field operacontact pressure and any parameter that appeared to tions, they developed laboratory facilities consisting

have a critical role in how well a vehicle performed. One primarily of a series of truly impressive soil bins that

problem with the "how well a vehicle performed" were mounted on rails so that they could be moved from

7
I :D I.

Figure 7. A 1/4 ton with little imnniediatefuture.

the test location to the soil processing station. The terrain/vehicle mechanics." Not too many people appresophisticated wheel carriage drive permitted high-speed ciate being called irrational, and Bill Tumbull and his

tests of single wheels and also allowed the introduction team were no exception. More about this later.

of limited steering angles. The automatic readout, stor- The basis of what 1 will call the Bekker approach was,

age and processing of performance data was high tech at the outset, the development of equations that defor the time. The system included a very accurate scribed wheel/soil and track/soil interactions based on

apparatus for soil processing, a problem that slowed the classical soil mechanics. Everyone in the laboratory.

tests conducted at many soil bin facilities. These bins including the secretary. had a copy of Terzaghi on their

were used to evaluate several wheel concepts proposed desk that was expected to be dog-eared. Greg developed

for the lunar roving vehicle; because of the critical the Bevameter, which had two parts: a shear annulus

importance of making the proper wheel selection, their used to establish the Mohr/Coulomb soil parameters and

ability to maintain tight control of soil conditions as- several plates that were pushed into the soil to allow

sured that the selection was reliable. The laboratory had calculation of an equation that produced three parama well-equipped soils laboratory that supported their eters that were related to the bearing strength of the soil.

soils studies. If an oversimplified characterization of the It was assumed that traction could be calculated on the

WES approach can be accepted, it would be that most of basis of the Mohr/Coulomb parameters and sinkage.

their early mobility studies, clearly not all, were experi- and hence motion resistance could be calculated from

mental, but that the results remain successful partly the bearing strength parameters. The fact that the two

because there has been little change in the principal things, sinkage and traction, were far from independent

object of their studies: the conventional vehicle, was accepted as being relatively irrelevant. The output

TACOM: The TACOM facility was established as from the equations was the drawbar-pull-to-weight rathe Land Locomotion Laboratory in the mid-fifties tio. and TACOM fell into the same trap as WES by

when Greg Bekker was enticed away from Canada with assuming that a better ratio meant a better vehicle. The

the promise of dollars, of equipment, of freedom to clash between the Bevameter users and the cone pendevelop an Ordnance mobility research program and of etrometer users probably clouded the whole issue of

all kinds of tender loving care. The birth of the labora- vehicle mobility and delayed recognition of the total

tory was also the birth of a decade of fierce animosity vehicle/terrain interaction problem by a decade. Bekker

between the Bekker camp and what had become the left TACOM in 1962. but, unfortunately, even today

Tumbull camp of WES. The whole misunderstanding there is an undercurrent at mobility conferences of the

could likely have been avoided if the Ordnance program earlier clashes over the two approaches, which may well

had not become touted as the "rational approach to have been equally flawed.

8
Bekker shared Grabau's viewv that mobility was limits to all military vehicles except in the winter when

more than soft soil and early on began a series of studies the bogs were frozen and were no longer barriers. The

to relate ground roughness to vehicle speed. This work, studies of vehicles operating in trails and unprepared

by Bogdanoff and Kozin at Purdue, was groundbreaking terrain began as being observational in nature and

in the sense that their use of stochastic methods applied gradually changed in complexion to be fairly carefully

to describing vehicle ride represented a new level of instrumented and documented. The change was a result

sophistication in terramechanics. It stirred up a great of the gradual realization that understanding vehicle/

amount of interest both in academia and industry, and terrain interactions was hugely more complicated than

mobility researchers started going around talking like originally thought. Because tht change in perspective

aeronautical engineers, saying things like deviatoric, was so important, I will take a few minutes of your time

constitutive or algorithmic. In a more serious vein, one to relate the change: based on ideas about terrain feaof the major impacts of the work that was developing at tures being advanced by Grabau, it was decided that a

the Land Locomotion Laboratory (LLL) was the recog- team of researchers would look at a series of soils

nition that the computer age was around the comer and having the same pedological identification but sepathat we could look forward to solving problems that we rated by as large distances as possible. The proposition

could only think about at the time. There was a move- was that if two soils are so similar that they have the

ment to bring in the best brains that could be found in the same series name, then they should have the same

universities to begin to attack the difficult problems of strength properties given the same moisture contents oi,

soil mechanics, vehicle ride, vehicle stability and a new at least, similar contents. The test was totally inconclurange of topics. This movement spread throughout the sive because in every test site selected, the soil was so

Army Mobility Labs. strong that our vehicularly mounted Bevameter could

Because of the approach of the LLL, there was an barely measure shear strength and was totally unable to

orientation toward laboratory studies supported by field penetrate the soil to establish bearing strength paramstudies. The laboratory had one small soil bin, two very eters.

large soil bins, a vehicle ride facility (consisting of a These results led to a test at the field station to relate

track that had a profile whose power spectral density performance to drawbar pull. The measure of perforfunction was representative of reasonably rough ter- mance was average speed achieved on a test course that

rain), a four-wheeled vehicle model whose characteris- included trails, steep slopes, rough surfaces, stream

tics could be changed to match those selected for any crossings and wooded areas. The drawbar-pull ratios of

particular analytical analysis, and a water basin for the a group of vehicles, including the D7 tractor (Fig. 8), a

study of amphibious vehicles. The basin had a test Weasel and a Polecat (two Weasels joined with an

section large enough to allow the testing of 1/4-scale articulation joint, Fig. 9) were the most significant in the

models in water moving at speeds up to 2-1/2 miles per test. The D7 had the best pull-to-weight ratio, followed

hour. -i , re was a machine shop and a soils laboratory by the Polecat, which was followed by the Weasel. The

to providc in-house independence, results were revealing in that the order of performance

Most of the field studies were conducted at SIPRE's was the reverse of the ratios because the D7 can't go

Keweenaw Field Station located near the campus of the very fast and the Polecat is twice as long as the Weasel

Michigan Technological University. When SIPRE was and is at a disadvantage in conditions requiring agility.

integrated into CRREL, the station became TACOM Attitudes and opinions didn't come crashing down, but

property. Field testing was concentrated in the winter doubts began to creep in.

and mid-summer; to keep the station from being greatly Because LLL was a part of the organization responunderused, TACOM wrote a contract with Michigan sible for automotive development, it had, if not a charTech stating that they could use the facilities toconduct ter, an opportunity to indulge in the investigation of new

any research that they were able to find support for. concepts for vehicles and vehicle components. Thus, in

TACOM's program considered four topical areas: soft addition to the study of terrain/vehicle interaction, a

soil, muskeg, trails and unprepared off-road terrain and significant amount of energy was expended on the

snow. The soft soil testing had the objective of improv- development or evaluation of new ideas. The list of

ing the equations used to predict traction and motion ideas and concepts is fairly lengthy: the spaced link

resistance by identifying differences in laboratory and track (Fig. 10); the hubless wheel (later dubbed the

field conditions. Muskeg testing had the objective of hopeless wheel when it didn't live up to expectations);

trying to find a useful way to measure the strength of the several varieties of elliptical wheels; a stream of articuvegetative mat; unhappily the attempt began with the lated vehicles, each of which had some new idea such as

idea that a modified Bevameter could do the trick and a controllable pitch joint or a capability to inch forward

ended with the conclusion that muskeg terrain was off when immot! ',_ed; walking machines; force feedback

9
Figure 8. The venerable D-7 "Cat."

control systems; flexible frames to permit negotiation major role in conducting their research studies of soil

of severe geometric obstacles; wheels for amphibious and in the construction of vehicle concepts that were

vehicles that acted as propulsion pumps; wheel shrouds aimed at the light-weight end of the scale of TRECOM's

to increase the efficiency of wheeled vehicles operating interests. The TRECOM program was initiated in 1951

in water; flotation bags to convert conventional wheeled with a study of the changes in vehicle requirements that

vehicles into amphibians; and the list could go on. had occurred in the post-WWII period. This study

TRECOM: The Transportation Corps' program was identified two primary needs: to increase the underlargely conducted out of house, with Nuttall playing a standing of how soil behaves and how to relate that

Figure 9. The Polecat; an articulated version of the Weasel.

10
Figure 10. The Cobra with a spaced-link track.

behavior to vehicle operations, and to develop high- became stuck. Become stuck they did, with bonemobility, high-cargo-capacity equipment for negotiat- crushing regularity that slowed progress to several

ing desert. arctic and marshy terrains. An initial reaction miles per day. The results of this remarkable effort

to the selection of this terrain set might be one of demonstrated that given enough time, enough energy

surprise: in 1951 the Korean War was in progress, so and enough will power a team of men can negotiate

that the challenges of hilly terrain, rice paddies and poor jungle terrain. Swamp Fox II was considerably more

roads would seem to be paramount. Evidently the study "tester friendly" in that the tests were of an engineering,

was directed to future needs rather than current needs, rather than operational, nature so that machines, not

which were not likely to benefit from research efforts in men, were stressed to the utmost.

the nearand long terms. That Dick Kerrwas aconsultant The criterion that TRECOM selected to evaluate

to the Transportation Corps can explain the interest in performance differed from the WES and TACOM crimoving heavy loads over deserts. The importance of the teria in that it was tons of cargo moved per hour. The use

DEW Line and the need to resupply the DEW sites by of this criterion had a major impact on the kinds of

ground transport could explain the need to develop an automotive equipment that they considered because

arctic heavy-load capability. It is difficult to find marshy speed became secondary to load, making it possibly

terrain as being of vital interest as a transportation better to move a large load slowly than a light load

problem simply because major military operations are quickly.

not conducted in marshes. In the mid-Vietnam war, In developing their research program, the TRECOM

there were operations in the Rung Sat and in the Plain of people decided that the first priority was to develop an

Reeds, both of which qualify as marshy terrain, but analytical basis to guide the conduct of scale model

these operations were at the squad, platoon or company studies. If very large concepts were to be evaluated, it

level and did not involve extensive logistical support. would be cost-effective to deal with scale models that

One explanation is that the 1951 study found that the could demonstrate concept feasibility without breaking

mainstream development activities ignored marshes the bank. Nuttall (of Wilson, Nuttall and Raimond) and

and that the problem should at least be studied. This Finelli (of Stevens Institute) were contracted to develop

position was reflected by the two major exercises that the critical scaling laws and soil parameters required to

TRECOM conducted in the jungles of Panama. The assure the credibility of scale model test results. Infirst, Swamp Fox, was almost an exercise in futility in cluded with the identification of critical soil parameters

that it consisted of driving a fleet of military vehicles was a need to develop apparatus to measure the paramthrough an untamed, unmodified jungle, relying solely eters and methods to extract the data needed. Nuttall and

on on-board equipment to recover vehicles when they Finelli developed the scaling laws successfully but

II
found dealing with the critical soil parameters a difficult a not-very-small model and a very large prototype. The

chore, as did virtually every other research team who second purpose of obtaining the Marsh Buggy was to

followed them in attempting to conduct model tests in evaluate its potential as a heavy load carrier for marsh

soil. The Nuttall/Finelli work served as a valuable operations. It is not clear that it served its second role as

starting point for many subsequent studies, so their well as its first.

efforts can certainly claim success. The arctic areas selected to serve as a development

The TRECOM vehicle developmental concepts were laboratory were the ice cap regions that required moveinteresting both in their individual originality and in ment over great distances and that placed a premium on

their variety of application. The decision to develop moving a lot of stuff with a high degree of reliability.

heavy load movers in desert, arctic and marshy terrains The approach settled upon was the concept of a land

demanded variety at the outset, since each terrain type train; so firm was the train concept that the first unit was

had its peculiarcharacteristics (although a goodsolution called a locomotive to emphasize the fact that its sole

for the Arctic might work well in desert terrains), function was to provide power to the three trailer units.

Because of Kerr's remarkable success in solving the The locomotive and all trailers were powered; the deheavy load movements of ARAMCO, it is evident that sign payload was 90,000 pounds to be moved at a

it was determined that the technology, equipment and maximum speed of twenty miles per hour. Two models

operational doctrine were on hand that could be quickly of the train were constructed, one of which was tested in

exploited if desert operations became a fact; this took Greenland (Fig. 11). Stability problems were encounabout 40 years to occur, and re-supply by land transport tered at about fifteen miles per hour, and later Nuttall

was hardly a factor in Desert Shield or Desert Storm. was approached to provide a solution. He constructed a

Thus, the emphasis of the TRECOM vehicle studies was four-unit train using quarter-ton vehicles and looked at

on marsh and arctic operations. power control stability and steering stability, but the

The development of the Marsh Buggy was an inter- passage of time had made the study obsolete.

esting program because of its dual function. First, a full- The development of the PoleCat II by TRECOM was

scale version of the four-by-four vehicle, which had a reflection of their pursuit of heavy load movement

120-inch-diameter tires, was purchased, and a 1/4-scale capabilities. The PoleCat had been developed for SIPRE

model was constructed. The pair, which eventually to support their snow studies. As mentioned earlier, this

became affectionately known as Mutt and Jeff, was used vehicle consisted of two Weasel chassis connected with

to evaluate the validity of the scaling factors and was a joint that transferred power from the front unit to the

likely one of the first opportunities to conduct tests with rear unit and also provided steering. The vehicle was a

Figure 11. The Letourneau Land Train.

12
great success and was used extensively in support of potential performance capabilities of both their own

SIPRE's and CRREL's work in Greenland. TACOM vehicle fleet and the threats'. The outline of the model

used several Polecats as workhorses to support the was agreed upon, and the next several years were

winter and summer tests in northern Michigan and in devoted to developing, collecting and providing input

Greenland. The success of the PoleCat prompted to the model. The deficiencies of the model have been

TRECOM to consider a much larger version, having the the driving force for most of the studies that have been

potential of tripling or quadrupling the load-carrying initiated since the introduction of the model into the

capability of the original machine. The vehicle was built vehicle procurement process and by its acceptance as

by Nuttall and performed well enough that it was the NATO mobility model.

decided to build an amphibious version, the Terrapin, The CRREL mobility research program for the past

named after the large turtle that inhabits the salt marshes 20 years or so is a demonstration of the dominance of the

in coastal areas. The Terrapin was a success, but time needs of the model. Emphasis was transferred from the

had also passed it by. interaction between vehicles and deep snow to shallow

In 1962 an event occurred that would have a pro- snow. Reason: except for the BV206 (Fig. 12), there are

found effect on the Army's mobility research program, no vehicles in the inventory that can operate in deep

along with virtually every aspect of the Army. The snow; hence we have no need to develop a deep snow

Army Materiel Command was formed, and the R&D model. In addition, the Canadian mobility research

responsibilities of the technical services were handed program is directed to the deep snow problem so that a

over to the direct control of the new command, with the parallel U.S. study would be superfluous. The primary

exception of the Corps of Engineers, which had major soft soil problem facing military operations is the clasresearch duties but was responsible for almost no devel- sic mud season when we have to attempt to operate in

opment programs. The impact on mobility research was thawing soils; thawing soils were never included in the

that one man now monitored all research in progress, model because no work had been done to study the

including WES's because their mobility research ap- problem. Therefore, CRREL developed a program to

,.,dto AMCNaCid not to the Corps. The one man, Robert study this particularly difficult analytical and operaPhillipe, was disturbed with what he found and eventu- tional problem in order to expand the capabilities of the

ally formed a committee, chaired by Dick Kerr, to model.

survey the research and development in progress and Contributions of the mobility research community:

assess its value to AMC and the Army. The Kerr There have been literally millions of dollars spent over

Committee spent several weeks visiting the three main the past 40 years on mobility research, learning about

players, receiving in-depth briefings and tours and vehicles, aboutvehiclecomponents, about terrain, about

being dragged to desperate lunches, cocktail hours and the fundamental behavior of soil and snow, about the

dinners. The group prepared its report, which was not interaction of vehicles with terrain and the components

very flattering to any of the labs involved, and it recom- of the terrain, so that it is reasonable to ask what all this

mended that the WES and TACOM programs continue effort has produced. Frankly, it is hard to answer the

with the understanding that programs would be coordi- question, partly because one of the contributions of the

nated. Because CRREL's program was low key, they mobility community was negative, because it could

weren't taken behind the barn, but the message was recommend to not do something and back up that

clear that business was not to continue in the future as recommendation with fact. An example from the past

in the past and that the Army's program would be that would not happen today because of the knowledge

subjected to frequent scrutiny, that we have gained overthe years was the Snow Cruiser

A day of reckoning occurred in the mid-sixties when (Fig 13), designed and constructed to support a Byrd

it was agreed that TACOM and WES would either have expedition to the Antarctic. The design was given

a coordinated program or there would be no program. A careful attention, and all details appeared to be adseries of meetings produced the AMC Five Year Mobil- dressed. Unfortunately Dr. Thomas Poulter. the engiity Plan. The goal of the plan was a verified mobility neer/scientist responsible for the vehicle development.

model whose primary functions were to develop vehicle assumed that since snow was granular and sand was

concepts to meet a given set of environmental condi- granular, it would be valid to test the vehicle in sand and

tions and to evaluate concepts proposed by other people infer the over-snow performance from the sand tests.

to meet the stated conditions. A secondary objective That nothing could be further from the truth was demwas to assess the potential of the model produced by the onstrated by the performance of the Snow Cruiser when

WES/TACOMteam, laterexpandedtoincludeCRREL, it arrived at Antarctica. It was able to debark from the

to be used by field commanders to assist in making ship that delivered it but was able after much effort to

decisions relative to route selection and to identify the move only about a hundred yards in the snow. Thus, for

13
Figure 12. The B V206. mna;ter i¢f snaw tcountrY.

the lack of a little knowledge, the Snow Cruiser was the majority of the mostly u1siuccessful attemipts that

downgraded from the primary science support vehicle have been made to provide newy leekl, of oft-road

to a stationary office and laboratory. Eventually the vehicle perfornance. Virtually all of the prototv pe, of

Snow Cruiser became a component of an iceberg and high mobility concepts that haN e been constructed have

sank to a watery grave somewhere near the Antarctic involved the goal of providing device,, and \ ehicle, that

continent. can operate in extremely soft soil. The nnLInber Oft \\ heel

Before addressing contributions that can be consid- concepts. of track concepts,, of hybrid ,,uspen,,ion conered significant, I think that it is important to examine cepts. of hybrid vehicle concepts that have been proFigure 13. The Sn,-Cruiser.

14
posed to conquer demon mud would take weeks, per- The militarization of Gama Goat involved a process of

haps months, to catalog. Sadly, the expert has been as increasing weight while decreasing wheel diameter

guilty of misreading the mobility problem as the ama- with the mobility community attempting to set things

teur, but he has been more often able to get his ideas into right. The scraper was not intended to be a highway

hardware because of having expert status and thus vehicle and therefore no suspension was provided.

capable of inflicting more damage than his idea de- Large, low-inflation tires worked well in the scraper

served, role, but when placed on the highway the vehicle

In defense of the mobility expert. I offer a purely bounced so badly that 15 miles per hour was about tops.

random chance event that occurred in my attic in the The articulated vehicle concept was not at fault; the

very recent past. While looking tbr a door handle, I saw application of the concept was at fault. When the rethat the shelving holding our National Geographic quirements for the Small Unit Support Vehicle (SUSV)

collection had failed. I walked over to the stack, and the were published, it was clear that the requirement could

topmost issue had on its cover as its first article "'The only be met with an articulated concept. When hands-on

Coming Revolution in Transportation"; the issue date evaluations of available vehicles were completed, the

was September 1969. What things did I find that were BV206 was the clear winner. However, the Swedish

to be responsible for that revolution? The air cushion Army would never have selected an articulated vehicle

vehicle wafting us across heavy seas with barely a concept as their mainstay if U.S. Army mobility rebump. The Concorde soaring into a new age. The people search had not established, analytically and experimencapsule eliminating the need for your car in the urban tally, the remarkable advantaoes of this vehicle form for

environment: dial your destination and sit back in peace some terrain/operational environments.

and comfort. VERTOL aircraft solving airport conges- Probably the contribution that has brought more

tion. Trains, trains: single rail, push-pull with a gas satisfaction to more people in the mobility community

turbine at either end; "Bullet" trains in Japan operating is the user recognition, after years of cajoling, that it is

at 130 miles per hour and so smooth that you can drink possible to make gains in wheeled-vehicle off-road

your tea without fear of spillage. The Boeing 747 has performance and save money at the same time. Save

lived up to and far exceeded all of the predictions made money first: although it was difficult to establish exact

in the Geographic article, but all of the other problems figures, the best data that could be found stated that the

that the revolution was going to solve are still with us average life of the NDCC tire, regardless of manufacand, in most cases, are more intense. The point of this turer, was of the order of 7000 miles. It had also been

defense is that good solutions to problems may not be established by tests that the NDCC tread on a bias-ply

useful solutions because the cost of implementing them carcass was the worst performer of any currently availmay be greater than the cost of living with the problem. able tires except on ice, where it was as good as any

This situation may well explain why what appear to be other tire. By switching to all-season tires with radialgood solutions to proposers are viewed as being bad ply construction, performance could be increased, but,

solutions to potential users. more important to the user who buys the tires, life could

One of the contributions that can be attributed to be dramatically extended. Performance next: the couArmy mobility research is the articulated, over-the- pling of radial tires with a central tire inflation system

snow vehicle: the BV206 produced by Hagglunds in and locking differentials can provide a major perforSweden (Fig. 12). Curiously, perhaps, the articulated mance increase. The radial tire can be deflated to very

form was conceived of early in this century to provide low pressures, which increases contact area with a

a long, narrow track that would reduce motion resis- minor increase in contact width, resulting in an increase

tance in soft soil and thereby increase net traction. Mr. in net traction. The central tire inflation system allows

Diblock. in submitting his 1918 patent application, did tires to be deflated rapidly, on twe order of 5 minutes for

not. I am sure. describe his invention in those terms, but a five-ton truck as compared to 50 minutes when done

that is whatheachieved. SIPRE.TACOMand TRECOM manually. After moving back on the road, the tires can

were all involved with the exploitation of the articulated be re-inflated while on the move. The locking differenvehicle concept and rushed forward with an articulated tial is a device that extracts the maximum traction

vehicle solution for any new vehicle requirement that available from a soil/wheel system: with a standard

appeared on the scene. The introduction of a successful differential, what is called a 2x4 is actually a i x4 when

articulated vehicle was delayed by attempts to milita- soil surface strength is low. A differential is a torquerize either successful civilian prototypes such as the splitting device so that all of the driving torque is

Gama Goat or vehicles such as the Letoumeau scraper, developed by the wheel operating in the weakest soil.

which performed exceptionally well in roles not really Similarly, a 4x4 is a 2x4 and a 6x6, a 3x6. Point made.

compatible with the military heavy transport scenario. By activating locking differentials when the going gets

15
tough, the operator, regardless of the configuration of supply system will be flooded with a mishmash of

his vehicle, at least doubles available traction. The new oddball tires, with the result that the system would

five-ton trucks and HMMWVs coming off the assembly become over-burdened.

line have radial tires and central tire inflation systems; The most important contribution of the Army mobilat least we got two out of three. The acceptance of these ity community is the mobility model that contains the

new (old) ideas is based on the fact that the user could results of the efforts several hundred people over sevbe shown that he could have an increase in performance eral decades. It is comprehensive in that it includes all

without paying an unacceptable penalty. of the critical elements of the highway and off-highway

The switch from rear dual wheels to rear singles also environments; it includes the constraints imposed by

represents a major victory for the mobility research the vehicle and by the operator. Currently the operator

community. It had been established both by theory and only enters the analysis as a limit to speed in rough

by experiment that a properly selected single tire can terrain because there is a well-identified limit to the

provide better performance than a set of duals. The vibration input that operators will accept. An expanded

reason is straightforward: traction is a function of con- operator module is appropriate but has not been develtact area; motion resistance is a function of both contact oped to date because of concern over stepping on the

area and its orientation. A wide tire produces more human engineering turf. The model is still far from

resistance than a narrow tire, as any Model T Ford perfect, but it is gradually reaching the point where

owner would tell you. However, to produce the same changes will be less and less significant.

contact area with a narrow tire as that produced by a Given this circumstance, where do we go from here?

wide tire, it is necessary that the diameter of the narrow I'm sure iiiat there will always be fundamental questire be greater than that of the wide tire. The large- tions that will excite our imagination and when andiameter tire was slow to receive acceptance because it swered will improve the model, but I wonder whether

made cargo loading a bit more difficult, and the idea serving the model will use our talents most effectively.

didn't seem to make good intuitive sense to the user. The search for a better understanding of all elements of

The combination of nagging by the mobility research the terrain-vehicle system is a worthy end itself and

comimunity and the rejection of the dual tire configura- hardly needs defense. But what of the rest of ourenergy?

tion by almost every army in the world convinced the I see a body of knowledge that has been developed and

user to cave in to the forces of progress. An important that continues to grow, and it is our job to seek out the

point is that the change could be accepted because it problems facing the users of automotive equipment and

could be shown that a performance improvement would develop appropriate solutions. If the mobility research

beobtainedaccompaniedwithacostsaving.A6V6now community has done nothing else, it has generated a

had six tires instead ten tires and six wheels instead of perspective of what is really important and has achieved

ten wheels, clearly a cost saving. It is apparent that the a maturity of viewpoint that can provide a dispassionate

overwhelming criterion for acceptance of change is at assessment of the worth of a new idea or of a solution to

least a dollar return for every dollar invested, a problem and then act on that assessment to produce a

One of our contributions has been elusive in its positive change.

implementation. This is the development of a new way Perhaps during this workshop, while you are disto specify tire requirements, in which the automotive cussing our current approaches to the analysis and

industry would be given a level of performance that had evaluation of off-road vehicle performance, you can be

to be achieved and it would be the responsibility of formulating in your mind what you view as the most

industry to meet the performance specifications in any important future needs that we should be addressing. It

way that it chose. The tire selection would not have to should be possible for us to take a few minutes near the

L. e radial ply or bias ply because the sole criterion is end of the week to examine your collective thoughts.

delivery of the required performance. There has been Examples of vehicles developed to operate in exconsiderable user happiness with the concept, but the tremely soft soil that range from the almost practical to

procurement people balk because they worry that the the bizarre are shown in Figures 14-17.

16
li.gutv 14 The Rohi n .N:ut t c.•uNid on the Ala2skan No'rth Slo pe

Figure 15. The Terra-Star desgi,uedkfOr operation in deep mud.

17
44A 

~

Ampt

Figure 17. A version1 of the Archimedes screw vehi/cl.

18
2. PREDICTION AND TESTING METHODS

19
Predicting Vehicle Mobility On Snow-Covered Slopes

PAUL W. RICHMOND

U.S. Army Cold Regions Research and Engineering Laboratory

Hanover, New Hampshire 03755-1290

ABSTRACT

Recently, a semi-empirical model for shallow snow mobility predictions was developed at

CRREL in support of an evaluation of wheeled and tracked vehicles. These equations were

developed from a large data base of traction and resistance data obtained on level, snowcovered terrain using current U.S. Army military vehicles. Winter military operations will

not be limited to level terrain; thus, it is important to be able to predict mobility characteristics

on snow-covered, sloped terrain as well. This paper describes a simple modification to the

CRREL shallow snow mobility model to account for sloped terrain and compares mobility

predictions to go-no-go mobility tests on snow-covered slopes. Go-no-go data were

available for nine vehicles (both wheeled and tracked), all obtained at the Keweenaw

Research Center, Michigan, using their test slopes. Snow conditions ranged from a thin layer

of hard packed snow to 60 cm of 150-kg/im3 density snow. Go-no-go predictions using the

model were correct for about 70% of the test data available. It was found that the surface

underlying the snow may have more effect on traction on slopes than it does on level terrain,

at least for shallow, low-density snow layers.

INTRODUCTION load on each wheel (track). In cases of marginal mobility, vehicle momentum must also be considered. This

Recently, researchers at CRREL presented and veri- analysis examines snow-covered slope mobility and

fled an oversnow mobility model (Blaisdell et al. 1990, compares predictions with available test data.

Richmond et al. 1990). This model was developed from

traction or drawbar and resistance tests on level or

nearly level, snow-covered terrain using a variety of TRACTION

current military vehicles. Since these vehicles are also

expected to be able to travel over sloping terrain, it is On level, snow-covered ground, the gross traction

also important to know their limitations on snow-coy- generated by a vehicle can be estimated by

ered slopes. Measurements of traction and resistance on

snow-covered slopes are difficult to obtain, and the Tg = 0.851 (N/A)0.82 3 p < 550 kg/im3 (1)

author is not aware of any such data. Results of go-nogo tests on various snow-covered slopes were presented Tg = 0.321 (N/A)0.97 p > 550 kg/m3

by Green and Blaisdell (in prep.) and by Osborne and (Richmond et al. 1990) (2)

Guitar (1986).

The main effect of slopes is the redistribution of the where Tg is the gross traction generated per driven

force of gravity on the vehicle body forces (Yong et al. wheel (track) in kilopascals, (N/A) is the normal load on

1984). This redistribution is seen as an additional resis- the wheel (track) divided by the contact area in units of

tance term due to gravity and a reduction of the normal kilopascals and p is the snow density. If we assume that

20
there is no change in the failure mode of snow under a Tnet = Tg - Rs - Rg (6)

wheel (track) on a slope then,

where each term represents the sum of traction or

Ns = N cosO (3) resistance for the whole vehicle. The resistance due to

running gear, tire deformation, etc., has already been

can replace N in eq 1 and 2 where 0 is the slope angle. removed in obtaining the Tg term (eq 1 or 2). Tnet, the net

(Ns is the normal force acting on the tires or tracks of a traction, must be positive for vehicle mobility.

vehicle on a slope.)

MOMENTUM

RESISTANCE

Vehicles can negotiate short, steep slopes by makA number of equations exist to determine the inguseof momentum built upduring the approachtothe

motion resistance due to deformation of a snow cover, slope, i.e., a running start. Using Newton's second law

In selecting an algorithm for the CRREL shallow snow (F = ma), the work required to move an object can be

mobility model, Blaisdell et al. (1990) choose a model written

proposed by Liston (1974).

Work= F dx= mvdv. (7)

Rs= pbhpo{ [l/(pf- po)] ln(pdpo) - (l/pf))

Solving the right side equality for F, we can obtain an

Po< Pf (z > 0) (4) average force in terms of vehicle speed, which can be

added to the traction generated on the slope in question

Rs = 0 P. = Pf (z = 0) if required (i.e., we only need to account for this if the

net traction is negative).

where p = tire inflation pressure

b= maximum tire or track width F-= W (2_v2) (8)

h = snow depth 2gx

p, = initial snow density (prior to tire

or track passage)

pf maximum (final) snow density Table 1. Empirical equations used to predict Rs, from

(after vehicle passage) Richmond (1990) and Richmond et al. (1990).

z=sinkage.

Cons tant* Exponent Vehicle

Richmond et al. (1990) tried to develop a general (d) (e) data Vised

empirical relationship from a large data base of different (d)_ _e) _dataused

vehicles (which included both wheeled and tracked 100.8 0.59 HMMWV

vehicles); however, on the average it was not any better 146.7 0.6 LAV25

than that proposed by Liston (only within 50% on 275.43 0.5 HEMrT

137.25 0.61 HMMWV. HEMiTr LAV25t

average, for resistance). Richmond et at. (1990) pre- 145.18 0.8 SUSV

sented relationships for each vehicle they tested and 14.71 1.6 M1 13AI

Richmond (1990) combined some of these data and 306.54 0.9 BFVS

presented separate empirical relationships for wheeled 157.54 0.83 M 113. SUSV. BFVS**

and tracked vehicles. These equations are presented in

Table 1. * The equations are of the form

A vehicle attempting to negotiate a snow-covered Y dx

slope must overcome gravity in addition to expending where x = parameter (Po x b x a) a = length of wheel (track) in contact with snow energy in compacting and deforming the snow. The b = tire (track) width

resistance due to gravity Rg can be described by po = initial snow density

y = external motion resistance due to snow on a per

Rg = W sino (5) tire or per track basis.

The SUSV was assumed to have two tracks because of its extremely

low ground pressure, and thus the second pair of tracks do not seem where W is the weight of the vehicle, to behave as trailing tires.

By use of this approach, the general mobility equa- t Used for M34 truck predictions.

tion for vehicles on slopes is ** Used for M60 tank predictions

21
where W = vehicle weight Results of 38 tests are presented. Equations I and 2 were

v0 = initial velocity (base of slope) used to estimate gross traction (eq 2 was only used for

v, = final velocity (crest of slope) the 560-kg/m 3-density snow case). Rs, used in eq 6 to

x = length of the slope determine Tn.t, was calculated using the equations from

g = gravitational constant. Table 1, since it was thought that these individual

vehicle equations would provide more accurate resistance values than the more general relationship (eq 4)

RESULTS used in the CRREL shallow snow model. Total resistance from the CRREL Fha~low snow model is preGo-no-go data for vehicles on slopes were ob- sented for reference and the overall slope prediction

tained from two sources, Green and Blaisdell (in prep.) performance is not different from using the empirical

and Osborne and Guitai (1986). All of the tests reported resistance equations. Equation 5 was used for calculatwere done on slopes at the Keweenaw Research Center ing the effect of the slope angle (Rg). Equation 8 was not

(KRC), in northern Michigan. The author was also able included since most of the tests were done from a

to obtain video tapes of some of the tests reported by standing start at the base of the slope. The relative

(Jrýen and Blaisdell. The test slopes, along with other magnitude of this term is discussed below.

roads and test areas at KRC, generally become underlaid with a layer of packed snow as the winter progresses. Even though the slope surfaces are soil, for DISCUSSION

snow test purposes, the underlying surface must be

considered hard packed snow. This observation is con- Initially, 13 mobility predictions indicated that the

firmed by the tapes, which show, for example, an Ml 13 vehicles should be able to successfully negotiate the

with its tracks locked, sliding backwards down a slope, slopes where they did not. There were no cases where

Table 2 contains vehicle characteristics data for the no-go conditions were predicted and the vehicles did

vehicles used in these comparisons. Tables 3 and 4 negotiate the slopes. This means that the analysis either

present the go-no-go data and calculations of Tnet. under-predicted resistance orover-predicted gross tracTable 2. Tire and track data for military vehicles.

Inflation Contact

Tire pressure Radius* Widtht area** Weight

Vehicle nomenclature (kPa) (im) (in) (n12 ) (kN)

HMMWV 37.00 x 12.5 R 16.5 138/152 0.429 0.33 0.074 33.45

36.00 x 12.5 LT 138 0.425

HEMTT 16.0 R20 241/276 0.617 0.475 0.171 268.56

139/207 0.589 0.483 0.149

LAV25 12.50/75 R20XL 207 0.445 0.378 0.100 119.63

103 0.414 0.343 0.141

11.00 R 16 x L 290 0.434 0.314 0.058

165 0.417 0.332 0.102

M34 2.5T 11.00-20 NDCC 241 0.536 0.287 0.063"'- 75.62

SUSV Track - 32.50 0.6096 1.180 61.34

BVFS Track - 250 0.533 2.090 223.30

MI i3AI Track - 210 0.381 1.020 104.09

M60 Track - 350 0.66 2.80 467.06

* Radius for wheeled vehicles, entrance angle for tracked vehicles.

t Maximum deformed width.

** Hard surface contact area, per tire (track)

tt Data from Harrison (1975).

22
Table 3. Tracked vehicle data.

Snow Snow Slope

depth density tested T9 Rt Rs* Rlt R4 o**

(cm) (kg/n-) (%/1.) Go-no go (kN) (wN) (kN) (AN) (AN)

SUSV (after Green and Blaisdell, in peep.)

5 560 19/11 go 17.9 11.7 0 - 6.2

30-60 230 30/17 go 32.0 17.9 10.1 1.9 4.0

5 560 25/14 go 17.9 14.4 0 - 3.5

5 560 25/14 no go 17.9 17.9 0 - 0

10-15 80 25/14 go 32.3 14.4 2.0 4.6 15.9

10-15 80 30/17 no go 32.0 17.9 2.0 4.6 12.1

30-60 150 19/11 go 32.6 11.7 8.8 2.1 12.1

30-60 150 25/14 no go 32.6 14.4 8.8 2.1 9.4

MII13AI (after Green and Blaisdell. in prep.)

5 560 19/II go 29.2 19.9 0 - 9.3

5 560 16/9 go 29.3 16.3 0 - 13.0

5 560 19/I1 no go 29.2 19.9 0 - 9.3

10-15 80 19/1I go 43.5 19.9 1.3 11.0 22.3

10-15 80 25/14 no go 43.1 25.2 1.3 11.0 16.6

30-60 150 16/9 go 43.7 16.3 24.6 5.0 2.8

30-60 150 19/I1 no go 43.5 19.9 24.6 5.0 -1.0

30-60 230 25/14 no go 43.1 25.2 32.1 4.7 -39.0

M113 (after Osborne and Guitar 1986)

17 300 25/14 go 43.1 25.2 4.0 1.1 13.9

14 130 19/I1 go 43.5 19.9 2.1 1.2 21.5

14 130 25/14 14 mtt 43.1 25.2 2.1 1.2 15.8

18 130 30/17 7.6 mtt 42.6 30.4 3.1 1.5 9.1

BFVS (after Green and Blaisdell, in prep.)

5 560 19/Il go 62.5 42.6 0 - 19.9

30-60 230 25/14 no go 91.7 54.0 36.6 6.9 1.1

M60 (after Osborne and Guitar 1986)

23 190 19/11 go 178.9 89.1 5.5 5.4 84.3

23 190 25/14 go 178.9 113.0 5.3 5.4 60.4

Using equations from Table I.

t CRREL shallow snow mobility model (eq 4).

** Tnr using equations from Table I.

"tt Distance traveled up a 20-m slope (no go).

lion. The simple resistance equations used here do not resistance calculations. Additionally, for the data of

take into account two potentially large contributors to Green and Blaisdell (in prep.), the snow densities were

resistance: belly drag and slip-sinkage. An examina- not measured on the slopes but in an adjacent area, so

tion of vehicle sinkage calculations and ground clear- they are only indicators of what the actual snow densiance showed that unless significant slip-sinkage oc- ties might be.

cuffed, belly drag would not be a reason for under- Figures 1-4 illustrate these uncertainties by showpredicting snow resistance under these snow condi- ing a plot of net (available) traction predicted using eq

tions. Slip-sinkage is generally small compared to 6 versus snow density for various depths of snow. The

sinkage due to snow compaction; its effects become shaded areas in these figures show the snow conditions

greater as a vehicle bogs down. and results of the actual tests. Where the lines of equal

Since the greatest amount of data is for the Ml 13, snow depth pass below the 0 net traction line the

these data were examined first. Tables 3 and 4 indicate prediction is no go.

that in some cases a range is given for the snow depth. In Figure 2 (the 19% slope) a large shaded area is

When this occurred I used the maximum value in the indicated as no go. This agrees with the predicted

23
28

24

20 c

816

04

> 12

.8

0

-4 60

40 80 120 160 200 240 280 320 360

Snow Density (kg/rn3)

Figure 1. Mobility of the M113 on a 16% slope.

20

16 c

20

212 03

12 0

-4

06

-8E

40 80 120 160 200 240 280 320 360

Snow Density (kg/rn3

Figure 2. Mobility of the MI 13 on a 19% slope.

24
40 180 12 16 14 20 28 1 32 3801 

SNoGo w DeoSnow No D( rh

115 cm

8 30

U.

4-

40

40 80 120 160 200 240 280 320 360

Snow Density (kg/m3r)

Figure 3. Mobility of the MI13 on a 25% slope.

12

10

S6 Snow Depthh

S~25 cm

S4•

S2 30

-6 40 80 120 160 200 240 280 320 36

Snow Density (kg/m 3)

Figure 4. Mobility of the Ml13 on a 30% slope.

25
Table 4. Wheeled vehicle data.

Snow Snow Slope Test

depth density tested results TS R9 Rs* Rt T.**

(cm) (kg/M3 ) t%1) Go-no go (kN) (WN) (WN) (AN) (AN)

HEMTT (after Green and Blaisdell, in prep.)

5 560 19/I1 go 52.8 51.2 0.0 - 1.6

30-60 230 25/14 no go 87.6 65.0 18.2 30.! 4.4

5 560 19/11 go 52.8 51.2 0.0 - 1.6

5 560 25/14 no go 52.2 65.0 0.0 - -12.8

30-60 150 17/7 go 89.2 32.7 15.5 32.6 41.0

30-60 150 16/9 nogo 88.7 42.0 15.5 32.6 31.2

HMMWV (after Green and Blaisdell, in prep.)

5 560 19/11 go 38.9 6.4 0.0 - 32.5

30-60 230 25/14 no go 12.0 8.1 3.8 11.2 0.I

10-15 80 25/14 go 12.0 8.1 1.6 3.0 2.3

10-15 80 30/17 no go 11.9 9.1 1.6 3.0 0.5

LAV25 (after Green and Blaisdell, in prep.)

5 560 19/11 go 31.9 22.8 0.0 - 9.1

30-60 230 25/14 no go 37.7 28.9 10.3 17.6 -1.5

10-15 80 19/11 go 37.5 22.8 4.1 4.1 10.6

10-15 80 25/14 no go 37.7 28.9 4.1 4.1 4.7

M34 21/2-ton truck (after Osborne and Guitar 1985))

23 130 5/3 7 mtt 25.2 4.0 4.3 6.7 16.9

* Using equations from Table I.

t CRREL shallow snow mobility model (eq 4). ** Tm using equations from Table 1.

tt Distance traveled up 20-m slope (no go).

performance only for the greatest snow depth. It was not The data from other vehicles with this snow condiclear from the video tape of this test if the vehicle's belly tion (snow depth 10-15 cm, Po = 80 kg/m 3) were exwas dragging in the snow, but calculations showed that amined in this light. The SUSV prediction would now

ground clearance would be marginal at a snow depth of agree with the observed no-go performance on the 30%

60 cm. For the 25 and 30% slopes shown in Figures 3 slope, and a go prediction is still obtained for the same

and 4, no-go conditions were observed in shallow, low snow condition on the 25% slope, which the vehicle

density snow. Speculation that excessive slip-sinkage negotiated. The LAV25 prediction also becomes no go

may occur under these conditions led to the sinkage for the 25% slope (agreeing with the observed perforwithout slip being examined. From the shallow snow mance) and is still agoforthe 19% slope. The HMMWV

mobility model, the sinkage estimates were 12.6 cm was able to climb the 25% slope (and was barely

(initial snow depth 15 cm), 10.4 cm (initial snow depth predicted to). Changing the traction equation for this

14 cm) and 13.3 cm (initial snow depth 18 cm). It would case causes the prediction to change to no go. On the

be reasonable to assume that the small layer of com- 30% slope a go prediction was changed to no go,

pacted snow (2-5 cm) could easily be ejected from agreeing with the test results. Review of the video tapes

underthe spinning track. The underlying layer ofpacked showed that that the HMMWV had no difficulty climbsnow (mentioned earlier) would then provide the trac- ing the 25% slope under these conditions. Table 5

tive surface and probably offer a smaller amount of summarizes the above discussion.

gross traction. Equation 2 would then be more appropri- From the data in Table 4, it appears that the 25%

ate for calculating gross traction. A recalculation of the slope is about the limit for wheeled vehicles. Figure 5

net traction using this assumption showed that the shows available traction for the HEMTI, HMMWV

MlI 13 would still be able to make it up the 25 and and LAV25 on a 25% slope with 60 cm of snow. Tests

30% slopes, but with a lot less available traction in showed that none of the vehicles could climb this slope

reserve. when the snow cover had a density of 230 kg/m 3. The

26
Table 5. Comparison of the observed and calculated available traction on snow-covered

slopes. (Snow depth: 10-15 cm; initial density: 80 kg/m3.)

Predicted traction (kN)

Slope

Vehicle (%/I) Test results T*T.t T,**

Mi 13AI 19/11 go 22.3 8.0 -1.7

M! 13AI 25/14 no go 16.6 2.3 -7.4

SUSV 25/14 go 15.9 1.3 -1.3

SUSV 30/17 no go 12.1 -2.4 -5.0

LAV25 19/11 go 10.6 5.0 5.0

LAV25 25117 no go 4.7 -1.4 -1.4

HMMWV 25/14 go 2.3 -0.3 -2.0

HMMWV 30/17 no go 0.5 -2.5 -3.9

* TS using eq 1 and R, from Table I.

t T. using eq 2 and R, from Table 1.

** Ts using eq 2 and Rs from Table 1.

prediciions bear this out, except for the HEMT, which a no-go condition prevailed in an initial test. In general,

in general had difficulty climbing slopes. It is not clear running starts did not improve slope negotiation. Osborne

why this was. and Guitar did theirtests at the fastest speed possible or

In the above analysis, momentum was not consid- prudent.

ered. Green and Blaisdell (in prep.) did most of their If it is assumed that the vehicle speed was 16 kmph

tests from a standing start at the base of the slopes, (10 mph) at the base of the slope and that the vehicle is

although in some cases a short running start was used if still -nnoving at 1.6 kmph (1 mph) at the crest of the slope,

I I I I I I I I I I I I I 1 -

28 - "**' E

z _HEMTT

(U No Go " ~60 cm >MMWV HMMWV

4 -

_• LAv 2,5

NoGo

-8 -60

I I I I I I I I I

40 80 120 160 200 240 280 320 360

Snow Density (kgg/m3)

Figure 5. Mobility of three wheeled vehicles on a 25% slope.

27
Table 6. Effective force due to momentum, more general equations of the shallow snow mobility

model, but with the effects of slopes included and

F* selecting the packed snow traction equation for condiVehicle (kN) tions when the snow layer was thin. There does appear

M113 5.2 to be a problem predicting performance of the HEM3T

SUSV 3.1 (a heavy wheeled vehicle), but the reason did not beBFVS 11.1 come clear during this study.

LAV25 5.7

HMMWV 1.7

HEMTT 13.4

ACKNOWLEDGEMENTS

*Initial velocity: 16 kmph.

Final velocity: 1.6 kmph.

Slope length: 20 m. I would like to thank Charles Green of the Waterways Experiment Station tt the providing CRREL

with the video tapes of his tc ., and for some additional

unpublished notes on his tests. I also express my apprethen for any vehicle, eq 8, in terms of force (kN) ciation to S. Shoop and G. Blaisdell who provided

becomes technical reviews of this paper.

F = 0.997 Wx (9)

LITERATURE CITED

wherex is the slope length in meters and W is the vehicle

weight (kilonewtons). It can be clearly seen that this Blaisdell, G.L, P.W. Richmond, S.A. Shoop, C.E.

momentum "force" will have the greatest effect on short Green and R.A. Alger (1990) Wheels and Tracks in

slopes and with heavy vehicles. The slopes at KRC are Snow: Validation study of the CRREL shallow snow

about 20 m long; using this length in eq 9 for various mobility model. USA Cold Regions Research and Engivehicles produced the values in Table 6. Given the same neering Laboratory, CRREL Report 90-9.

hypothetical snow conditions and the values in Table 6, Green, C.E. and G.L. Blaisdell (In prep.) U.S. Army

these vehicles could negotiate slopes about 2.5 degrees wheeled versus tracked vehicle snow mobility program.

steeper when momentum is used compared to when it is Waterways Experiment Station, Vicksburg, Mississippi,

not. In marginal cases of slope negotiation, momentum WES Technical Report.

could provide enough force to make the slope nego- Harrison, W.L. (1975) Vehicle performance over snow.

tiable, particularly if the slope is short. USA Cold Regions Research and Engineering Laboratory, Technical Report 268.

Liston, R.A. (1974) Operation of the M151 1

/4-ton

CONCLUSIONS truck in shallow snow. USA Cold Regions Research and

Engineering Laboratory, Technical Note (unpublished).

Elements of the CRREL shallow snow mobility Osborne, M.D. and S. Guitar (1986) Determining the

model and empirical resistance equations were com- effectiveness of snow-covered slopes as vehicle obbined with a simple method of introducing the effect of stacles. Keweenaw Research Center, Michigan Techslopes (i.e., adding gravitational resistance and reduc- nological University, Houghton, Michigan.

ing normal load on the driving elements) to obtain Richmond, P.W., G.L. Blaisdell, G.L. and C.E. Green

values of net predicted traction. These values were (1990) Wheels versus tracks in snow: Second validation

compared with the results of go-no-go tests. It was study of the CRREL shallow snow mobility model.

shown that this model works fairly well. Additionally, USA Cold Regions Research and Engineering Laborait seems that for thin layers of snow (<15 cm), the tory, CRREL Report 90-13.

underlying material is more important on slopes than on Richmond, P.W. (1990) Vehicle motion resistance due

level terrain. After taking this into account, the pre- to snow. 1990 Army Science Conference.

dictions of go-no go were correct 28 times out of 39. Yong, R.N, E.A. Fattahand and N. Skiadas (1984)

Similar results (26 out of 39) were obtained using the the Vehicle Traction Mechanics. New York: Elsevier.

28
An Experimental Method for

Vehicle Mobility Research on Freezing/Thawing Soil

S. SHOOP, E. BERLINER AND S. DECATO

U.S. Army Cold Regions Research and Engineering Laboratory

Hanover, New Hampshire 03755-1290

ABSTRACT

The Cold Regions Research and Engineering Laboratory has constructed a test basin

where full scale vehicle mobility testing can be performed under simulated winter conditions.

Although mobility testing is primarily performed on freezing and thawing soil, other surfaces

can also be used. The test basin is 36.6 meters long, 12.3 meters wide and 3.6 meters deep.

The deeper part of the basin is filled with a gravelly sand in which a water table can be allowed

to fluctuate. In the top 106 centimeters of the basin is the test soil, which is changed

periodically. Refrigeration panels are used to freeze the soil from the top down. Soil moisture

and temperature are monitored during the freeze/thaw and can be varied as desired. The soil

is generally first tested in an undisturbed condition, and then again after trafficking. Soil

parameters such as moisture, density, cone penetration, and strength are measured prior to

vehicle testing.

An instrumented Jeep Cherokee is used for traction and motion resistance testing. The

vehicle has load cells and velocity sensors on the front wheels and both a sonic speed sensor

and a fifth wheel to measure vehicle speed. The sensors are read and recorded using a

computer-controlled data acquisition system. A typical test sequence consists of three

traction and motion resistance tests, as well as a baseline hard surface resistance test, for each

tire pressure or type.

INTRODUCTION ity testing can be performed under controlled conditions

(Shoop, 1989).

Freezing and thawing ground can cause difficult The test basin is located within the Frost Effects

conditions for vehicle mobility. Vehicle traffic on un- Research Facility (FERF) along with other freeze/thaw

paved and secondary roads is often restricted or even experiments. Our experimental program is designed to

prohibited during thawing periods. Even when passage study the effects of different soil parameters (primarily

is possible, it can result in severe environmental damage soil type, moisture and density) and conditions (rate and

(i.e. rut formation and consequent erosion). Although depth of freeze/thaw and depth of water table) on

thawing ground conditions are common, field vehicle vehicle mobility. Tests are performed in a large basin

mobility testing on thawing ground can be difficult where freezing and thawing are controlled by varying

because of the short and erratic nature of the thawing air temperature and using refrigeration panels placed on

events. Therefore, researchers at the Cold Regions Re- the soil surface. Moisture content in the soil is varied by

search and Engineering Laboratory (CRREL) have changing the water table depth, by adding surface water

constructed a test basin where full scale vehicle mobil- to simulate rainor snow melt, and by controlling the rate

29
of frost penetration. The soil temperature and moisture atures. Thus freeze and thaw rate, as well as soil moisare recorded throughout freezing and thawing. The ture, can be controlled.

amounts of frost heave and ice formation are measured The mobility test basin occupies the entire north half

by surface elevation surveys and inspection of soil of the FERF. It is 36.6 meters long and 12.3 meters

cores, respectively, across, as shown in Figure 1. The mobility testing area

To date, a large number of mobility tests have been is divided in half longitudinally. Testing occurs on one

completed on various conditions of a thawing silty sand. half of the test basin during thawing while the other half

Results indicate that the thaw depth strongly affects of the test basin is being frozen. This large area allows

both traction and motion resistance, the degree of influ- a comnlete suite of full scale mobility tests, including

ence depending prima dly on the moisture content of the repetitions, on undisturbed soil. With a skilled driver,

soil. However, since the frozen layer restricts soil drain- several test suites can be completed within the area.

age, and water accumulates in the thawing layer, thawing soils become even wetter than under unfrozen Soils

conditions. These results have been discussed (Shoop, The test section currently consists of a bottom layer

1989, 1990) and will not be addressed here. of fill and atop layeroftestsoil separatedby ageotextile

(Figure 2). The purpose of the fill material is to simulate

a natural environment (i.e. to eliminate having a rigid

MOBILITY TEST BASIN impermeable layer directly below the layer of test soil)

and to allow for a water table to be added and varied

Frost Effects Research Facility relatively quickly. The fill soil is a bank run sand from

The unique capabilities of the FERF allow full scale Pompy Pit, located in Thetford, Vermont. The top 106

vehicle testing to be conducted under carefully con- centimeters of soil is the material to be tested. The first

trolled experimental conditions. Freezing conditions soil tested (1988-1990) was a silty sand, and the present

can be created throughout the year. Refrigeration panels soil type is a clayey silt, both from Lebanon, New

can supply temperatures from -40 0C to +50 0C, and the Hampshire. The test soils are marginal road material

air temperature can be dropped to -10°C or raised as and are typical subgrade or off-road material in New

high as +30°C, depending on ambient outside temper- England. The grain size distribution curves of the three

i 36.6 m

Figure 1. Plan view of the soil test basin in the Frost Effects Research Facility (hatched area). TC refers to Test Cell.

Instrumentation SlySn

30 Figure Ploss ~ ~ of Fi' the soilit 2. seieio inteFotEfetseer test basin howciity (acoheigarea).tCeeroonetel

of oil tst bae fll Indgoxteas wl scto fitrumentation.

Wate ightSilt San
U.S. Std. Sieve Size and No. Hydrometer

-4 4 10 40 200

100 I I I

I I i

80 I Moulton PitSilt

• I I I

>60

[- I I Pompy Pit I

I I I Gravelly Sand 1 05 4 0 - I I I I 40

I I I I Lebanon I Sand

20o100 10 1.0 01 0.01 0.001

Grain Size (mm)

Gravel Sand

C'rse I Fine Crse MediumT Fine SiltorClay

Figure 3. Grain size distribution curves of the test soils (Lebanon sand and Moulton Pit

silt) and the base fill (Pompy Pit gravelly sand).

soil types mentioned are shown in Figure 3. Based on concern to vehicle mobility on thawing ground. Near

results from the standard CRREL frost heavetest (Chain- the surface, the thermistors are placed at 2.5-cm interberlain, 1987) and the Army Corps of Engineers soil vals and the tensiometers at 5-cm intervals. The vertical

classification scheme (Berg and Johnson, 1983), frost distance between the instruments increases with depth.

susceptibility of the base fill material is low, while both The basin is instrumented at six locations, three on each

test soils are highly frost susceptible. side, approximately 9 meters apart. Figure 4 shows the

vertical configuration of the instrumentation and the

Geotextile location of each instrumented section in the test basin.

A needle-punched polyester geotextile separates the The thermistors were installed on a polyethylene rod

test soil and the base fill at a depth of 107 cm. It was andthen placed inaholedrilledinthe soil. Thetensiomechosen as a separator for the two soils based on Corps ters are each placed individually within the soil by

of Engineers Civil Works Guide Specification CW- careful augering and backfilling at each location. The

02215, March 1986, using Filter Design Criteria. It is top 30 cm of instrumentation is removed after vehicle

placed over the entire test basin with the exception of testing so that the soil can be rototilled and recompacted

two circular holes of 1.2 meters (4 ft) diameter cut in the to specifications before freezing for the next test series.

fabric, each containing a vertical string of tensiometers The soil temperature is recorded every 2 hours

and thermistors in the center. These sections without throughout the freeze and thaw cycle using a computerfabric are used as reference sections tomonitorthe effect controlled data acquisition system. These data arm reof the fabric on moisture migration during the freeze/ duced and compiled automatically every 24 hours to

thaw cycles (Shoop and Henry, 1991). The fabric is calculate frost depth and thaw depth. Tensiometers are

present at all other instrumentation locations, read manually, as these instruments need more human

attention (i.e. they need to be checked for air in the tube

Test cell instrumentation linings and periodically refilled with glycol). The tensiTemperature and soil moisture tension are moni- ometer data are then entered into a spreadsheet and used

tored using thermistors and tensiometers throughout to track the moisture migration in the soil as a result of

each freeze/thaw cycle. The instrumentation is concen- the advancement of the freezing front or other conditrated in the upper 30 cm because this is the area ofmost tions. Figure 5 illustrates the workings of a tensiometer.

31
40 .0

0

80

""- Fabric

1 00

0/ Basin Cross Section

Instrumentation Locations *0

160 o S+ +

200 --Bottom of Basin- Basin Plan View

Figure 4. Instrumentation configuration in the test basin.

standpipes were connected to horizontal pipes located I

foot from the bottom of the test cell in the base fill. These

Gg pipes are perforated to allow the water to seep into the

Porous soil and are covered with a fabric to keep the soil out.

Ceramic Cup The water level is measured in each of the standpipes

and is also inferred from the tensiometer data. Watercan

be released through four drains in the floor of the test

basin.

Vent Tube

Cup Tube

Assembly

Figure S. Construction and major components of a soil moisture probe tensiometer. These are filled with glycol for

use in freezing environments.

Their use in monitoring soil moisture is discussed more

in Shoop and Henry (1991).

Water table

One of the features of the large test basin is the

capability of maintaining and controlling a water table.

Water can be added to the basin through four standpipes Figure 6. The CRREL Instrumenwed Vehicle in the FERF

(wells) near the comers of the basin. The vertical mobility test basin.

32
THE CRREL

INSTRUMENTED VEHICLE (CIV)

Mobility testing is accomplished using an instrumented 1977 Jeep Cherokee (Figure 6) with significant

modifications. These changes include the addition of

specialized equipment and the removal and modification ot some stock equipment.

Each of the wheels is instrumented to measure the

forces at the tire/ground interface and the wheel speed.

Load cells mounted on the axles (Figure 7) measure

SProximity forces up to 6000 lb in three mutually perpendicular

Gauge directions: longitudinal (direction of travel), vertical,

Lock-out/ and transverse (across direction of travel, usually genHub •erated in turning maneuvers) as illustrated in Figure 8.

• Load To accommodate the annular load cells at each wheel,

Cell we replaced the stock axles with longer ones.

Aside from the triaxial load cells, a uniaxial load cell

mounted on a coupling can be used to measure drawbar

forces. In addition, we are considering using more

sensitive torque meters, which are easily added and

Speed Indicator removed from the vehicle as needed. These would be

Pins attached to the outside of the wheel, and would be in

place only during experiments needing accurate measurement of very small loads.

Individual wheel speed is measured using a proximity gauge and counter. The gauge detects the passage of

the equally spaced nodes on the disk brakes, allowing

for the calculation of revolutions per minute. Total

vehicle speed measurements are made using a fifth

wheel and an ultrasonic speed sensor (Figures 9 and 10).

The fifth wheel uses a tachometer generator and an

Figure 7 An annular load cell mounted on the vehicle optical encoder (50-pulse-per-foot output) and can also

axle. measure distance traveled.

Wheel speed can be controlled either by the standard

accelerator foot pedal or by a computer-controlled

stepper motor, which governs the engine throttle. The

motor controller was specially designed to provide

stepping motor control from 0. 1 revolution per second

Vertical

"onq-ltudlnol

Figure 8. The load cells measure force in three mutually perpendicular

directions.

33
. ., 1" . , o, °

Figure 9. Fifth wheel used for measuring vehicle speed Figure 10. Ultrasonic speed sensor used as an alterna -

and distance traveled. tire method of measuring vehicle speedi

Figure 11. Heath/Zenith industrial computer and monr- Figure 12. Keithlev Model 575 Measurteu'nt and C(onitor which controls data acquisition and testing. trol Svstem.

to 9.9 revolutions per second in 0. I-revolution-per- static inverter, which converts front 12 volts, dc to 115

second increments and from 10 revolutions per second volts ac power. Also, to allow more variation of whcel

to 99 revolutions per second in 1.0-revolution-per- and tire size. we installed a 4-inch lift kit at each axle.

second increments (Blaisdell, 1983).

Warn locking hubs were installed on all axles. These Data acquisition system

hubs, combined with the Jeep's emergency four-wheel- In November of 1990. a high-performancc. PCdrive system, provide for any combination drive sys- based data acquisition system replaced the outdated

tern: four-wheel-drive, front--wheel-driveorrear-wheel- configuration. The new computer is a 386. 1 Mili,

drive. The emergency drive system ensures that engine rack-mountable industrial grade computer with a VGA

torque is transferred equally to the four wheels through monitor (Figure 1I). l)ata acquisition is accomplished

the stock series of differentials, overcoming the Jeep's through a fully software prograninable commercial

standard Quadra-Trac. measurement and control system & igure 12)) %jibh ,dhiiThree further modifications have been made to the tional in-house-designed signal conditioning. The softvehicle. Additional braking capability is provided by ware is a combination of product-specific softm are and

dual calipers at each wheel. As with the drive system. CRREL-developed programs w ritten in compiled B.\-

braking is applied to either the disk brakes on all four SIC and C.

wheels, or only through the front or rear brakes. The Signal conditioning is handled separatel% for the

engine contains an additional heavy-duty alternator, load cell and proximity gauge inputs. The load cell

which is used for recharging apairof 12-volt deep-cycle inputs first pass through a shunt/short circuit. T'he

marine batteries located in the rear of the vehicle. They function of this circuit is determined bN either a set of

power the data acquisition system through a sine-wave DIP (Dual Inline Package) switchcs on the circuit

34
ntShr +I 10 -- ,I 

Load Cell input Load Cell Signe Cod* (I of IS)

Pulse Inputs =

Pulse Inputs (1 of 6)

Spare Analog

Inputs

Figure 13. Block diagram of the signal conditioning circuit.

board, or by a remote, user-accessible switch. If the primarily for system diagnostics. The other is a menuswitch is in the neutral position, there is no change in the driven program written in C, which prompts the user

signal. When the switch is held in the shunt position, a through vehicle calibration and a set of resistance and

precision resistor is placed in parallel with the signal. traction tests. This program acquires and stores to disk

This simulates a known load, and is used for calibration up to 1800 data points per test, although increased

purposes. With the switch in the short position, the load memory on the computer will allow more data points to

cell signal is ignored, and system diagnostics can be be taken.

performed. Because the load cell signals are on the order Once the data have been written to a C array, they are

of millivolts, it is important to amplify the signal before converted from voltages to the appropriate engineering

processing. Thus the next step in the signal conditioning units, kilometers (or pounds) per hour and Newtons (or

is to amplify the signal by 100. Also, at this time the pounds) for the velocities and loads, respectively. The

signal is changed from double-ended to single-ended. data are then saved to an ASCII file on a floppy disk for

Finally, the signal goes through a low-pass filter and on further manipulation after testing is complete.

to the data acquisition system. Input from 15 load cells After testing, the data are imported into a spreadcan be processed with this system. sheet-based analysis program where they are graphed,

Conditioning of the six velocity (or pulse) signals is and calculations are performed to yield traction and

more straightforward. The signal is first conditioned resistance data. The spreadsheet contains a series of

into a square wave and then passes to a frequency-to- macros which arrange and manipulate the data. Averagvoltage converter. From there, it feeds directly into the es and standard deviations are calculated and plots of all

data acquisition system. A schematic of the signal the data are created. If the file is from a resistance test,

conditioning is shown in Figure 13. the process ends there. For traction tests, the macro then

begins a series of calculations: differential interface

Software velocity (DIV = wheel velocity-vehicle velocity), slip

Data acquisition is controlled by one of two software (slip = DIV/wheel velocity), tractive coefficient (g =

programs written at CRREL. One is a compiled BASIC longitudinal force/vertical force), and the average peak

program which scans all of the assigned channels, tractive force (average of top 20% of the longitudinal

writing all data to the screen only. This program is used forces).

35
A more complete description of the CRREL Instru- cells are very sensitive to the load distribution (and,

mented Vehicle and its components can be found in therefore, tilt) of the vehicle; even very small slopes

Berliner et al. (in prep) and Berliner and Shoop (in affectloadtransferonthewheels.Therefore, thevehicle

prep). must be calibrated on as level and smooth a surface as

possible.

Finally, the vehicle is driven on a smooth, flat surface

MOBILITY TESTING PROCEDURES at 8 kilometers per hour, and the velocity readings are

equated to that speed to calibrate the velocity channels.

Soil preparation

To prepare a frozen or thawed soil for vehicle testing, Vehicle mobility testing

freezing panels are placed on the soil surface and the soil A mobility test sequence consists of both traction

is frozen from the surface downward. The freeze rate is and motion resistance tests. To measure traction, the

controlled by adjusting the temperature of the coolant in vehicle is driven at a constant speed (generally 5 or 8

the refrigeration panels. When the desired frost depth is kilometers per hour) in front-wheel-drive. The speed of

obtained, generally adepth of 40 cm or more, the panels the front wheels is then gradually increased (either

are removed. The soil surface is surveyed to determine manually or automatically using the stepper motor)

the amount of frost heaving, and soil cores are taken to while the brakes are applied to the rear wheels to hold

determine ice lens growth and for soil strength measure- the vehicle speed constant. The resulting slip of the front

ments in the laboratory. The soil is then allowed to thaw wheels is reported as the wheel-to-ground differential

by maintaining "spring-like"conditions withinthe build- interface velocity (DIV), which is equal to the speed of

ing (70 to 13*C). Vehicle mobility is tested primarily the wheel minus the speed of the vehicle. Traction is

while the soil is thawing. After vehicle testing on the reported as a tractive coefficient (longitudinal force

undisturbed soil, the surface is often trafficked by divided by vertical force) and is plotted as a function of

running 50 passes with a truck (to simulate the passing the DIV.

of a military company) and then tested again. When the Motion resistance is determined by measuring the

soil is thoroughly thawed, the top 30 cm of instrumen- longitudinal force on the front wheels with the vehicle

tation is removed and the surface is tilled and recom- in rear-wheel drive. Again, the vehicle is operated at a

pacted for the next freeze/thaw cycle, constant speed. Motion resistance is reported as the

average longitudinal force or as a motion resistance

Vehicle calibration coefficient (longitudinal force divided by vertical force).

The vehicle instrumentation is calibrated at the be- The motion resistance on deformable terrain is someginning of each test series and intermittently if it is times reported as terrain resistance (also called external

turned off, if the conditions change significantly, or if resistance), which is that part of the motion resistance

the tests take a very long time to complete. Although caused only by the terrain deformation (i.e. it does not

there are several methods of calibrating the vehicle, include the effects of tire deformation or flexing of the

they contain mostly similar elements. A standard cali- running gear). Terrain resistance is calculated by subbration before testing in the FERF is as follows. tracting the motion resistance measured on a hard

The first step is always to temperature-soak the surface from the total motion resistance measured on

vehicle in the FERF. This involves activating all me- the deformable terrain. The hard surface motion resischanical and electronic systems and allowing the vehi- tance is measured on a level paved road just outside the

cle to sit in the FERF for not less than 20 minutes. When FERF.

the vehicle temperatures have stabilized, the front end General guidelines and recommended procedures

of the vehicle isjacked clearof the ground so the wheels for testing with the CRREL Instrumented Vehicle are

are free from load, and the two wheels are manually outlined in Shoop (1991). As applied to the FERF, they

spun and allowed to come to rest. In this position, the are as follows.

vertical channels of the load cells are read and equated 1) Before testing, calibrate the vehicle as described

to zero load and the velocity channels are read and above. Temperatures should be periodically monitored

equated to zero velocity, using thermocouples at various places inside and outThe vehicle is then lowered and a dynamic calibra- side the vehicle andrecorded. If the temperature orother

tion is performed. This entails driving the vehicle with conditions change significantly during the course of the

the rear wheels on a smooth level surface at 1.6 kilome- tests, it should be noted and the vehicle recalibrated.

ters per hour while reading the longitudinal and hori- 2) Execute a hard surface motion resistance meazontal channels. These readings are then taken to be surement for each set of test conditions. This should be

zero value or datum for the horizontal loads. The load performed immediately prior to or after mobility testing

36
on the deformable terrain, and for each tire inflation Acknowledgments

pressure used. The hard surface information will serve The authors thank Paul Richmond, Dr. Richard Berg,

as a baseline for the mobility measurements taken and Stephen Bowen for their thoughtful reviews of the

throughout the day. paper.

3) Perform either one long rolling resistance test (the

full length of the test section) or three shorter tests,

followed by three traction tests. LITERATURE CITED

4) Record the time of the calibration and of the

subsequent tests. Additional information that should be Berg, R. and T. Johnson (1983) Revised Procedure for

recorded for each test series includes calibration meth- Pavement Design under Seasonal Frost Conditions.

od, speed of tests, etc. CRREL Special Report 83-27.

A full complement of tests will usually include three Berliner, E., S.A. Shoop, G.M. Trachier and G.L

tire pressures: 240 kilopascals, 180kilopascals, and 103 Blaisdell (1992) Upgrades and Modification to the

kilopascals. At each tire pressure a hard surface rolling CRREL Instrumented Vehicle. CRREL Special Reresistance is performed for approximately 20 seconds, port.

followed by one to three rolling resistance tests on the Berliner, E. and S.A. Shoop (1992) An Instrumented

test material (approximately 20 seconds of data or 200 Vehicle for Traction and Motion Resistance Measureindividual data points) and at least three traction tests. ments. In Proceedings of the Symposium on Pavement

Response Monitoring Systems for Roads and Airfields,

Lebanon, NH, September 1991.

SUMMARY AND CONCLUSIONS Blaisdell, G.L. (1983) The CRREL Instrumented Vehicle, Hardware and Software. CRREL Special Report

Part of the CRREL mobility research program is the 83-3.

study of vehicle mobility on thawing ground. When Chamberlain, E.J. (1987) A Freeze-Thaw Test to

frozen ground thaws, from the surface downward, the Determine the Frost Susceptibility of Soils. CRREL

underlying frozen soil acts as an impermeable layer and Special Report 87-I.

traps any moisture from rain or snow melt in the thawing Shoop, S.A. (1991) Precision Analysis and Recomlayer on th,' surface, forming a very wet, weak soil layer mended Procedure for Vehicle Mobility Measurements

over strong frozen ground. This creates problems for Made Using an Instrumented Ve' iicle. CRREL Special

vehicle mobility. Roads are often closed or weight Report (in prep).

restrictions applied and off-road mobility may be im- Shoop, S.A. (1990) Mechanisms Controlling Vehicle

possible. Mobility on a Thawing Soil. In Proceedings of the 10th

These conditions are difficult to test in the field International Conference of the International Society of

because of the erratic nature of thawing soil. However, Terrain Vehicle Systems, Kobe, Japan, August 1990,

in the FERF, thawing conditions can be created through- Vol. 1, p. 301-312.

out the year and soil conditions can be carefully con- Shoop, S.A.(1989) Vehicle Mobility onThawing Soils:

trolled. Interim Report on CRREL's Test Program. CRREL

From this type of study we can determine the mech- Special Report 89-31.

anisms involved in vehicle mobility in thawing soils Shoop, S.A. and K.S. Henry (1991) The Effect of a

and the soil parameters critical to vehicle mobility in Geotextile on Water Migration and Frost Heave in a

thawing ground. This information will be used to devel- Large Scale Test Basin. Transportation Research Board

op a scheme for predicting vehicle mobility under 70th Annual Meeting, Preprint 91-0532 (accepted for

thawing conditions, publication in TRB Record).

37
Ice Cleat Design And Testing For

Tracked Military Vehicles

MARK D. OSBORNE

Senior Research Engineer

Keweenaw Research Center

Michigan Technological University

Houghton, Michigan 49931

ABSTRACT

The mobility of military tracked vehicles is poor on snow and ice due to the rubber pads

that are typically used on tracks. Various types of ice traction aids or ice cleats have been

designed and tested for all types of the military tracked vehicles ranging from the Ml 13 APC

up to the MIAL. The Keweenaw Research Center (KRC), a research agency of Michigan

Technological University (MTU), has been involved in ice cleat testing for over eight years.

Through the years KRC has developed a set of tests and test procedures for evaluating the

performance of the ice cleats. Although they are not officially specified as a Test Operating

Procedure (TOP), they have been accepted by the U.S. Army Tank-Automotive Command

(TACOM). TACOM has funded the majority of the testing.

Most of the ice cleat designs have been done by TACOM. This past year KRC proposed

and performed a laboratory study to determine the optimum design in a cold room and reduce

testing costs. A design was developed and tested during the winter of 1991. Some redesigning

was required to obtain significant improvement in tracked vehicle mobility on ice and snow.

During the laboratory and field testing process a theory was developed for optimum ice cleat

design.

The opinions expressed in this paper do not necessarily coincide with those of the U.S.

Army or the Government of the United States and the information provided here shall not be

construed as an official endorsement or approval of this product or company by the U.S.

Government.

INTRODUCTION The Keweenaw Research Center (KRC), a research

agency of Michigan Technological University (MTU),

Mobility of military tracked vehicles in northern has been involved in ice cleat testing and evaluation for

climates is usually limited because rubber track pads are over eight years. Most of the testing has been sponsored

standard equipment on these vehicles. Although these by the U.S. Army Tank-Automotive Command

vehicles are generally more capable of maneuvering (TACOM) and has been performed at KRC. In the late

through deep snow and on hard-packed snow surfaces winter season of 1984 the Marine Corps sponsored an

than wheeled vehicles, handling is difficult and on ice, ice cleat evaluation during NATO war exercises in

traction is just as poor as wheeled vehicles. These northern Norway.

tracked vehicles weigh anywhere from 13 to 70 tons and KRC has tested several tracked vehicles including

when coupled with almost no traction on ice, present a the M113 APC, M109 self-propelled howitzer, the

dangerous situation for military personnel in and around M 110, the Bradley IFV, the Marine Corps Amphibious

the vehicle. Poor mobility has resulted in the develop- Assault Vehicle, M60 tank and the M I and M 1A I Main

ment of traction aids to improve traction on ice and hard- Battle Tank (MBT).

packed snow. Over the years, KRC has developed a test course

38
specifically designed for testing and evaluating military KRC is located on the Keweenaw Peninsula, which

tracked vehicles. The test course includes an ice rink is nearly surrounded by Lake Superior. The climate is

which is 200 feet wide by 700 feet long, a hard-packed ideally suited for testing as winter temperatures aversnow test loop consisting of winding curves, gentle hills age 10 to 20*F and rarely rise above freezing or drop

and straight sections, deep snow areas and iced slopes, below -10°F. The winter season generally runs from

There are two types of iced slope areas, a vertical mid-November through the end of March. The annual

variable slope ranging in grade from 0 to 30 percent and snowfall of over 200 inches provides plenty of fresh

a variable side slope ranging in grade from 0 to 25 snow for creating deep snow areas and resurfacing the

percent. Shown in Figure I is a diagram of the hard- hardpacked snow aaeas.

packed snow test area. Figures 2 and 3 show the layout

of the variable vertical and side slopes, respectively. The

ice surfaces are constructed by first packing snow and DESCRIPTION OF TESTS AND PROCEDURES

allowing the ground to freeze. Next, the packed snow

surface is flooded lightly in several layers to build up a KRC has developed a specific set of tests and test

strong, smooth ice surface. The surfaces are maintained procedures for evaluating ice cleats on tracked veby grading the snow off of the ice surface, plowing with hicles. The tests include braking on ice, slalom on ice,

pick-up trucks, sweeping the surface with arotary broom slope climbing and side slope traversing on ice, speed

and finally flooding with a water truck. Through trial and handling on hard-packed snow, drawbar pull and

and error KRC has found that this is the best method for motion resistance on snow and ice and deep snow

maintaining a consistent, smooth surface which is nec- mobility.

essary for comparable evaluation of ice cleat perfor- Braking tests demonstrate a vehicle's stopping abilmance. ity on ice. The best ice cleat design will provide the

TO KRC

SLOPES

ICE RINK

Figure 1. Diagram of hard-packed snow test area.

39
30

- 25

z 2 0

0 ....................................

0-20 40 60 80 100 120

a0 1.= HORIZONTAL DISTANCE (ft)

Figure 2. Diagram of the variable vertical slope.

shortest stopping distance of all designs tested on the if the vehicle turns slightly the added distance is acsame vehicle, under the same conditions and at the same counted for. Vehicle speed is measured using a radar

speeds. Tests are conducted at vehicle speeds of 5, 10, gun as the vehicle speedometer is typically inaccurate.

15 and 20 miles per hour. The vehicle is accelerated to Vehicle speed is radioed to the driver so he can control

and held at the desired speed priorto entering the ice rink his final speed just before applying the brakes. Braking

area. The driver is signaled to apply and hold the brakes. decelerations are recorded using a commercially availWith the brakes locked, the vehicle slides to a complete able electronic accelometer. The accelometer is interstop and the distance of the skid is measured. Stopping faced with a laptop portable computer and braking

distance is measured to the front of the vehicle such that deceleration data is transferred to floppy disks. This data

* Mi}lTI . N OF ysf .

LETA:t•lVM. o

* . . . .

30 . 40 50 60 70 : 0 90 100 11 120o

* , ... *.- . (52% 7.0%) (8.7V (10.6} (12.=g (14.0•) (15.61} (17.60 ( 19.414 " 2i.3M

a0" . . . .

* . . . .

* . . • :

* . . • ..

0 20 40 60 80 100 120 140 M80 M80 200

MOUMNAL DISTANCE (ft)

Figure 3. Diagram of the variable side slope.

40
( \ 0/ \ o0o 0 -FINISH

I-0joI.0

o0 -- START

Figure 4. Diagram of slalom on ice.

is used to generate representative plots showing fore ered variable vertical slope which varies from 0 to 30

and aft accelerations and decelerations, and right and percent in grade. To conduct this test the vehicle is

left accelerations which occur during each braking test. positioned at the base of the slope. When given a signal.

A minimum of six tests are run at each speed in an the vehicle is driven up the slope approximately 20 feet.

attempt to obtain a statistical data base. The driver is then signaled to stop. When signaled

The speed test on hard-packed snow is a timed test of again, he drives another 20 feet up the slope. This

vehicle maneuverability. The test is conducted on a procedure is continued until the vehicle either climbs

closed-loop course adjacent to KRC and which is shown the hill, can not advance up the hill any further or slides

in Figure 1. The course is 1.3 miles long, consisting of down the hill. The point of the vehicle's furthest ascent

a mixture of straight-aways, gradual curves and tight up the hill is marked for distance and inclination. Three

curves. The objective of this test is to maneuver the test runs are usually conducted during this test because of

vehicle over the course in the fastest time possible. To the damage that occurs to the ice on the slope by the time

minimize driver bias, six runs are conducted, three in a this test is completed.

clockwise direction and three in a counter-clockwise The vertical hill climb test is similar to the track

direction for each arrangement tested. Data is then holding test in that it involves the negotiation of an ice

statistically analyzed to determine the average speed for covered variable grade slope. The difference between

each ice cleat type or track arrangement. the two tests is that instead of advancing up the slope in

The slalom test is designed to assess a vehicles' short stop-and-go steps as is done in the track holding

maneuverability on ice. A diagram of the slalom course test, the hill climb involves driving the M I A I up the

is shown in Figure 4. The objective of this test is to slope in one continuous attempt from a dead stop at the

negotiate the course in the fastest time possible. Typi- base. To run this test, the vehicle is positioned at a

cally, six runs are made to obtain a statistical average of starting point at the base of the slope. When given a

the vehicles handlingcapabilities by measuring the time signal, the driver drives the vehicle up the slope until it

required to maneuver through the course without hitting either climbs the slope or loses traction and slides down

the pylons. The driver has to be careful not to accelerate the slope. The point of furthest advancement up the

too fast or he may lose control of the vehicle. slope is marked and measured for distance and inclinaThe track holding test is conducted on the ice coy- tion. Three tests are usually conducted.

41
The side slope tests a vehicle's ability to traverse tests except the load vehicle pulls the test vehicle

across an icy slope. The slope used for this test varies along at approximately 5 mph and the test vehicle is

from 0 to 25 percent. To run this test, the vehicle is usually kept in neutral. The steady state force repositioned at the starting point, which is at the 0 percent quired to pull the test vehicle in neutral at a steady

end of the slope. When given a signal, the driver drives speed is then measured and recorded for both ice and

the vehicle across the slope at approximately 5 mph. He hard-packed snow conditions with the same load cell

continues until the vehicle traverses the entire slope or and data acquisition system used for the drawbar pull

the vehicle loses traction and slides sideways down the tests. At least three drawbar pull and motion resistance

slope. The point where the vehicle begins sliding is tests are conducted for each track configuration for

measured for inclination. This test is conducted three comparison.

times for each track configuration. For all of these tests it is important to ensure that the

The deep snow mobility test is subjective and is test surfaces are as consistent as possible to obtain

conducted to determine if the vehicle performs better in comparable results. KRC generally measures the static

snow two to four feet deep with a particular track coefficient of friction of the ice surface for comparison

arrangement. For this test, the driver negotiat-s the purposes. Unfortunately, for tests with ice cleats, fricvehicle through a large snow covered field. The snow tion measurements are not critical. What needs to be

generally consists of several layers of snow ranging measured is strength of the ice. This should be a dyfrom a strong, dense layer near the bottom to a light, namnic compression and inear strength test. To date

fluffy layer near the top. Normally the driver does not there is no known method that is widely accepted for

have any problem in negotiating this terrain, even with measuring ice strength. KRC has several idea:; but has

pads, but ice cleats do tend to help control the vehicle, not had the funding to develop and refine this idea.

Deep snow mobility would be improved more if the Strength of ice may change by the hour, depending on

track had a larger surface area to provide better flota- temperature, solar radiance, etc. This has been one of

tion. the problem areas in the past.

Drawbar pull and motion resistance tests are conducted with the vehicle to determine maximum pulling

power or tractive effort on hard-packed snow and ice. A ICE CLEAT DESIGN

load cell of appropriate size is normally used to measure

pulling force and resistance to motion as a function of Over the years, several ice cleats have been designed

time. All data is recorded using a portable computer and for many vehicles. Because each vehicle has its own

is saved on floppy disks for later analysis. Actual track type of track, each vehicle has its own ice cleat design.

speed is measured by D-C tachometers mounted on Most have been the "X" shaped grouser type that fit in

each sprocket of the vehicle. Actual vehicle speed is the shoe on a replaceable pad track. Some have been

measured using a D-C drum tachometer instead of a designed for installation on non-replaceable pad tracks

fifth wheel which may slip or may produce noisy results such as the crows foot T 156 ice cleat that bolts onto the

on the rough terrain. This past year an ultrasonic speed center guide. FMC has designed a slightly different ice

sensor was also used to measure actual vehicle speed cleat for a replaceable pad track, the T157 cleat. These

and appeared to produce fairly good results. The main designs are shown in Figure 5. Ice cleat design theory

emphasis in these tests is to measure maximum pull will be discussed later in this paper.

force and resistance to motion. The procedure for con- KRC has run a number of tests on different vehicles

ducting the drawbar pull tests requires connecting a pull to determine the optimum configuration and spacing.

cable, block and tackle and the load cell between the test On tracks with two pads side by side ice cleats were

vehicle and a load vehicle. In situations where more installed side by side and staggered, i.e., on one side at

than one load vehicle is required to stop the test vehicle, the first installment and on the other side on the next

another cable is fastened between the first and second installment and so forth along the entire length of track.

load vehicles. All drivers and the engineer operating the The side by side installation always provided the best

computer data acquisition system communicated using traction. Also, when cleats were installed on every fifth

two way radios. The test vehicle is brought to a speed of track shoe performance appeared to be optimized. Cleats

approximately 5 mph and held as constant as possible at on every third shoe did have better traction but the

that speed. When this speed is attained a load is applied improvement over every fifth shoe was insignificant

by braking the load vehicle(s) until the test vehicle is and for the extra work involved to install the additional

stopped completely. The procedure for conducting the cleats, it was not worth the extra effort.

motion resistance tests is similar to the drawbar pull Typically, cleats are designed at TACOM and then

42
T158 T156 T157

Figure 5. Typical ice cleat designs for military tracked vehicles.

field tested at KRC during the winter season. If the cleat. Tests conducted in 1989-90 showed an insignifiresults are not good they are redesigned and then tested cant improvement. The 86 original and 89 modified

the following winter. As an example, the ice cleat for the designs are shown in Figure 6. Building a test course

M I A I T 15 8 track was originally designed and tested in and conducting tests is expensive. Being able to test one

1986. KRC recommended that performance may be or two designs per winter season is -n expensive way of

improved by increasing ice cleat ground pressure. arriving at a final product. In 1990 KRC proposed

TACOM redesigred the T158 ice cleat in 1989, increas- running a series of tests in a cold room to determine an

ing ground pressure by midling out the center area of the optimum design. By testing on a fixture in a cold room

86 ORIGINAL 89 MODIFIED

Figure 6. Drawing of the 86 original and 89 modified T158 ice cleat designs (actually bottom view).

43
Figure 7. Drawing of the 90 radius cleat Figure 8. Drawing of 91 taper ice cleat design

design for the MIA] T158 track. for the MIA] T158 track.

a number of designs could be tested inexpensively, enough to withstand loading on concrete. The rounded

thereby screening out the poor ones and leaving the best bottom edge appeared significantly better in the laboradesigns for the winter field test. tory tests as compared to the flat edge with the same

A test fixture was constructed out of steel to test the thickness or the original 86 and 89 designs. Figure 7

ice cleats for the resistance to motion. This would shows a drawing of the 90 radius cleat

directly simulate two of the most critical areas, braking Winter tests showed imnprovement with the 90 radius

and slope climbing on ice. It did not account for dy- cleat in all areas except braking. For example, this was

namic effects because the cleat., were pulled at slow, the first time ever that the MI A I was able to climb the

steady rates rather than at the high speeds that are typ- entire slope (30%) using ice cleats. The problem with

ically seen on the test course. A hydraulic cylinder was the braking results was thought to be due to the radius

used to apply the normal load to the track block simu- edge. The edge was milled flat and the cleats were raised

lating the roadwheel load. Load cells were used to mon- supposedly to the same height as the 90 radius cleat. It

itor normal load and the force necessary to pull the track was felt that the dynamic action was not accounted for

block across the ice surface. An ice surface was formed during the laboratory tests and that the radius allowed

in a steel box for each test and room temperatures were the tank to ride up on top of the ice at high speeds after

kept as constant as possible to evaluate ice cleat perfor- initial penetration. This 91 taper design, shown in

mance on an equal basis. Data was collected and re- Figure 8, was tested with about the same results as the

corded using a computerized data acquisition system. 90 radius design. It was then found that the 90 radius

A large number of tests were conducted for several cleat was 0.125 inches lower in height than the 86 and

designs at various normal loads. It was decided that the 89 designs and that the 91 taperdesign was 0.205 inches

5,500 pound normal load (for one half track block) was lower than both. (TACOM was concerned that too high

the appropriate normal load as it is the approximate a cleat would damage the tank sponson units but the

average maximum load applied to an ice cleat on the height difference was really either an oversight or the 86

MIAl tank. The final design was developed through and 89 designs wel )utoftolerance in terms of height).

several iterations or modifications of the original 86 Since the 91 taper design performed as well or better

cleat. The final design was a cleat with 1/4 inch thick than the 90 radius design even though it was lower in

webs and a radius on the edge of the web. A simple height, it was decided that the final design would be the

structural analysis showed that the web would be strong 91 taper design raised to the same height as the 86 and

44
ICE SURFACEJL 1986 ICE CLEAT

PENETRATION

TRACK PADTRCPO -----------------------

ICE SURFACE .. ]L .. J. 19 9 1 TAPERED ICE

CLEAT PENETRATION

Figure 9. Illustration showing how ice cleat penetration is limited by either ground pressure or track

pad thickness.

89 designs. The cleats were raised to this height but not equal penetration depth, the cleat with the largest area

tested due to the early spring weather. This study also will perform the best. Also, the squared off edges will

resulted in a theory for ice cleat designs. perform better than a radiused edge.

For optimum traction, ice cleats need maximum

penetration and maximum interfacial area. The 91 taper

design with its thinner web area has high ground pres- SUMMARY

sure yet still has plenty of strength. Our theory is that

penetration is limited by the height of the cleat and the A standard method for testing traction aids on milisurrounding track pads. Figure 9 illustrates this point. tary tracked vehicles has been developed at KRC.

As shown in the upperportion, it is felt that the 86 design Specific test courses allow these tests to be conducted

was not penetrating to the pad surface. The higher under relatively the same conditions. Through field

ground pressure of the 91 taper design allows this experience and laboratory testing, a theory for ice cleat

penetration. design has been developed at KRC. Effective ice cleat

The 86 original cleat design had an estimated ground design requires the following and depends on the

pressure of 797 psi while the 89 modified design was vehicle's track shoe design:

1,060 psi. The 90 radius had a ground pressure of 1,410 1.) As thin a web as possible for highest ground

psi while the 91 tapered design has a ground pressure of pressure possible.

982 psi. 2.) Web thickness has to be thick enough not to break

The 91 taper design ground pressure was nearly the while driven on concrete.

same as the 89 design but the 91 design has a larger 3.) As large of an interfacial area as possible.

interfacial area. As illustrated in Figure 10, the larger These criteria allow for the greatest penetration and

the interfacial area the better the stopping ability be- tractive forces, whether they are stopping, accelerating,

cause the force is distributed over a larger area. For slope climbing or handling.

45
Figure 10. Drawing illustrating the interfacial area concept.

46
3. VEHICLE MOBILITY

47
BV 206

A Proven Concept In Winter Mobility

JAN UUNGGREN, MME

Design Manager, BV 206

Higglands Vehicle AB

0misk1ld~vik, Sweden

ABSTRACT

In the early seventies the Swedish Army Materiel Administration started to plan for a

successor to the By 202, which was one of the most capable All Terrain Vehicles in the world.

The technical specification for the new vehicle was naturally set higher in all important areas,

for instance higher payload, 2,000 kg vs 800, higher top speed 55 km/h vs 35 and no increase

in overall dimensions. There was also a very high requirement on reliability, availability and

maintainability. On top of this, there was a requirement that the maintenance cost for the

vehicle was to be stated in the tender and to be tested on production vehicles and have a

considerable influence on the price of the vehicle.

In 1974 Higglunds was chosen, in competition with other Swedish manufacturers, to

develop and produce the Bv 206.

The Bv 206 is an articulated steered vehicle with all four tracks driven. It is to be used to

support army units carrying 2,000 kg payload or 17 combat equipped soldiers on or off roads,

summer and winter. It will also be used towing trailers up to 2.5 tons.

The low ground pressure in combination with the articulated steering gives the vehicle a

very high degree of mobility over soft grounds such as swamps and snow. It is also

amphibious without preparation, propelled in water by the tracks and steered by the

articulation.

INTRODUCTION primarily wanted to improve were load capacity and

maintenance cost. The mobility capacity of the 202 was

The story of Bv 206 starts in the early seventies, considered adequate, but one weak point was the risk for

when the Swedish Army started to look for a successor shedding a track. This risk had to be minimized. Some

to the old Bv 202, which had been in service since 1965 otherdrawbacks with the 202 were also the ergonometric

(Fig. 2). When it was introduced, it meant an extremely conditions for the driver, with high noise level, poor

high increase in the off road mobility of the army units, visibility and heavy steering.

primarily in wintertime. Earlier they had to use horse

transports, skies and sledges.

The introduction of an articulated carrier in the DEVELOPMENT

Swedish army units meant a very high increase in the

fighting power, not primarily because of the quicker The invitation for tenders for the new vehicle was

transport, but because they arrived together with their sent out in 1971 with the technical requirements, which

equipment and in a condition good enough to use it. had a strong concentration on total lifetime cost. The

The basic design of the 202 was done in 1955-460, so companies giving a quotation had to state a maintenance

it was of course a bit out of date. The characters they cost, which was to be tested in a carefully specified test.

48
o 3jc ~ C3

Figure 1. BV 206.

F ue 2. BV' 202.

49
PrOJCT PLAM314 31M Un we7 MW6 UIM1 

I pa0U."IkeMhE8e OOLM uaululAOT PRODUCTw

M M6TMA giV A to I 2A7

I I

I *

II oRiwnPcui1

Figur 3. Prjc tim pln

3,gI I I 0 

A l

The proved maintenance cost would then have an few components were specified. I can only remember a

important influence on the final price of the vehicles, so small map light and the tow hook. The performance was

that a low maintenance cost gives a higher price to the on the other hand very carefully specified.

producer. The most important requirements for the new One important basic requirement that governs the

vehicle were: whole design is the articulated steering principle, which

1. Load capacity 2,000 kg needs a special explanation:

2. Articulated steering, amphibious The high requirement for off road mobility rules out

3. Lifetime 15 years or 30,000 km all other steering systems. A tracked vehicle is normally

4. Spec. ground pressure 12 kPa steered by varying the track speeds with some steering

5. MDBF 2,500 kmn (prohibitive failures) device. This means that you introduce brake forces

6. MITR 1.8 h between track and ground. These brake forces, which

InJune 1974 Hagglunds was awarded the contract to increase with smaller turning radius, mean that the force

design and manufacture a number of test vehicles in available for pulling the vehicle is reduced when it is

three different batches. If the technical tests came out most required. The split on two vehicle parts means that

successfully, we were guaranteed to get the production you get a more advantageous relation between track

contract (Fig. 3). During the development, it was indi- length and width for the steering forces (Fig. 4).

cated that we had to make two more batches of test Another very important requirement on the vehicle

vehicles to verify' the performance. was the payload capacity of 2,000 kg, which is two and

When starting the design phase of this vehicle, very a half times the capacity of the old vehicle, without

50
WHY ARTICULATED STEERING?

LESS STEERING FORCES - HIGHER NET PULL

NET PULL

l3ki Awrkq / idm i100 P, -A gomimed

ft if

U0dso "Win

LESS SLIP - LESS DAMAGE TO GROUND SURFACE

SLIP

I IQ

\ ArSlkWl mwr e cm. ,.i.

10 15I 20 as 30 (ml.

LONGER TRACK LENGTH ENHANCED AGILITY

I a

Figure 4. Reason for articulated steering.

51
increase in overall dimensions and ground pressure. To occurred in temperatures around - 10°C, although the

reach this difficult requirement, we had to use very light basic material does not become brittle until -45*C or

design solutions and use a lot of light construction lower. The low friction on icy roads meant that the

material. The body is built in glassfiber reinforced vehicle was very difficult and dangerous to drive on

plastic, which is unusual for this type of vehicle, roads. The high wear rate meant that the life requireAnother extreme solution was to make the tracks ment of at least 6,000 km could not be met. We reached

from Hytrel, a plastic material. We also did increase the only 2,000 km, so we had to go to a conventionally

width of the track from 500 mm to 620 mm. The high designed rubber track of the same type as on By 202.

demand on reliability has forced us to carefully study This meant a weight increase of 350 kg. These tracks

possible trouble areas and choose design solutions were naturally not completely trouble-free either, but

according to this. after some development of the integral steel parts we

Since one ofthe trouble areas on the old vehicle is the have reached a life of at least 10,000 kin, which is

clutch and the manual transmission, this is one reason adequate. The track has been developed in cooperation

for using an automatic on the new vehicle, with the manufacturer, Skega AB.

When designing the track assembly we had two The development of the track assembly has, like for

important requirements to consider, firstly the risk for the track itself, been difficult. The first test vehicles had

shedding a track should be minimum and secondly the six pair of roadwheels (Fig. 5) mounted on three sub

need for maintenance should be as small as possible. By frames individually sprung from the track beam (Fig.

designing the assembly with two rows of roadwheels 6).

and double sprockets and idler, we have got a wide and This system was much too optimistic on dynamic

solid contact base between the track itself and the track forces, and we quickly had to introduce a stronger

assembly. This is very important, because the track is design. Therefore, we made the roadwheels bigger (Fig.

very flexible. 7), and we reduced the number of roadwheels to four

Very important for a vehicle like this is that it shall pairs, mounted on two sub frames with four wheels in

be very easy to repair and maintain infield service, since each track assembly (Fig. 8).

the repair possibilities in field conditions are always This design was much better in mechanical strength,

restricted. To make this easier, we have designed By but the spring rate was too high, so we got a very bumpy

206 so that it is very easy to exchange broken parts, if ride and too high vibration level. The final solution

they cannot be repaired on the spot. The whole track turned out to be very fortunate. It is designed with a

assembly can be removed after loosening four bolts. cylindrical rubber torsion spring carrying two railing

The track can be exchanged by three men in less than 20 arms for a pair of roadwheels.

minutes when ambient temperature is -I 5oC. A com- The steering device is another very complex unit,

plete power unit can be replaced in less than one hour. which is evident from Figure 9 showing the required

When selecting components for this vehicle, we relative movements between the two vehicle parts. To

have tried to use components manufactured in large complete the picture, one should remember the shaft

quantities and available also in the future. transmitting power to the rear car.

When entering the production phase, we had pro- The first steering device was a welded construction

duced 46 test vehicles in five different batches with with a conventional design and very heavy (Fig. 8). To

redesigning and modifications. The test vehicles have a improve the situation we redesigned it, and it is built

total mileage of 400,000 km. Looking back at the with an open box torsion bar instead of a bearing for roll

development phase, there are a lot of things to remem- movement.

ber. We have tested three different petrol engines and one

The development of a new track has been long and diesel engine during the development period. The revery troublesome. The first test vehicles were equipped quirement said that we should have a petrol engine of

with tracks made from Hytrel, a new plastic material approximately 100 kW. The first engine we tested was

produced by DuPont. The track was injection molded in Volvo B30, a 3 L, 6-cyl. in-line engine, but it was rather

sections, which could be joined together to a complete difficult to install and was to go out of production 1978,

track. This new material meant that track weight was so we left it after the first test batch. The second engine

reduced by 50% compared to a rubber track. Unfortu- was the English built 3 L, 600 V-6 engine 2614E. It was

nately, this new material did not correspond to our very easy to install due to its compactness, but producexpectations. We ran into problems with cracking, low tion plans for it did not suit us, and we also had some

friction on icy roads and high wear rate. The cracking problems with overheated pistons. The third engine,

52
Figure 5. Wheel unit, first design.

Figure 7. Wheel unit, second design.

which we finally selected, was the German built Ford mechanically strong enough, and we soon switched

2,8 L, 60', V6, 2658E. This engine was equally easy to over to Mercedes W4 A-0 l8 and we now use W4 A-040,

install and has proved to be very tough, though the mean which are a development of their transmissions for

power output is much higher in Bv 206 than in a normal passengers cars.

passenger car. In our model, the transmission has a special shift

We have also tested Mercedes turbocharged diesel pattern to suit the Ford engine. The fitting of the engine

engine, an in-line 5-cyl. and 6-cyl. prechamber diesel. to the gearbox and the connecting development worn

These are very qualified engines for this vehicle, but it has all been done by H-igglunds.

was on the market too late for being evaluated by the Although the development line has not always been

Swedish Army. We expect other buyers of Bv 206 to so straight, the basic concept for this has remained

select this engine, unchanged, and in June 1979 we received the producThe automatic transmission was with the Volvo tion order from the Swedish Army of some 3,500

engine a Borg Warner BW 35 unit, but this was not vehicles.

Figure 6. Chassis, first design.

53
Figure 8. Chassis, second design.

3- 4

54.
DESIGN Transfer gearbox is a manually operated two step

gearbox, which distributes the power to the front and

The engine was originally the gasoline engine Ford rear differentials. High, neutral or low range can be

2658E. We used this engine for the Swedish Army and selected by the driver with a hand lever, but the lever

initial export orders from Finland and U.K. This corn- must not be operated when the vehicle is in motion. The

pact V-6 engine has been very successful, although the transfer gearbox is bolted between the central beam of

mean power output is 2-3 times higher than in the the front chassis and the steering unit. The housing of

passenger car. the gearbox is an integrated part of the chassis structure.

Today, we use Mercedes 6 cyl. turbocharged diesel The differential is a hypoid unit conventionally deengine. This design is very unique, using aluminum signed. Front and rear units are identical. Like the

cylinderhead and lightdesigns, resulting in same weight transfer gearbox, the differential housings are parts in

and higher power output than the Ford gasoline engine, the chassis structure.

For very dusty environment, the engine can be equipped

with a heavy duty air filter of self cleaning cyclon type. Chassis

Each chassis consists of a central beam, two transDriveline verse leaf springs and two track assemblies (Fig. 11). In

The automatic transmission is a Daimler Benz W4 the front chassis, the central beam also houses the

A-040 four speed unit. The transmission is controlled propeller shaft from transfer gearbox to front differenthe normal way by a hand lever, with which you select tial. Each track assembly consists of track, track beam,

a suitable range, Reverse, Neutral or Drive. Since we sprocket assembly, four pair ofroadwheels mounted on

have modified the shift pattern to suit this type of trailing arms to four cylindrical torsion rubber springs,

vehicle and engine, it is very easy to operate the gearbox and idlers sprung identical to roadwheels. The track

by the accelerator. The transmission has a secondary tension is adjusted with a bolt between the idlers accespump, which makes tow starts possible. sible through tooth gap.

S• MERCEDES O03..603A

MlERCEDES W4 -A 3 49

•• DISC BRAK

S~TRANSFER GE.ARBOX

S• STEERING DEVICE

Figure 10. Driveline.

55
Figure 11. Chassis, final design.

The track is an endless unit made in rubber, rein- some of the few components that have been unchanged

forced crossways with steel beams and lengthwise with throughout the development phase.

glassfiber. The guide horns are bolted through the steel

beam. Brake System

The brake system consists of a hydraulic service

Steering System brake and a mechanically operated parking and emerThe steering system of By 206 is a hydrostatic articu- gency brake. Both systems operate on one single disc,

lated steering system operated by a steering wheel and mounted on a separate hollow shaft on the transfer

activated by hydraulic cylinders on each side of the gearbox, always in connection with the output shaft.

steering unit (Fig. 12). The hydraulic components are independent of the position of gear lever.

I IF

Figure 12. Steering design.

56
'bI

Figure 13. Body panels, front car.

Body good compared to a skid-steered vehicle, especially

The body is made in glassfiber reinforced plastic, and when you have to make sharp turns.

most of it is a sandwich construction with PVC foam as Payload is 2250 kg or 17 combat equipped soldiers,

distance material. Steel reinforcements and strong points and it can tow trailers up to 2500 kg.

are embedded in the structure. The bodies are built from Top speed on paved roads is 55 km/h and in water

a numberof panels, which are bonded together (Fig. 13). approximately 3 km/h.

The panels are manufactured in the reinjection method. Grade ability is limited only by the friction between

They have been developed in cooperation with the track and ground. 400 has been recorded. Sideways it

maker, AB Bofors Plast. can take 420 before tilting over.

For the Swedish Army we have developed three The vehicle is extremely simple to operate and

different versions of the vehicle, firstly standard ver- handle, so driver's training is very short. It has been

sion or the carrier, secondly an anti-tank version (Fig. driven by a 10 year-old girl.

14) armed with a 90 mm recoilless gun or a Tow missile and thirdly a command post vehicle fully radio

suppressed. PRODUCTION AND SALES

From Bv 206 production plant, the first vehicles

PERFORMANCE rolled out March 1981. The first years, the production

rate was some 50-200 vehicles and the capacity is now

By 206 has off road mobility far above most other 800 vehicles per year.

vehicles. It is as standard designed for operation in The original contract from the Swedish Army was on

temperatures ranging from -45*C to +35*C and with 2000 vehicles, but was later increased to 4500 vehicles.

minor modifications, it can operate up to 49'C (1 20'F). The export sales have been very successful, and the

It is fully amphibious without any extra kits, propelled vehicle is now in service in more than 20 countrics.

in water by its own tracks. Its oversnow capacity is very Most of the vehicles are in operation in the armed forces,

57
figure 14. Anti-itank version-soIrcý cioped a spec". Ttact. This

riiios we ave dev tta Iube deep

Suc cod ti~ s~ outside th St'Xic b1h int we h~ave

t ciilian roles, uh wic n a vet b"' this txacV',

in n d Ives yu . W tttdent

alsos ued ge rattes so re no~ w 'd hige o gJ in deitp

butsole te'hicesin 1Vparlope W ehave cxino ,edala ha 

re s c u e 

y w n 2Sia 

V e l w s o ec V n e d M r ld' a~stt 

b u o l tianei s n ~w i n t e r t i mi e 

t o 9 f e .2 6 .i s n u s e b y

tas Was up . te X.e 2 6 s Svede 1. It is used

to~ od~oetaivehicles' ,lOe TnO 

Thei the ~~

ve es ic f 0 rp assen g ve hite. S w~edish It AN at f 1~ y in and a d S w ei ght up

our bigge it IS inte a m .dot ope rtn a ge nel The B 0 Ca be .. lade 'n

outside cu5Ns d~o dt One veye~ USA.x 0 nedn

N n y . s a n l o i f i n l i a -to lo t

0 r s

Al'ocountfrles a20 in; otehooeae hev- t edoe naodSscut

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tey-adt

l ar e e t O f13 6 .0 P A t n 5s r ic e at c o n d itio n s

. c s t o e r S ? l i s t i s i n r eg u l a r e, ( t re m~ e

interesin gli~ 1

inou n an sI th s and Othe

attdSabove400m1O
Operability: The First Step To Mobility

DEBORAH DIEMAND

U.S. Army Cold Regions Research and Engineering Laboratory

Hanover, N.H. 03755-1290

ABSTRACT

Virtually all major operations on earth involve the use of automotive and construction

equipment. Although most of these operationz are located in relatively undemanding

surroundings, some take place in extremely inhospitable environments. Special provision is

necessary to assure reliable operation of the equipment under these adverse conditions. One

of the most difficult environments for effective operation of this sort of equipment is extreme

cold.

All engineering equipment has some problems, even in ideal conditions. As winter

approaches and temperatures fall, problems gradually become more frequent, more numerous, and more serious. At about 00 C their number rapidly increases as the performance of the

soft and fluid elements of the engine and associated systems begins to deteriorate. Lubricants

thicken, seals stiffen, batteries lose power and freeze, and ice forms in fuel lines, carburetors,

and anywhere else water can possibly enter. Difficulty in engine starting is encountered.

These problems slowly proliferate down to about -40'C at which temperature another rapid

increase in problems occurs. This is because problems with hard parts are added to the gallery

of already existing difficulties. Differential expansion and contraction of different metals

cause jamming. Metals, rubbers, and other elastomers become brittle; structural members

crack; push rods and cylinders break. Below this temperature, equipment operation becomes

extremely difficult and in some cases impossible. Since very few vehicles are designed

specifically for performance in cold regions, the remedies for these problems have largely

resulted from local ingenuity fueled by the need of the moment. This paper describes some

general solutions fcr many operational problems encountered at -40'C and below.

INTRODUCTION long periods, these problems evolve from a nuisance

into a very serious operational problem.

Many of the problems associated with equipment The primary area of concern is starting the equipoperation at low temperatures are familiar to most of us. ment. Diesel engines are especially difficult in this

Below the freezing point of water, antifreeze must be regard because of the nature of the fuel and the ignition

used in water-cooled engines. Engines become hard to process, and many modifications are usually needed to

start because of decreased battery power and increased assure that a machine designed for use in temperate

oil viscosity. This can usually be overcome by tuning areas will function in extremely cold climates. In genthe engine and changing to a lighter oil. Tires lose some eral, this involves the installation of heaters for various

of their pressure in the cold. These sorts of concerns are components, devices to improve heat retention in the

common in the continental United States and have little engine compartment, and measures to improve ignition.

more than iwisa.;ce value. However, in extremely cold Once the engine is operating normally, its excess

areas such as Alaska, Canada, and Antarctica, where heat can be used to warm other parts of the machine,

temperatures may hover around -40°C or below for such as the cab, fuel tank, and hydraulic reservoir.

59
While there are many auxiliary heaters on the market for and subsequent recharging. Batteries should be housed

these purpowes, a properly winterized engine should in an insulated box equipped with either an electric

produce enough excess heat to satisfy all of the heater (usually about 100 W) or a thermostatically

equipment's heating needs. Therefore, the proper op- controlled coolant heater. Excessive heat can damage

eration of the engine itself is the most important con- the battery because of the higher acid concentration.

cem, and it is the primary focus of this paper. Since more electric power is needed in cold regions

because of increased engine resistance on start-up and

greater use of lights, pumps, and so forth, a higher

WINTERIZATION M.EASURES capacity battery should be used than that normally

called for, or more than one should be installed. Further

The winterization of equipment broadly includes information on the use of batteries at low temperatures

any measure that will help to mitigate the adverse effect is given in reference 2.

of cold on normal operation. This includes the use of

arctic-grade lubricants and seals, the implementation of Elastomers

heat retention devices, and the installation of heaters. Fluid leakage reaches epidemic proportions at low

temperatures, especially in hydraulic systems where the

Lubricants fluid pressures are higher than in other systems. HowThere are a number of lubricants currently on the ever, oil commonly leaks out of transmissions, power

market that give satisfactory service at very low tem- steering, and other systems as well. Some of this leakperatures. 0W20 or 0W30 motor oils remain fluid down age may be due to metal contraction affecting clearto -50'C or slightly below. These oils are often used in ances between mating parts and the tightness of fastenhydraulic systems, certain transmissions and other ap- ers. However, the greater part of the problem is because

plications where the standard fluid becomes too viscous the materials used in seals, gaskets, and hoses shrink,

to use in the extreme cold. There are drawbacks in the crack, and lose their flexibility. Arctic-grade seals and

use of these oils, however, hoses should be used on all parts of the machine that will

First, if the oil is not changed often enough, the be exposed to temperature, of -40'C and below. Siliviscosity index improver additive may deteriorate, re- cone rubbers have proven very useful in these applicasulting in loss of the oil's high-temperature properties. tions, and a great number of seals and hoses are comIbis additive is a very large branched molecule that mercially available using this material. At temperatures

contracts at low temperatures and exerts little influence above -40'C, standard parts may be satisfactory in

on the base oil's viscosity. At high temperatures, it many passive applications and need not be replaced

expands, effectively thickening the oil and increasing unless leakage problems develop. These problems are

its viscosity. However, in the high shear conditions in discussed in reference 3.

the cylinders the branches of these large molecules can Another factor that should be considered in selecting

shear off, and in extreme cases what remains is the very suitable materials is their ozone resistance. In snowlight base stock, which cannot adequately lubricate the covered regions ozone concentrations are higher than

engine at operating temperatures. normal and many products will degrade in its presence.

Second, some machinery cannot tolerate arctic-grade

oils at all and must use standard 30 weight oils or Heat Retention Devices

heavier. Most light machinery can use OWxx oils, but A cold-soaked, uninsulated engine at -40'C will be

the heavier the equipment, the more likely it will be that almost impossible to start and, once started, will never

they will be adversely affected by these oils. The prob- achieve normal operating temperatures. The result will

lems and use of lubricants are discussed further in be frequent breakdowns and high maintenance and

reference 1. repair costs. In an average machine operating under

normal conditions about a third of the energy available

Batteries in the fuel is used for useful work; another third is lost

The best way to ensure reliable battery power at low through exhaust heat, while the remaining third is

temperatures is to keep the battery warm at all times. transferred to the cooling system. In a well-insulated

Since this is not always feasible, batteries for arctic use engine, much of this waste heat can be retained, and the

ust illy use heavier electrolytes than those in warm engine will achieve normal operating temperatures while

areas, often with a specific gravity of 1.300, which the excess can be used to warm other areas of the

improves low-temperature performance and lowers the machine such as the cab, batteries, hydraulic reservoir,

freezing point. Nevertheless, some heating will still be and so forth by installation of suitable heat exchangers

necessary to achieve sufficient power output for starting in the cooling system.

60
Figure 1. This loader is equipped with both winterfront and

side blankets to minimize heat loss from the engine compartment. The winterfront can be partially opened using the horizontal and vertical zippers that meet at its center point.

Closed cell vinyl insulation 6 mm thick or greater is the engine can achieve before heat is removed by the

a popular choice for insulation in cabs and can be used cooling system.

in the engine compartment as well if treated with a flame The implementation of winterization measures will

retardant. A protective steel liner is also a good idea. improve the engine performance at low temperatures

Many vehicles are equipped with sound-insulating foam and in some cases may enable starting and operation at

in the engine compartment, which also serves as ther- temperatures as low as -30*C, but below this, the

mal insulation to a degree. addition of heat is desirable in all cases and inescapable

Other commonly used heat retention devices are inmost. Further discussion of winterization measures is

winterfronts and side blankets such as those shown in given in reference 4. The following sections give a brief

Figure 1. Virtually all machinery in use on Alaska's discussion of the types of heaters commonly used in

North Slope in the winter is equipped with winterfronts, automotive applications and criteria for their selection.

which are usually designed so that they can be partly or More information on heaters and heating is given in

fully opened in case the temperature rises. These pre- reference 5.

vent ambient air from entering the engine compartment

during operation and restrict heat loss during shutdown.

Side blankets serve the same purpose in machinery with TYPES OF HEATERS

open side panels. Under-engine protection is also used

either in the form of a plastic or metal shield or a more Engine preheating is either continuous during shutor less closely fitting insulated covering for the oil pan. down (standby heating) or on demand for a short time

Thermostatically controlled cooling fans reduce or prior to starting a cold-soaked engine (quick-start). The

eliminate fan operation, again reducing heat loss from main difference between standby and quick-start heatair infiltration. High-temperature thermostats are also ers is the heat output. Standby heaters are either run

routinely used to increase the maximum temperature continuously or controlled thermostatically while en61
106-

._ . . . . .. . .. .. ..:....:. .:...:.|.:. : ..: .:..::.. " .. ." ~~. .• .' .' .° .° .

15-QUICK-START S. . . . HEATERJ$-' j . . . .. .X ..I..: . .. ...

............. ,. ~ ".. ° ~ . . . . . . . . . ... . . .~.. •" ..' ..i-•. . i " .' " "i. ... .. . .. °- .

L .° o." . .o ."°o o"o. . oo

101-

*raw ,. Cook o .o .. .. .. .° .°. .

Electaic Prpaew Liquid fuels ..

Energyso"u.rc

Figur 2. Hea oupu rags. vaiu t.e of auto

•~~ ~ %-°%°.•°°°

tive heaters:

" 103- .

gines; are not operating and are often manually or usually much higher than for those used for warming oil

automatically tumned on as soon as the engine is stopped. because of the danger of charring or degrading the oil.

They maintain the engine temperature, therefore, only Immersion heaters for these two applications should not

at a sufficient level to ensure startability. Quick-start be interchanged. Thlese units are either mounted into

heaters must have a much greater heat autput than existing ports in the engine, such as the oil drain plug or

standby heaters because they must heat a cold-soaked frost plugs in the water jacket (which they replace), or

engine to normal operating temperature within a rela- are preassembled as a unit designed to replace a small

tively short time. section of the lower radiator hose so that the warmed

Most heaters either supply heat directly to the com- fluid will rise by convection, flowing into the block to

ponent being heated or indirectly through the coolant, a hb: replaced by cold fluid from the radiator.

notable exception being the Herman Nelson, which Externally mounted pads or coils are commonly

uses forced hot air. The heat output of the many units used where an immersion heatercannot be used. The soused in automotive applications ranges from about 50 to called silicone heater is widely used in Alaska, where it

1,000,000 watts. In general, stand-by heaters produce is commonly used to warm the oil pan as well as

up to about 100 kW, while quick-start systems fall into components such as the hydraulic reservoir, fuel tank,

the higher output ranges. Within this wide range the or other parts with a flat surface. The wire heating

specific heater types occupy a narrower niche, as shown element is sandwiched between two thin layers of

in Figure 2. silicone rubber resulting in a flexible unit about 2 mm

For the most part, electric heaters are the easiest to thick that is applied to the metal surface with highinstall, most convenient to use, and easiest to control. temperature silicone cement. Silicone pads are comThey are available in a great number of types, sizes, and monly available in sizes ranging from about l0 x 15 cm

power densities. There is really no engine component to 15 x 30cm with wattages from 150 W to 450 W. Other

that cannot be heated electrically. Figure 3 shows three sizes can be custom made, and special-purpose pads are

of the most common types of electric heaters used for manufactured for drums, cylinders, and the like.

automotive heating. Batteries are normally heated with very low-power

Immersion heaters are used in the cooling system plates (underneath the battery) or blankets (surroundingo

and in the oil sumps of both the engine and gear boxes. the battery). Batteries should only be heated enough to

The wattage of those used in the cooling system is assure sufficient power output and should never be

62
exposed to elevated temperatures for extended periods, subject to the same fuel problems as the engines themThe last common type of electric heater is the tank- selves, i.e., waxing and low volatility. The problems of

type, which is plumbed into the cooling system in such fuels at low temperatures are discussed in reference 6.

a way that water is drawn in from a point near the bottom Thermoelectric generators are very reliable, if costly,

of the system and returned to it at the top. The power devices that convert heat directly to DC electricity

output is usually greater than that of the other types of through a solid-state energy converter. They produce

electric heaters, but this advantage is partially dimin- electrical power at about 7-9% efficiency and produce

ished by the increased heat loss to the engine compart- a large amount of waste heat. Small units that use diesel

ment. These heaters are usually passive systems and fuel, kerosene or gasoline have been designed for use on

rely upon convection to circulate the heated coolant. automotive equipment. Heat from combustion of the

They are therefore limited as to the areas to which heat fuel is applied to one side of the energy converter. The

can be distributed. other side is cooled by circulating engine coolant. The

Fuel-fired heaters have a similar design in which the resulting temperature differential causes DC power to

water jacket surrounds the combustion chamber, as be produced. The electricity produced runs the pump,

shown for a propane-fired heater in Figure 4. Heaters of and any excess power can be used to charge the battery,

this type have the highest heat output of the on-board if desired. The net power output is about 60 to 400 W.

units and are often supplied with pumps so that the The excess heat is absorbed by the coolant and amounts

heated coolant can be distributed to many different to about 6 to 12 kW. Power required for startup is about

areas in the equipment rather than just the block. Heat 420 W maximum (15 amps at 28 V), but the unit is selfexchangers can be installed in the cab (usually stan- sustainingduringnormaloperation.Theseheaterswould

dard), oil pan, battery box, fuel line, hydraulic reservoir, appear to have great potential value in cold regions

rearview mirror, air intake, and other areas where space where electric power is limited.

permits the installation of the necessary tubing. Active In many cases the use of an auxiliary quick-start

systems of this sort are often used for stand-by heating, system is the most effective choice in terms of both fuel

and the larger units can be used as quick-start heaters to economy and heating time before start-up. The gasopreheat a cold-soaked engine, although this could take line-fired Swingfire heeter used by the military is a

as long as several hours. Their major disadvantages are

that they need electricity to run the pump and they are

Outlet

ab.

Water jacket

Inlet

Burner assembly

Figure 3. Common types of electric heaters, a) Immersion heaters designed for installation in existing ports

in the engine; b) silicone pads attach to anyflat metal

surface on the engine or elsewhere in the machine; c) Figure 4. Fuel-fired heater in which the coolpassive tank-type heater in which the coolant flows by ant flows through a water jacket surrounding

convection through the heater. The ball at the intake the combustion chamber. It may be either pasprevents backflow of the coolant when the engine is shut sive, in which the coolant flows by convection,

down. or active, with an associated pump.

63
multipurpose device that can be used for coolant heat- 7200 -

ing, space heating, forced hot air heating, and so forth. 6400 - V-engin s

A heat exchanger designed to accept the Swingfire is In-line ines

installed on the machinery to be heated, and the unit is 5600

moved from one machine to the next. Their heating

capacity ranges from about 10 to 20 kW, and they (n 4800

require only a small amount of electricity on start-up and / /

none thereafter. 4000

Other types of coolant preheaters use fast-disconnect 3200

couplings to connect the heating unit to the cooling

system and pump the hot coolant through whichever 2400 __

heat exchangers are enabled. Tbe power for the pump

can be taken either from the battery of the unit being 1600 0,20

heated or from the vehicle used to transport the heater.

These heaters are designed to use various kinds of fuel 800

and can be almost any size. J

The Herman Nelson heater is a fuel-fired forced hot

air heater that blows hot air through conduits to the parts 500 1000 1500 2000 2500

to be heated. It is normally used in conjunction with a Displacement (cubic in.)

shelter of some sort, whether an insulated compartment

integral to the machine or a temporary shelter enclosing Figure 5. The amount of heat required to warm the block

all or part of the equipment. The heat output may be as of engines of various sizes to -1 0

Cfrom the indicated

high as 1,000 kW. ambient temperatures using immersion heaters. Additional heat would be required ifa tank type heater were

used or if other areas were heated.

MAGNITUDE OF HEAT INPUT REQUIRED

At temperatures below -30'C most equipment that is cous and harder to vaporize and because ignition denot stored in a heated garage will require at least some pends on the heat of compression alone, which is often

heat input for starting. The amount of heat applied and insufficient at ambient temperatures below about -

to which parts of the machine depends on many factors: 10'C. There are a number of devices in use to heat the

intake air either electrically or through the use of coolEngine size ant heat exchangers or partial combustion of the fuel

The size of the engine has a strong influence both on before it reaches the combustion chamber. One of these

the rate at which heat is lost from an engine and the should be used on diesel equipment even in moderately

amount of heat that must be applied for a successful start cold conditions, and at extremely low temperatures the

from a cold-soaked condition. Figure 5 shows the size of intake air should be heated even during normal operathe heater required to warm the block to I 0

C for engines tions. This is often accomplished by locating the intake

of various displacements. The data from which this near the supercharger or some other hot place in the

graph was drawn were derived from measurements engine compartment.

made on engines in still air equipped with immersion In terms of engine configuration, the more compact

heaters that were able to bring the block temperature up V-type engines require less heat than in-line types.

to -1° in 12 hours, with 80% of the temperature rise In terms of the overall machine configuration, the

taking place in the first 5 hours. If a shorter heating more compact the design, the easier it will be to warm

period is required, a larger heater must be used. If tank the necessary components. If the fuel tank and hydraulic

type heaters are used, the wattage values should be 50% reservoir can be enclosed in a common insulated envehigher than those shown. Any other necessary heat input lope, both can be heated more effectively. On the other

such as for the oil pan, battery, or cabin would be in hand, some machinery such as cranes by their very

addition to this. Note also that in-line engines need more nature cannot be made in a compact configuration.

heat input than V-engines with the same displacement. These are difficult to winterize and are usually not used

at very low temperatures if it can be avoided.

Type and configuration of the equipment

Diesel equipment requires more attention than gaso- Operational schedule

line-powered equipment because the fuel is more vis- The length of time a machine will be shut down inthe

64
course of normal operations has a considerable influ- kept in heated garages except certain emergency veence on the amount of heating it will need before it is hicles. However, whenever possible equipment should

restarted. A machine that is used continuously may not be kept in a shelter of some kind to retard heat loss from

need any integral engine heaters. For example, in a wind chill and to prevent infiltration of blowing snow.

mining operation where the equipment is used on a 24- In windy conditions the amount of energy required to

hour basis and is never turned off except when it is in the preheat an engine is greatly increased and the period of

heated maintenance facility, the engine will never zool time the engine will retain enough heat to start unassufficiently to need heat input for starting. On those rare sisted is much reduced.

occasions when such equipment has been allowed to Temporary shelters are commonly used when using

cold soak, it can be warmed in a temporary shelter using a hot air quick-start heater to preheat cold-soaked maa quick-start heater. chinery. Parachutes are often used, as shown in Figure

A well winterized engine may retain enough heat to 6, ora tent ortarpaulin-anything, in short, that will cut

start after 4 to 8 hours without additional heating de- the wind and reduce heat loss. Coolant heaters are less

pending on ambient conditions. However, an engine dependent on wind conditions since they pump heated

that has been allowed to cool for as much as 16 hours coolant directly to the heart of the engine.

must be considered cold-soaked and treated accordingly. If the equipment is routinely shut down for a Degree of winterization

period that might be long enough to cold-soak the The use of heat retention devices is a good idea beengine it should be equipped with a stand-by heating cause they will improve engine life and performance by

system that will maintain a sufficiently high tempera- ensuring that the engine will be able to reach and mainture in the engine for reliable starting throughout the tain its design temperature and will increase the amount

shutdown period. of engine heat that can be made available for other uses.

A closed and insulated engine compartment also indiLength of time available for heating rectly assists cold-starting by reducing the amount of

For several reasons the most efficient engine pre- heat that must be applied for a successful start.

heating technique is the quick-start method where a

relatively large amount of heat is applied in a relatively Availability of electric power

short period. The shortest possible time is desirable, but If virtually unlimited electric power is available,

because of the size of heater required and the damaging electric heaters can be used to warm all necessary parts

effect of raising the temperature of engine parts too of the engine. They are reliable, inexpensive, compact,

rapidly, heating time should not be less than 15 minutes easily controlled, and available in an enormous number

to 1 hour at -55'C (-65'F), depending on engine mass. of sizes, types, and power outputs. However, a large

In general, the shorter the time allotted for preheating, piece of equipment may need an intolerably large amount

the greaterthe size of the heater required and the greater of electricity to preheat it in a reasonable amount of

the complexity of the preheating system. Quick-start time. Similarly, the electric power supply may simply

systems are virtually essential when cold-soaking of a be inadequate to meet the heating demands of the

vehicle is unavoidable. Usually quick-start heaters are number of machines needing preheating. In this case

stand-alone units exteriorto the machine such as Herman fuel-fired heaters should be used. Many of these need a

Nelson heaters or a hot coolant transfusion unit, and small amount of electricity to start up or to operate

usually there is not a large number of them available at pumps, but the heat itself is produced through the

a particular site. Therefore, if many machines must be combustion of fuel.

started up at the same time, a single heating unit would

have to be shared by a number of machines, so that it

could take several hours to start up all the engines. In CONCLUSIONS

this situation it would make sense to install highcapacity preheating units on each machine capable of There is no way to achieve flawless operation of

warming the engine to starting temperature in a few automotive equipment at very low temperatures. Howhours. The preheating system can be controlled by a ever, by proper winterization of the equipment. use of

timer that would automatically start up the heaters at a arctic-grade lubricants and fuels, and choice of a suitpreselected time so that all machines should be ready to able heating system, the life and performance of the

start when they are needed. equipment can be much improved. Unless it is run

continuously, all machinery will need some degree of

Type of shelter available heat input below -30'C. The choice of an appropriate

Very little equipment used in cold regions can be heating package depends upon:

65
Figure 6. A bucket loader is heated prior to operation by enclosing it in a parachute and blowing hot air into the

enclosed space through elephant-trunk conduit from the space heater on the left. The ambient temperature is about

-35 0C.

"* The size of the engine 2. Diemand, D. (1991) Automotive Batteries at Low

"* The type and configuration of the equipment: Temperatures. U.S.A. Cold Regions Research and En-

"* The operating schedule: If the engine is normally gineering Laboratory, Cold Regions Technical Digest

shut down for a relatively short period, a standby No. 91-4, May 1991.

system would probably be the best choice; if the 3. Diemand, D. (1991) Automotive and Construction

equipment is often shut down for long periods, a Equipment for Arctic Use: Materials Problems. U.S.A.

quick-start system would be the most efficient. Cold Regions Research and Engineering Laboratory.

"• The amount of time available for heating: The Cold Regions Technical Digest No. 91-5, November

shorter the heating time available, the larger and 1991.

more complex the heating system. 4. Diemand, D. (1992) Winterization and Operation of

"* Available shelter Automotive and Construction Equipment in Arctic Use.

"* The degree of winterization U.S.A. Cold Regions Research and Engineering Labo-

"* The type and number of auxiliary heating units that ratory, Cold Regions Technical Digest No. 92-1. Separe available tember 1992.

"• The availability of electric power. 5. Diemand, D. (1991) Automotive and Construction

Equipment for Arctic Use: Heating and Cold Starting.

U.S.A. Cold Regions Research and Engineering LaboLITERATURE CITED ratory, Cold Regions Technical Digest No. 91-3. April

1991.

1. Diemand, D. (1990) Lubricants at Low Tempera- 6. Diemand, D. (1991) Automotive Fuels at Low Temtures. U.S.A. Cold Regions Research and Engineering peratures. U.S.A. Cold Regions Research and EngiLaboratory, Cold Regions Technical Digest No. 90-1, neering Laboratory, Cold Regions Technical Digest

December 1990. No. 91-2, March 1991.

66
Wheeled Vehicle Mobility Evaluation In Deep Snowpack

D.M. XU, A.M.O. MOHAMED, R.N. YONG

Geotechnical Research Centre

McGill University

817 Sherbrooke St. West

Montreal, Quebec, Canada H3A 2K6

GJ. IRWIN

Defence Research Establishment Suffield

Vehicle Mobility Section

P.O. Box 4000

Medicine Hat, Alberta, Canada TI A 8K6

ABSTRACT

This paper proposes a computational model to evaluate the wheeled vehicle mobility in

deep snow pack. The snow plate footing and the snow direct shear test data are used to offer

the basic parameters required in the model. The contact length under the vertical load on the

tyre is determined at first so that the average normal and shear stresses on the contacting

surface can be evaluated. The energy conservation principle is subsequently employed to

evaluate the tractive efficiency, etc. A computational example is given for demonstration

which offers a great deal of information for vehicle design.

1.0 INTRODUCTION circumstances the need to account for soil property

variation for correlation between changes in soil propPresent procedures utilized for predicting vehicle- erties and vehicle performance is obvious. Thus, measnow performance are by and large ad hoc in nature, or surements of penetration resistance or shear resistance

based on adaptations of methods used in the field of in soil material appear to be acceptable for application

vehicle mobility on soil terrain. In the case of vehicle- with the associated methods of analysis for both desoil interaction, the methods used for predicting ve- scription of and assessment of soil-vehicle performance.

hicle-soil performance rely on procurement of soil Snow however presents a different picture. The

material property on information through field testing problems existing in ordinary vehicle-soil interaction

tools. These tools, e.g. cone, vane-cone, bevameter, etc. become significantly more complex in a vehicle-snow

together with their associated methods of data interpre- interaction phenomenon because the material (snow)

tation and application presume a certain degree of properties are significantly more complex. An insight

material property invariance. This assumption is not into some of the reasons why snow is much more

valid in the strictest since, but finds some measure of complex responsive material compared to soil in the

application in the field of mobility on soil material area of vehicle performance predictions follows.

because the widespread difference in vehicular loading

schemes and surficial topography are by and large Density

significantly greater than the general differences in Snow pack density is a very popular measurement in

local soil properties. snow classification schemes but tells little about the

Variations in soil conditions encountered when mea- snowpack without knowledge of grain size, in situ

suring vehicle performance in soil influence the re- temperature and thermodynamic history. By and large,

sponse of different loading system. In view of such snowpack density varies with age and normally has a

67
profile of values increasing from the surface downward. analogy fades because:

A knowledge of this is important not only from the (a) the mechanical properties of sand are by and large

density-variation point of view but also from the view- insensitive to seasonal temperature variationspoint of detailing with respect to stratigraphy. Since as opposed to snow. Note that in most locations

initial vehicle flotation relies on snowpack stability vis- and instances, snow completely disappears in

a-vis bearing support, structural configurations in the the summer period and that the properties of the

snowpack are important conditioners. Thus, one can material throughout its seasonal life are reflecnote that various methods of packing can produce tive of the life cycle.

identical density. In turn, these various packing or (b) The effects of stress history in sand strain-rate

structural configurations can produce varying strengths loadings are vanishing small. These effects are

due not only to packing states, but also bonding mecha- significant and influential factors in production

nisms. Density measurements do not reflect these as- of snowpack response.

pects of the phenomenon. Note also that the snowpack (c) Volume changes under loading in sand are small

is subject to large changes in density during vehicle- in comparison to snow.

snow interaction.

Devices for measuring snow properties for mobility

Grain size distribution prediction purposes

This is an important factor relates to shear strength In the examination of devices presently used for

and potential or actual bonding. It also is a factor in the measuring snow properties for mobility prediction purdensity of the pressure bulb which forms beneath the poses, it is significant to note that technology transfer

vehicle traction element. The grain size distribution (from mobility on soil to mobility on snow) has been

characteristics of a snowpack is affected by age, tem- made on a one-to-one basis. Relegating snow as another

perature variations, climatic conditions during and after kind of soil material, and using not only the same testing

deposition, and possibly other cases, tool but also the same kind of data reduction, analytical

techniques and equations, can lead to severe errors in

Temperature assessment of vehicle-snow interaction. This kind of

Local temperature has a pronounced effect on the technology transfer ignores the true and real differences

strength properties of snow. It is not uncommon for the in material response-which are indeed large in the case

near surface layer in a snowpack to vary 20*C in a 24- of snow and assumes that the interactions themselves

hr. period. It is also significant to note that in conjunc- are identically duplicated vis-a-vis vehicle-soil and vetion with elapsed time, the variations in temperature hicle-snow interaction.

will contribute to the thermodynamic history of the Thus for example, if one presumes that soil can be

snowpack. Thus, the corresponding or related changes modelled according to elastic-plastic and elastic-work

in snow resistance properties can be identified, hardening relationships, the implication from technology transfer thinking is that snow will conform to the

Depth same requirements befitting that of elastic-plastic or

Whilst a knowledge of the depth of the snowpack elastic-work hardening materials. Note that the exgives only documentary information, by itself it be- tremely high volume change effect is not satisfactorily

comes extremely important when coupled with vehicle accounted for in the above models. Hence, one comdimensions. The method of performance analysis for pounds the difficulties indirect transfer through not only

operations in a snowpack which completely contains the large difference in volume change and linearity

the effects of vehicle sinkage is different than for performances but also the attendant problems of temoperations where the snowpack behaves as a layer perature and strain-rate.

compacted between the vehicle and the ground. These In addition to the requirement of likeness in constituvehicle performance conditions are labeled as over tive performance between soil and snow as a natural

snow and through snow, respectively consequence of the application of technology transfer,

the adoption of the soil-snow analogy carries on the

Snow-soil analogy imposition of the two-parameter Mohr-Coulomb theory

If analogies were attempted between soil and snow, as a "valid" failure criterion for snow. The consethe closest and most realistic analogy would be between quences of the application of the theory of a failure to

dry sand and granular (dry) snow. Both materials can be snow can be dramatic since the outcome of the theory is

co•'zk!e~d as tw,, p__se .r-.erials where porosity and the identification of two material strength parameters C

grain size distribution are reasonable descriptors of the (cohesion) and 0 (angle of internal friction). Since the

materials. Beyond this particular context, however, the theory of failure requires that the total energy needed to

68
fail a test sample is expended along a rupture plane, and (tyre) on snowpack in terms of the well known energy

not in volume change or any part thereof, it is clear that balance equation.

the application of such a theory to materials which suffer

undue volume change under loading cannot be directly Input energy = output energy + energy losses (1)

accomplished without accountability for volumechange

energy expenditure. Thus the concepts or values of C With the quasi-static assumption, the vehicle is asand 0 obtained in medium to high volume change sumed to move on the snowpack at a relatively low

materials need to be properly scrutinized and placed in speed so that dynamic effects (including vertical vibraperspective in order that their application to problem tion of vehicle system and snow damping) can be

analyses may be correctly situated. Note that in the case neglected. The energy balance equation in terms of

of soils, the volume changes encountered under loading power can be written as:

are generally sufficiently small-thus allowing for a

viable application of the two-parameter Mohr-Coulomb Puse = Pinput - (PsUp + Psnow + Ptyre) (2)

theory of failure.

The preceding highlights that in order to predict where: Pm = the useful power, Pilmt = the total power

vehicle snow performance, it is essential that the mecha- input to wheel; Pslip = the power dissipated due to tyre

nism of compaction and shear between the traction slip; Psow = the powerdissipated in snow deformation,

elements and the snow is understood. If the prediction is and Ptyr = the powe: dissipated in tyre deformation.

based upon sampling the reactions of the snow to This method of mobility evaluation (Xu et al. 1990

external forces and imposed deformations, logic dic- and 1991) is especially suitable for the initial stage

tates that if a proper rational prediction of performance when the vehicle begins to move on a specified terrain

is to be made, a similarity in the development of snow surface from the "at-rest" condition. It not only answers

response between the reaction element and test and whether the vehicle can or cannot move i.e., "go or no

direct shear tests are used to obtain the required param- go" question, but also gives a reasonable estimation of

eters which characterize the snowpack. In this study a vehicle mobility for the assumed conditions: (1) slow

plate loading and direct shear tests are used to obtain the speed, and (2) no vibration effect.

required parameters which characterize the snowpack.

Furthermore, a wheeled vehicle mobility model is de- Input energy

rived based on the energy conservation principle. In The input energy, through the applied torque To on

brief, the method works with an analysis of the displace- the tyre during time to is given by:

ment around the contact boundary between the loaded

tyre and the supporting snowpack. The contact length is Einput = To0

Wto (3)

first determined so that the subsequent calculated stresses

on the contact boundary can be specified. The slip rate or

and the traction efficiency are given as a natural outcome based on shear test data and the energy conserva- Pinput = ToW (4)

tion principle.

where: Einput = total input energy (kN.m.rad); Pinput =

total input power (kN.m); co= tyre angular velocity (rad/

2.0 THEORETICAL FORMULATION sec); To = applied torque (kN.m), and to = time (sec).

In applying the principle of energy conservation to Slip energy

the evaluation of tyre performance on deep snowpack, The slip (dissipated) energy due to the applied torque

the different energy components participating in the To on the tyre during time to is given by:

interaction between the loaded tyre and snowpack need

to be calculated. The energy concept for evaluation of E$1ip = TooyoS (5)

traction was formally introduced by Yong and Webb

(1969) for motion performance of rigid wheels on soft or

soil. Subsequently, the energy model was extended by

Yong and Fattah (1976), Yong et al. (1978, 1980), and Pslip = T 0

os (6)

Xu et al. (1990) and (1991) to predict pneumatic tyre

performance on soft soils, where: Eslip = the dissipated (lost) energy due to tyre

The basic principle used in the energy model evalu- slip (kN.m.rad); P,1 ip = the dissipated power due to slip

ates the moving performance of the tractive element (kN.m), and S = the slip rate, which is given by:

69
axial load on the wheel from the vehicle weight.

S = wr (7) The simplification of a quasi-static assumption is to

(mr guarantee that the normal force F, is constant, which in

where: S measures the efficiency of the transfer of the turn is not violated by the dynamical effects. Therefore,

tyre rotational motion into the horizontal vehicle mo- one can evaluate the snow dissipated energy using a

tion; r = rolling radius (m), and v = translational velocity simplified set of calculations. To calculate the snow

(m/sec). dissipated energy, the normal stresses on the contact

area must be calculated first. The normal stress distribuSno- dissipated energy tion on the contact area is usually assumed as a parabolic

When the vehicle moves on the snowpack, it con- shape according to Hertz contact theory as:

tinuously "loads" the undisturbed snow and hence snow

will be deformed and energy will be dissipated due to (u) = 3Fv (1- Y 3

-for 0 _< u_< t (1 3a)

snow deformation. This energy is directly related to the 4Vb t2

normal stress distribution on the contact area between o(-u) = o(u) (13b)

tyre and snow surface. For the snow surface, the loading

situation can be considered in terms of a distributed where: Fv = the axial load on the wheel (kN). To

stress along the contact length moving at vehicular simplify the calculation an average normal stress oav is

speed. suggested as follows

The moving boundary loading condition can be

specified as follows, any concentrated point load F(kN) 0av = Fv (14)

acting at a distance xo from the origin of the coordinates 21b

may be described by When the vehicle moves a distance Ax, the energy

dissipated in deforming a new undisturbed snow eleF(t) = F8(x - xo ) or F <x - xo >- (8) ment takes the following form:

AEsnow = oavb5Ax (15)

where S(x - xO) is the Dirac-delta function defined by:

where 6s is the snow sinkage (m). Substituting Eq. (14)

(0when x<(xFL into (15) gives

8(x-x°)= limi-when Xo(x- <x< (Xo+F AEsnow - - (16)

E '2 2 2'1 2U

Owhenx> Xo+2-) (9) Furthermore, if the vehicle moves from xo =0 to x =

Xl, the total dissipated energy is given by

For the problem under consideration, the point load F I

F and the distance xo take the following relations: Esnow - FAS jd&

F, =b O(u)du, and (10) _Fs x (17) f 21

Xo = vt (11) Since xj = vt! = (I - S)wrt, one obtains

where: (o(u) = normal stress distribution along the Esnow- FvSs(I-S)wrt! (18)

contact length (kN/m 2), I = half contact length (m); b = 2t

tyre width (in), and u = distance ranges between -t to t The corresponding dissipated power is given by:

(in). It can be noted that Eq. (10) implies that along tyre

width b the stress distribution is uniform. Substituting Ps - F, s (I1 - S )o), (19)

Eqs. (10) and (HI) into Eq. (8), the vertical load F,(t) is 2t

given as: Tyre dissipated energy

The tyre dissipated energy can be calculated in a

Fv(t) = Fv < x - vt >-I =b a(u)du. < x - vt >i- similar way to snow dissipated energy. The resultant

(12) equations obtained are:

where: x = the transverse coordinate measured from the Etyre =F,,t ( I - S )rtl (20)

tyre centre to a stationary reference (m), and F, is the 21

70
where TTF = tractive force (kN), which is the force

Ptyre F--L (1-S)or (21) capable of doing useful work. Substituting Eq. (26) into

21 Eq. (22), the following expression for the tractive force

where: 8t = the tyre sinkage (in). can be obtained

Useful energy

According to Eqs. (2), (3), (6), (19) and (21), the Fp = (1- S) L-F--L- (8t+ 81 (27)

useful energy or power can be calculated as follows: 2Ir 2

It can be seen from Eq. (27) that when the slip rate

equals zero, the tractive force reduces to the same PUN Too3- [STo + Fs(1 -)8r t I-S)wr+ L (1 -S )] expression presented by Eq. (25). Furthermore, when 21 2J the slip rate equals 100%, the tractive force is reduced

=O)(1-S)[To- E- (,, + 81 (22) to zero.

Traction efficiency

The traction efficiency h takes the following form: 3.0 PARAMETER CALCULATION

Si)Pi[n • (8t +8 (23) The following parameters: (1) halfcontact length (1);

Pin W, (2) snow sinkage (8s); (3) tyre sinkage (8t), and (4) the

slip rate (S) need to be calculated.

Draw-bar pull

It has been known that the useful power is given by (1) Contact length

the following Since both the tyre and the soil are assumed to be

deformable, curve AB, as shown in Fig. 1, is the

Puse = FDP x v (24) resultant contact profile which represents a compatible

displacement curve in the final state after the load F, is

where: FDp = Drawbar pull (kN). Substituting Eq. (24) applied. The curve AB depends on both tyre and soil

into Eq. (22), the draw-bar pull takes the following compression characteristics. Two extreme cases as

expression shown in Fig. 2 can be discussed: (1) the soil can be conr,] sidered as a rigid surface, hence the resultant curve AB

FEp -=o (1-S) To- Fr (8t + 8s is a line as shown in Fig. 2a, and (2) if one considers the V I 2-t tyre as a rigid disk, the resultant curve AB is a part of the

- -I (St + 8s) (25) tyre circumference as shown in Fig. 2b. The real situa- r 21 tion is somewhere in-between the two extreme cases.

Let us compare the contact length 211 (Fig. 2a) and

The draw-bar pull presented by Eq. (25) is the force 2t2 (Fig. 2b), in the case that the tyre size and the

required to mobilize the traction forces minus the mo- inflation pressure are the same but one is rigid terrain

tion resistance of the wheel. It can be seen that as the while the other is a deformed terrain. The conclusion

input torque increased the draw-bar pull increased and can be reached that 2ti is larger than 2t2. Since the

the draw-bar pull is not a function of the slip rate. At a terrain is deformable, it allows the tyre to sinkmore. The

given constant tyre rotational velocity o), the horizontal spring constant of two springs connected in series is

translation velocity v is affected by slip rate S. At S = 0, always less than that of either spring taken individually.

v= or, whileatS= 100%, v=0. Furthermore as the input That is why one cannot just take the tyre compression

torque on the wheel increases, the slip increases. At test data to obtain the contact length without considercertain limit of torque values, the slip reaches 100% and ing the terrain characteristics.

the vehicle is not able to move because the soil loses its Hertz theory has been widely used to calculate the

shear resistance. At the same time, the attached drawbar contact length by many authors. The subsequently obpull FDp reaches maximum value at S = 100%. How- tained contact length, which based on presumed disever, this force is "handicapped," with no ability to do placement field, yields the following approximate relaany useful work (as the vehicle does not move). Based tion

on such observation, it is wise to take the constant r4Fvr I I-vlt' 2 2 

velocity or as observational base and express the useful 1 2 (28)

power Puse as: R - EJ

Puse = TTF x or (26) where: Es and Et modulus of elasticity for soil and tyre

71
As

SAt

Figure 1. Geometric representation of soil and tyre compression areas.

tyre respectively. Since, neither soil nor tyre are elastic, equation after Yong et al. (1990):

one has to search for a new method to calculate the

contact length based on both tyre and snow characteris- I p- (YA' 'sl 

tics. The following highlights the technique used in this As. . (29)

study to calculate the contact length. 3 \ Po Jcj+Optan \Oc

From a rigid circular plate load test data on snow,one where: initial snow density; pc = critical snow

obtains a relationship between the vertical applied load, w

F,, and the snow deformation, As. The theoretical rela- dest;x tesdsrbto ntepae= D =

tionships between snow deformation, As and the vertical plate diameter, Oc = stresses at critical snow density; c,

applied load, F, can be represented by the following *, and k = snow material parameters which can be

A l B ^2 A B 2

a. Contact length AIBj for soft tyre and b. Contact length A2 and B2for rigid tyre

rigid terrain, and soft terrain.

Figure 2. Schematic diagram showing contact length.

72
determined from Eq. 31 and the experimental relation At = r2 (01 - sin0! cos0i) (33)

between ap and 4.

Since plate disk loading is different from rigid wheel where: r = tyre radius; 01 = an angle which characterizes

type loading on a snow, transformation of plate type sink- half contact length, which can be determined from the

age into wheel type sinkage has to be performed. After following relation

transformation, the final Aso takes the following form:

10.1 \ k 6 r.srAtj() Ao0 (PC + q )( ) (30) (b) from a rigid circular plate test data and Eqs. (30) and

(31), Aso can be calculated. The snowdeformed area,

where: t = half the contact length; b = tyre width; t = As, in a vertical cross section can be determined from

average stress distribution on the contact length = ap- the following relations as shown in Fig. 2b.

plied load on the tyre/contact area; contact area = 21b.

From experimental data on different types of snow, the A, = r 2 (02 - sin 02 cos 02) (35)

following material parameters are assigned: c = 3 kPa;

* = 5.70, acr = 423 kPa; k = 0.25, and Pc = 0.597 Mg/m3

. where: 02 = an angle which characterizes half contact

It should be noted that these parameters are similar to length, which can be determined from the following

those determined by Blaisdell et al. (1988). However, relation

from the geometrical relation, Aso can be determined

from the following relation. 02 = arccos t -, (36)

Aso - r - (r 2 - 12 )0.5 (31) (c) inconsidering the real case whereby both the tyre and

the snow are deformable, the total sinkage 8 can be

To solve for the appropriate Aso numerically, an determined by considering Ato and Aso as representiteration technique is used. Given a firs. tried value I = ing the displacement of two springs connected in

r, from Eqs. 32 and 33, one determines two values for series. Once 6 is obtained, the tyre sinkage, N1, and

Aso, named Aso(l) and Aso(2). Since I is tried value, the snow sinkage, St, can be determined according to

Aso(1) is not equal to Aso(2). If ABS[(Aso(1) - Aso(2))/ the ratio of 8t to 8s. It should be noted that 8t and 8s

Aso(l)] is not less than 1%, then £ = I - dt, where I is a are not Ato and Aso The relationship between As and

small value = r/l000. Such an iteration procedure will Al is given by

continue until the above comparative condition is satisfied. The corresponding I and Aso are the solution. A = As + At = r 2(0o - sin0ocosOo) (37)

(2) Tyre and soil deformations where: 0, = an angle which characterizes half contact

As a vertical load Fv applied on the axis of a tyre, length as shown in Fig. 1. Based on the geometrical

which is exerted through the vertical total weight, both representation in Fig. 1, the following relationships can

tyre and snow will be deformed after contact. The total be obtained:

sinkage of the tyre, 5, can be determined. The detailed

algorithm to calculate 8 involves the following steps: t = rsin0o (38)

(a) from a tyre compression test data for a given tyre

inflation pressure on a rigid surface, one obtains a and

relationship between the applied load, F,, and the

corresponding deformation of the tyre, At. By using 8 = 8, + bt = r - rcos 0o = r -(r2 - !2)Q5 (39)

a numerical interpolation method, the tyre deformation, Ato, which corresponds tothe vertical load, Fro, Eq. (37) can be written as follows:

on the tyre to be modelled can be determined from

the following relationship: A =As+ A 1=r 2 '[o in (40)

Ato=-Ati+ Fvo (A+ -Ati) (32) when 0o is small \Fvi + I - Fvi/

where: Fvo = the vertical load between the two points i (0)

and i + 1. The tyre deformed area At, in a vertical cross sin 20 =-202- °- ..- ,and (41)

section can be determined from the following relation as 2

shown in Fig. 2a: coso = I .- p ... (42)

2

73
Substituting Eq. (41) into Eq. (40), the following rela- (b) The equivalent contact length, L. for a tyre with

tions can be obtained width (b) is:

A- 2(Oo-__ (200-!O&2 +.))Or (43) L =sh (51) 2 4b

Substituting Eq. (42) into Eq. (39), the following rela- (c) Assuming that a wheeled vehicle moves a circumfertion can be obtained ential distance L during the forward movement of

the vehicle, a horizontal backward movement U of

8 r ( - I - 2 (44) the snow due to shear stresses is induced. The slip

rate S can then be obtained as follows:

From Eqs. (43) and (44), the relationship between A and

8 can be expressed as follows S= U - 4Ub (52)

L

A = 2r8 (45)

(d) Eq. (52) is valid only for smooth tyres. To include

Since A is proportional to 8, As and At can be assumed the effect of treads, one has to calculate the effect

to be proportional to8 and 8t respectively. The relation- of snow-snow and rubber-snow contact and their

ship can be written as follows: ratios. Since, the tyre has a unique shear displaceAs_ 8s ment, U, the following condition has to be

At 8t (46) satisfied

With the aid of Eqs. (37), (39), and (46) the snow and t sTs + tr r= r av (53)

tyre deformed areas can be obtained as follows:

where: ar, = average shear stress on the contact area

A (47) which is given by A

&t=At 8 (48) rav= T, (54)

A 2b&

and E and E = fractions of treaded and nontreaded areas

20.5 respectively, and '"r and Ts = the developed shear

8= r -(-£2) (49) stresses at the contact areas for rubber-snow and

snow-snow respectively.

where: 8= total deformation due to tyre deformation, St,

and snow deformation, 8s. (e) From direct shear experimental data, the relationships between , vs Us and 'r vs Ur can be obtained

(3) Slip rate, S and represented by the following relationships:

In the original sense, slip rate S is defined as represented by Eq. (7). If the rotation of the tyre is completely (1) Snow-snow condition

transferred to a horizontal motion, v = oar and S = 0. This

situation requires that snow is very stiff. However, in Us a

case of fresh snow, a backward movement of the snow )(U I for Us < Usma

takes place due to the induced shear stresses. In order to Ts -

calculate the slip rate direct shear tests on the specified "smax J for Us > Usma

snow are required. The reduction of data from direct I (55)

shear test into slip rate of a tyre can be proceed as

follows: where a = a positive number, and Tsmax = maximum

shear strength. If ;s is beyond rsmax the snow is con-

(a) For a circular sample in a direct shear test, the sidered to be in a state of shear failure. From experisheared area i.e. the contact areacan be expressed as: mental data, the following empirical formulas are obtained: A sk,= f-dsh (50)

=4 

(a) parameter, a

where: Ash and dsh = cross sectional area and diameter

for the tested sample in the direct shear test. a = 0.7 - 2.0 P0- C (56)

74
(b) maximum horizontal backward movement, Usmax The shift displacement, U, is calculated by using

iteration method as a numerical technique. This can

Usmax = 20.0 - 76.0 (Po - 0.25) (57) be explained as follows: Given an initial value of U,

which should be a small value, let us say U = 0.001

where: Usma in mm and Po in Mg/m 3 mm, "ts, -tr and 'ra, can then be calculated from Eqs.

(c) maximum shear strength tsmax (55), (59), and (54) respectively. The iteration procedures will be continued with new values of U = U

"tsmax = 40.0 - 2.5 (Po -0.25) + 3.5on (58) + dU, where dU = a small increment, until the

following criteria satisfied.

where: an = the normal stress in kPa.

ss+ ýrJr- Tay, <1% (61)

(2) Snow-rubber condition Jsts+ ýrTr

Rubber material at the tyre contact with snow

appears to have differeitt characteristics compared The slip rate, S, can then be calculated from Eq. (52).

with the snow-snow contact case. The most obvious

differences is that the shift shearing displacement,

Ur, is small at the initial stage of loading. As shear 4.0 COMPUTER SIMULATION

load increases, shear failure occurs at relatively

lower shear stress, 'tr. These data show that the tr - A computer program named "TR89SNOW" has

Ur curves are very sharp. Since the tread effect must been develooed for the wheeled vehicle mobility evalube considered in the mobility evaluation, thistypeof ation over a deep snow. An example is given here to

contact is as important as snow-snow contact. The show the simulation results.

test data were analyzed to yield the general empirical Table I shows the input parameters and tyre specifi-

'I)nula as follows: cation. TI.- tyre used in this study is Michelin 7.0

(treaded). The initial snow density is 0.34 Mg/m 3.

127.29 Ufor tr < t Figure 3 pictoi ially shows the tyre size and loading

T-rr -/ conditions.

"trmax 1 for1r > rmax Table 2 and Fig. 4 show the tyre compression test

(59) data on a rigid surface for a specified inflation pressure.

This was done at the Geotechnical Research Centre of

where: Trrnax = 0.5265 yn; On = normal stress in kPa. McGill University. Furthermore, Fig. 5 and Fig. 6 show

the snow footing curves and the snow shearing curves

(f) for tyre movement on snow the total backward respectively. These curves were obtained from the

movement U is equal to both U, and Ur, i.e. analyzed formula demonstrated in material parameters

determinations. The physical results are presented in

U = Us = Ur (60) Table 3. These results are produced for a specified

SInput data *

a) Constant Parazmeters:

Tyre naue:Nichelin 7.(trealed) Trye inflation pressure: 3459( Xpa) Snow initial densitu:9,34(Kg/w3) Table .1: Parameters

ParaN., R d R R2 Pe TO OEGA

Ualue 9,39( X) 0,20( H) 8,400 0,608 1,60( XE) 0,14(K(N-M) 1,?8(pai/s)

Note:RIR2-area ratios of tread I nontread parts of tyre, respectively

75
OHEG R)RON tread

Figure 3. Tyre size and loading conditions.

h) Tre coNpesion test data:

(Tests ape done in CRC.)

Tale 2:P-L I P-delta data

HO. P(NN) L( ) delta( N)

1 0.0N o.Heo 0.0900

2 0.43 0.069 08.9062

3 ,70 0.093 0.0113

4 1.00 0.112 0,0165

5 1.30 0.126 0.9219

6 1.60 0.142 9,0270 7 1.90 9.159 0,0300

L(* 9.150 H)

Is

.4

12

0 I I I

9 .2 .4 .6 . 1

PC(. 1,99 ]H)

Figure 4. P-L curve of tyre.

76
p(kpa) 9.35,3.38,4.25 (WA/ca3)

508

a IN 2663H64N 5H 4(m)

Figure 5. Snow footing curve.

p5) normal pressure(lpa) Tspl)

1og 24 25NI nossr~ka

89 698 249 16 8 29151 ,: ,, ,, ,: , 1 6 ,39(Mg/cN3) 19 . ."",,,,, . . 16,,,,".... •

9 2 4 6 8 10 Ui(NH) 6 ,2 ,4 .6 ,8*1iU(NN) a) snow-snow shearinq h) snow-'~tiJbr shearing

Figure 6. Snow shearing curves.

Table :3 Physical results

Slip Input rate power slip PA 3,829 (C,) 6,169 y(1-N/s)

slip dissipated energy P2 6,664 (kN-N/s)

Snow dissipated energy P3 6,65683 (1W-HiNs)

Tyre dissipated energy P4 6.622 (NHl-H/s)

Utseful power P5 6.626 (1W-N/s) Tractive efficiency ETA 24.977 (7)

lra-24a pull 6 DP .987UR (841)

data 

For 

points 

sane n tsre 

request, loading conditions on the sane soil, for other procedure continues by specifying ne. torque,

"77
Pt(* 6,498?(]1I-N/S)

.4

,8

,6

,4

,2

o T(7,638[G1N]) .2 .4 .6 8.8 

Figure Slput 7. power P versus 2 torque T.

P2(* 0,49927[](4-7/S])

1

.9

,6

,4

,2

I ' T(49639C1]1-])

9 ,2 ,4 ,6 ,8 1

Figure 8. Slip dissipated power P2 versus torque T.

78
,8

'4

,2

, 2 .4 .6 ,8 1

Figure 9. Soil dissipated power P3 versus torque T.

torque value. If the applied torque T varies, one will be the vehicle driving since the resistance increases in an

able to obtain more computational results. In program exponential manner.

"TR89SNOW" this is judiciously programmed so that The relations betweer, P1, P2, P 3 and slip, S are

torque T varies properly. The calculated change of presented in Fig. 17. One notices the following: 1) the

power PI P2, P3, P4 and P 5 with the increased torque T slip rate dissipated power is more harmful, and 2) high

are presented in Figs. 7-11. The change of tractive tractive efficiency occurs at slip rate (S) around 20%.

efficiency TI, slip rate S and draw-bar pull DP with

torque Tare presented in Figs. 12 to 14. From Fig. 12,

one concludes that the highest tractive efficiency ii is 5.0 CONCLUSION AND REMARKS

about 57%, which is at torque T=0.36 KN.m. From Fig.

13, one observes that slip rate S sharply increases with The present model is a sound tool to investigate the

increased torque T. The maximum DP is about .65 kN vehicle mobility over a snow covered road, offering a

at T =.42 KN.m as shown in Fig. 14. great deal of information to vehicle engineers. The

The relation between TI and S is presented in Fig. 15. model not only answers the basic question that the

It is noted that the best tractive efficiency occurs at slip vehicle can or cannot go over a snow covered road, but

rate, S, around 20%. When the slip rate increases, the also gives detailed information as to how it can achieve

tractive efficiency decreases quickly. the best benefit according to the payload requirement.

The relation between motion resistance MR and the This model is easy to use in a personal computer. Any

driving force TR is presented Fig. 16. With an increase parameters can vary to visualize the adequate change

in driving force, the motion resistance MR increases. It which brings the vehicle designer the best benefit.

is clearly evident that a high driving force is not good for The following points are under investigation at the

19
P4(1 6.1211[IIN/S])

.12

,8

,4

,2

, .2 ,4 .6 ,8 1

Figure 10. Tyre dissipated power P4 versus torque T.

Ix

.1

,8

,4

,2

9 T(uB.631[]II-N])

S ,2 ,4 ,6 ,8 1

Figure 11. Remain usefld power P5 versus torque T.

80
ITAC 18.572U[NOHDININTJIOMLI)

I

,8

,4

.2

9 L 1 IM16,3O[] ND)

9 ,2 .4 .6 ,8 H

Figure 12. Tractive efficiency ETA versus torque T.

S(* I.fB[O[HOJNDI !IOALI))

I

,8

,'

'4

,2

S T(U.,636[]II-N))

, 12 .4 .6 .8 1

Figure 13. Slip rate S versus torque T.

81
HO~ 8,652131M])

I

,6

a'

,4

,2

O T(u9,G39[Rq-N])

.,2 .4 .6 .8 1

Figure 14. Draw-bar pull DP versus torque T.

!IA(O 9.57290[H0 UNIT])

.4

.2

I A S(*I,O99[HO UNIT])

9 12 .4 16 .9 1

Figure 15. Tractive efficiency ETA versus slip rate S.

82
N0( 1,61997[•N)

!

.6

,4

,2

7/R(*1 629UX]) .,2 .4 .6 .8 1

Figure 16. Motion resistance MR versus driving force T/R.

P(* 8,49127[1I-N)

,6

,4

9 8 2 Sl41519[lHo unit]) .4 ,A ,8 1

Figure 17. Power versus slip rate S.

83
Geotechnical Research Center to enhance the model dation Study of the Shallow Snow Mobility Model)"

capability: Report, CRREL and WES, Hanover, New Hampshire.

(a) a field snow compression test under loading of Xu, D.M.,Yong, R.N.,Mohamed, A.M.O.,and Irwin,

the rigid tyre-shaped disk. GJ. (1990) "Tyre Performance Prediction Using a

(b) dynamical effect and the road roughness effects Quasi-Static Moving Boundary Displacement Method"

will be considered in the furtherdevelopment of Proceedings of the lASTED International Symposium

the model. Modelling, Simulation and Optimization, Montreal,

(c) upgrading TR89SNOW to predict the per- Canada, May 22-24, ed. Jacyno, 2. pp. 107-110.

formance of the whole wheeled vehicle. This Xu, D.M., Yong, R.N., and Mohamed, A.M.O. (1991)

can be achieved by taking into consid- "Modeling of Tyre-Clay Soil Interaction Via Quasieration vehicle axle/wheel configuration and Static Moving Boundary Displacement Method" J. of

the difference between driving and towed Forest Engineering, Vol. 2, No. 2., pp. 7-19.

wheels. Yong, R.N., and Webb, G.L. (1969) "Energy Dissipa-

(d) calibration of the developed wheeled-vehicle tion and Drawbar Pull Prediction in Soil-Wheel Interacmodel with the actual field data of an instru- tion" Proc. 3rd Int. Conf. ISTVS, Essen, Vol. I,

mented wheeled vehicle in measured snow con- Yong, R.N., and Fattah, E.A. (1976) "Prediction of

ditions. Wheel-Soil Interaction and Performance Using The

Finite Element Method" J. Terramechanics, Vol 13, No.

4, pp. 227-240.

ACKNOWLEDGMENTS Yong, R.N., Fattah, E.A., and Boonsinsuk, P. (1978)

"Analysis and Prediction of Tyre-soil Interaction and

The work performed in this study was in partial Performance UsingFiniteElements"J.Terramechanics,

fulfillment of the study requirements for Defence Re- Vol. 15, No. 1, pp. 43-63.

search Establishment Suffield (DRES) under contract Yong, R.N., Boonsinsuk, P., and Fattah, E.A. (1980)

arrangement with Department of Supply and Services "Tyre Load Capacity and Energy Loss with Respect to

(DSS), Canada. Varying Soil Support Stiffness" J. Terramechanics,

Vol. 17, No. 2, pp. 131-147.

Yong, R.N., Mohamed, A.M.O., and Xu, D.M. (1990)

LITERATURE CITED "Correlation of Snow Trafficability with the Physica!

Properties and Conditions of Deposited Snow" Defence

Blaisdell, G.L., Richmond, P.W., Green, C.E., and Research Establishment Suffield, DSS file No. 0-

Alger, R.G. (1988) "Wheels and Tracks in Snow (Vali- 3SG.27702-6-02884. P. 84.

84
The Army MANPRINT Program and Its Relationship To Industry

DAVID A. SLOSS AND MICHAEL A. KRIZ

Emerging Systems, Concepts and Planning Directorate

U.S. Army Tank-Automotive Command

Warren, Michigan 48397-5000

MANPRINT DEFINITION RELATIONSHIP TO INDUSTRY

MANPRINT is an Army term which refers to the MANPRINT success depends on the combined efcomprehensive technical effort to assure total system forts of specialists in the Army and industry. Although

effectiveness by integrating into the materiel develop- they each have their own responsibilities, their interests

ment and acquisition process all information concern- mesh in the communication on MANPRINT requireing: ments and the development of design solutions. The

a. Manpower-The human resource requirements Army must articulate its MANPRINT goals and conand authorizations needed to operate, maintain, straints throughout the acquisition process, and indusand support an item of hardware. try must strive to deliver products that will compensate

b. Personnel-The aptitudes, experience, and other for the finite capabilities of soldiers and training bases.

human physical and mental characteristics re- Chart 1 depicts the MANPRINT crosswalk/relationquired to operate, maintain, and support equip- ship between the Army and industry for developmental

ment. systems. The Training and Doctrine Command

c. Training-The instruction, time, and other re- (TRADOC) represents the soldier or "market." The

sources necessary to impart the requisite knowl- Army Materiel Command (AMC) is the system develedge, skills, and abilities to qualify personnel for oper or manager. The builder or producer of the system

operation, maintenance, and support of fielded is industry. TRADOC develops a statement of needs,

equipment. AMC interprets the needs into technical terms for

d. Human Factors Engineering-Designing mate- industry which proposes a design, schedule, and cost.

rie! to ensure that its use is compatible with the Note: There is extensive interaction between the Army

capabilities of the individual soldier in an opera- and industry throughout the acquisition process.

tional environment. MANPRINT is also an important element in the

e. System Safety-The attainment of the optimum acquisition of nondevelopmental (NDI) systems, in

degree of safety consistent with mission require- which the government does not pay research and develments. opmental costs. During the search for a NDI solution,

f. Health Hazards-Applying medical knowledge to the market investigation, the Army identifies potential

identify, evaluate, and control risks to the health MANPRINT problems and addresses them in detail in

and effectiveness of the personnel who use the the requirements documents, solicitations, and in the

equipment. user criteria portion of the market investigation. The

The objective is to ensure that Army systems can be Army then uses the MANPRINTdata obtained from the

operated and maintained by the fully equipped soldier market investigation to influence the selection of items

within stated mental and physical limits; i.e., the "tar- or components to be assembled, the design of any

get audience description." It is up to the Army and modifications, and the integration of the components.

industry to take the actions necessary to ensure that this This is true even for "off-the-shelf" items.

question is answered: Can the soldier, with this training, MANPRINT is a critical element in the Source

perform these tasks, to these standards, under these Selection Evaluation Process. Offerer's proposals are

conditions? evaluated on:

85
.]ltahilit\ Thn111il~at olacontractortomtnteerate \IANlPRlNl dNW;r I Ili, I%ý

relIated aI tenrI atves. c onilsaInt. [int" and l l \ NIs re- pCiIoIlitlk. Ili ilk ~i~cei1 ' ' II

,flits. tisI.LIll\ O&)IIlIIlMCd ss 1111 11n '1 t ( n 'i I

h. The proposed filetIi ods bN thle corttiactor it, (Iocu NJ", IF .Al. 14, A teeN I lAid )\1 \N;. ihc

inent anid ieport NIANPRINT relitcd aitecrna- li derhII cf e 11cmmc' I 'c

tkyes.trade csa~ faa ieienpiaiis N01t el. andl ti'lillI-i iIsksth'It \\ 'ijs'd 111 ;1w t

Industries that ha~e not Intention or- desire to dio predecessorN tea T.hte plidlit 4'1 p

business with the Arm',N call still benef'it f'romi .cesses IN qunItC ed dat th I I' ItI i CsNkI deiion InI.'li

NIANIPRINT rnethodologv. lEssentiallN. the process xtithl infortiwitimi (III coruipetlileý plop)I-doIISliii ll(m

exanmines howt well a product canl be used and sup- themtlo assess the Impact ot inarilpokx ci,1)ý ()III wiil.111

ported. The problems that the general puLblic hlas- had trnie qrneisn-stnc cclens.ipI

xx th programming VCRs Lire a 1_ox d example of' abilits, and life~ dCcosts. Pthe Anu WOMAN

industrý s f'ailure to understand thle capabilities of its fiet hodolog\- hiirdtx are \ CINLIN i p r

"~target alildience." It has been stated that less, than 310; tratet in (ihart 2,

of, VCR ownrers, are capable of progranninie- thecir

equ~ipmllent to record a television programl.

MANPIN IANIOPLR\UI NS NIS1 ITI( R I

(O&S) COSTS

METFHOD)OLOGY TO SUPPORT X1ANIPRINT

'Ilucre Is a mawltr etfo)Iill [inte \nns to eduJlce

The Arm, developed a coniputericd MAN PRI N (M)&S costs bý lip-fill alt ~ I l aIhI l pl thil iii n [He

anialy"siscalled "! ' RD)NAN." li,,RDMA.N is anl ana- Ieamson 1,01 th is emlphiasis is Nli1, ,\s n 111 ( hart 31. [BI\ the

lx tCica tool wýhich p~redicts the quan~titativeC tnntpmt, r. ltime \sve ha\ve cottipleted thle G1c neep 1., ftitilitik ill Ii'

Persontnel,. and trainlino demands required to su~pport a1 Cess" (CIT ) prouratt icttelttIIt t lii,\cii h~il inl

devehopntental s\se.All of' these eleitieiits areC sig 1- aht)Lt 71) percent of the N\5 steiNll ife c.\ce c ist)ts.

86
HARDMAN METHODOLOGY

STEP 3 CURRCULA

:RESOURCES (CLASSROOMS.

DETERMINE INSTRUCTORS. MATERIELS. TOS)

TRAINING

STEP i STEP 2 RESOURCE SE REQUIREMENTSSTP

SYSTEM DETERMINE CONDUCT

ANALYSIS & MANPOWER IPACT

ESTABLISH REQUIREMENTS ANALYSIS

CONSOLIDATED

DATA BASE STEP 4

* MPT/DESIGNJ 0 MOSIASI DETERMINE _ TARGET SUPPORT PROBLEMS

MISSION 0 GRADE PERSONNEL 0 IDENTIFY ALTERNATIVES

* SINGLE DATA S #8 OF PEOPLE REQUIREMENTS PERSONNEL SELECTION

OURCE REQ. - TRAIMING CHANGES

SDESIGN CHANGES

- OTHERS

* PIPEUNE FLOW

* RECRUIT RATE

STEP 6 RESULTS

PERFORM MANPOWER,

TRADEOFF PERSONNEL &

FIGURE IX ANALYSIS TRAINING REOUIREMENTS

* COSTIBENEFIT ANALYSIS 0 AUDIT TRAIL OF

OF SOLUTIONS FINDINGS

CHART 2

LIFE CYCLE COST EFFECTIVELY RENDERED

UNCHANGEABLE FOR

A GIVEN DESIGN

LIFE CYCLE COST

ACTUALLY EXPENDED

CHART 3

87
There are several studies which show that a problem Task Descriptions list the following information:

that can be corrected for a dollar in the concept stage a. Task Description (narrative)

will cost between $1,000 and $10,000 to correct in the b. Rationale (why is it necessary)

production stage. From this perspective, an unparal- c. Resources (personnel and dollars)

leled opportunity exists in the initial phases of a pro- d. Time to Complete (optimistic, nonnal, pessimisgram to save an enormous amount of money. This tic)

can also translate into higher potential profits for in- e. Responsible Agency (lead agency)

dustry. f. Dependencies (prior tasks which must be comMANPRINT is the Army's effort to control one of pleted first)

the major O&S cost drivers--personnel. The up-front g. Feeds (tasks requiring completion of this task

planning document for MANPRINT is the System first)

MANPRINT Management Plan (SMMP). The SMMP There are other aspects to the SMMP; however, this

identifies the important MANPRINT issues anticipated overview demonstrates the complexity of the effort; the

in the system acquisition and functions as an audit trail commitment by the Army; and the potential payoff to

to record decisions affecting these issues. The SMMP the Army and potentially to industry.

will be discussed in detail later. In general, the SMMP

is used to plan for the acquisition of soldiers needed to

operate and maintain a system; to plan for resources MANPRINT AS PART OF THE ARMY

needed for required training; and to predict the amount MATERIEL ACQUISITION PROCESS

of time needed to complete maintenance and mission

support activities. All of these aforementioned resources MANPRINT is only one of a number of activities

affect the life-cycle costs (LCC) of the item. For indus- that occurs before a commitment is made to allocate

try, this translates into lower warranty costs and added development or procurement dollars. Chart 4 shows the

value for the customer. acquisition documentation required to initiate a program. Each of the 73 documents shown forms the basis

MANPRINT PLANNING for contractual requirements. Specific documents relating to MANPRINT are:

The Army SMMP provides the strategy to be em- a. System MANPRINT Management Plan (SMMP)

ployed in implementing the MANPRINT concept for a b. Ma,-powei, Personnel & Training (MPT) Assessspecific system. The SMMP considers the materiel de- ment

ficiency being addressed, mission, operational environ- c. System Safety Assessment Report (SSAR)

ments, design versions or alternatives, and essential total d. Human Factors Engineering Assessment (HFEA)

system (Man in the Loop) performance characteristics. e. Health Hazard Assessment Report (HHAR)

The SMMP is updated at each system review point f. MANPRINT Assessment (MA)

and serves as an audit trail of all of the decisions made The total acquisition process which is a process

which will have a direct impact on the system des;gn where the soldier's need is defined and a solution

and/or MANPRINT issues. The plan also identifies all developed. The process is depicted in Chart 5. At

assumptions being made which are not documented program initiation, the "environment" in which the

elsewhere. For example, the average soldier operating system is initiated is considered, as is the total program

the present system is mental category IIB*; therefore, life cycle that ends at system upgrade or disposal. The

the average soldier operating the new system will also purpose is to insure that a process is set in motion to

be mental category IIIB. develop all necessary information for a future "busiA critical element of MANPRIN"'T planning is a ness"decisionconsistentwithtoday'stechnology,polidetermination of what data will be available to support cies, and legal prerequisites. It is essential that this "upthe associated analysis activities and a corresponding front" work be done as thoroughly as possible, or a

risk assessment. The risk assessment includes the im- penalty will be paid throughout the life cycle of the

pact of the level of MANPRINT effort and when the system.

various analyses are to be conducted based on the Each phase of the life cycle--definition of what is

availability of data and resources. needed; development of a solution; production and

Planning activities include a comprehensive support of the system; and improvement or replaceMANPRINT schedule showing what is to be done by ment-has distinctive documentation. The Operational

whom from research exploratory development through and Organizational (O&O) Plan developed by the solfirst-unit-equipped. The "what is to be done" is docu- diers provides the authority for program initiation. The

mented with Task Descriptions. plan describes how a system operates, its role in the

88
REGIONS RESEARCH AND ENGINEERINO LAB HAINOER NH

UNCLASSIFIED 0 L BLAISDELL J.U 93 93-17 XA-CRREL•M1

ImllillllI-E

""liEEE".llll

E"EE"EE'EEE'l 'liE"EE'EE'E'E~l
-0

Association for Information and Image Management ( 4 J,

1100 Wayne Avenue, Suite 100 44

1v2 3 4 5 6 7 8 9 10 11 12 13 14 15 mm

1 2 3 4 5 Inches 111, .0 f 'oo

illlN IIIII'.

/4/TO

4/' MPUFPCTUED PI9

BY IMPE, PPLIE IC. A~-4
MATERIEL~e~ REURMN 9 SUPRAULTL 15

PROGRM MAAGEMNT 6 MANPINT,

PROCURMENT 5 PERFORANCE

PRODUCTION(I.~K 3 ET&EALAIN1

COSTFUNDNG 1 INTROPEABILTY
Army's organizational structure, how it will be used, a modification of an existing system. The next best

and what it will do toward solving the apparent defl- choice is an "off the shelf"item. An example of the latter

ciency. The plan also addresses two significant system is commercial construction equipment. The soldier usuconsiderations: logistics and MANPRINT. ally assumes that a developmental program is the most

Although the majority of the process discussed is desirable. The premise is that the desired system will be

Army-specific, there is a movement toward a Depart- custom designed and built for a specific application.

ment of Defense Acquisition System which uses many When cost, schedule, and technical risk are considered,

of the Army processes. If industry has any real interest, the attractiveness of a development system fades.

or if there is an intention to compete for development or The initial documentation for any system requires a

production of an Army system, then it is to industry's market investigation. Available information on comadvantage to know the process. In addition, many mercial, developmental, foreign and existing systems

aspects of the Army acquisition process can provide a are examined forcandidates. An advertisement is placed

potential benefit to the industry by providing a system- in the Commerce Business Daily to solicit information

atic way to produce an optimized system. on systems that are not generally known or advertised.

The results of the market investigation are used to

determine if a commercial item can be used (or modiTHE ACQUISmON SPECTRUM (AND fled), or if a development program is required.

MARKET INVESTIGATION)

The Army looks at a variety of "materiel solutions" NONDEVELOPMENT ITEM (NDI) EXAMPLE

to meet a specific or general requirement. Chart 6

illustrates the "Acquisition Spectrum." The ideal solu- The Special Operations Forces (SOF) came to the

tion is something we already have in the DOD system or Army with a request for a snowmobile, which in Army

CHART 6

90
terms became the Mobile Over-Snow Transport or d. Sled durability was low.

MOST. Our initial perception was that this was a e. Sled stability was poor.

straightforward procurement. The SOF used snowmo- f. The snowmobiles could not be started below

biles and sleds in Colorado and encountered no prob- -40 0 F.

lems. The last point provided some insight into the differThe Army has a program for testing NDI candidates ences between "sport" use of snowmobiles and the

to develop realistic performance specifications. NOTE: needs of the SOF.

The purpose is not to select a specific candidate but to The Alaskans normally keep their snowmobiles in a

become knowledgeable in the use and performance of garage or sheltered area. They start the machines up

the system in general. NDI tests also provide the soldier before leaving home and carry them with the engine

an opportunity to refine operational doctrine, running, usually in a pickup truck, to wherever it is they

MANPRINT issues are developed during this period. want to use the snowmobile. The SOF want to leave the

Tests were conducted in Alaska where the environ- machines for up to two weeks in -65*F temperatures

mental and operational conditions were similar to those and have trouble-free starts after that period.

that could be expected in SOF operations. These condi- The impact of the tests was that a "sport" type

tions were distinctly different from those encountered snowmobile did not meet the requirements by a wide

in Colorado. The test results showed that: margin. It also was apparent that the use of this type of

a. The snowmobiles became immobilized in deep machine could lead to mission failure.

new snow. The test series was very successful in identifying the

b. Required loads could not be carried on the snow- MANPRINT issues shown in Chart 7. Fortunately, we

mobile. found through continued market investigation that sevc. Required loads could not be carried on towed eral manufacturers were developing "workhorse" snowsleds. mobiles. This type of snowmobile solves most of the

technical problems related to load carrying and stabil-

*NOTE: Mental category l11B is the second lowest of five categories ity. We are continuing to try different sleds and modiin the Anned Forces Qualification Test (AFQT). It represents the 31- fications to resolve those problems.

49 percentile of the general population. We were able to establish that:

SYSTEM MANPRINT MANAGEMENT PLAN

QUESTIONS TO BE RESOLVED

"* MANPOWER INCREASE WHEN SYSTEM FIELDED?

"• CAN SFOD-A TEAM MEMBERS BE TRAINED TO DO

LIMITED IDS MAINTENANCE IN THE FIELD?

• OPERATION/MAINTENANCE IN ARTIC/NBC GEAR?

"* WILL EXHAUST BE A PROBLEM?

"* MISSION PROFICIENCY AFTER 6 HOURS ON

SNOWMOBILE OR SLED?

"• WHAT SAFETY HAZARDS CAN BE EXPECTED FROM

COMMERCIAL SNOWMOBILES?

TACJU7h441^*

CHART 7

91
a. A new "MOS" or Military Operational Specialty selected. There is no commercial interest in such a kit.

was not required for "Snowmobile Driver" or We believe that the MOST program demonstrates

"Snowmobile Mechanic." that the MANPRINT process is both workable and

b. A small increase in mechanics will be required necessary for nondevelopment equipment purchased

because mechanized equipment is replacing skis by the Army.

and snow shoes.

c. The operator can be trained to perform limited

direct support maintenance. This may be very SUMMARY

difficult at times, due to environmental conditions and arctic clothing, but it is doable. MANPRINT is an integral part of the way the Army

d. Exhaust discharge can be directed to avoid CO does business and part of "up front" planning required

poisoning. for new Army systems. We demonstrated that

e. Further testing is required to determine if soldiers MANPRINT issues can be integrated into the acquisican perform theirmission afteroperatingasnow- tion process and can have an impact on improving

mobile for six hours. human performance, while reducing life-cycle costs. It

f. Noise levels require ear protection. calls for an expanded focus which encompasses the

g. No hazards from edges, rotating/reciprocating man-machine interface and addresses the total system,

parts were found. increasing customer satisfaction and product value. The

A follow-on study is being conducted to determine if objective of the MANPRINT program is to optimize

a cold start kit can be developed. The objective is to system performance and to provide our soldiers with the

acquire a kit that could be applied to any snowmobile best and safest equipment possible.

92
4. MOBILITY ENHANCEMENT

93
Cross-Country Mobility of Tracked Vehicles

BJORN ANDERSSON

Since the beginning of the sixties terrain vehicles SPECIFIC GROUND PRESSURE

have been developed with very high intensity. The

reason for this has partly been an increasing need for On hard ground, roads, dry meadows and so on the

military and civilian transports as well as the technical specific ground pressure is of very little importance. In

development has made it possible to make terrain- snow, on marshland and wet meadows it could be a

adjusted tyres and tracks with good durability and matter of go-no go.

acceptable prices.

Good cross-country mobility often results in high Definition

purchase and operational costs in relation to the trans- The specific ground pressure of tracked vehicles is

port capacity and must therefore not become an end in defined as GIA

itself. Needs and costs must be weighed.

On hard ground, marsh and in snow the tracked where G = gross vehicle weight

vehicleswithlow groundpressure are superiorto wheeled A = ground contact area of tracks = (LI (+L2))

vehicles, no doubt. x 2b

One should, however, state that in forestry almost

exclusively wheeled vehicles are used. Forest terrain is With G = 20 tons, Ll = 3.5 m and b= 0.5 m the ground

often troublesome but a combination of good cross- pressure is p

country mobility of the vehicle and the options to

reinforce the ground result in a transport capacity worth 20,000 = 0.57 kp/cm-2 or

its price. For military vehicles cross-country mobility in 350 x 100

all sorts of terrain is often required without preparation

in order to make it possible for the vehicle to fulfill its 204,000 _ 58.2 kPa

mission. In this case tracks are a must. 3.5 x 1

The criterion of cross-country mobility is that available tractive force and friction coefficient at all stages A low ground pressure gives in principle a low sinkshall exceed the external rolling resistance. The rolling down, low rolling resistance and low shear force to the

resistance is caused by sinking down on soft ground, ground.

grade-ups, local obstacles etc., while the tractive force On soft ground, the rolling resistance increases in

very often is dependent on available friction coefficient. principle quadrangularly by the weight, decreases

The cross-country mobility of a vehicle is governed by quadrangularly by the track length in contact with the

a number of parameters. ground and decreases proportionally by the track width.

The essential ones are: A high rolling resistance results in a high shear force

-- specific ground pressure per unit area on the part of the ground under the tracks.

-- capability to negotiate obstacles If this shear force is limited and not directly proportional

-- steering system to surface pressure and friction coefficient there is a risk

Various types of vehicles, tracked or wheeled ve- that the ground will break which generally means addihicles, slip steered or articulatedly steered offer differ- tionally reduced tractive force and thereby bogging

ent types of space for these parameters. down.

94
b

Figure 1. Track steered vehicle; articulatedly steered vehicle.

The design of the track assembly is of great impor- ground pressure is the same. As the ground pressure of

tance. the articulatedly steered vehicle is considerably lower,

Rowland and Wong have developed methods for the its sink-down and consequently its rolling resistance

estimation of effect on sink-down, rolling resistance etc will be lower in comparison with corresponding track

in view of the geometry of the track assembly. steered vehicle.

Track steered and articulatedly steered vehicles have

different possibilities to meet the requirement of a low

ground pressure. CAPABILITY TO NEGOTIATE OBSTACLES

On a track steered vehicle the track relation, i.e. the

contact ,urface area of the track divided by the track The suspension of a tracked vehicle is to offer

gauge, should not exceed 1.6-1.8. The vehicle will thus increased comfort for the crew and thereby permit

be relatively quadrangular. higher speed on road and in terrain.

On an articulatedly steered vehicle the track relation The capability of the suspension to level out the

is of no importance. Compared to a track steered vehicle vehicle pressure against the ground is, however, of great

of the same size, the articulatedly steered vehicle is importance to the mobility as well. It is essential to

slimmer and longer. avoid comprehensive raising of the centre of gravity

On Bv 206 the tracks are wide and they are posi- whichmightresultinahighfrictioncoefficientbetween

tioned under the bodies. This results in a large area of the ground and tracks.

tracks and a low ground pressure. At the same time the In very rough terrain the suspension cannot level out

vehicle is slim and can be driven through narrow pas- all the uneven parts of the terrain. One must therefore

sages. see to that the vehicle is completed with some kind of

A long track on a track steered vehicle results, on the turning joint, bogie function or similar in order to avoid

other hand, in lower rolling resistance compared to two a dramatic raising of the centre of gravity, which will

short tracks after one another provided the specific require a high friction coefficient.

95
Figure~~~ ~ rc ~ n riuaelyserdvhce ~ 2.Eapeo ftesm ie

L1 I

Figure~~~~~~~~~~~~~~~~~~ riuae 3.Takwdh4tlwdho tee eil v26adamue rce eicl

RLSphpnzj) IM 

I 96
TP

TP

TP

TP

Figure 4. The raising of centre of gravity for stiff respectively articulated

vehicles.

Off-road trucks generally have a weak frame which One can see here that a single vehicle (A) which has

enables it to turn, e.g. forwarders and dumpers have a to negotiate the obstacle on its own requires a high

kind of turning joint and often bogie-suspended wheels. friction coefficient while two vehicles linked together

This gives an even pressure against the ground and a (B) manage the obstacle even though the friction coefminimum raising of the centre of gravity. ficient is considerably lower.

In Fig 4 is indicated the raising of the centre of Note that the raising of the centre of gravity can be

gravity and required friction coefficient for various relatively flatduring themajorpartof the negotiatingof

track and wheel assemblies, an obstacle but steep during a short period of time. It is,

97
s-r

SL /7%SL II

SL I

A L ST S

[ SL

Figure 5.

A 4 1,1 ,2'

40 , 1.0

10

- -0.9 ___ ft 0,6 /L

0.5- -1

I ~0,4,

0,2

i0.7 1.'O 1 2.0 i

L/ 0.7 1.0 1.5 2.0

Figure 6. Track force in % of GVWX coefficient offriction. Different Nos. of road wheels.

Track slip in Mlrad and different Nos. of road wheels. Value must be multiplied with distance between

track centre.

98
Figure 7.

however, the steepest part that is crucial to GO-NO GO. 3. The track width = Nought

When negotiating an obstacle the raising of the centre of 4. Vehicle speed is low and invariable

gravity should be as even as possible.

The general case, track steered vehicle

A track steered ,ehicle is steered by giving the outer

STEERING OF TRACKED VEHICLES track a higher speed than the inner track. Thus the outer

track will slip backwards while the inner track slips

The steering of a tracked steered vehicle is accom- forwards.

plished by giving outer and inner tracks various speeds. The longitudinal slip is invariable along the whole

Thus the tracks slip longitudinally and laterally against track while the lateral slip is proportional to the distance

the ground. from the centre of the track Y.

When steering an articulated vehicle the front and The slip of a partial element longitudinally (SL) and

rear cars are turned round a common steering joint, laterally (ST) results in a slip (S) which varies in size and

Even in this case the tracks will slip but considerably direction according to Figure 5.

less. On top of this slip which results in a turning of the

In both cases the track forces and track slip can be vehicle the rolling of the vehicle is stored and the

calculated as a function of the geometry of the track combination results in a steering radius.

assemblies. It should be observt. :hat the forces and slip Based upon this the track forces and slip can be

which area fact when driving through a curve with track calculated resulting in Figure 6.

steered vehicles are completely independent of the

design of the steering system. In order not to complicate Articulatedly steered, tracked vehicles

the calculations certain idealizations have been made When steering a tracked steered, tracked vehicle the

regarding the incorporated parameters: inner track must be braked or given less tractive force

1. The substructure is completely flat and plane than the outer track. This is detrimental to the mobility.

2. The friction coefficient is the same in all directions An articulated vehicle is steered by angling the front and

99
C.

Figure 8.

Track force, % of GVW % Slip

10.1

1.0

* Thear

10 20 30 40 50 RM 50 RM

Figure 9.

100
% Gg SKID-STEERED % G9 ARTICULATED

35

30

25 0% o Measured (By 206)

20 1,0

15

10 measured 0,5

5

toI Rm

1Rm 0 20 30 40 50 Rm

Track force in %.of GVWxu for skid-steered and articulated vehiales

10 SKID-STEERED 0,1-- ARTICULATED

5

100 200 Rm 50 Rm

Slip in %

Figure 10.

rear car to each other. Thus full tractive force can be M2 =_R 2 - dy

maintained on all tracks. A certain slip, however, is a L - d S 2R 2 + Y

fact. This is due to the tracks which through their length

primarily skid laterally when driving through a curve,

and this creates a moment around the fulcrum which To achieve moment equilibrium of the vehicle the

must be compensated by tractive force in the tracks. following applies:

When calculating, the simplification is permissible, The integrated turning moment around any optional

that the vehicle is considered single-tracked: point of the vehicle is to be equal to nought.

One cannot suppose that the tracks are turned around For the sake of simplicity the centre of the steering

their centres, i.e. d = L/2. unit is chosen and the moment is calculated for one car.

The driving moment around the fulcrum C is then: L

L - d M3 =G..R Y

MI = G.ER SR dy 21 f$S2R2 +y 2

L Id JS 2R 2 + y2 d

The braking moment M is: (a+ L - d- y)dy=0

101
Conditions:Ml = M2 M3 = 0 L=2.0 a= 1.Om

G = 8000kg p = 1.0

This gives:

The following curves for track force and slip are ob1. G_ R SR d y - GpL A vehicle with good cross country mobility must be

L fS 2R 2 + y

2 L design with:

-- low ground pressure

- d -low weight

2dy -many road wheels

fS 2R2 + y2 -high track tension

d---good suspension

---articulated steering

- d y ()A carefully designed track steered vehicle can have

2. qR SR d .a+ L - d- y =0 a very good cross-country mobility. The Swedish IFV

L 2+ y2 'S72R 2 90 has seven road wheels and a GVW of 22 metric tons.

It uses M2 tracks. It has an excellent mobility in snow.

Articulated steering anyhow increases the mobility

After calculation the following curves are obtained: dramatically and must be recommended for highly

with mobile vehicles.

102
Investigation of Forces Incurred During Snow Plowing

WADE STEIGER, ANDREW HANSEN AND KYNRIC PELL

Center for Information Technology

Department of Mechanical Engineering

University of Wyoming

Laramie, Wyoming 82071

INTRODUCTION Frink America Reverse-a-Cast plow. This design uses

an ultra high molecular weight polyethylene (UHMWPE)

In 1988, the University of Wyoming was awarded moldboard 48" x 144" x 7/16" supported only on the top

the Strategic Highways Research Program contract H- and bottom edges. The moldboard was mounted in this

206, "Improved Displacement Snowplow and Blowing way to allow the geometry to be varied. The UHMWPE

Snow Control." The goal set out for this project was to material was chosen because, in addition to allowing

decrease the energy consumption of a snowplow by variable geometry, it has exceptional abrasion and im20%. Under this contract, the University of Wyoming pact resistance as well as low friction.

designed, fabricated and tested a snowplow that incor- The arms shown in Figure 1 can be adjusted, by

porated several new design features. A variable geom- means of turnbuckles, thus changing the shape of the

etry ultra high molecular weight polyethylene mold- moldboard. This plow used five 1 1/2" turnbuckles and

board and a double blade cutting edge were two of these one 3/4" turnbuckle to control the shape of the molddesign features. During testing at West Yellowstone, board.

Montana, the double cutting edge was found to be The design of the cutting edge was prompted by

successful both in reduction of the power required to analytical work concerning energy dissipation caused

push the snowplow and in improving the handling of the by a plastic wave leading the snowplow, as well as the

truck. This work is continuing with further analysis of comments made by numerous plow operators and mainthe data and the fabrication of a second experimental tenance personnel. During displacement plowing a nonplow and two prototypes to be tested in the winter of linear compression wave leads the snowplow in the

'91-'92. snow in front of the cutting edge. This compression

wave absorbs a significant amount of energy. Recent

work has shown that the energy adsorbed by this cornDESIGN OF THE EXPERIMENTAL pression wave could be reduced by using an inclined

SNOW PLOW cutting edge (Hansen (1991). The snowplow operators

indicated that a snowplow will cut ice much better if the

The snowplow used in the testing was designed and cutting edge is nearly normal to the road. This design is

built by the Department of Mechanical Engineering at an attempt to address both concerns.

the University of Wyoming. The plow is a 12' reversible The cutting edge used on this plow consisted of one

geometry, incorporating a husting hitch, designed to blade at a near normal angle to the road and one blade

mount to a Ford F9000 truck supplied by the Wyoming laid back at approximately 45 degrees. The front blade

Highway Department. This snowplow incorporated a is made out of one inch thick UHMWPE. The rear blade

new moldboard and cutting edge design. The design of was a standard American Association State Highway

this plow was done using the software package I-DEAS and Transportation Officials blade. The idea behind the

from Structural Dynamics Research Corporation. two blades was that the front blade would remove the

The design of the moldboard is an extension of the loose snow on the road while the rear blade removed the

103
UHMWPE modl

tumbuckles

adjustabl, arms

Figure 1. Variable geometry, reversible plow.

hard packed snow and ice from the road. The gap sufficiently, or break off during a tripping event.

between the two blades allows the material cut by the A diagram of the cutting edge is shown in Figure 2.

rear blade to flow up to the moldboard. The UHMWPE

blade will be referred to as the snow scoop in this report.

There are three four foot wide segments of the cutting DATA ACQUISITION

edge. Each of these segments is able to trip independently. The trip action is controlled by a four inch A personal computer based data acquisition system

diameter air cylinder attached to the back of each trip was installed on the snowplow. A portable IBM 80386

edge segment. The UHMWPE snow scoop will deflect computer with a Metrabyte 16 channel analog to digital

AASHTO

cartide cutting

S~UHMWPE

/ snow scoop

Figure 2. Dual cutting edge design.

104
strain gauged member

orientation of the calibration load

Figure 3. Tripping edge instrumentation.

converter was used to record the data. With this system, computer board through a line conditioning amplifier.

sampling rates of 10 to 1000 Hz per channel were used. The load cells on the trip edge are calibrated to

There are eight strain gauge based load cells mounted at measure the horizontal force at the cutting edge/road

the plow-truck interface. For testing, three more strain surface interface on each of the three individual trip

gauge based load cells are mounted in place of the air edges. These load cells were calibrated using a refercylinders on each trip edge. There are also two stain ence load cell. The configuration of the loading was

gauge based load measuring devices in the moldboard such that the load cells on the snowplow measured the

positioning arms at each end of the moldboard. Each of horizontal force at the bottom to the trip edge directly.

these load cells is connected to the data acquisition The resulting linear calibration curves were put into the

Figure 4. Hitch mounted load cells.

105
high enough to measure accurately. Because the moldboard changes shape, a Fortran program was written to

convert the force measured at the turnbuckle to the force

applied to the top of the moldboard. These tumbuckles

were calibrated in the Instron machine, as well as on the

snowplow. These load measuring devices are shown in

Figure 5.

A Hall Effect proximity switch was put in the brake

backing plate in the froi-it right wheel, and five magnets

were mounted in the brake drum of the same wheel. This

pulse generator was connected to the counter on the A

to D board in the computer. This creates a digital

speedometer. By knowing the distance traveled between each pulse and using the internal clock in the

computer to time-stamp the data, a speed can be calculated. The five magnets used increased the resolution of

the speedometer. No signal conditioning was needed on

the speedometer other than that done by the A to D

board. A time and speed were recorded for each data set.

The test program was conducted on the entrance

. road to the West Yellowstone airport in Montana. This

S airport is closed for the winter months so the access

. : .roads made a good closed test course.

s::The goals set out for the trip to West Yellowstone.

Montana were to document the performance of the

snow scoops and various geometries of the moldboara

in terms of energy consumption, cast distance, and

Figure 5. Strain gauged turn buckle. moldboard flow. Energy consumption estimates were

based on the recorded load cell data. The cast distance

tests were based on mass displacement measured on a

discrete grid. The moldboard flow tests were done by

data acquisition software such that loads are output video-taping the flow of painted snow over the molddirectly in pounds force. A diagram of the calibration board.

loading is sho~vn in figure 3. In West Yellowstone on March 2. 1991. a power

Micro-Measurements CEA-06-125UW-120 strain consumption test was conducted. This test was run to

gauges were used in a full bridge circuit. The load cells determine the effectiveness of the UHMWPE snow

were made of annealed 17.2 -.;aitiless steel, which was scoops. Before each test, adata set was taken with all the

subsequently heat treated. load cells in an unloaded state. This allows the offsets

The eight load cells mounted on the plow hitch were induced in mounting the load cells to be taken out

calibrated in an Instron axial test machine in compres- numerically. Conditions for this test were as follows:

sion only. An offset was introduced into the calibration temperature. 24'F: snow depth. 2.75": snow density.

due to mounting the load cells on a surface that was not 8.73 lb/ft3. The moldboard shape is the unsymmetric

as flat as the surface on which they were calibrated. The shape, which was consistent thought this test. This

calibration curves were also put into the data acquisition moldboard shape closely resembles a conical one way

program, as was done with the load cells on the trip snowplow. To do this test, the snow scoops were on for

edge.TheseloadcellsusedMicro-MeasurementsCEA- the first runs and were then taken off for the follow06-125TW-120 strain gauges in a full bridge circuit. ing rons. Plots of the resulting data are shown in Figures

These load cells were also made of 17-4 stainless steel 7-9.

in the same manner as the ones on the tri-i edge. The The tests conducted involving different moldbonrd

mounting of these load cells is shown in - ,. shapes had the same goal as that for the trip edge

The load measuring devices in the control arms were geometry, that is to measure the energy consumption. In

created by strain gauging the turnbuckles that control addition, measurement of cast characteristics was also

the shape of the moldboard. To do this, the turnbuckles attempted. Due to limitations imposed by time and the

had to be machined down enough that the strains were size of the test course these tests were not done in

106
-'~4X, - 61

AP ~ 7". 7 -~rO Z. _'

hr

.110to _rFigure 6. Map of the roads used on the West Yellowstone Airport.

identical snow conditions. Due to the various condi- F = force,

tions the comparison of the forces involved were done p = density of the snow,

in a nondimensional way. The nondimensional force V = velocity of the truck,

parameter used was D = depth of the snow,

W = width of the plow cut, and

F x g~gc = gravitational constant

p xV 2 xD XW The data shown in the next three plots were taken

where, with the snow scoops on. Figures 10 and 12 show that

107
'4- SUM OF THE THREE TRIP EDGE FORCES

-01400.00 - SNOW SCOOPS ON, 55 ft/s SNOW OFF, 55 ft/s

LLJ 1200.00

LLi 10 0 0 .0 0 \ II I 

a- t it

- 800.00

z

0 600.00

LJ 0

4r 400.00

0

LL

200.00 -J

0 o 0.00 ......... .. .. . . . . . . . . . . o.oo0 0.1o 0 .2 .0 0.. 40 TIME (seconds)

Figure 7. Plot of the sum of theforce measured by the three trip edge load cells.

NORMALIZED FORWARD FORCE AT THE HITCH

TRUCK INTERFACE

SNOW SCOOPS ON, 55 ft/lq 1.00 ~ I' • " SNOW SCOOPS OFF. 55 W/s

'," iI i? 1 L'/

o ~ Il LI- . O I

0.80 I

o II I. I'

N

<0.40

0

z 0.20

0.0. b.6 ....... 6.6 ....... 6o16 ....... d'.ii ....... '.Ao

TIME (seconds)

Figure 8. Forward force on the hitch, sum offour load cells.

108
NORMALIZED SIDE LOAD ON THE HITCH

TRUCK INTERFACE

1.00 _ - SNOW SCOOPS ON .55 ft/s SNOW SCOOPS OFF, 55 ft/s

r00 .80 '

0.60 1 1 '

060 I I

N

< 0.40

0

z 0.20

0. 0.0 00- .... 08. 0.10 . ....... d 0o.20 26 ....... 0o.30o .3 ....... d. 0.4041

TIME(seconds)

Figure 9. Sumn of the two load cells on the right side of the hitch.

0.60 NONDIMENSIONAL FORWARD FORCE ON THE HITCH

SYMMETRIC MOLDBOARD SHAPE

Ll • .-. ,-, UNSYMMETRIC MOLDBOARD SHAPE

0

_j 0.50 I

0 .3

- 0.20

z

0

Z 0.10

"0.00 0.10 0.20 0.30 0.40

TIME (seconds)

Figure 10. Nondimensionalforward force on the hitch.

109
LiJ TOTAL NONDIMENSIONAL TRIP EDGE FORCE

UNSYMETRIC

0.40 - SYMETRIC

0

LL0

LwJ 0.30

a.

0.20

0

0.10 A

1,.5

Z A

0

U0 0.005....._......... o0o V.1o6. 0.20 0.30 0.40

TIME (seconds)

Figure 11. Nondimensional force on the trip edge.

NONDIMENSIONAL SIDE LOAD ON THE HITCH

0.20

0

LL_ 0.15

-j

z

o

0)0. 10 I I

z

Z 0.05 Y 0

v $4 SYMMETRIC

-*~UNSYMMETRIC

0.00 0... .10 0.20 0.30 0.40

TIME (seconds)

Figure 12. Nondimensional side load on the hitch.

110
120-

Po = 160 kg/M 3

ýb = goo

(D = 700

80O

0

Q)/

0L., /iI

~/J

40 - - - - - / /

0 5 10 15 20 25 30 35

Velocity (m/s)

Figure 13.

the forces for the unsymmetric moldboard shape are than at 700 but still not enough to explain the entire

higher than those for the symmetric moldboard shape. decrease in force that is seen in the test results.

This can be attributed to increased rehandling of the

snow done by the unsymmetric shape shown in the

video data. PROJECT CONTINUATION

Figure 13 taken from Hansen (1991) may explain

part of the reduction in force seen with the snow scoops The reduction of the data obtained in West

on. The angle represents the angle of the cutting edge Yellowstone is still underway. Current analytical work

with (D = 90' representing vertical orientation. The is focusing on a finite difference code to predict the

reduction in force shown in this plot is due to a reduction compression wave leading the snowplow. This work

in the compression wave that leads the snowplow. The and more testing may yield a better understanding of the

reduction in force is predicted to be even greater at 45' energy absorption mechanisms involved in plowing

Figure 14. Cast right con- Figure 15. Center con- Figure 16. Cast left

figuration. figuration. configuration.

I ill ] Ill
snow. There is also work being done in reducing the cast plow and two prototypes currently being designed and

characterization data. fabricated will be field tested next winter.

The other aspect of continuation of this project

is the design and fabrication of a second experimental

snowplow. This second snowplow wili be desigr -d LITERATURE CITED

with the same cutting edge geometry, but with

a different moldboard. The reason behind the new Hansen, A.C. (1991) "An Analysis of Energy Dissipamoldboard is the complex control system that was tion Caused by Snow Compaction During Displacerequired by the current moldboard design. The new ment Plowing," Trnsportation Research Board (In

design will have a two piece moldboard with only Press).

"-'-o "".,trol element to control the shape of the moldboard. Diagrams of this moldboard are shown in figures

14-16. ACKNOWLEDGMENT

In the design of this second snowplow, emphasis is

being placed on reduction of weight and cost, as well as The research described herein was supported by the

improving the mechanical systems involved. The test Strategic Highway Research Program (SHRP). SHRP

program for this snowplow will be quite similar to the is a unit of the National Research Council that was

one done for the first experimental snowplow so the authorized by section 128 of the Surface Transportation

results from the West Yellowstone testing can be veri- and Uniform Relocation Assistance Act of 1987.

fied.

DISCLAIMER

CONCLUSION

This paper represents the views of the authors only,

The work done to date shows that significant reduc- not necessarily reflective of the views of the National

tions in the energy required for snowplowing can be Research Council, the views of SHRP, or SHRP's

made with the use of better cutting edge geometries, sponsors. The results reported here are not necessarily

Further analysis of the data from the West Yellowstone in agreement with the results of other SHRP research

testing should yield a better understanding of how these activities. They are reported to stimulate review and

improvements are made. A second experimental snow- discussion within the research community.

112
Theoretical and Experimental Results of Using Binders for

Snow Roads and Runways in Antarctica

MICHAEL BARBER AND ROBERT L. BROWN

Civil/Ag Engineering

Montana State University

Bozeman, Montana 59717

ABSTRACT

The consequences of adding wood as a binder material to snow is discussed in this paper.

A modified mixture theory, based upon volume fraction, is proposed. Field and laboratory

experiments, conducted in the laboratory using a 50k MTS press with a cold chamber, are

presented. The laboratory samples were allowed to sinter and then cuonpressed at two

different strain rates. This laboratory data suggests the suitability of binders to strengthen the

snow matrix. Mixtures of wood/snow pavement test sections were constructed in the

Antarctic at two sites, McMurdo and Amundson-Scott South Pole Stations. Test sections

were monitored for three months during the austral summer and tested again a year later.

Rammsonde penetrometer, density and temperature profiles were used to evaluate material

behavior. Field results indicate snow pavement strength depends upon temperature history,

initial material properties, and construction processing techniques. Satisfactory strengths, for

supporting wheeled aircraft, were obtained at depths below 20 cm at both stations. Field

evidence shows that with an improved surface processing technique, such as heat processing,

adequate strength may be obtained to support wheeled aircraft landing in the antarctic.

INTRODUCTION transport materials from the aircraft into McMurd.o, via

a five mile long snow road. When temperatures rise,

During World War H wood was used with ice to these vehicles have difficulty on the snow road. In

create "ice-crete ships" for use in the North Sea, as particular, the reduced strength due to the snow becomdescribed by Moser (1963). During the Olympics at ing wet resulted in rutting, formation of potholes and

Squaw Valley, wood was used to strengthen and in- washboarding. A process whereby the road is made

crease the durability of the parking lot. When mixed passable for all vehicles during the entire season would

with wood, the characteristicsof snow undergoa change increase the efficiency of the support services. This

in mechanical behavior. When the need to improve the technique would also facilitate landing the aircraft on

roads and runways in Antarctica became evident, the snow runway with wheels instead of skis.

compaction and use of binder materials was investi- South Pole station has consistent low temperatures

gated. This study investigates the change in material and exists at an altitude of 2805 m. Due to the altitude

properties when sawdust is added as a binder to a snow and cold temperatures, aircraft are taxed in their ability

matrix. to carry heavy payloads out of this site. The increased

McMurdo has runways and taxiways that exist on ski friction below -20'C and decreased performance of

approximately eight feet of snow atop of the Ross Ice the aircraft at that altitude could be enhanced by aircraft

Shelf. During the austral summer the temperatures rise on wheels. If the runway and taxiway were constructed

above freezing for several weeks, causing the surface such that wheeled aircraft were able to land, it may be

layer of snow to become isothermal, resulting in some possible to utilize aircraft with a larger payload, allowmelting. Trucks and vans equipped with special tires ing fewer flights to provide the necessary resupply each

113
3000.00

2500.00

2000.00

Stress [kPa] 1500.00 -

_.____ _____Ro0% Slow 5oW.00 0% Fast

500.00

0.00 0.05 0.10 0.15 0.20 0.25

Strain

Figure 1. Stress-strain curves (100% snow at 2.5 mm/s and 25.0 minis).

season. In addition, use of C-141 aircraft on wheels wood.Twostrainrates,25.0mm/sand2.5mm/s(inthis

would allow nonstop flights from Christchurch, New paper referenced as fast and slow), ,vere used to comZealand, an obvious improvement in the logistics prob- pare the rate effect on the stress-strain relation. The

lem for the South Pole. average density of the snow samples were 0.532 g/cm 3

Over the past 20 years, much research has been plus or minus 0.007 g/cm 3. Samples with a larger wood

conducted on ways to develop and improve snow com- content had a lower density, while those without wood

paction techniques. For example, a well known fact is were more dense.

that snow sinters and hardens at a faster rate than the Figure I shows the general difference between strain

normal metamorphic process when it is agitated and rates for snow without any wood content. This is as

compacted, Abele and Frankenstein (1967). Past re- expected, for the higher the strain rate the stiffer the

search utilizing sawdust and woodchips as binders in a matrix should be. Figures 2 and 3 indicate how the

snow matrix is repored by CRREL, Abele (1963). percent cf wood effects the stress-strain behavior of the

The mechanics of the process whereby snow and snow matrix for the two different strain rates. Notice,

wood bonds together is not totally understood, but a for the faster strain rate, the pure snow matrix is stiffer

method of constructing a useful mathematical model is for small strains than that achieved with wood added. As

proposed as well as the field and laboratory test results. the strain increases, the effect of the added wood becomes more influential and the strength exceeds that of

pure snow. This becomes more pronounced with the

LABORATORY TEST RESULTS slower strain rate. From figure 3 we can conclude that

with wood the stress-strain relationship does increase

Snow from Grayling Pass in Montana was stored in for strains exc-eding approximately 8% strain.

the cold room at Montana State University for a period As previously mentioned, the density for pure snow

of 2 months. This snow was then agitated and mixed was higher than for wood/snow mixtures. It is further

with the appropriate amount of sawdust to achieve the proposed by Barbcr, Brown, and Lee (1989) that the

correct mixture contents. The samples were placed in sintering process is different for the ice grains than with

sonotubes and compressed at the rate of 2.5 mm/s until ice and wood particles. As deformation takes place,

a stress of 0.2 MPa was reached. The entire batch was bonds fracture, allowing the pure snow samples to

then stored in the cold room for 27 days until testing. decrease in relative strength. The ice grains in the snow

Mixture contents of 0%, 2.5%, and 10% w(od were matrix containing wood will also fracture, but the wood/

tested. Those samples without wood were mixed and ice bonding may not fracture giving larger particles

compacted in the same manner as those containing withinthecollapsingmatrixfromwhichtogainstrength.

114
3500.00 - -

3000.00 

A

2500.00 -- -

2000.00 - -

Stress kPa e1500.00 E o0%Fast

1____0 E32.5% Fast

50.oo 10% Fast

0.00

0.00 0.05 0.10 0.15 0.20 0.25

Strain

Figure 2. Stress-strain curves (% wood at 25.0 m/ins).

ANTARCTICA TESTING grains are approximately 0.2 mm with rounded edges

and some minor faceting. Initial densities were on the

A testing program was established at McMurdo order of 0.35 g/cm3 to 0.45 g/cm 3.Early in the summer

Station, Antarctica and at South Pole Station, Antarc- the snow had a low free water content while later in the

tica to evaluate the properties of wood/snow mixtures in season it rose dramatically. The snow road and runway

the field. The data taken for evaluation were tempera- are on the lee side of a ridge that descends from Mt.

ture profiles, density profiles, California Bearing Ratio Erebus, which causes significant deposition of snow

test (CBR), Clegg impact tests and the Rammsonde adjacent to the ridge than near the runway. The snow,

penetrometer test (resulting in a Ram value). This paper about 2.5 m deep at the runway and 5 m deep near the

does not address the CBR and Clegg test results. beginning of the snow road, lies on top of the Ross Ice

During the austral summer at McMurdo the tempera- Shelf which is approximately 8 m above sea level at this

tures ranged from -17'C to +50

C. The in-situ snow point. Most of the melt runoff from the ridge runs onto

3000.00 -

2500.00-

2000.00 - -

Stress [kPa] 1500.00 - - 0% slow

IOOO.Oo -E[] 2.5% Slow

500.00 - 10% slow

0.00 0.05 0.10 0.15 0.20 0.25

Strain

Figure 3. Stress-strain curves (% wood at 2.5 mmls).

115
the ice shelf near the transition zone of the dirt road with Due to the altitude and the hardness of the existing

the snow road. snow, the snow blower ceased functioning properly. A

South Pole Station temperatures ranged from -45'C Sprite, similar to a van with 2 cleated tracks, was used

to -17*C during the initial testing while during the to try to mix the wood into the snow until the snowwinter months temperatures can be lower than -80'C. blower was repaired. As will be noted later, the properThe snow grains are about 0.1 mm, rounded and very ties of this 20 cm layer were quite different from the

dry. These grains precipitate from the atmosphere and other layers above and below it. The snow temperature

then blow about the surface for many years. Due to the was -30'C to 49'C while the ambient temperature

blowing ice particles and the 10cm pe; annum accumu- during construction was -40'C and a windchill of -

lation, the initial densities are higher than at McMurdo. 80*C. It was not possible to break the existing snow

There is a moderate transition from the ice granular matrix into a fine powder. due to the density.

surface to the ice approximately 30 m below. However At both the South Pole and McMurdo, test sites had

the firn at the South Pole does show a definite stratigra- plots of 10% sawdust/90% snow and 5% sawdust/95%

phy Gow (1965) which has an annual periodicity show- snow to volume ratios plus a 100% snow plot used as a

ing alternating layers of a wind crust formed during the control. In all plots, pulverization and compaction were

winter and a temperature gradient layer formed during identical except for the 20 cm layer in the South Pole

the summer and fall. The maximum solar intensity taxiway. After initial construction of the plots the

available is at an angle of incidence, 23.30. Rammsonde penetrometer test (with a 30' cone), temFour testing plots were established, two at each base. perature profiles and density profiles were performed to

At both McMurdo and South Pole stations, a test plot monitor the change in properties as it varied with time.

was situated on a taxiway. In addition, McMurdo had a In addition, at the end of the season core samples were

plot on the shuttle road used by vans, and the South Pole taken to determine density and temperature profiles

had a plot on the cargo berm area utilized by tracked within the sample plots.

vehicles forcargoandpersonneltransport.Eachsample Ram values presented demonstrate the change in

section was 6 m wide by 12 m long by approximately 1 material properties due to processing, temperature flucm deep, except for the McMurdo taxiway section, tuations, material composition and aging. The surface

which was 9 m by 8 m to allow aircraft use. Each plot temperature represents the current ambient air temperawas constructed by a bulldozer (D-6), equipped with ture. Ram values are not given for the first 15 cm below

low ground pressure width tracks. After scraping out to the surface, since this distance is needed before the cone

a depth of one meter, four lifts of 15 cm each were is fully inserted into the snow. The densities for the

placed on top of a 30 cm layer of compacted snow. region from the surface to a depth of 50 cm are given.

Sawdust was then placed over each lift and mixed with

a Honda snow blower. In the control sections (100% McMurdo Station results

snow, no sawdust) pulverization was achieved by using The results of the field studies at McMurdo (Willthe snow blower. Each lift was then compacted by a low iams Field road and taxiway) are illustrated in Figures

ground pressure bulldozer traversing the test sections 4-7. The temperature profiles were obtained at the time

twenty times. Optimal mixing was not achieved at of density determination, Figure 4 gives a typical proeither site, since the snow blower did not have sufficient file. Temperatures are recorded starting with the surpower to adequately pulverize the dense snow, charac- face, then to a depth of 70 cm. There had been approxiteristic of Antarctic snow. mately one week during which temperatures exceeded

Temperatures during construction of the snow road +4'C each day; then a cold front with wind and snow

at McMurdo Station ranged from -5°C to -15'C, and arrived to lower the air temperature. Daily highs were

the snow had ambient temperatures of-5°C to -10°C. about 0°C on the day the snow road sections were tested

During the construction of the taxiway site the ambient for the last time, while the high temperature was -2°C

temperatures ranged from -1 0C to +10C with snow when the taxiway sections were finally tested. For the

temperatures of 0°C to -8 0C. When building the snow snow road the 10% wood mixture cores ranged from -

road test site, the weather was clear and sunny. With 2.20C to +0.40C, the 5% wood mixture ranged from -

afternoon temperatures near the freezing mark, the sun 2.20C to 0.0°C, an average of-1.0°C to -2.5°C for the

warmed the wood so quickly that the snow became very 100% processed snow and for the 100% unprocessed

wet and difficult for the snowblower to process. When snow the temperature ranged from -0.80C to--0.20 C. At

the taxiway site was constructed the weather was over- the taxiway site the 10% wood mixture cores had

cast and heating of the sawdust was not such a problem. temperatures of +0.5°C to -2.0°C, the 5% wood mixAt the South Pole Station similar techniques were ture ranged from -0.5°C to -3.0°C and the 100%

used except for the area between the depths of 20-40 cm. processed snow ranged from- 1.00C to -5.0°C. It should

116
00

0i-I 100% Snow #1

Temp .2-0 100% Snow #2

-3 - 5% Wood

o .- 10% Wood

-5.

-6

0 10 20 30 40 50 60 70 80

Depth [cm]

Figure 4. McMurdo Station temperature profile final day of testing.

be noted that these test sites are only one kilometer during the year are recorded. Notice how the maximum

apart, across the flat Ross Ice Shelf, with tests done on densities increased with those sections containing wood.

succeeding days. The densities for the 10% wood mixture were higher

Rammsonde value measurements were taken than the 5% wood mixture and the 100% snow sections.

throughout the austral summer. The average Rammsonde With high temperature gradients, there was not a large

values taken at 15 days and the average of tests between change in the densities. It must be remembered that

15 days and 47 days yielded the following results in extreme melting took place in the wood sections due to

Table 2. Table I shows how density varied with wood the solar insolation. This meltwater percolated downcontent and location. Additionally, the density changes ward and refroze, thereby increasing densities further

3500

3000 ]0

2500 0- 100% Snow

2000 0- 100% Unproc. Snow

Ram Value .U0- 5% Wood

1500 ---- A-----O 10% Wood

1000 C-14

500 0[

0, I I I I I I I I

0 2 4 6 8 10 12 14 16 18 20

Depth [oc]

Figure 5. McMurdo Station Rammsonde values (15 days).

117
3500

3000

2500 4- 100% Snow

0- 100% Unproc. Snow

Ram Value 0- 5% Wood

1500 a- 10% Wood

1000. A- C-141

0 2 4 6 S 10 12 14 16 18 20

Depth (an]

Figure 6. McMurdo Station Rammsonde values (23 days).

3500

3000 0

2500 0 4- 100% Snow

2000- -0- 100% Unproc. Snow

Ram Value- I - - 5% Wood

1500 /-• -E- 0- 10% Wood

S.-j A- C-141

0 2 4 6 8 10 12 14 16 18 20

Depth [ciin]

Figure 7. McMurdo Station Rammsonde values (37 days).

118
Table 1. McMurdo Station density ranges.

% Wood Minimum density Maximum density

0% (Taxiway) 0.62 g/cm3 0.62 g/CM 3

5% (Taxiway) 0.65 g/cm 3 0.74 g/cm 3

10% (Taxiway) 0.70 g/cm 3 0.80 g/cm 3

Unprocessed (Snow Road) 0.60 g/cm 3 0.60 g/cm 3

0% (Snow Road) 0.65 g/cm 3 0.70 g/cm 3

5% (Snow Road) 0.70 g/cm 3 0.75 g/cm 3

10% (Snow Road) 0.65 g/cm 3 0.85 g/cM3

Unproc. (Snow Road I yr.) 0.41 g/cm 3 0.60 g/cm 3

0% (Snow Road I yr.) 0.66 g/cm 3 0.19 g/cm 3

5% (Snow Road I jr.) 0.73 g/cm1 0.86 g/cm3

10% (Snow Road I yr.) 0.70 g/cm 3 0.87 g/cm3

Table 2. McMurdo Station Rammsonde values.

Range of Maximum

% Wood Average value values value

0% (Taxiway) 450 375-870 1050

5% (Taxiway) 750 525-1125 1950

10% (Taxiway) 1050 750-1500 1950

0% (Snow Road) 450 300-750 2250

5% (Snow Road) 750 600-1050 2700

10% (Snow Road) 1050 900-1200 3000

2000,

1500 *- 100% Up Snow

o- 100% Snow

Ram Value 1000 n- 5% Wood

0 0- 10% Wood

A- In-situ

500 C3

05 10 15 20 25

Depth [CM]

Figure 8. McMurdo Station Rammsonde values (season average).

119
5000

4500 0

4000- /

3500 0- In-situ R/W

3000 0- In-situ Taxiway

Ram Value 2500 / m- 5% Wood 404 Days

2000 / 0- 10% Wood 404 Days

1500 4, C-141

1000 " / / &- C-141

500 0 0

0 10 20 30 40 50 60

Depth [an]

Figure 9. South Pole Station Rammsonde values (1 year).

down in the snow cover. The decrease in density from the surface to 40 cm is

From Table 2 and Figures 5-8, it may be observed due to the change in compaction and mixing technique

that as the percent of wood increases so does the average as noted in the processing procedure. The expectation of

Ram value. This must be contrasted with the observa- a large difference with the in-situ density versus the

tion that densities did not differ greatly between differ- compacted density was not evident; this may be attribent wood contents. Notice, the maximum Ram values uted to the high initial density as it exists at the South

occur in those sections with the highest percent of wood. Pole in the cargo berm and taxiway, both areas of heavy

Additionally, the highest lower bounds for the Ram traffic. Further, the density in the sections containing

value also occur in the sections with the highest percent sawdust were slightly higher than the 100% snow

of wood. The average Ram values for McMurdo Station samples although there is a moderate drop in the samples

taken as one sample are given in Table- 2. taken during the initial season compared with later

samples.

South Pole Station results The Rammsonde profiles reflect the layering proThe effect of the processing may be observed by cess in the taxiway test section. The values decrease in

examining Figure 9 and comparing the profiles of the the region 20-40 cm below the surface where there was

test plots, existing taxiway and the runway, thereby inadequate compaction and mixing due to the snow

indicating how the processing increases the Rammsonde blower becoming inoperable, requiring hand mixing

values. and compaction by the Sprite. This demonstrates the

Table 3. South Pole Station densities.

% Wood Minimum density Maximum density

0% (Cargo Berm) 0.64 g/cm3 0.69 g/cmn

5% (Cargo Benn) 0.62 g/cm3 0.66 g/cm 3

0% (Taxiway) 0.55 glcm 3 0.58 g/lcr 3

5% (Taxiway) 0.50 g/cm3 0.61 glcm 3

10% (Taxiway) 0.58 g/cm3 0.59 g/cm 3

120
Table 4. South Pole Station Ranmmsonde values.

Range of

Average Ramisonde

% Wood Ramrsonde value values

0% (Cargo Berm) 993 750-1633

5% (Cargo Berm) 1977 982-3261

0% (Taxiway) 567 99-1401

5% (Taxiway) 562 145-1308

10% (Taxiway) 1092 192-2610

0% (Taxiway I yr.) 792 439-1639

5% (Taxiway I yr.) 837 472-1561

10% (Taxiway I yr.) 1599 370-3108

necessity of thorough pulverization and compaction for where wa e R is a weighting factor and

obtaining high strengths. n

Temperature gradients from the South Pole show I o a •0.

that there was not an appreciable effect of the wood a =1

mixture on the temperature profiles. Average tempera- The restriction in this paper will be for the weighting

tures ranged from -22*C at the surface to -23*C at a factor % > 0, for all o. The velocity of the mixture a is

depth of 60 cm at the time of final coring. denoted by

For the 10% wood mixture the Ram values had & xa (Xa,t)

higher average numbers then either the 5% wood mix- ta & (2)

ture or the 100% snow. Ram values increased with t

respect to time faster for the 10% wood mixture than for The choice of weighting factor %oa will determine the

100% snow and the 5% wood mixture. At depths below mixture theory derived. Consider first the factor o0a =

40 cm, the average Ram value for the 10% wood ca, where ca is the concentration of the ath constituent.

mixture was much greater than the other samples, Then,

particularly after 404 days. As noted above, the density n n n

for the 10% wood mixture was slightly higher than the ca Cta , I -Aa I Pat a

other mixtures. X= = = P x= t

I] cc [IE I PC

a=1 a=i P a=1 (3)

MATHEMATICAL MODEL

Snow is an elastic-viscoplastic material. Many physi- which gives the classical mixture theory definition of

cal and mathematical models have been proposed in the mean mixture velocity, Truesdell and Toupin (1960)

past. Here, we propose to model snow mixtures using a and Bowen (1976).

modified mixture theory proposed by Hansen (1989). A different choice made by Hansen (1989) is for the

Classical mixture theory, as proposed by Truesdell and weighting factor to be %oc = va, where va is the volume

Toupin (1960) considers each constituent within the fraction. This is the amount of the body that is constimixture separately. Balance equations are proposed for tuted by constituent ca. This results in the following

each constituent which depend upon the independent definition for mixture velocity,

variables of that constituent. A rigorous development of n

classical mixture theory may be found in the work of I Vata n

Bowen (1976). xaaa(

Truesdell and Toupin (1960) introduced the notion I Va a= 1

of baricentric velocity given by a=1

n since we impose the restriction that

I (0ta n

a= I

121
Equations (3) and (4) give very different results for summed constituent balance equations which

the mixture velocity in both magnitude and direction. reduces to the balance equations of a single

Equation (4) is associated with the mixture theory mixture as a special case.

proposed by Hansen (1989), which will be called in this Notice, the kinematic definition for velocity now conpaper the modified mixture theory. The theory based tains only terms that are kinematic in nature and the

upon eq (3) is called the classical mixture theory. There mixture behaves in accordance with the summed field

are different assumptions which are fundamental to equations. While this answers the objections of Hansen

each theory. (1989), it does not answer all those of Segev and

Truesdell (1984) lists the Three Metaphysical Prin- Taragan (1989). It appears that in using Eulerian coorciples to be followed when considering mixtures. dinates the constituent spaces will have the same dot. All properties of the mixture must be mathemati- main with forces from the same field. Thus this paper

cal consequences of properties of the constitu- will limit itself to using Eulerian coordinates.

ents. Based upon the above analysis, the modified mixture

2. So as to describe the motion of a constituent, we theory will be utilized to model mixtures of cohesive

may in imagination isolate it from the rest of the elastic-viscoplastic materials. For our case, these matemixture, provided we allow properly for the rials are mixtures of snow and wood.

actions of the other constituents upon it. The mean velocity of the modified theory does not

3. The motion of the mixture is governed by the same have a good physical meaning which is very different

equations as is a single body. from that mean velocity defined in classical mixture

These fundamental principles relate the properties and theory. This loss of physical meaning results in a gain in

field equations of each constituent to the properties and understanding of the physical boundary conditions.

field equations of the body as a whole.

Classical mixture theory is based upon the choice of Balance equations

weighting factor wa = Ca and metaphysical principle With the assumptions made by Hansen (1989), the

number 3. These are founded upon the two assump- balance equations become the following,

tions.

1. The mass weighted mean velocity of the mixture 0 + padiv(,) + (8)

is given by

n p'j' -div (ta)- paba= a (9)

1 Pa. Pata . (6) T +t

ta- ta = Mct (10)

2. The sum of the constituent equations must result

in the equations of the mixture. Pad a - tr (tT.La) + div (qa) - para +e (

These give the complete classical mixture theory.

Hansen (1989) has pointed out that the mean velocity along with the restrictions imposed by the second law

of the mixture contains the notion of linear momentum. which has the form,

Since velocity is a purely kinematic term it does not

seem reasonable to define kinematics in terms of linear

momentum. Furthermore, Segev and Taragan (1989) prj + I div (qa + pa.arlaU -Par0>0 (12)

discuss the restrictions of adding forces that are mem- aOa"a -

bers of different vector spaces. In general, stress fields

must have the same domain and the forces must be of the The terms on the right hand side of equations (8) to (11)

same vector space to add the constituents to get the are the supply terms. These account for the interaction

results for the entire mixture. forces between constituents. Truesdell and Toupin

Hansen (1989) proposed what will be called modi- (1960) show that the summation of these supply terms

fled mixture theory. In this theory the choice of weight- must obey certain rules. Hansen (1990) demonstrates

ing function is %. = Va. Additionally, the third meta- that to be consistent with kinetic theory the following

physical principle is altered. These assumptions are as rules must apply.

follows.

1. The mean mixture velocity is given by Summing rules

n The rules for summing eq (8) through (11) must

= I V ..it (7) result in the following relations for the supply terms,

a=l

2. The behavior of the mixture is governed by the ' =0 (13)

a

122
I a =0 (14) Constitutive equations

a To complete the number of differential equations

I Act = 0 (15) with the number of variables we relate the variables

a through the constitutive equations. Following Coleman X • =0. (16) and Gurtin (1967) as well as Lubliner (1990), we

at propose modeling the elastic-viscoplastic behavior with

As shown by Hansen (1990), this is different from the the use of internal state variables. These variables

classical mixture theory which contains diffusion ye- describe the relations at the microscopic level. For our

locity terms, making the solution much more compli- particular application, this method allows the incorpocated. ration of interactions between constituents in the form

Assumptions regarding the behavior of the mixture of surface energies.

as a whole are also made. The compilation of all Each constituent depends upon its own independent

constituents should behave as a single constituent. This variables. In the use of mixture theory we require an

restriction is placed on the balance equations by sum- accounting of how the constituents interact with each

ming the densities, stresses, heat fluxes, body forces, other. This is accomplished with the supply terms.

energies, heat sources, and entropy. The form of these Additionally, we propose a constitutive relation for

summations is shown to be, each supply term. We assume that the constitutive

relation for the supply terms may depend upon the

P= I Pa (17) independent variables of all constituents. Thus, we have

ct two sets of constitutive equations to formulate: one for

t at e (18) each constituent as if it behaved as a single constituent

a and the other, for the supply terms for each constituent.

q= X qy (19) The use of internal state variables gives us the ability

a to analyze the physics of the problem and to use this

b = I caba (20) analysis as the basis of our constitutive equations.

a Hansen (1985) considered the description of snow by

e = caeat (21) internal state variables. We assume some of his list but

at include additional terms to describe the surface energy

r = car (22) effects between wood and snow. Internal state variables

a listed below are by no means independent of each other.

'I= I ctl a (23) Current research is being conducted in deriving and

a identifying the relations between these variables.

These variables describe the microstructure of a

Summing the constituent balance equations with the wood/snow mixture. The cohesive aspects of the mixabove rules then leads to a system of nonlinear partial ture are accounted for by the surface energies, while the

differential equations. geometric and kinematic microstructural behaviorcomes

from the first six variables as described by Hansen

(1985) and Edens (1989).

This mathematical model allows us to describe the

Table 5. Internal state variables for a wood/snow microstructure of the snow matrix as well as the intermixture, action between the snow and wood constituents. Hansen

r mean bond radius (1991) has successfully used this model, without the

I mean bond length internal state variables, to describe the behavior of

L mean grain length composite materials. While this is not the only model

R mean grain length available, it has an increasing usefulness to applied

n3 mean number of bonds per grain engineering problems. Our development will further

Nav mean number of grains per unit volume the transition from theory to application of the valuable

Vg mean volume of a single grain mathematical model.

Vb mean volume of a single bond

Sg mean surface area of grains per unit volume

Sb mean surface area of bonds per unit volume

Sbg mean surface area of bond to grain contact per unit volume CONCLUSIONS

ag surface energy of the grain

ab surface energy of the bond

(7w surface energy of the wood Laboratory and field tests indicate that use of wood

as binder material in a snow matrix increases strength.

123
It appears that with large strain, this increase in strength Abele, G. and Frankenstein, G. (1967) "Snow and Ice

is more evident. Temperature plays a vital role in the Properties as Related to Roads and Runways in Antarcsintering process of the mixture of snow and wood. For tica," USACRREL Technical Report 176.

this reason, solar insolation may enhance or destroy the Barber, MJ., Brown, R.L., and Lee S. (1989) "Imstrength integrity. For laboratory tests, solar insolation proving Snow Roads and Airstrips in Antarctica,"

was not a factor. South Pole Station was not affected by USACRREL Special Report 89-22.

the amount of solar insolation while McMurdo Station Barber, MJ., Brown, R.L., and Lee S. (1989) "Bindwas greatly affected. ers for Snow Roads and Runways in Antarctica," JourThe tests indicate that the microstructure of the nal of Cold Regions Engineering, Vol. 3, No. 2.

snow/wood matrix is a measure of strength. Ram values Barber, MJ., Brown, R.L., and Lee S. (accepted)

that were extremely high were in regions of high wood "Laboratory and In Situ Study of the Effect of Additives

concentrations. Note, this is true for both McMurdo and on Compaction Strength of Snow," Journal of Ocean

South Pole Stations. This indicates that the strength Engineering and Technology.

gained is from the wood interactions as well as from ice Bowen, R.M.(197 (, - heory of Mixtures," Continuum

formation due to melting, for melting did not occur at Physics 111, Eringeii, A.C. ed.

the South Pole. Coleman, B.D. and Gurtin, M.E. (1967) "ThermodyIn order to quantify the strength of snow/binder namics with Internal State Variables,"Journal ofChemimixtures, we chose to model the behavior with the cal Physics, Vol. 47, No. 2.

modified mixture theory. This has often been termed Edens, M. (1989) "Determining the Change in Snow

too complicated, but we are rewarded with a compre- Microstructure During Large Deformation Processes

hensive theory describing the microstructural behavior by the Method of Quantitative Stereology," Masters

allowing access to the physics of stresses and deforma- Thesis, Montana State University.

tion. The extra work seems to be worthwhile for mix- Gow, AJ. (1965) "Snow Studies in Antarctica." USA

tures of materials. CRREL Research Report No. 177.

This model is applicable to other engineering prob- Hansen, A.C. (1985) "A Constitutive Theory for High

lems. Mixtures of materials containing several con- Rate Multiaxial Deformation of Snow," Ph.D. Thesis,

stituents may be modeled by developing and relat- Montana State University.

ing new internal state variables. Future research will Hansen, A.C. (1989) "Reexamining Some Basic Defiapply these theories more comprehensively to the nitions of Modem Mixture Theory," Int. J. Engng. Sci.,

wood/snow problem. Additionally, we can describe Vol. 27, No. 12.

materials containing numerous additional constituents, Hansen, A.C., Crane, R.L., Damson, M.H., Donovan,

limited only by our numerical methods and computing R.P., Homing, D.T., Walker, J.L. (1991) "Some Notes

power. on a Volume Fraction Mixture Theory and a Compaiison with the Kinetic Theory of Gases," Int. J. Engng.

Sci., Vol. 29, No. 5.

ACKNOWLEDGMENTS Hansen, A.C., Walker, J.L., Donovan, R.P. (1991)

"A Finite Element Formulation for Composite StrucThe authors would like thank Dr. Sung Lee, Albert tures Based on a Volume Fraction Mixture Theory," (to

Wuori, Dr. Wilbur Haas, and Mark Bott for their sup- be published).

port in laboratory and field testing. Appreciation is also Lubliner, J. (1990) "Plasticity Theory," Macmillan

extended to the National Science Foundation for their Publishing Co., New York, New York.

support in funding this project under (DPP-8517148 Moser, E.H. (1963) "Navy Cold-Processing Snowand DPP-8612951). Compaction Techniques." In Ice and Snow Kingery,

W.D. (ed), MIT Press, Cambridge, Mass., 459-484.

Segev, R. and Taragan, E. (1989) "Stresses in Mixture

LITERATURE CITED Theory," Int. J. Engng. Sci., Vol. 27, No. 12.

Truesdell, C. and Toupin, R. (1960) "The Classical

Abele, G. (1983) "Feasibility of Constructing a Snow FieldTheories,"Handbuch der Physik, Vol [1113,Flugge,

Runway at the South Pole Station for C-141 Aircraft." S. Ed.

Technical Note, Nov. 1983, prepared for Naval Civil Truesdell, C. (1984) Rational Thermodynamics,

Engineering Laboratory, by USA CRREL. Springer-Verlag, New York, New York.

124
The Influences of Adjustable Tire Pressure (CTIS) and Anti Skid Devices

When Driving In Snow

STURE BERNHARDSSON

Defense Material Administration, Mobility Directorate

Transport Behicles Division, Test Center

S-645 83 Strangnas, Sweden

Vehicles equipped with an arrangement to adjust the Volvo C3 is 170 kPa. The dimension of the tires are 280/

tyre pressure from the driver's seat (Central Tire Infla- 85-16 and the load is about 850 kg/wheel.

tion System, CTIS) have been used for a long time in How the surface contact area increases with reduced

Eastern European States, mainly in the Soviet Union. tire pressure appears from figure 3 and from the diagram

The system was used in the West on certain special in figure 4.

vehicles during the second world war. In the United The strength of the surplus drawbar pull was meaStates this method to improve passability on soft ground sured in roughly 40 cm deep snow. The snow was

seems to have received an increased interest in the past mainly of hardness class 1, with a layer of 5 cm thick

few years. During the "Desert Shield" and "Desert frozen crust on top of about 20 cm of old coarse grain

Storm" a lot of experiences have proved the advantage snow. The results are shown in the bar diagram, figure

of CTIS. 5. This diagram shows that the drawbar pull increases

Different solutions of CTIS arrangements have been by roughly 2.5 times when the tire pressure is reduced

discussed and shown at previous conferences, among from 200 kPa to 50 kPa.

others, by Robert Kaczmarek. With the type of wheel used, there is a danger of

I will here confine myself to tests which have been skidding between the rim and the tire at very low air

carried out at the Swedish Defence Materiel pressure.Thetypeofemergencydrivingequipmentyou

Administration's Test Center, and bring forward only find on heavier cross-country trucks of the Swedish

results which fall within the theme of this conference. Defence Forces assures that the tires remain attached to

In order to find out to what extent the CTIS influ- the rim even at low air pressure. Figure 6; cut through

ences a wheeled vehicles advancement, we have wheel with bead clamps.

equipped a 4x4 vehicle, Volvo C3, (Mil = TGBIL 11), Returning to the diagram (figure 5), we pass directly

figure 1, with such a system, figure 2. Since a complete onto my next report, concerning driving with snow

system was not available we had to put together compo- chains, or anti-skid devices as we prefer to call them in

nents from what we could find. With a control at the the Swedish Defence, and the reason for that is that we

driver's seat desired tire pressure can be selected and the use the chains all the year round on slippery ground

pressure can be read on an indicator. All four wheels (clay, wet stones). The results from draw bar pull tests

obtain the set air pressure. Normal air pressure for in identical snow conditions show that with normal tire

125
1' j rw

Figure 1. Terrdngbil I11 (Volvo C3).

126
Ro seal

LLi

Control valve

Circuit

breaker

SAir vessel

ElectricCo arN

Pressure switch

Batet 24 volt

a. Circuit diagram TGB 11.

Figure 2. Central tire inflation system.

127
SSeal rk Outer beannt

MouWeiag nut SeaJ ring Tube

b. Front wheel gear TGB 11.

Figure 2 (cont'd). Central tire inflation system.

Aradmrg 504 465 599 8u60

b.Frntwhee gea "G 1.-l /,1

Figure 3. Rest s2face on firmed ground, TGB i1i, tyre - 28085-1e6.

128
Tyro patch

area (cm)

900-

800

700

600

500

200 150 100 50 Air pressure

(kpa)

Figure 4. TGB 11, Goodyear 280185-16.

Draw bar pug AN

- rImp -4"C

13-

"5cm WId

3cm k13

6cm IdI

10- 6cm MJ5

18 cmkIl

5

.S

c U

70

.C0

170 50 60 80 100 120 140 160 180 200 kpa

Figure 5. Adjustable tyre pressure TGBI I in 40 cm snow depth.

129
The =yeIm longer and

win t busL

The Trelleborg Run Flat System

is tubeless, which means longer

life than normal as the tyre generates

less heat. The tyre being tubeless, also

implies that the risk of tube failure is

eliminated.

Low weighL

Thanks to the simple construction, the system is

light which assists the riding performance. The

unsprung weight is low.

Figure 6. Trelleborg Run Flat System.

130
pressure and anti-skid devices, the draw bar pull in- the pull increases moderately. This is one of the reasons

creases considerably. All new cross-country trucks of why all 3-axle trucks are equipped with only 4 anti-skid

the Swedish Defence (Volvo C3 4x4 6x6, Scania SBA devices at the delivery to troop.

4x4 and SBAT 6x6) are at the delivery equipped with The various designs of anti-skid device are not of

anti-skid devices. These have been developed by major importance to the drawbar pull in snow.

Gunnebo AB in close cooperation with the Defence Next figure (8) shows tests with different kind of

Materiel Administration. At drawbar pull tests with chains on a wheeled tractor on hard, compact snow. The

SBAT6x6(Mil=TGBIL40)inabout45cmdeepsnow, bar diagram shows that the old transversally linked

we obtained the results shown in the bar diagram on standard chains increase the drawbar pull twice, while

figure 7. This diagram shows, that in exactly these snow the recent speidl chains with square links or special

conditions, the truck with all wheel drive and differen- grip studs respectively, only give a somewhat stronger

tial locks only has a surplus drawbar pull of 0.8 kN. pull.

Anti-skid devices on only the first bogie axle increase When the design of anti-skid devices and their feathe pull to 6 kN and with another 2 or4 anti-skid devices tures are discussed the drawbar pull is often given

Draw bar pull AN

100-

90 -

80 -

70

60

50

40

30

20

10

0 2 4 6

NUMBER OF CHAINS

Figure 7. Drawbar pull with standard chains TGB 40

(snow depth 45 cm).

131
Draw bar PA AN

15

10"

5-

Chain Ioen SkIngl Square Spkd cai

eUidwd Inked

Figure 8. Drawbar pull with three types of chains (wheeled

tractors). Hard packed snow on road.

132
TGOIL 14414

4 Snow chains 16k MI I i~

mlka

Hall normal fire 1

pressure

Normal fire 6M

pressure

900 ka

VW-Bus

SYNCRO 41A

4 M(Engine Snow chains 9 -eines

pressure 3 4 E

Normal tire 4M 1"Snwc dtos

pressure ýi

VW500kg x2MItTemperature: -15-C

Hal nrma freHardness: Grads 1

pressue W(Frozen 1 crust

presure5 cmn below

Normall tire 50e kufSe

pressure (No surplus traction)

0 5 10 15

Drawbar - pull kM 

Figure 9. Drawbar pull. VWV Bus 4)a, 4x4 Syncro and TGBIL 11 4x4.

133
a. Reduced air pressure. b. Normal air pressure and chains.

Figure 10. "Floating" position in snow.

attentionout of proportion. The following factors should increased from 0 (zero) to 9 kN (Volkswagen) and from

be considered at the evaluation as well: 6 to 16 kN Volvo C3 (TGBIL 11).

-Handling (easy to mount and demount)

-Durability (wearing qualities)

-Effects on the vehicle (vibration, wheel balance) SUMMARY

-Effects on the tires (risk of puncture)

-Riding quality (in curves, at braking) The CTIS gives a skillful driver the possibility to use

-- Contact against the tire (fit-up, throw out) the wheel equipment in an optimal way on various

-Wear on the road ground conditions. In certain snow conditions it can

-Maintenance (damage frequency, spare parts, TTR) give a better passability than anti-skid devices, since it

-COSTS (LCC) gives the truck a higher floating position (figure 10).

Comparison of different steps to increase traction (fig- The anti-skid device can not be replaced by the CTIS.

ure 9); We have compared Volkswagen Transporter/ A combination of anti-skid device and CTIS does not

Bus2x4,4x4SyncroandVolvoC3 4x4at the same time work well. The driver should be able to adjust the tire

and in the same snow conditions. Depending on differ- pressure in such a way, that each pair of wheels has a tire

ent designs and different actions the drawbar pull has pressure corresponding to each axle load.

134
The Negatively Buoyant Jet/Plume

With Applications to Snow Plow Exit Flow Behavior

WILLIAM R. LINDBERG AND JOSEPH D. PETERSEN

Department of Mechanical Engineering

University of Wyoming

Laramie, Wyoming 82071

ABSTRACT

This paper presents the initial findings of an ongoing study of negatively buoyant jet/plume

behavior. The motivation for this research is to quantify the dynamics of the exit snow plume

from displacement and rotary snow plows. The effects of injection angle and cross flow on

the jet/plume behavior have been of particular interest in this phase of the study.

A water tow tank was used for the experiments, where the exit jet was towed through

quiescent water at a constant velocity. Photographic records of the jet/plume structure were

used to measure the jet/plume dimensions. Dimensional reasoning yielded a set of dimensionless parameters which correlated the jet/plume length scales over a wide range of the

experimental parameters.

Three flow regimes have been identified, which depend on the cross flow Froude number,

Fo:

F. << 1 : negligible cross flow,

0 < F0 < I: weak cross flow,

F.> I :strong cross flow.

where: F0 = Uo/(g'r0 )1

/

2 , Uo is the cross flow velocity, g" is the reduced gravity and ro is the

jet radius. Correlations of the measured length-scales with F0 were determined for all three

flow regimes.

1. INTRODUCTION ment in understanding plow performance, including

cast distances, plume trajectories and dilutions, visibilAn important aspect of the performance of snow ity and the potential for altering these characteristics via

plows is the behavior of the snow after it exits from the plow design and operator control.

moldboard. The exiting snow experiences a very differ- Very little prior work applicable to exit plume beent dynamic environment than the flow conditions havior has been reported. In order to begin to address

along the moldboard itself. At the exit plane, the flow this shortcoming, a laboratory program was initiated to

has acquired considerable momentum in the transverse systematically examine the characteristics of negadirection (i.e. normal to the plow motion). The flow then tively buoyant jets/plumes subjected to a cross flow. A

persists as a free jet whose trajectory depends on this very fundamental approach to this study has been

momentum and the modifying external forces. The adopted, where the full complexity of the problem is

forces on this exit fluid include gravity and a complex initially reduced in order to focus on the basic flow

three-dimensional interaction with the surrounding air, phenomena. Additional parameters may then be introin the forms of entrainment and drag. duced and theireffects placed in the context of previous

Knowledge of the exit plume flow for a variety of observations. This paper summarizes the initial results

operational conditions is viewed as an important ele- of this research program.

135
2. BASIC CONSIDERATIONS- large-scale turbulent motions are dynamically similar

THE NEGATIVELY BUOYANT PLUME for flows with widely differing Reynolds numbers. It is

the large-scale motions which dominate such processes

The wide variety ofcircumstances where knowledge as entrainment, momentum transfer and mixing. All of

of the behavior of a jet or plume whose density is these processes are central to the dynamical behavior of

different than its surroundings has stimulated research jets and plumes. Laboratory studies where the basic

on this topic for decades. The majority of this work has shear flow is turbulent may then be used to simulate

centered on the positively buoyant case, where the flows whose Reynolds numbers are different, but whose

density deficit of the jet or plume provides a body force basic behavior is similar.

in the same general direction as tfe initial injection A dimensional analysis of jets and plumes may be

direction (i.e. a light fluid injected upward, or a heavy performed to identify the basic parameters of these

fluid injected downward). Examples of this positively flows. Figure I provides a schematic of the geometry of

buoyant jet/plume include a cumulus cloud, an indus- the negatively buoyant jet/plume in an ambient flow.

trial smoke-stack or the rising column of smoke from a The jet, of density pj, exits the nozzle, of radius r., at a

campfire. velocity of Uj, into ambient fluid surroundings of denA negatively buoyant jet/plume has a body force in sity Pa. The ambient flow velocity is U0 . For the studies

the opposite direction as the vertical component of the to be reported in this paper, the axis of the jet is inclined

injection velocity. In this case, equilibrium heights or an angle 0 from the horizontal in a plane perpendicular

flow reversals are always present. The term "vertical to the ambient flow direction.

component of the injection velocity" is used because The two most important dynamical parameters of the

these jets can be aligned at an angle to the vertical, initial jet are the jet momentum (M) and buoyancy (B)

Examples of this type of flow include the vertical fluxes (normalized with jet exit density):

injection of a dense gas into the atmosphere, the introduction of saline water into a lake or river and for M = 2U2

present interest, the behavior of a plume of snow particles after exiting from a snow-plow blade. B = xro2Uj [(pj - Pa) / P' g

A distinction is made between a jet and a plume. A

jet is a flow which is due to a source of concentrated where g is the gravitational acceleration.

momentum such as the flow induced by the discharge The desired observable geometric parameters infrom a pipe or orifice. The driving force for a plume is clude Xm, Win, Xt and a, where Xm is the (x,y,z) length

the body force or buoyancy of the plume itself. As an scale triad when the jet is at its maximum height, Wm is

example of this distinction, an initially buoyant jet will the jet width (Wy, Wz) at the same location, Xt is the

expand, slow down and dilute with increasing down- (x,y) length scale forthe return of thejet/plumecenterline

stream distance. Eventually, the momentum of the fluid to the original height of the jet and a is the spread-rate

will decrease to the same order as the fluid buoyancy. At parameter (dWy/ds, dWz/ds, where s is directed along

this point, the jet becomes plume-like, as buoyancy the jet/plume centerline). Dynamic parameters such as

begins to dominate the flow dynamics, and different velocity scales anddilution rates are also of importance,

behavior would be expected. The same processes are but have not been measured in these studies.

present for a negatively buoyant jet/plume, with the A dimensional analysis, using the defined paramdistinction of the reversed body force for the plume, eters, yields the following functional set of dimensionwhich retards upward motion and ultimately reverses less parameters:

the vertical motion.

The presence of an ambient cross-flow further com- L* = FJ f [F., Rej, 0] (1)

plicates this process. This external flow can have the

effect of turning the jet/plume flow toward the downstream direction and will also alter the internal flow where L* = L/ro (or aE)

behavior of the jet/plume itself.

Laboratory studies of turbulent jets and plumes have L = dimensional length scale (i.e. Xm, Wm or Xt)

proven to be very useful in applications where the

prototype and laboratory scales are considerably differ- Fj = Uj / [g'ro]t12 (the jet Froude number)

ent. Dimensional and dynamic similarity arguments are

insufficient to justify this success without the underly- F0 = U0 / [g'ro]'/ (the cross-flow Froude number)

ing premise of Reynolds number independence in these

turbulent shear flows. It has been observed that the Rej = 2Ujro v (the jet Reynolds number)

136
U 0

/ 

y

x

Figure 1.Basic geometry of the negatively buoyantjet/plume

which is translating relative to the ambientfluid.

g'= [(pj- Pa)/ pJ g (the reduced gravity) points between various modes of the jet/plume behavior.

v = kinematic viscosity. z - lb: jet-plume transition (for negligible ambient

flow),

The assumption of Reynolds number independence z -tm: transition point for bent-over jet in an ambient

for sufficiently large Rej (Re 5500), reduces the nura- flow,

ber of independent parameters to three: Fj, Fo and 0: z - 4: transition point for bent-over plume in an

ambient flow.

L*-= Fj f[Fo, 0]. (2)

Not all of these length-scales are independent, as:

It is in this form that all the present experimental data Fo - (Vb/lp)1/3 - (4b/1m). (4)

will be presented.

Three vertical length-scales for this flow may be We may then characterize the effect of the ambient

identified [Lindberg and Petersen (1990), Fischer et al. cross-flow in terms of the magnitude of Fo as:

(1979)]. These length-scales are based on the vertical Fo << 1: negligible cross flow,

scale where there is a dynamical balance of the various Fo < 1: weak cross flow,

forces acting on the jet/plume: Fo > 1: strong cross flow.

Lb = (M sin 0)3/

4 / B'/2 (3a) Additionally, the ratio offb to ro is proportional to Fj:

m. M l/2sin 0/ U, (3b) tb/ro = (nE sin 0)3/4 Fj

p=Bsin 9/U 03 (3c) Since there is a transition region ofapproximately I Ojet

diameters for the basic jet shear flow to develop, small

These length scales represent the vertical transition values of Fj would indicate that the flow was still

137
developing when the buoyancy forces were beginning from 0.53 to 0.68. Shalman (1973) cites the following

to be important. Low values of Fj were avoided, form for T1d:

At this point it is appropriate to point out those

parameters which have not been included in this study. hd = Tanh[ao (Hrs) 1/21

The four most important parameters are the cross-flow

Reynolds number, Reo, the fluid density ratio, Sr, the where: ao = 6.2 [cm3

/gm m] 1/2,

azimuthal jet angle, f, and the nozzle geometry, where H = undisturbed snow depth [m),

Ps = undisturbed snow density [gm/cm3]. Reo = Uots/V

Sr = p/p,, Such a formulation is probably most appropriate for

Is = transverse length scale of the jet/plume, wet, cohesive snow, where the plume entrains little, if

0 = the jet angle in a vertical plane relative to the any, surrounding air, similar to the behavior of a water

plane normal to the cross-flow direction (identi- jet. The appropriateness and/or the limitations of this

cal to a spherical coordinate system). type of approach is not at present resolved.

In contrast, an exit plume composed of dry, coheStudies have clearly shown that cross flows directly sionless snow will behave as a heavy fluid, characteralter the internal dynamics of jet/plume flows, but the ized by strong entrainment, drag and mixing with the

resulting flow behavior is relatively insensitive tovaria- surrounding fluid. It is this situation which is most

tions in Reo, provided Reo is sufficiently large. appropriately modeled by the approach of the present

For the present experiments, the flow is approxi- research.

mately Boussinesq [i.e. Sr- 0(1)], so these experimen- The fluid dynamical modeling of snow avalanche

tal results should be adequately modeled without the motion using water tanks has been discussed by

inclusion of Sp as an independent parameter. It should Hopfinger and Beghin (1980) and Hopfinger (1983).

be noted that the density ratio is incorporated in the They were successful in properly scaling many of the

buoyancy flux parameter, B, as it is defined in this observed features of avalanche behavior in the laborapaper, which does reflect non-Boussinesq effects. tory. The non-boussinesq effects of Sp > 1 were examAs was discussed in the Introduction, this study was ined and found to be relatively minor up to Sp - 10.

intended to provide the benchmarks for comparison to Studies of negatively buoyant jet/plumes are quite

other studies incorporating such effects as large density limited. In particular, only a few laboratory studies of

ratios, azimuthal injection angles and non-circular exit these flows have been reported [Bodurtha( 1961), Turner

jet geometries. At present, the importance of these (1966), Holly and Grace (1972), Pincince and tist

effects remains unresolved. (1973), Hoot, Meroney and Paterka (1973) (see also

Hoot and Meroney, 1974), Anderson et al. (1974), Chu

(1975) and Badr (1984)].

3. RELATED STUDIES An experimental study of a vertically injected dense

jet in a watertank was reportedby Turner ( 966), forthe

A very limited amount of study of snow plow plume case of no cross-flow. Unfortunately, Turner incorbehavior has been performed. As has been pointed out rectly reported his correlated results, and the error has

by Minsk (1981), the cast distance (Ym,) for a snow been propagating in the literature since that time. The

plow has historically been modeled by equations of the correct result for the maximum rise height of the vertiform: cally injected dense fluid is:

Y* = hd g(q,f) (hFo)2, (5) Z*max = 4.17 Fj (6)

where: TIB = dynamic efficiency, This result is consistent with the dimensional arguments

g(0,f) = sin 2q sin f of the previous section [Eq (2)].

,q = moldboard efficiency (-Uj / Uo). The workoffHoot, MeroneyandPeterka (1973) [also

Hoot and Meroney (1974) and Meroney (1980)] is of

This functional form ofthe cast distance has its theoreti- particular significance, both in its scope and in the

cal origin in simple particle trajectory analysis. The quality of the experimental measurements. They report

effects of drag, entrainment, turbulence and density are on wind tunnel studies of dense gases injected vertically

accounted for in the dynamic efficiency parameter, rid. in a low turbulence flow. Their quiescent flow studies

For example, Vinnicombe (1968) reports rid to range were in complete agreement with Eq (6). Density ratios,

138
Sp, of between 1.5 and 3 were used. An integral analysis the same ambient fluid. The waterjet is attached to a tow

for the case of a cross-flow was performed and corn- carriage which may be moved at a constant velocity

paredtotheirexperimentalresults.Thefunctionalagree- along the tank's horizontal axis. The speed of the

ment was excellent, and their data correlate well with carriage may be varied between 0 and 12.4 cm/s. Thejet

the following relationships: flux is controlled by a valve located between a constant

1 F

1 head tank and the jet nozzle. The flow rate is measured

_L = 2.1 F (7) by a tapered tube flowmeter (calibrated for the variation

Fj Pin the fluid density). The resulting jet behavior is reX*max./Fj = Fo (8) corded photographically with two cameras, located at

the side and end of the tank. The side camera uses a

where Z CL= Z = ZCL / r. (at the plume centerline). shadowgraph technique to record the projected image

Other measurements, including concentration distribu- of the jet/plume density structure on an opaque grid

tions and longitudinal touchdown distances, were also surface. The end camera records an illuminated slice of

reported, the jet which is produced by directing a sheet of light

Based on a very brief review in Ooms and Duijm from the side of the tank and using a small amount of

(1984), it would appear that the work of Anderson, white temperapaint in thejetsolution. Examples of the

Parker and Benedict (1973) is of direct relevance. images recorded by this technique are shown in Figures

Unfortunately, the work was never published and a 2, 3 and 4.

copy of their report has not been obtained. They used a The experimental program consisted of 260 separate

water flume and varied 0 between 450 and 900. tests. Table I lists the range of the experimental paramThe response of a neutrally buoyant jet in a cross- eters used in these studies.

flow has been studied extensively. A summary to 1981 A typical experiment began with the installation of a

has been given by Crabb, et al. (1981). The characteris- selected nozzle at a predetermined angle setting. The

tics of the jet deflection entrainment rates, mean turbu- tow tank was then filled and allowed to reach thermal

lent flow properties have all been measured and docu- equilibrium with the laboratory overnight. The vertical

mented. The observation of a double vortex structure in temperature structure was measured prior to testing.

the downstream portion of the jet has intrigued investi- Thermal stratification within the tank never exceeded

gators for years [see Abramovich (1963), Chapt. 12, 2°C/m, so that internal wave motion and stratification

Keffer and Baines (1963)]. The interest lies both in the within the tank was not important. Approximately 2

mechanism of generation and in the subsequent influ- liters of water at the tank temperature was placed in the

ence on thejet's boundary shape, trajectory and entrain- constant head tank. Sodium chloride was added to the

ment rate. water in this supply tank until the desired jet density was

In terms of numerical/analytical models of nega- reached. Density was determined with a hand-held

tively buoyantjet/plume behavior, the survey by Hanna refractometer. A small amount of white tempera paint

and Drivas (1987), the volume edited by Britter and was then added to the mixture in negligible amounts to

Griffiths (1982) and the brief review by Ooms and affect the density. A series of tests at various towing

Duijm (1984) represent most of the currently available speeds and jet velocities were then made, without the

models and provide a comparative assessment of these necessity to drain the tank. The tow tank density was

models to the fairly small experimental data base. monitored during these tests to insure that the tank

density above the level of the jet remained unstratified.

Photographic enlargements of the side and end views

4. DESCRIPTION OF THE EXPERIMENT were made for each run. Measurements of the various

length-scales were then made from the photographs. A

A tow-tank was used to simulate the ambient flow. A single operator performed all of the measurements. In

round tube (the jet source) was towed through the tank order to provide a check on any bias this procedure may

at a constant velocity. The use of a towing facility have imposed, random tests were chosen and indepeninsures a very uniform, repeatable and low turbulent dent measurements of the length scales were made by a

mean flow (as seen by the jet/plume). The working fluid second observer. There was good agreement between

in the tow tank is water where the tank dimensions are the two estimates of these length scales.

394 cm long x 40.6 cm wide and 50.8 cm deep. Salt A summary of the experimental uncertainties in

water of various densities was used for the injection these measurements is included in Table 2. However,

fluid. The water jet is mounted 10 cm above the bottom the major source of scatter in the data is the inherent

of the tank so that multiple test runs may be made with convoluted shape of the instantaneous boundary of the

139
17

Figure 2. Side and end views ofajetlplumefor the case of negligible cross

flow; Fj = 25.2, Fo = 0, Y* = 67.2,Z* = 60.2,9 = 60*. The grid in the side

(shadowgraph) image is 1 cm square.

140
V.

Figure 3. Side and end views of ajetiplumefor the case of weak cross floNv;

Fj = 28.9, Fo = 0-51, X* = 34.9, Y* = 54.6, r* = 813, 0 = 60.

141
Figure 4. Side and end views ofajetlplumefor the case of strong cross flo,

Fi =84.5,Fo 55 SX* =J79.0,Y* =67.0,Z* =95.0, 0= 60 0.

142
Table I. Ranges of experimental parameters. Table 2. Composite uncertainties of dimensionless

parameters

Parameter Range of values

Parameter Uncenerminy (% )

Vi 8o-280 cm/s

Uo 0-12.4 cm/s Fj 9.1

0 30PL900 F0 2.4

ANppj 0.01-0.20 V 9.6

ro 0.046-0.24 cm L*JFj 13.3

Rest 870-9220

Reat 0-700

Fj 12-170

Fo 0-15

teased on jet diameter. on the inside of the double vortex is unmarked external

fluid which is being entrained in a very preferential way

by this vortical structure. The photograph also illusjet/plume. It is the instantaneous structure which is trates the elliptical cross-sectional shape of the plume,

captured in the photographs, whereas, the average bound- whose minor axis is aligned in the same general direcary shape would require averages over a number of tion as the initial jet angle. The entrainment processes

observations, observed are in sharp contrast to the turbulent interfacial

entrainment processes of negligible or weak cross flow

jets and plumes.

5. EXPERIMENTAL RESULTS

AND OBSERVATIONS 5.2 Quantitative results

52.1. Comparisons with previous work

5.1 Observations The special case of 0 = 90* has, as has been noted,

A complete photographic recordof all tests has been some limited prior research history. Turner's (1966)

obtained. Examples of these photographs are given in

Figures 2, 3 and 4. These three photographic pairs are

for the three ranges of Fo applicable to negligible, weak

and strong cross-flows, respectively.

The observed variability in all length scales increased at low F0 and the higher values of 0. At these

conditions, the plume length scales were observed to

fluctuate with time around a mean value. These fluctuations were of the order of ±20% of the mean length

scales, while at the same time, the jet flow rates were

observed to be very constant. These low frequency

fluctuations are then a result of the interaction of the jet/

plume with the column of fluid which is falling back

around tl upward directed flow. At the lower angles

and higlhr values of Fo, this interaction was not as

pronounced, ordid not occur, and the variability in these

length scales was much smaller. The highly convoluted

entraining interface of these jet/plume flows is also

quite apparent in these photographs, where the large

scale turbulent motion imposes ahighly irregularboundary between the jet/plume fluid and the surrounding

lower density fluid. The difficulty of determining the

mean interfacial length scales from a single photograph

is apparent, and the scatter of the measurements is

predominantly due to this very convoluted structure.

The double vortex structure mentioned in Section 3

is illustrated in the photograph in Figure 5. This was for Figure 5. Double vortex structure, as seen from an end

a strong cross flow situation (F0 > 1). The darker fluid view; Fj = 51, Fo = 4.0, 0 = 60 '.

143
work, for Fo = 0, has been discussed, where a principal effect of such a procedure would be to record the

result of this work is Eq (6). Figure 6 shows the data for maximum excursion over the time duration of the

0 = 900 and Fo = 0, for the present study, along with Eq photograph.

(6). The best fit line for this data (based on 8 teits) is: A direct comparison to the data of Hoot et al. (1973)

for the case of finite Fo is also possible. This comparison

Z* = 3.7 Fj, (9) is made in Figure 7, where the present data are shown

along with Eq (7) over the range of the experimental

which is 11% lower than that predicted by Eq (5) or the data used to obtain the correlation. The low Fo data of

results of Hoot et al. (1973). The observed fluctuations Hoot et al. was consistently below their reported asympof the plume for high 0 and low Fo provide some totic curve, in agreement with the present notion of a

explanation for this discrepancy. The maximum plume transition for Fo = 1, as is discussed below.

height excursion was not recorded (unless by chance),

and a small number of instantaneous photographs were 5.2.2. Data correlations

obtained. This procedure results in effective plume We shall discuss in some detail the measurements of

heights which vary over the range of instantaneous the maximum vertical excursion of the plume, Z*, as a

plume heights. Given a sufficiently large set ofobserva- function of Fj, Fo and 0. Many of the features of the jet/

tions, the data would then reflect the average plume plume behavior are apparent from these observations

height, rather than the maximum observed height. For alone. The other scales will then be presented and

these observations, a consistently lower value by 10% briefly discussed.

would then be expected. For the case of finite Fo, some Maximum Plume Rise, Z*. There is an ambiguity in

visual averaging of the photographs was performed, to the interpretation of the definition of maximum plume

remove some of the instantaneous large-scale excur- rise when Fo is varied continuously from 0 to values of

sions from the data. This procedure is in contrast to the the order of 15. For very weak (or negligible) cross

time-lapse photographs used by Hootet al. (1973). The flows (Fo < 1), the only observable is the maximum

400 /

Turner(1966) //

300 //

NI

/ Present Data

200-/

/ ,/

/"

100 /

0

0 20 40 60 80 100 120 Fj

Figure 6. Comparison of vertical jet/plume behaviorfor no cross flow, with the results of

Turner (1966).

144
0.1 110

Fo

Figure 7. Comparison of verticaljet/plume behazvior in a cross flow with the results

of Hoot et al. (1973). Equation (7) is shown as a solid line, over the limits of the

experimental data of Hoot et al.

plume "top," as the plume descends in the near vicinity This choice was for reasons of consistency, where Z.,,

of the initiating jet. This definition of plume rise was is defined the same way for F, < I and for Fo > 1.

used in the previous subsection for the Fo = 0 case study. Additionally, the experimental techniques used require

For strong cross flows (i.e. Fo > 1), the plume is separate determinations of both Zmaxtop and Wmx. The

advected in the downstream direction, so that a plume increased uncertainty of combining these measurecenter-line may be considered. Te example compari- ments is avoided by this choice. (Such increased experison study for finite Fo in the previous section used such mental uncertainty is in evidence in Figure 7 of the

a definition. The two ways to define Zmax are not previous section.)

consistent, but may be related as Logarithmic plots of Z*/Fj versus Fo are shown in

Figure 8(a-d). Ile dimensional arguments leading to

Z"- Z.,n CC= Zmax. top- W/2 , Eq (2) are seen to be valid representations of the

processes involved, as the data is reasonably well corfor Fo >0. Fornegligible cross flows, the exact interpre- related. There is a definite change in the functional

tation of Z, c• is not clear, since the internal dynamics behavior of Z*/Fj in the neighborhood of Fo - 1, which

of an ascending jet/plume and the subsequent annular marks the transition between a weak cross flow and a

descending flow is noteasily reduced to asingle vertical strong cross flow.

length scale. The choice of the definition of Zinax for the For the Fo = 0 cases, Z*/Fj = f,,o(0). The values of this

data to be presented is: angular dependence for Fo = 0 were determined from a

regression analysis of Z* versus 1ý, as was done in

ZMaX = Zmax,top . Figure 6. The linear dependence of Z* on Fj was very

145
- 0 •

0 * Figure 8a. Dimensionless maxiiJb. ,mum plume rise, Z*lF1 , in a cross

S flow as a function of cross flow

* • • .. , Froude number, Fo; (a) 0 = 90",

N 1 (b)0=60',(c) =45-and(d)0

=30*.

* I I 55 |53 I I I I I tII |

1 10

Fo

• o• • °°Figure 8b. Dimensionless maxiA° mum plume rise, Z*!Fj, in a cross

•o •flow ,• • as a function of cross flow

I •• • o• o''•,ooFroude number, Fo; (a) 0 = 90,

S• •,, • *(b) 0 = 60 0, (c) 0 45*and (d) 0

e • =-300.

110 Fo

146
Figure 8c. Dimensionless maxi-

" mum plume rise, Z*/Fj, in a cross

flow as a function of cross flow

0 0% Froude number, Fo; (a) 0 = 900,

N N •, (b) O=600

t(c) O=45Oand(d) B

*. =300.

NI

I I I 1 e | ii H U I

1 10

Fo

S- a % **Figure 8d. Dimensionless maxi-

- - -mum ,* plume rise, Z*/Fj, in a cross

flow as a function of cross flow

b4 o~* .% Froude number, Fo; (a) 0 = 900, L7, • . a (b) 0 = 600, (c) 0 =45 *and (d) 0 •* ."* = 300.,

NI_ 1 .6.3'

NN

SN"

*@ N

Fo

147
Table 3. Linear regression analysis results for Z* is very similar to the Z*/Fj data of Figure 8. Adequate

behavior, representations of this data are thus:

lnia jet fyo(6) Fo=0

agng, 0 f) GO(O) nZ Y*/Fj = fy(0) : 0 F < 1 (12)

900 3.70 3.61 -0.53 fy(e)Fon F0 > 1

60' 2.46 3.01 -0.59 4530 .76 2.53 -0.53 A data correlation summary, similar to Table 3, is given

300 1.47 2.14 -0.50 in Table 4.

With the exception of fyo(45°), both fy,o and fy

increase with decreasing 0. The dependence of Y*/Fj on

consistent for all cases. The weak cross flow (F0 < 1) Fo continues to have an approximate Fo-]/ 2 behavior,

behavior is essentially Z*/Fj - fz(0), which is consistent although the calculated slopes are even more negative.

with the scaling arguments leading to Equation (2). For Analysis of end-view photographs of plume behavF0 < 1, Ib < tab so the transition to a pure plume would ior subsequent to the maximum plume rise location

be expected before the effects of a cross flow became indicates that Y does not appreciably increase further

important. For Fo > 1, the slope of the data in the form: downstream. The initial y-momentum has become so

diffuse, through entrainment, at this point that further

Z*/Fj = f,(O)Fon (10) transverse transport is small. For the present, then, we

may take Y* to be indicative of the maximum transverse

was also determined from a regression analysis. A plume distance, at least for F0 > 1.

summary of the results of these correlations is given in Longitudinaldistance,X*. The downstream location

Table 3. where Zm. occurs is defined as Xff". The scatter in the

A comparison of the values of fz,o(0) and fz(0) X* data is significant for F0 > I and illustrates thi

indicate that as 0 decreases from 900, the value of fz,o(0) difficulty of determining Xnm when the irregular plume

decreases much faster than fz(0). A plausible explana- boundary is essentially horizontal for a finite distance

tion for this behavior is the observed change in the downstream. Within the limits of the data, an asympinteraction of the descending fluid with the rising cen- totic equation of the form:

tral column of fluid. Comparison photographs of this

process indicate that the interference of the descending X*/Fj = fx(0 ) Fonx (13)

fluid on the jet/plume decreases for F0 > 0, where the

low momentum descending fluid is advected by the correlates the data for F0 > 0. Table 5 summarizes the

cross flow. Without this sweeping away ofthis descend- linear regression analysis for this data. We should note

ing fluid, the rising/falling fluid interaction is stronger, that Xax = 0 for F0 = 0.

both by increasing the mixing rate within the plume and From Table 5, the variations of fx(0) are not signifiby an increased momentum exchange between the two cant, however the comparison of nx for 0 = 90* and all

flows, other angles is to be noted. The asymptotic theory of

The asymptotic analysis of Lindberg and Petersen Hootetal.(1973)andLindbergandPetersen(1990),for

(1990) yielded a scaling for Z*/Fj for the case of a jet 0 = 900, predict that X*/Fj - F0 [Eq (8)], in agreement

with weak cross flow (i.e. F. < 1) and 0 <900. The with the measurements. For 0 < 900, this exponent, nx,

experimental values of fz(O) agree with the following decreases by as much as afactoroftwo. A more detailed

equation to within 4%: analysis will be necessary to clarify this observation,

however it is clear that the nature of the downstream

Z*/Fj = fz(0) = 2.3[sin 0(1 + sini/2 0)11/2. (11) plume trajectory changes when the initialjetangle is not

vertical.

As would be expected, the values of fzo(0) do not Plume width scale, W*. Observations of the plume

correlate well with this expression, where it is noted that width scale, W*, were made at the Z7g location. These

the entrainment hypothesis used in the analysis is only measurements were made from the side, shadowgraphic

consistent with a weak cross flow behavior, images, so they represent the total vertical width of the

Transverse Distance, Y*. We define Y* as Y d/ro, plume at that location. Due to the elevation of the

where YIM* is the measured maximum transverse dis- injection jet above the bottom of the tow tank, some

tance of the jet/plume at the same location as Zmn. measured widths exceed Zm, however, these data

Figure 9(a-c) shows the measured Y*/Fj values as a were retained.

function ofF0 .The asymptotic behaviorof Y*F with F0 Table 6 summarizes the regression analysis for the

148
Fiur 9a. Diesols

transverse length scale, Y*IFj,

Se * in a cross flow as a function of

crossflow Froude number. F.:

. (a)O=60,(b)0=45 and(c)

S = 300.

S10

Fo

- a N 0". Figure 9b. Dimensionless

• N transverse length scale, Y*/Fj,

>- N in a crossflow as a function of

• • ".crossflow Froude number, Fo.

S(a) 0 = 60 o,(b) 0 =45 and (c)

\ ~ O= 3V°

N

e I 11l l I I l I l'

1 10 F•

149
• • ••Figure 9c. Dimensionless

transverse length scale, Y*IFj, *•, • "in a cross flow as a function of .""% " crossflow Froude wnuber, Fo;

1 •(a) .<. 0 = 60 o(b) 0 =45 0 and (c)

• • O 300.

010 10

Fo

four angles for Fo > 1, for the same asymptotic forms as write equation (12) as:

Equation (12). The similar values offw(0) and nw for the

various injection angles indicate that the vertical plume L*i = T1 fit0) Foni + 1 (14)

widths, for all injection angles, are very similar. If a

conceptual elliptical shaped plume in the downwind for values of F• > 1, which is appropriate for most

direction is used, the lower injection angles have a displacement plowing operations. Note that the length

smaller Zmnax, but a larger projected plume width, due to scales depend linearly on the moldboard efficiency, T1.

the tilting of the ellipse. Since nominal values of ni for Y* and Z* are of the

order of -0.5, the exponent on F• in the above equation

is of the order of +0.5, in sharp contrast to the squared

6. APPLICATION TO SNOW PLUME exponent of Equation (5). The characteristic lengthBEHAVIOR scale for these laboratory, studies has been the nozzle

radius, to. An equivalent circular length-scale for the

In terms of predicting snow plume cast distance or case of a snow plume yields the following scale:

plume height for snow plow applications, we may rero,e = [Aexitir]1/2 = [bH/nrlqa]|/2,

Table 4. Linear regression analysis results for Y*

behavior. Table 5. Linear regression analysis results for X*

behavior [for all values of F• > 0].

injection

angle, 0 fy.0(0) f),(0) nv injection

9 0°• angle, 0 G x( 0) nX

60* !1.7 1.7 -0.5 i 90* 1.20 0.92

45* 1.6 2.2 -0.59 600 1.61 0.55

30* 3.0 2.7 -0.62 450 1.43 0.48

•-Y* is zero for 0 =90*.3(1.804

150
Table 6. Linear regression analysis results for W* snow density, Ps = 100 kg/m3,

behavior [for F0 > 1]. plow efficiency, ri = 1.0,

plow angle, * = 00,

Injection effective exit radius, ro~e = 0.46 m.

anigle, 0 f,(O) a.

90, 2.5 -0.54 Figure 10 also shows the prediction of cast distance

600 2.2 -0.61 using Equation (5) with the estimate of Tid as suggested

450 2.2 -0.55 by Shalman (1973), for the case of 0 = 45'.

300 2.2 -0.55 The calculations are presented to illustrate the potential benefit of the current research in exit plume behavior. It should be kept in mind the current limitations on

where b,H are the width and depth of the plowed snow, the parameters examined to date.

and a is the ratio of the final to initial snow densities.

This equivalent scaling is limited to plow flow exit areas

which are approximately circular (or elliptical). 7. SUMMARY AND CONCLUSIONS

Example predictions of cast distance, Y.ax and

maximum cast height, Zmu, using Equation (14), are The results of an experimental research program on

shown in Figures 10 and 11. The assumed parameters the behavior of negatively buoyant jets/plumes are

for these calculations are: summarized in this paper. The effects of initial jet angle

and cross-flow have also been investigated.

snow depth, H = 0.20 m, Plume trajectory behavior, in the form of coordinate

plow width, b 3.3 m, length-scales at the location of maximum plume height,

I

= /60n0

0

C,

0

0 03 10 20 30

Plow Soeed (m/s)

Figure 10. Predicted cast distance as afunction ofplow speedand initial moldboard

exit angle, 0. The example parameters are summarized in the text. The dashed line

is Equation (5),for 0 = 45'.

151

L
4-J

S05=900

=450

a,,

Plow Speed (m/s)

Figure)11. Predicted snow plume cast hzeight for the same pa rameters as Figure 10.

was determined from photographs of the visualized objectives were to:

plumes. These length-scales are seen to be functions of • examine the effects of injection angle and cross

jet angle, 0, and the two Froude numbers: Fj and F0 .To flow on jet/plume behavior and relate the observathe accuracy of the observations, the results have been tions to previous work,

correlated to an asymptotic power law as a function of * attain a wide range of parameter values to demonflow regime in the form of: strate the validity of the scaling analysis of Section

2,

f iu(0) ;FI = 0 o determine the parameter space which may be idenwas = f r(0) ;o < Fo < 1 (15) tifved with the various asymptotic flow regimes.

fp(e)Feni ;Fle> 1 (F0 >0 for X*) Within the limits of a photographic study, a large range

of parameter space and a reatively small number of

The flow regimes of F0 =0 (no cross-flow), 0< F0 < 1 tests, the objectives of the study have been met.

(weak cross-flow) and Fso> i(strong cross-flow) ex- Further laboratory study will be directed toward the

hibit significantly different dynamical behavior, as is following objectives:

seen in the experimental observations o and in the length- study the effect of changes in the exit jet geomcti

scale results. on jet/plume behavior, with emphasis on the strong

This study has successfully demonstrated the useful- cross flow regime,

ness of using a water tow-tank for the present jet/ptume • include the azimuthal angle to study the effect of

research. The range of parameters attainable in this fa- both fore and aft injection angles,

cility has allowed for a clarification of the distinct 0 flow investigate the non-Boussinesqeffect ofSp signifiregimes which have been discussed. Observations and cantly different than one, by using different solphotographic records have revealed much of the detail utes and suspensions,

of these jet/plume flows from a variety of view angles. * examinthe t interaction between adjacent objects

At the outset of this phase of the study, the primary and the downstream plume behavior, including

152
the incorporation of flow control devices attached ing, Trans. ASME, Vol. 103, pp. 142-153.

to the adjacent structures, Fischer, H.B., EJ. List, R.C.Y. Koh, J. Imberger.

" compare jet/plume behavior in a quiescent flow to N.H. Brooks (1979) Mixing in Inland and Coastal

a turbulent environment, Waters, Academic Press, New York, Chapter 9.

" extend the analytical work to include higher level Hanna, S.R. and PJ. Drivas (1987) Guidelines for

numerical models, primarily integral-based mod- Use of Vapor Cloud Dispersion Models. American

els. Institute of Chemical Engineers.

Holly, F.M. and J.L. Grace (1972) Model study of

dense jets in flowing fluid. J. Hydraulics Div., Proc.

ACKNOWLEDGMENTS ASCE, Vol. 98, No. 9365, pp. 1921-1933.

Hoot, T.G., R.N. Meroney and J.A. Peterka (1973)

The research described herein was supported by the Wind tunnel tests of negatively buoyant plumes. Fluid

Strategic Highway Research Program (SHRP). SHRP Dynamics and Diffusion Laboratory, College of Engiis a unit of the National Research Council that was neering, Colorado State University, Report No. CER73-

authorized by section 128 of the Surface Transportation 74TGH-RNM-JAP- 13.

and Uniform Relocation Assistance Act of 1987. The Hoot, T.G. and R.N. Meroney (1974) The behavior of

authors would like to express their appreciation to negatively buoyant stack gases. Proc. 67th Annual

Wayne Foslien, Jeff Rogers and Roland Miller for their Meeting, APCA, Denver, Colorado, Paper No. 74-210.

help with the data reduction and to Dr. R.N. Meroney of Hopfinger, E.J. (1983) Snow avalanche motion and

Colorado State University. related phenomena. Ann. Rev. Fluid Mech., Vol. 15, pp.

This paper represents the views of the authors only, 47-76.

not necessarily reflective of the views of the National Hopfinger, EJ. and P. Beghin (1980) Buoyant clouts

Research Council, the views of SHRP, or SHRP's appreciably heavier than the ambient fluid on sloping

sponsors. The results reported here are not necessarily boundaries. Proc. 2ndlnt. IAHR Symp. StratifiedFlows.

in agreement with the results of other SHRP research Trondheim, pp. 495-504.

activities. They are reported to stimulate review and Keffer, J.F. and W.D. Baines (1963) The roundturbudiscussion within the research community. lent jet in across wind. J. Fluid Mechanics, Vol. 15, pp.

481-496.

Lindberg, W.R. and J.D. Petersen (1990) The negaLITERATURE CITED tively buoyant jet/plume in an ambient cross flow. Fluid

Mechanics Technical Report. FMTR-90- 1, Department

Abramovich, G.N. (1963) The Theory of Turbulent of Mechanical Engineering, Univ. of Wyoming.

Jets. MIT Press, Cambridge, MA. Meroney, R.N. (1982) Wind tunnel experiments on

Anderson,J.L.,F.L.ParkerandB.A.Benedict (1973) dense gas dispersion. J. Hazardous Materials, Vol. 6,

Negatively buoyant jets in a cross flow. EPA-Report nos. 1-2, pp. 85-106.

No.660/2-73-012, (as referenced by Ooms and Duijm, Minsk, L.D. (1981) Snow removal equipment. InHand1984). bookofSnow, D.M. Gray and D.H. Male, eds., Pergamon

Badr, A. (1984) Temperature measurements in a nega- Press, New York, pp. 648-670.

tively buoyant round vertical jet issued in a horizontal Ooms, G. and N.J. Duijm (1984) Dispersion of a stack

cross flow. In: Atmospheric Dispersion ofHeavy Gases plume heavier than air. In Atmospheric Dispersion of

and Small Particles, G. Ooms and H. Tennekes, Eds., Heavy Gases and Small Particles. G. Ooms and H.

Springer-Verlag, pp. 167-176. Tenekes, Eds. Springer-Verlag, New York, pp. 1-23.

Bodurtha, F.T. (1961) The behavior of dense stack Pincince, A.B. and E.J. List (1973) Disposal of brine

gases.J.AirPt llution ControlAssociation, Vol. l Lpp. into an estuary. J. of the WPCF, Vol. 45, No. 1i. pp.

431-437. 2335-2344.

Britter, R.E. and R.F. Griffiths (1982) Dense Gas Shalman, D.A. (1973) Snowplows, Construction.

Dispersion. Elsevier Scientific Pub. Co., [aboundcol- Theory and Design, 2nd Ed. (in Russian).

lection of papers which constitute J. of Hazardous "Mashinostroenie," Leningrad.

Materials, Vol. 6, parts 1 and 2]. Turner, J.S. (1966) Jets and plumes with negative or

Chu, V.H. (1975) Turbulent dense plumes in laminar reversing buoyancy. J. Fluid Mech., Vol. 26, pp. 779-

cross flow. J. Hydraulic Research, Vol. 13, No. 3, pp. 792.

263-279. Vinnicombe, G.A. (1968) Comparative tests on model

Crabb, D., D.F.G. Dura6 and J.H. Whitelaw (1981) vee snow ploughs. Rept. LR 180, Road Res. Lab.,

A round jet normal to a crossflow. J. ofFluids Engineer- Crowthome, U.K..

153
5. MATERIALS PROPERTIES

155
Viscosity Measurements on Very Wet Soils

SALLY SHOOP

U.S. Army Cold Regions Research and Engineering Laboratory

Hanover, New Hampshire 03755-1290

ABSTRACT

Springtime and intermittent thaws are often accompanied by soft. wet ground conditions

and thaw weakening of the soil. Water added during snow melt and spring rain accumulates

in the thawed layer because drainage is limited by the relatively impermeable frozen soil

below. This added waterdecreases the strength of the thawing soil even further. Forthese very

wet soil conditions the soil can be considered a non-Newtonian viscous fluid. Information

from viscosity tests can then be used in analytical ornumerical models where the thawing soil

is modeled as a semi-viscous fluid for determination of the drag -resistance of wheels in

viscous mud.

This paper describes apparent viscosity measurements on three soil types-sand, silt and

clay- chosen to cover a wide range of grain sizes. Extensive mobility test data and

supporting information, such as shearing resistance, grain size and Atterberg limits, were also

readily available for each of the soils tested. Six to eight soil-water mixtures, ranging in

consistency from a paste to a slurry, were tested for each soil type.

The viscosity was found to be strongly influenced by water content, as expected. Below

the liquid limit, when the soil samples were paste- like, the viscosity was very high (39 to 85

Pa.s), and was difficult to measure because the soils behaved as a semi-solid. At or near the

liquid limit, the viscosity of all the soil types was approximately 40 Pa.s. As the percentage

of water increased beyond the liquid limit, the viscosity decreased dramatically and then

steadily declined as additional water was added. The lowest viscosity value measured, for the

very wet clay (over 100% water content), was approximately 0.07 Pa-s. In general, the values

obtained in this study extend smoothly beyond the range of previously published data.

INTRODUCTION a viscous fluid. For a Newtonian (perfectly viscous)

fluid the shear stress, T, is proportional to the rate of

Thawing soil is primarily a two-layer configuration, shear, 7:

where a soft and wet soil layer overlies the hard frozen

ground (Figure 1). Because the frozen ground can form = 97 j (1)

a relatively impermeable barrier, any moisture added to

the system during Lhawing, such as rain and/or snow where the proportionality constant, g, is the viscosity. A

melt, becomes trapped in the thawing layer, making it Bingham plastic fluid also behaves as a linear function

exceptionally wet and weak. Under these very wet of the rate of shear but requires an initial yield stress, Ty,

conditions, the soil can be considered as a viscous fluid to cause displacement:

(Shoop, 1990). These kinds of conditions can be very

difficult for vehicle mobility. Vehicle traffic is often = r Ty + p.y1. (2)

restricted on secondary roads and may be impossible on

unpaved roads and off-road. In addition, when vehicles The behavior of viscous soils (and mud) has been obcan pass, they may leave excessive ruts, causing severe served to be somewhere between these two, as shown in

road or terrain damage and subsequent erosion. Figure 2.

In the study of vehicle mobility on thawing ground, Dynamic or absolute viscosity can be expressed in

when the thawing soil is very wet it can be modeled as several different units. Historically, viscosity has been

156
the drag force on a tire (after Rowe and Hegedus, 1959)

can be expressed as

FD = 2pVA 1/8 + 8zb/2 + pV2

A2/2 (4)

fy where D = drag force

P = viscosity

SWNt V -• relative velocity

T wet G sl y= specific weight

" " "k '• " FROZEN Hard A, and A2 = tire contact area

impmeabe sd 8 = boundary layer thickness

z = thaw depth

Figure 1. The nature of thawing soils. b = tire width

p = fluid density.

expressed in units of poise (from Poiselie). The official

SI unit is Pascal seconds: The velocity of the tire and the soil's density, specific

weight and thaw depth can be easily measured, along

I Pa.s = 10 poise = 1000 cp (centipoise). with the contact area and object width. The boundary

layer thickness can be estimated from the literature, so

Kinematic viscosity, v, in units of length squared per the viscosity of the mud is the primary unknowr.

second, is related to absolute viscosity as follows: Not much data for viscosity of mud exist in the

published literature. In the late fifties, Hegedus (1958)

v=Wp (3) and Rowe and Hegedus (1959) performed viscous flow

experiments on a tire moving through bentonite clay. In

where p is the fluid density. The viscosity measure- addition, the Asia/Pacific mobility researchers somements discussed in this paper are absolute, or dynamic, times use fluid flow theory to simulate vehicle moveviscosity and are also apparent viscosity since the fluid ment through puddled rice paddy fields (Xie and Shoa,

is non-Newtonian. 1988). Another subject area that considers soil as a

If thawing soil is considered as a viscous fluid, then viscous fluid is that of massive mudslides and landthe movement ofa tire through the soil can be calculated slides (Maa and Mehta, 1988). Sewage treatment engias the viscous drag on the tire. The equation to calculate neering has also considered the viscosity of soil and

sludge mixtures (Vesilind, 1975). These published values, as well as those of other common materials, are

listed in Table 1.

Table 1. Viscosity of selected materials.

Pa-s Reference

U) Air (200C) 1.86x10"5 Jaeger (1962)

4 Water (200

C) 1.0x10-3 Jaeger (1962)

SMercury (20"C) 1.56x I0--3 Jaeger (1962)

SCastor oil (20*C) 0.72 Jaeger (1962)

Pitch (15"C) 2x1010 Jaeger (1962)

(50 0C) 2x106 Jaeger (1962)

Glass (20"C) 1021 Jaeger (1962)

(575°C) i.ix1012 Jaeger (1962)

Lava flow 4x 103 Jaeger (1962)

Sludges: Raw primary 0.028 Vesilind (1975)

Mixed digested 0.092 Vesilind (1975)

Activated A 0.006 Vesilind (1975)

B 0.005 Vesilind (1975)

j, Rate of Shear C 0.007 Vesilind (1975)

Mud: Bentonite 4.5 - 17 Hegedus (1958)

Figure z. Shear stress vs shear rate for Newtonian and Coastal, clayey 60 -- 300 Maa and Mehta (1988)

non-Newtonianfluids and mud. Clay. loam 0.002 -+ 4 Xie and Shao (1988)

157
Because of the wide range in the published values of Table 2. Atterberg limits.

soil viscosity, I decided to measure the viscosity of

specific soils which had been used in our vehicle mobil- PL LL P1

ity test program. These values will be used in predictive Lbanon Sand - 20 -

calculations (like equation 4) to check the theoretical MoultonPit Silt 26 27 1

results against mobility test data. LeToumeau Clay 23 32 9

EXPERIMENTAL METHOD the relationship between the viscometer output voltage

and viscosity. All samples and standards were set in a

Three soil types were chosen for viscosity testing: a constant temperature bath for approximately 30 minsand, a silt and a clay. The soils were chosen to cover a utes in order to equilibrate at a temperature of 20'C.

range of grain sizes and also because of the existence of Each soil mixture was then tested for viscosity, weighed,

data from mobility testing and strength testing in the lab and placed in an oven to dry. The dry weights of the

and field. Lebanon Sand is a fine-grained silty sand mixtures were used to calculate the moisture content of

obtained from the banks of the Connecticut River in each sample.

Lebanon, New Hampshire. Moulton Pit Silt is a clayey The viscosity of the samples was measured using a

silt, also from Lebanon. LeToumeau Clay is a low Brookfield Viscometer (Figure 4) according to ASTM

plasticity clay from just south of Vicksburg, Mississip- Standard D 2196-86, Test Method A for Apparent Vispi. Their grain size distribution curves are shown in cosity. The viscometer measures the torque required to

Figure 3 and the Atterberg limits are listed in Table 2. rotate a spindle within the specimen at a constant speed

Six to eight samples of each of the soils were pre- set with an adjustable-speed motor. The viscosity of the

pared to cover a wide range of consistencies from a very sample causes a torque on the spindle, which is convertwet slurry to a dry paste. I tried to test at least one sample ed to voltage using an electronic pressure transducer.

that was below the liquid limit from each soil type but Output voltage was recorded on a strip chart recorder.

this was difficult as the soil behaves more as a solid at The viscometer can be set so that the spindle constantly

these water contents and is difficult to test in the vis- moves up and/or down within the sample by using the

cometer. helipath stand. This causes the spindle to cut a helical

A suite of ASTM viscosity standards, covering a path through the sample, always cutting into fresh

wide range of viscosities, were measured to determine material and eliminating problems with channeling or

U.S. Std. Sieve Size and No. Hydrometer

34 4 10 40 200

100

I I ILeTourneau

80 Percent Passing No. 200 Sieve

LeToumeau: 98

* Moulton Pit: 90 I I Moulton Pit 60 Lebanon: 33 e I II I I_

r 40 - SLebanon

20 -- I I I I

- I I I I

20

100 10 1.0 0.1 0.01 0.001

Grain Size (mm)

Gravel Sand Silt or Clay

COrse Fine C'rseI Medium I Fine Sl o

Figure 3. Grain size distribution curves for Lebanon Sand, Moulton Pit Silt and LeTourneau Clay.

158
Viscometer settling of the material. The viscosity can also be measured at a constant level within the sample.

Because of the effect of speed on viscosity for nonNewtonian or pseudo-plastic fluids, the spindles and

settings of the viscometer were held constant for all

samples, including the standards. Spindle F(a T-shaped Chuck, weight bar with a crosspiece diameter of 1.09 cm) was chosen and closer

assembly and rotated at a constant speed of 100 rpm. This configunt T-bar spindle uration was chosen because of the high viscosities

expected for the soil pastes. However, since the speed at

the outside edge of the crosspiece (0.05 m/s) is less than

the speed used in running the moltlity tests (1.34 m/s),

the viscosity values may be different than those encountered in the field situation.

RESULTS

The apparent viscosities were calculated by measurFigure 4. Brookfield viscometer. ing the voltages recorded on the chart and comparing

them to the voltages obtained from standards of known

viscosity. Six different standards of a wide range of

viscosities were measured (Figure 5). Because the relationship between the viscosity and voltage is not linear

within the wide range of'viscosities tested, a polynomial

y---1111.93x2 + 19873.3x - 129.6

60

40

Viscosity (Pa • s) Standard at 200

C

20- 5-6 0.00945

N35 0.08521

N350 1.193

N2000 8.705

S8000 33.550

S30000 78.470

0.00 1.00 2.00 3.00 4.00 5.00 6.00

Volage (mV)

Figure 5. Curve fit of the viscosity standards to viscometer output voltage.

159
Table 3. Soil viscosity values, possible between the liquid limit and the plastic limit,

Moisture Apparent and yielded viscosity values upwards of 80 Pa.s.

content viscosity Near the liquid limit the soil viscosity of all the soils

(%) (Pa-s) is similar (Lebanon Sand is 38.8 Pa-s, Moulton Pit Silt

is 40.3 Pa.s, and LeToumeau Clay is 41.2 Pa-s). At these

Lebanon Sand moisture conditions, viscosity may be independent of

19 38.761

23 4.713 the soil type. This would agree with Casagrande's

26 2.604 (1932) discussion of the physical significance of the

29 2.604 Atterberg limits, which states that the shear resistance at

32 2.178 the liquid limit is a constant value (20 to 25 g/cm2; Seed

35 1.003 et al., 1964) for all soil types. The liquid limit test is

Moulton Pit Silt primarily a measure of the shear resistance of the soil,

32 40.332 and viscosity is also a measure of shear resistance. Thus,

37 24.291

42 16.502 at the liquid limit, shear resistance and viscosity can be

46 7.826 expected to be the same value for every soil type. It

47 5.550 should be noted that while Casagrande's work referred

71 0.574 primarily to cohesive soils, these data suggest similar

LeTourneau Clay results for non-cohesive soils or soils with very low

29 84.807 cohesion.

31 82.599

33 41.162 To compare the three soil types, the results were

40 7.756 plotted on a single log-log plot (Figure 7). The results

44 3.412 for the silt and clay are very similar (as are their grain

47 1.256 size distributions), while the sand is offset. This is likely 63 0.168 because of the coarser particles in the sand sample

101 0.069 settling out of suspension.

The results of these experiments are plotted alongside data presented in Xie and Shoa (1988) in Figure 8.

The soil types are similar to the soils I tested and are

listed in the legend. (Note that the soils I used are named

regression was fitted to the data to be used for calculat- based on the Unified Soil Classification System, whereing the unknown viscosities of the soil mixtures. The as Xie and Shoa used an agricultural soil classification

second-order polynomial shown in Figure 5 fits the system.) The water content of my samples ranged from

standards very well. The viscosities of the soil mixtures, 19% to 101%, and the water contents of their samples

calculated using this equation, are listed in Table 3 ranged from 50% to 800%. Since they were working

along with the corresponding moisture contents. with paddy soils they were naturally more interested in

the extremely wet conditions when the fields are floodDISCUSSION ed. However, both data sets overlap within the same

range of moisture contents and my data extend smoothThe apparent viscosity of each of the mixtures was ly, following the same trend into the range of lower

compared to the water content and is plotted in Figure water contents.

6 for each of the soil types. In general, decreasing the

water in the sample increases the viscosity, as expected.

Starting with the highest water content and decreasing SUMMARY AND CONCLUSIONS

the water, the increase in viscosity is gradual until the

water content is near the liquid limit; viscosity then Thawing soils can create severe problems for vehicle

increases rapidly. This trend was consistent between mobility; roads are often closed or restricted and offtwo of the samples, but for the silt the increase in road travel becomes nearly impossible. When passage

viscosity (with decreasing water content) was more is possible, the resulting rutting can cause extensive

gradual, and water contents below the liquid limit were environmental damage and subsequent erosion. Moisnot tested. For non-plastic soils (the sand and silt) at ture from snow melt and spring rains accumulates in the

moisture contents below the liquid limit, the soil be- surface layerof thawing ground, creatinga very wet and

haves like a solid and the viscosity measurements are weak soil layer over the strong frozen ground below.

both difficult and not particularly applicable. For the This wet soil can behave as a viscous fluid and, thereslightly plastic clay, additional measurements were fore, vehicle mobility can be simulated using the equa160
405

35-

30-

,25-

2• - a. Lebanon Sand.

10-

18 20 22 24 26 28 30 32 34

Water Content (%)

45.

40 b

35

230

*25

2D 0 b. Moulton Pit Silt.

15 •

10-

Water Content (%)

g(] -I I I I I I I I I

C

80-

70-

60-

4- - c. LeTourneau Clay.

30-

20-

10-

20 40 60 80 100

Water Content (%)

Figure 6. Viscosity vs water content. The value of the liquid limit is shown by the vertical line.

161
100 I=

Moulton Pit

10 Silt

Lebanon > 1.0 Sand a

LeTourneau

Clay

0.1 _----

10 100

Water Content (%)

Figure 7. Log-log plot of viscosity vs water content

for the three soil types tested.

100 oso (Xie and Shoa)

-(Shoop)

10

1.0 a

"> Sitlay

0.1 - Silt Loam

Silt Clay

0.01 - la

0.001

10 100 1000

Water Content (%)

Figure 8. Comparison of viscosity data for the three soil

types with results of Xie and Shoa (1988).

162
tions of viscous drag from fluid flow theory. LITERATURE CITED

The apparent viscosity of three soil types-a sand, a

silt and a clay-was measured using a Brookfield Vis- Casagrande, A. (1932) Research on the Atterberg

cometer. The soils were chosen to cover a wide range of Limits of Soils. Public Roads, Vol. 13, Oct, p.

grain sizes and also because of existing mobility data, 121-136.

strength data and other basic soil behavior information Hegedus, E. (1958) Drag Coefficients in Locomotion

on these particular soils. over Viscous Soils, Part 1. U.S. Army, Land LocomoSix to eight samples of each of these soil types were tion Laboratory Report No. 25, AD 201 183.

prepared to cover a range of moisture contents and soil Jaeger, J.C. (1962) Elasticity, Fracture and Flow.

consistencies ranging from a paste to a slurry. In gener- John Wiley and Sons, Inc., New York, 208 p.

al, the viscosity is strongly dependent on water content, Maa, J. P.-Y., and AJ. Mehta (1988) Soft Mud

particularly near the value of the liquid limit. At water Properties: Voight Model. Journal of Waterway, Port,

contents below the liquid limit, the soils behave as a Coastal and Ocean Engineering, Vol. 114, No. 6, Nosolid or plastic, making the validity of the technique vember, p. 765-770.

limited. Near the liquid limit, the viscosity values of Rowe, R.S. and E. Hegedus (1959) Drag Coefficients

each of the soil types is similar (approximately 40 Pa-s), of Locomotion over Viscous Soils, Part II. U.S. Army,

as expected since the shear resistance for all soils is Land Locomotion Laboratory Report No. 54. AD 235

equal at the liquid limit. Beyond the liquid limit, the 703.

viscosity decreases rapidly as water is added to the scil, Seed, H.B., RJ. Woodward, and R Lundgren (1964)

dropping as low as 0.07 Pa's for the clay slurry at awater Fundamental Aspects of the Atterberg Limits. J. of the

content of 101%. Soil Mechanics and Foundation Division of the ASCE,

Knowing the viscosity of the soil as a function of Vol. 90, No. SM6, November, p. 75-105.

water content, the motion resistance of a tire moving Shoop, S. (1990) Mechanism Controlling Vehicle Mothrough the viscous soil can be calculated based on the bility on Thawing Soils. Proceedings of the I 0th Inequations of fluid flow. These calculations can be temational Meeting of the International Society of

checked against measured motion resistance to evaluate Terrain Vehicle Systems, Kobe, Japan, August, Vol. I,

the success of the prediction and either validate or p. 301-311.

modify the theory. Vesilind, PA. (1975) Treatment and Disposal of Wastewater Sludges. Ann Arbor Science Publishers, Inc.,

Ann Arbor, Michigan.

ACKNOWLEDGMENTS Xie, X.Y. and YJ. Shoa (1988) Analysis on the Pressure-Sinkage Relationship and Viscosity of Top Layer

The author thanks Mr. Alan Tice, Dr. Vincent Janoo Paddy Field Soil. Proceedings of the 2nd Asia/Pacific

and Mr. Stephen Bowen for their thoughtful reviews of Conference of the International Society of Terrain Vethis paper and Mr. Alan Tice and Dr. Patrick Black for hicle Systems, Bangkok, Thailand, Dec. 6-10, p. 79-

their technical assistance in setting up the experiments. 88.

163
The Relationship Between the Microstructure and

Mechanical Properties of Snow

MICHAEL Q. EDENS AND ROBERT L. BROWN

Civil/Ag Engineering Department

Montana State University

Bozeman. Montana 59717

ABSTRACT

The mechanical properties of snow are determined by the properties of the matrix material

(ice) and the microstructure of the material itself. Microstructure is defined to include such

factors as grain size, pore size, bond size, neck length, grain shape and three-dimensional

coordination number (number of bonds per grain). This set of microstructural relations from

quantitative stereology theory are presented along with relations and techniques required for

numerical evaluation of these variables. An experimental investigation is carried out to

determine changes in these variables for snow subjected to large compressive deformations.

Measurements at several stages of deformation are used to evaluate the changes in the

microstructure as functions of deformation. Grain size and bond radius were found to go

through finite changes during compression. The coordination number and specific free

surface area were found to go through large changes during compression. No discernible

patterns of change in neck length could be found in the experiments. A close relationship

between some of the microstructural variables and the stress response of the material were

observed. These results serve to contribute to the presently available data and understanding

of the microstructural behavior of snow.

INTRODUCTION nature of higher density material. It was found that the

initial density was a significant factor for final stresses

One of the most commonly observed features of < I MPa. The effects of higher initial density became

snow is its compressibility. It can undergo large volu- less obvious for loadings above I MPa. Their studies

metric deformations when subjected to moderate bulk also demonstrated the rate dependent nature of snow's

stresses. Snow's ability to undergo large deformation is load bearing ability. These results have also been veridue in large part to its porosity. In a natural state snow fled with a constitutive theory developed by Brown

exhibits a wide range of grain shapes and densities. (Brown 1979, 1980).

Abele and Gow (1975 and 1976) demonstrated the Microstructural parameters are now being included

effect snow's initial density has on its load bearing in many modern constitutive theories. Among the paability. From their experiments it was clearly demon- rameters being included are bond radius, neck length,

strated that if undisturbed snow with densities from 100 grain size, and three dimensional coordination number.

to 300 kg/m 3 is subjected to high rate deformation, then A grain bond intercepted by the section plane will

the smaller the initial density, the smaller the final appear as a linejoining two opposite edges of the ice in

density that is attained for a given final stress state. This the plane. To identify this line as a bond, three criteria

was attributed to the irregular shaped grains found in must be met. First, there must be a minimum constriclow density snow and to the more uniform rounded tion of the ice in the section plane. Secondly, the

164
"'h"--ip three-dimensional coordination number is the average

number of bonds per grain in the material.

Neck region A volumetric constitutive law based on a neck growth

model was developed by Brown (1980). This model

included structural parameters for change in neck ra2RI dius, neck length, grain radius and coordination numGrain ~'Grain ber. The resulting equation described qualitatively the

behavior of snow subjected to arbitrary deformation

histories for a range of initial densities. To obtain an

accurate quantitative description of the strains requires

empirical adjustment. A more general constitutive law,

Figure 1. Schematic of neck and bond as they appear in based upon nonequilibrium thermodynamics and the

a surface section. mechanical properties of ice, has been developed by

Hansen and Brown (1988) for snow subjected to high

rate multiaxial deformations. The microstructural propconstriction must be present on both edges of the ice. erties of snow in this theory are included in the form of

Finally, the constrictions must point approximately internal state variables. This theory was shown to pretowards each other (Kry 1975a). These are shown in dictbehaviorsuchasratedependence, stress relaxation,

Figure 1. and strain recovery. Over the past ten years other

A neck is assumed to begin at the point where the investigators have formulatedconstitutive relations with

surface curvature changes from convex outward to the use of microstructural variables. These include

concaveoutwardasviewedinasurfacesection.Incases Maeno and Ebinuma (1983), Ebinuma and Maeno

where a sharp change in surface slope exists, this is used (1985), Wilkinson (1988), Alley (1987), and others.

to define the juncture of the neck and grain. Figure 1 Accuracy of any constitutive relation is dependent

illustrates a neck connecting two grains and Figure 2 upon understanding the behavior of the microstructural

illustrates a surface section with a numberof grains with variables included in the theory. Most constitutive laws

their bonds shaded gray. Admittedly, the definition based on microstructural parameters are too compliused here to define the neck contains a degree of cated to be of use in practical applications. Simplificasubjectivity and at times is difficult to implement. The tions of these constitutive laws forspecial situations are

L

;'W .... ........................ ,, ................... ..........

V 

'r

Figure 2. A typical digitized surface section is shown with selected

measurement and a series of test lines. Within this rectangle measured

bonds are shaded gray region.

165
best accomplished with knowledge of which param- fallen snow was collected and stored in a cold room at

eters can be eliminated. At the present time little or no -10'C. Original sample volumes decreased by nearly

data on microstructural behavior exists for snow densi- 50% during the first two months in storage; volume

fled by large deformation to the 500 to 650 kg/m3 changes occurring after this generally were small. The

density range. The work of Abele and Gow (1975, main test apparatus configuration is depicted in Figure

1976) provides a strong basis for understanding bulk 3. This setup was then placed in an environmental

behavior of snow, subjected to high deformation rates chambermaintainedat-100 C andthe snow compressed,

and large strains, but, little or no data was obtained untilapredeterminedloadingwasattained, atanominal

relating the microstructure to the deformation. Gubler strain rate of 2.75 x 10-3 s-1. Maximum loads used were

(1978a, 1978b) and Kry (1975a, 1975b) carried out 44.8 kN, 22.4 kN, or 11.2 kN, corresponding respecextensive microstructural evaluation in their work but tively to Cauchy stresses of 1.55 MPa, 0.77 MPa, and

these studies were generally confined to final densities 0.39 MPa deformation, a 2.5 x 2.5 x 1.5 cm 3 section of

below 500 kg/m3 and to small deformations. the sample was removed. This was prepared for surface

It was the major purpose of this investigation to sectioning by saturating it with a mixture of

evaluate the changes in microstructural variables that Dimethylthalate-Methyl Blue, precooled to -3'C, then

result from large deformations. In addition, it was allowed to freeze solid. The frozen snowintended to measure microstructural variables which to Dimethylthalate-Methyl Blue was then microtomed

the present have not been adequately measured and and the resulting surface polished with lampblack to

mathematically described. prepare it for photographing (Perla 1982). A similar

procedure was followed to obtain surface sections for

the compressed samples.

EXPERIMENT AND RESULTS Each surface section was photographed and prints

were made with image magnifications ranging between

A series of confined compression tests were run at lOx and 20x. These prints were digitized and run

Montana State in which values of several microstruc- through filtering software supplied with the Thunder

tural parameters were measured. For these tests freshly Scanner digitizer on a Macintosh computer. The filter9.2cm

Figure 3. Schematic of compression ring with upper and lower platens.

166
ing process was used to remove blemishes and maxi- A + A

mize contrast. Resolution of the digitized images was L 3 = gA bA mean grain length

better than 0.033 mm/pixel. NgL (Underwood 1970) (7)

The snow was considered to be a three phase mixture

with air, necks and ice grains taken as the three phases S v = 4 NI_ -2 H R2 N 3 Ngv mean grain surface

(Hansen 1985). The subscripts representing each phase area (Hansen 1985) (8)

were respectively "a," "b" and "g." The variables used A + A

to represent surface section measurements were: V - A bA mean grain volume

Ngv (Hansen 1985). (9)

NgL: number of grains intercepted per unit

length of test line Two distinct ranges of grain size existed among the

NbA: number of bonds per unit area snow tested. Large grains corresponding to number I

NgA: number of grains per unit area samples had average grain lengths, L 3, ranging from .34

AaA: area fraction of air phase appearing in the to .39 mm in the uncompressed state. Small grained

surface section. number 2 samples ranged from .19 to .22 mm. The

AbA: area fraction of neck phase in the surface initial densities of the samples were all between 250 kg/

section. m3 and 320 kg/m3 so there was not a wide spread, in this

AgA: area fraction of ice grain phase in the variable, among the samples tested. The notation used

surface section. for identifying samples was:

132i: ith two dimensional bond diameter

f0: fraction of grains with 0 bonds appearing 1) maximum load to which a sample would be

in the section plane subjected is indicated by the first four terms

f 1: fraction of grains with 1 bond appearing (2k50, 2500 lbs (11.2 kN))

in the section plane 2) p or f indicates if the sample is precompressed or

f2: fraction of grains with 2 bonds appearing in its final compressed state

in the section plane 3) 1 or 2 indicates if the sample was tested in the first

f3: fraction of grains with 3 bonds appearing or second year, respectively.

in the section plane.

In what follows, an "o" subscript indicates initial or

Measurements of these parameters were then used to predeformation values and Ap = p - Po is the resulting

evaluate the following variables: change in density. The ratios of compressed to

uncompressed mean grain length, L 3/L 3o vs. Ap/po, are C 1 ratio of ice to snow plotted in Figure 4 and show a gradual decrease in grain AgA + AbA density, Pi/ps (Under- size with increasing density. Since the strain rates used

wood 1970) (1) in these tests were large, some apparent grain fracture

N did result. The straight line is the linear regression curve

E = -1 I harmonic mean of bond and the vertical bars represent the entire range of the

N i--= D2i diameter (Fullman data scatter.

1953) (2) The mean pore length, X, is the mean distance across

a pore from grain surface to grain surface. Values for

R 3 = mean three dimensional this parameter are listed in Table I. Equations (1), (5)

4 E bond radius (Fullman and (7) were combined, resulting in the equation

1953) (3) X.= L 3 (cz-l1) (10)

h = AbA mean neck length

NbvHn2 (Hansen 1985) (4) The solid curves in Figure 5 were generated using (10)

and by holding L3 constant over the entire density range.

mean pore diameter Forthe large grain curve, L3 =.39 mm (l OkO p) and L3

aN9L (Fullman 1953) (5) = .22 mm (5k002p) for the small grain curve. The data

points lie close to their respective curves, implying that

Nbv - 8 E NbA mean number of bonds little or no bond breakage occurred during the deforma1-2 per unit volume tions.

(Fullman 1953) (6) The ratio of X/L3 for the compressed samples de167
1.2-

1.1

0 1.0

0.9

0.8-

0.0 0.5 1.0 1'.5 2.0

Ap/ po

Figure 4. Normalized grain lengthplottedagainsthe corresponding relative change in

density. This figure indicates that some grain breakage may have occurred during the

large deformation testing.

creased from 0.99 to 0.62 mm while the corresponding values of h in Table 1, no definite trends in neck length

final loads increased from 11.2 kN (.387 MPa) to 44.8 could be unambiguously determined.

kN (1.55 MPa). This demonstrates that the load bearing Two and three dimensional bond diameters and radii

ability is closely tied to the mobility of the grains, and, are given in Table 2. The two dimensional bond diamas would be expected, the decrease in grain mobility eters D2 and three dimensional bond diameters R3 both

corresponds to an increase in load bearing capability, show a definite decrease corresponding to deformation.

The factors which collectively govern the change in This indicates that for large deformation, bond growth

neck length are fairly complicated thus predicting neck is less significant than bond fracture and new bond

length change is difficult. It suffices to say that for the formation as few ofthe bonds found in the uncompressed

densifications considered here, as can be seen for the state appear to survive the deformation process. There

Table 1. Mean intercept length, mean pore length and mean neck length.

Sample L3 (MM) A (mm) h (mm)

1OkOIp 0.3987 ± 3.5% 0.8850 ± 7.7% 0.0958 ± 14.6%

10ko1f 0.3405 ± 13.8 0.2114 ± 7.1 0.0708 ± 7.8

5k001p 0.3506 ± 8.0 0.6987 ± 8.5 0.0713 ± 13.3

RkOOIf 0.3209 ± 3.2 0.2612 ± 12.8 0.0877 ± 2.9

5kOO2p 0.2190 ± 1.3 0.6106 ±4.1 0.0650 ± 11.9

5kRO2f 0.1977 ± 2.2 0.1703 ± 12.6 0.0621 ± 5.1

2k501p 0.3501 ± 8.5 0.8022 ± 7.6 0.0667 ± 6.7

2k01 f 0.3416 ± 3.4 0.3112 ± 4.0 0.0607 ± 6.5

2k502p 0.1922 ± 0.8 0.5053 ± 3.4 0.0535 ± 8.9

2kAM2f 0.1820 ± 1.4 0.1796 ± 9.0 0.0588 ± 4.2

168
1.000+0O

8.00-1i

6.00*.- Large grain •Large grain

X(mrm) • Small grain

4.00.-1

Small gra

2.009-1

0.2 0.3 0.4 0.5 0.6 0.7

P(g/60

Figure 5. Shown are the curvesfor large and small grain groups using equation 10 and along with

the experimentally determined data. Error bars represent range ofdata scatter.

should be a point corresponding to decreased grain each bond. Over the range of loading conditions in this

mobility at which the average bond radius ceases to study, Nbv showed a 2.5 fold increase relative to the

decrease as a result of bond breakage and where the undeformed state at the 11.2 kN load (0.387 MPa) to a

average bond radius begins to increase. Some indica- 6.9 fold increase at the 44.8 kN load (1.55 MPa). The

tion of this can be seen in Figure 6 for the largest values of NbV are shown in Table 4.

fractional density change. The values of N3, the mean three dimensional coorComplementary to the grain bond size is NbV, the dination number, Ngv, the mean number of grains per

number of bonds per volume. This along with the bond unit volume, V, the mean grain volume and Sv, the

radius will strongly influence the stress concentration at mean grain surface area to volume ratio, obtained for

Table 2. Values obtained directly from measured 2-D bonds in the plane.

Sample D2 (MM) E(mm-1) R3 (Mnn) DT.• (mm)

lOkOip 0.1692±2.1% 07.2841 *±3.7% 0.1080:± 3.7% 0.0652 ±14.3%

10k01f 0.1299±0.2 09.2088 0. 1 0.08534±0.1 0.0434 ± 4.5

5k001p 0.1488 t 3.9 08.0084 ± 5.6 0.0984 1 5.6 0.0895 ± 5.0

RkOWf 0.14204±5.1 09.55674±6.6 0.08264±6.6 0.0413±0.9

5kO02p 0.0899 * 5.7 15.6394 1 3.4 0.0503 ± 3.4 0.0178 ± 21.9

MkON2f 0.0693± 0.4 19.5801 ± 3.1 0.0402 ± 3.1 0.0118 * 2.5

2k001p 0.1485 ± 3.1 07.8755 ± 0.8 0.0998 ± 0.9 0.0859 ± 0.5

2k501f 0.1315±"9.5 08.5692± 10.1 0.0926 ± 10.1 0.0703±-9.8

2k502p 0.080 ± 1.9 15.3586 * 0.8 0.0512 ± 0.9 0.0270 ± 9.1

2k502f 0.0677 * 0.8 18.8240 ± 2.0 0.0417 ± 2.0 0.0196 ± 42.9

169
1.1

1.0

CV)

t) 0.9

0.8

0.7 .

0.0 0.5 1.0 1.5 2.0

Ap/po

Figure 6. Normalized three dimensional radius versus the relative change in density.

The error bars represent the range of data scatter.

each of the five precompressed samples, are shown in is independent of the mean grain size. Ngv for the

Table 3. These could not be obtained directly from the compressed samples was obtained by using the followsection measurements as they generally require knowi- ing equation to obtain a first estimate,

edge of a grain shape factor. As alpine snow is irregularly shaped characterizing it by shape factor may not be Ngvf = P.- Ngvi, (11)

a valid generalization. Work done in Switzerland by

Gubler (1978a) and later modified by Hansen and where the subscripts f and i refer to initial and final

Brown (1976) provided a method to obtain the mean respectively and where p is the density. Figure 6 demcoordination number N3 and mean grain volume V onstrates the variation of the three-dimensional coordiwithout requiring assumptions about a grain shape nation number, N3 , for the density ranges covered in the

factor other than for an initial guess. Edens and Brown testing program reported here.

(in publication) found itnecessary tomodify the method Values of Sv in Tables 3 and 4, indicate an increase

further. Good results were then obtained for N3 , V and in the surface area per unit volume. This is shown in

correspondingly Ngv, and Sv for the uncompressed Figure 7. As would be expected, Sv increases steadily

samples. for much of the deformation where bond breakage is

The mean coordination number, N3, ranged from frequent and where there is some grain fracturing. It

2.28 bonds/grain to 2.67 bonds/grain. It appears that N3 then levels out as the density approaches 600 kg/m3

Table 3. N3, Ngv, V and Sv for the precompressed samples.

N3 Ngv V Sv

Sample (bonds/grain) (mm- 3

) (_m 3) (mm- )

10kO0p 2.28 ± 10.7% 02.09 ± 4.8% 0.15 ± 4.6% 2.80 ± 17.5%

5k001p 2.41 ± 7.1 02.80 ± 5.6 0.12 ±:5.4 3.41 ± 6.8

5k002p 2.64 ± 3.4 12.19 ± 3.9 0.02 ±:6.1 4.31 ±:8.5

2k501p 2.58 ± 10.6 03.05 ± 2.9 0.10 ± 2.8 3.00 ± 13.2

2k502p 2.36 ± 9.3 19.22 ± 6.5 0.01 ± 6.1 5.01 ± 2.6

170
Table 4. N3, NgV, V and Sv for the compressed samples.

N3 Ngv V Sv

Swnple (bondslgrain) (mm- 3

) (mm 3

) (mm-I)

iOkOIf 7.14 ± 19.6 04.74 ± 13.6 0.14 ± 4.6 5.83 ± 13.6

5kOOIf 5.85 ± 8.0 05.24 &6.0 0.11 ± 5.4 5.60 ± 7.20

RkOO2f 5.72 ± 6.6 27.69 ±4.1 0.02 ± 3.7 9.32 ±7. 10

2k.0S1f 4.17 ± 16.8 05.22 ± 3.0 0.10 ± 2.8 4.99 ± 6.10

2k502f 3.89± 11.9 37.48±7.0 0.01±6.1 9.49±10.2

(Ap/po approaches 1.75-2.0). At densities which are DISCUSSION AND CONCLUSIONS

higher than those studied here this ratio should begin to

decrease as bond breakage all but ceases and bond At the maximum density attained, there was approximobility approaches zero. mately a 3.5 fold increase in coordination number. The

One should not confuse the results shown in Figure increase in coordination number is not very rapid until

8 with what one would expect with thermodynamic densities of 500 kg/m 3 are reached. This corresponds to

consolidation of snow. Here we are stud):.-g the large strains of approximately 33% and occurs at the point

scale compaction of snow at large enotgh rates to where the stress response begins increasing rapidly

fracture grain bonds as well as grains. As a consequence during the compression. The stress is about 0.1 MPa at

new surface area is exposed due to the fracturing at high this point. At the maximum stress the density (639.4 kg/

deformation rates. This is in contrast to the slow con- M3 ) represents a 25% increase over that at 0. 1 MPa (500

solidation of snow as it attempts to reduce its free kgIm3). In this interval the axial stress increased 16 fold

surface energy by grain growth and densificntion. In and the coordination number was doubled. There is

this case deformations are so slow that no fracturing approximately a 60% decrease in the grain mobility as

occurs and a gradual reduction of free surface area indicated by X/L3 at 500 kg/m 3 and at 639.4 kg/m3

results. (Figure 9).

8.0/

7.0

8.0-

N3

5.0-

4.0

3.0

2.0 -

0.2 0.3 0.4 0.5 0.6 0.7

DENSITY (9/cc)

Figure 7. Density versus the three dimensional coordination number. Error bars are

for range of data scatter.

171
2.4

2.2-

2.0

Cl 1.8

Cn 1.6

1.4

1.2

1.0

0.00 0.25 0.50 0.75 1.00 1.25 1.50 1.75 2.00

Ap/po

Figure 8. Normalized surface area to volume ratio - ersus relative density change.

The largest relative decrease in bond radius (22%) rial stiffness is not a linear function of total bond area,

occurs at this maximum stress. This is a 38% reduction since LI. 3tructural rigidity of the ice matrix is strongly

in original bond area, but is countered by an increased influenced '-y the coordination number, in the sense that

coordinationnumberandafactorof 1.9 increase inbond a structurally indeterminant structure is much stiffer

area by over the entire deformation process. The mate- than one that is structurally determinant. Therefore the

1.6 Maximum Axial Stress 1.6 (Mpa)

1.4 (sample lOkOl)

1.2

Stress 1.0

(MPa) 0.8

0.6

0.4, 500 Kg/mr

0.2

0

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45

Strain((strains) or (m/m))

Figure 9. Raw data for axial stress versus Lagrangian strain. The approximate location of the point

corresponding to the 500 kg/m 3 density is shown.

172
coordination number is a dominant factor determining LITERATURE CITED

the material stiffness and strength.

This discussion indicates the effect that relatively Abele, G., and Gow, A.J. (1975) Compressibility

small order of magnitude changes in the microstructure characteristics of undisturbed snow, CRREL Research

have in increasing the load bearing ability of snow. As Report 336.

indicated by Brown (1979), the effects of reduced grain Abele, G., and Gow, AJ. (1976) Compressibility

mobility due to pore collapse may account for much of characteristics of compacted snow, CRREL Report 76-

this at high densities. 21.

The neck length parameter (h) has not been de- Alley, R.B. (1987) Fim densification by grain boundary

scribed in a satisfactory manner in this study. The re- sliding: a first model, Journal de Physique, Vol 48,

suits of the testing program and image analysis gave an (Colloque CI, Supplement au No. 3).

erratic behavior, as illustrated in Table 1. In some cases Brown, R.L. (1979) A volumetric constitutive law for

the neck length is seen to increase in value, while in snow subjected to large strains and strain rates, CRREL

other instances the results showed the neck length de- Report 79-20.

creasing. It was expected that the neck length would Brown, R.L. (1980) A volumetric constitutive law

decrease with compressive deformation, since compres- based on a neck growth model, Journal of Applied

sive stresses on the necks would shorten them. Forma- Physics, Vol. 5 1, No. 1, 16 1-165.

tionofnewbonds(andsubsequentlynewnecks)during Ebinuma, T. and Maeno, N. (1985) Experimental

densification would also serve to cause the mean neck studies of densification and pressure sintering of ice,

length to decrease since necks with nearly zero length Annals of Glaciology, Vol. 6, 83-86.

would be added to the averaging process. There are a Edens, M.Q.and Brown, R.L. (in publication). Changes

number of possible explanations for this apparent dis- in microstructure of snow under large deformations,

crepancy. One could be that an image analysis system Journal of Glaciology.

with a better resolution is needed to provide a more ac- Fuilman, R.L. (1953) Measurement of particle sizes in

curate measurement of the neck length. Also the defini- opaque bodies, AIME, Vol. 197.

tion of the neck length is difficult to implement and Gubler, H. (I 978a) Determination of the mean number

leads to a subjective criterion formeasuring h. Changes ofbonds persnow grain andofthe dependence of tensile

in the sign of the surface curvature as seen in the surface strength of snow on stereological parameters, Journal of

sections is difficult to determine with the system used. Glaciology, Vol. 20, No. 83, 329-342.

There are several experimental results that would Gubler, H. (1978b) An alternate statistical interpretacomplement this study. Values of L3 fordensity changes tion of the strength of snow, Journal of Glaciology, Vol.

of 25, 50, 150 and 200% will help verify any trends in 20, No. 83, 343-358.

grain size change that are occurring (Figure 4). It Hansen, A.C. and Brown, R.L. (1986) The granular

appears that the average grain bond radius may begin to structure of snow: An internal state variable approach,

increase at a density change of 150% (Figure 6). Mea- Journal of Glaciology, Vol. 32, No. 112, 434-438.

surements of R3 at 130, 150 and 200% are needed to Kry, P.R. (1975a) Quantitative stereological analysis

confirm this. The other measurement needed is for the of grain bonds in snow, Journal of Glaciology, Vol. 14,

coordination number at a final density of 450 kg/m3 . No. 72,467-478.

This shouldbe sufficient to define the point of transition Kry, P.R. (1975b) The relationship between the viscofrom low to high coordination numbers. In addition, the elastic properties .ad structure of fine-grained snow,

methods presented here can also be applied to evalua- Journal of Glaciology, Vol. 14, No. 72,479-500.

tion of changes in microstructure of snow due to ther- Maeno, N. and Ebinuma, T. (1983) Pressure sintering

modynamic sintering and also for low strain rates where of ice and its implication to the densification of snow at

grain and bond fracturing is much less significant. polar glaciers and ice sheets, The Journal of Physical

Chemistry, 1983, 87, 4103-4110.

Perla, R. (1982) Preparation of section ilanes in snow

ACKNOWLEDGMENTS specimens, Journal of Glaciology, Vol. 28, No. 98, 199-

203.

The work reported here was supported by the Army Underwood, E.E. (1970) Quantitative Stereology,

Research Office (Grant No. DAAG29-85-K-0259). The Addison-Wesley, Reading, Massachusetts.

authors wish to express their appreciation of the support Wilkinson, D.S. (1988) A pressure sintering model for

by the Geosciences Program in the Army Research the densification of polarfim and glacier ice, Journal of

Office. Glaciology, Vol. 34, No. 116,40-45.

173
Short Term Settlement of Footing On Snow Foundation

PUNEET MAHAJAN AND R.L. BROWN

Mechanical Engineering Department

Montana State University

Bozeman, Montana 59715

ABSTRACT

A constitutive theory for snow, developed by the authors, is applied to solve for the short

term settlement of a footing on a snow foundation. The constitutive law used in the study is

a microstructurally based formulation which includes the effects of bond deformation and

fracture. It also includes transient creep effects and strain hardening of snow.

The foundation problem is solved for stress and displacement distribution, with two

different loads of 0.008 MPa and 0.1 MPa distributed uniformly over a part of the top face.

The stress distribution matches closely with the existing theoretical results. The results

presented here have shown that the constitutive theory can be used to solve practical problems

such as the foundation settlement problem. With some additional development the theory

could be used to evaluate situations where high rates of loading occur, such as in vehicle

mobility problems.

INTRODUCTION determined by the type of metamorphism snow undergoes.

Snow is a porous viscoelastic granular material ca- Kerr (1962) treated the problem of foundation settlepable of undergoing large deformations. Any object ment rate on snow by representing the snow mass in the

placed on a surface of snow settles as a result of form of elastic and viscous elements. Dandekar and

combined effect of natural densification of snow and Brown (1985) used a modified version of a constitutive

penetration of the object. The differential settlement law developed by Brown (1979) to model long term

due to the penetration of object can impose se% cre settlement of a footing on snow. The transient creep

stresses in structural elements and is of primary interest effects were not included in this model.

to design engineers. In this paper we model the short term settlement of

In soils the settlement is kept within definite limits to a snow foundation, subject to loads low enough so that

ensure against abrupt failure by plastic yielding or no collapse of the snow structure takes place. The

rupture. In snow the settlement of foundations can constitutive law used here is one developed by Mahajan

continue indefinitely, and under constant load gradual and Brown (1990) for snow formed under equitemconsolidation of snow may lead to ultimate collapse. If, perature metamorphism. This constitutive law is based

however, the loading is sufficiently low compaction on the microstructure of snow and takes into account a

alone may not lead to complete failure of material, since number of intergranular deformation processes. It also

moderate penetration is accompanied by an increasing includes the effects of transient creep. This constitutive

resistance as the snow compact deforms (Dandekar and theory is discussed in the following section.

Brown, 1985).

For snow foundations, the grain size, neck length,

bond diameter and coordination number all influence CONSTITUTIVE THEORY

the settlement rate. The size of intergranular bonds,

developed during sintering of particles, is an important Snow which has existed under equitemperature confactor in determining the deformation resistance of ditions is made of spherical ice granules connected by

snow. The grain size and shape and the bond size are bonds or necks. The constitutive behavior of snow is

174
determined by the size of the ice particles and the and Brown (1990). The stresses at the points of contact

geometry of bonds connecting the grains. Because of of a representative particle, are calculated using the

their smaller cross section, the necks which connect the variational approach suggested by Kanatani (1981).

grains are subjected to much higher stresses when Next, the strains in the necks are calculate using equacompared to the ice particles and therefore undergo tions developed for constitutive behavior of ice. If

large deformations. It is the straining of necks which is fracturing of necks takes place, empirical relations are

responsible for deformation of snow, particularly at low developed to model the intergranular motion due to the

stresses. At higher stresses the necks undergo fracture, relative sliding between ice particles. The strains are

and interparticle slip becomes a significant deformation then averaged, over the representative particle to obtain

mechanism. It is this relative displacement between the the strains in snow.

particles which is responsible forstrains in snow at large Consider now a typical ice grain and the necks or

stresses. At these stresses snow behaves somewhat like bonds which connect it to other grains. To calculate the

other granular materials. The deformation of snow is stresses in the necks, a local coordinate system, as

therefore an averaged effect of the deformation of the illustrated in Figure 1, is set up at the contact point. The

unbroken necks avd of relative sliding between par- stress vector at the contact point or the ice neck is

ticles with broken necks. resolved into three components along the coordinate

A constitutive theory taking into account these de- axis of this local coordinate system. The unit vectors for

formation mechanisms has been suggested by Mahajan this coordinate system are

3

L/ '3'

"V2

e 2

Figure 1 .Coordinate system. 1-2-3 global coordinate system centered at the ice

particle center. se'-21-323neok coordinate system centered at the center of neck.

175
V I = cosa cosp e, + sin a sin3 e 2 - sin 5e3 The expressions for the various components as obV2 =-sina el +cosa e2 (1) served from equation (4) are

V3 = cosa sino el + sin a sino e 2 + cos 0 e3 . .e =(I+v). _ _

-1 ___ (7)

The stress vector in the necks, on the face with normal E E

n, is given by _ 1ic= d ( t

fz.(r)]-j-b "~' (8)

OATPP = a'te. (2) v dti( i 0 J 7 -

The vector n is same vector as V3 in equation (1) _ -(4 

above. AT is the contact area (neck cross sectional area), V 2

a is the grain radius, y is the solid volume fraction, and Instead of directly solving the integral in equation

P is the probability function which determines the (8), Szyszkowski and Glockner (1987) have approxiprobability that a point on the surface of a grain is also mated the equations (8) and (9) by a generalized Kelvin

located on a neck. body in series with a nonlinear dashpot. The equations

The components of stress on the face with normal n for the Kelvin body are written as

are given as:

Oi3= Vi "d (3) lf- = ij7y (10) VI

If averaging is done over the contact area lying (oij'r + c oiij' (oij)n- = E le-f (no summationX 11)

between the solid angle imbedded by angles a to a+Aa

and 0 to VA-, we obtain 'ij" +oiij = iij, (12)

jý+p a a where °iJ !s the effective viscous stress tensor defined

AIa [ot+Aa tnivE sin Otdo above, oij is the romponent of effective stress in the

(01i3)av = .aspring and aij"is the component of effective stress in the

f+Ao j ra+A a dashpot. The value of the constants v1 and V2 depends J au ATO on the stress in the necks. If the principal tensile stress

in the neck is less than 0.7 MPa the constants Vt and v2

A constitutive law for ice is now needed in order to havevaluesof 10.8 and235, respectively. Otherwise, V2

find the strain in these necks. This constitutive law is is equal to 5040. The values of the constants for two

based on the theory developed by Szyszkowski and cases are different because the deforming mechanisms,

Glockner (1987) and are given by the following re- as explained in reference (1), are different. If the maxilations mum principal stress in the necks is less than or equal to •=- (1 + V) •. E kk Sij + 0.7 MPa, superplastic deformation occurs, whereas for

E E stress higher than this dislocation creep becomes preI [t,* (tr)]nj (t0- "r)& + (4) dominant.

V I dtj0 V2 The strains in the ice necks are next transformed to

the snow coordinate system by the equation:

where Eij = QTri e, Qsj- (13)

ij = sij {1.5 I -1 Q is an orthogonal transformation matrix carrying the

(5) local coordinate system centered at the neck to the

S2 = 1.5 sijsij, global coordinate system centered at ice particle center

(Figure 1).

In equation (4) v is the Poisson's ratio, E is the Young's If the principal stress in necks is greater than 0.7 MPa

modulus, j is the creep compliance, and v I and V2 are and principal strain exceeds 5 x 10-3, we assume the

material constants. sij is the deviatoric stress. The strain neck has lost the ability to carry principal tensile stress

rate is decomposed into elastic, recoverable creep and andtherefore fractures. Afterthe occurrence offracture,

plastic components, denoted as: deformations in snow are due to interparticle sliding.

The tangential and normal velocities and displacements

eij = &P + e& + &p (6) are calculated using the equation

176
i= cj (T) [t n - 1 (14) of stress exists. The method followed in solving this

problems in a commonly used technique for solving

C= c 1 (G)In- (i/8n) C2 , (15) problems involving creep of structures. This method is

closely linked to the elastic solution procedure. This

where t and Y are respectively the velocity and the relation between creep and elastic solutions derives

component of traction in the direction normal to the from the fact that, after initial loading, creep strains

grain surface at the neck. i is the tangential velocity, r arising during the passage of time require that stresses

is the component of traction in the shearing direction, change by elastic straining to accommodate these

and disp is the relative current displacement between changes (Boyle and Spence, 1983).

the grains at a particular time. The expression 1/3 The stress strain relation for an isotropic elastic

appears because, as the sliding displacement increases, material is

the particles form new contacts with other particles, and

this impedes further relative displacement. This seems Yij= X&r + 2 g~j,

to account for much of the strain hardening in snow. The

parameter m was obtained, using a regression fit, as a where X and gi are Lame's constants. We can write this

functioa of effective strain in snow. The constant c 1, in last relation as

equations (14) and (15), has a value of 3.906x 10- 3.The

constantc2dependsontheratioofshear to compressive afij= X(ekk - ekk) 8ij+ 2 t(eij- dzj) (18)

stress at the point of contact. If the absolute value of the ( -x-- ýgk agi pj

ratio of shear to compressive stress is less than 0.5, then i - 8ij + + 2 e .

c2 is equal to 0.3. Otherwise it has a value of 0.40. The aXk 1 axj axi

constant n has a value of 1.8. The parameters Ch, c2 and

m have slightly different values for tensile stress states. Substituting this into the equilibrium equation we obFor tension cI is 5.468 x 10-0 and c2 is approximately tain the Navier's equation

0.1. The strain rate is given by the expression

Eii=l(1i (sinS+ sj n).+ tninj). (16) i.(V 2uj)+ (X+ p) VjV iui+pbj= X dk+2 a2dxj aXi

si and ni are components of the unit vectors n and s, (19)

where n is normal to the grain surface and s is in the

direction of the shear stress r. The strain in snow is the For the case of plane strain, the reduced Navier's equaaverage of strain in all necks. tions are

(Eij)av l sinoUda = I EipsinpU lxdo, (17) 142U+ 1 a ( x+ - i)p2)] iO J iO J 0 L l-2v c•lax1 ax ax pb (20

where Eijsino3dctdI3 on the right-hand side is obtained

from equation (13) or (17), depending on whether it is V2 u2 + 1 a +U+ PU2+p 2

a broken neck or a neck undergoing superplastic defor- 1-2 v ax2 1 ax2Iax;]

mation. (Eij)av is the strain in snow averaged over the

solid angle. (1+v)(1-2v)ax 2 + x2 (I~~~~~~ v t ++)( 

NUMERICAL SOLUTION OF THE 2G (ý§2 + adi. 2 (21)

FOUNDATION PROBLEM Dax2 5x-1

It has been experimentally observed that for sym- The boundary conditions are:

metrical loading, the vertical and horizontal extent of Top face:

the deformation zone (pressure bulb) in a foundation

extends to about two times the width of the footing X 2 = 2.25 m Q = Q0 0 _ x1 •5 0.45 m

(Reed, 1966). For simplicity we consider a rectangular Q =0 x I > 0.45 m

area underneath the footing as shown in Figure 2. The txy = 0 0:< x ! < 0.9 m.

dimensions of this rectangle are larger than theobserved

size of the pressure bulb. Plane strain has been assumed Using the above relations in the constitutive relation

for this problem, and therefore athreedimensional state (equation 18) we have

177
ditions are solved using the finite difference method.

Q 2p (!I 2)-Cý+ X('d'i - ell)- XeS3, Central finite differences have been used throughout. A

X2 chi 1 (22) grid with mesh refinement near the top face has been

used. The problem was solved for two different values

+___ ! (23) of Qo, namely, 0.008 MPa and 0.1 MPa.

ax1 26i2 Although not obvious, these equations are time dependent. The time dependence appears because the

Axis of symmetry: creep strains in the above equations change with time.

au2 0 1 The first step in solving these equations involves findu 1=0 0 <x 1 <0.9m, x2=0. ing the elastic solution at time t = 0. For this the creep axI (24) terms on the right-hand side are set to zero. The stresses

from this elastic solution are then used to calculate the

Bottom and right vertical side: creep strain rates using the constitutive equation pre0 _ x1 : 0.9 m, X2 = 0 sented in the preceding section. Once the creep strains

u1 =0, u2 =0 andxl=0.9m,0 _<x2<2.25m. have been calculated from these creep rate equations, they are substituted in the above differential equations

(25) which are solved for displacements at end of time step.

The new stresses at the end of time step are next

If we substitute the boundary conditions for the top face calculated. Due to the rather complex nature of the creep

into equations 20 and 21, we obtain equations, it is not possible to use implicit methods to

integrate the creep strain rate equations, and explicit

Gr(I+ 1• •U + 1- 1 ))u2] methods have to be used. This, unfortunately, poses a

( - 2 V) ax 12 (1-2 x 22 big limitation on the size of time step. The grain data

reported by Hansen (1985) was used. Fora compressive

(- vI)( E+ l I) + M3 + stress of 8 x 10-3 MPa with a time step of 120 seconds,

(X1 x vX1i a steady state of stress is not reached even after 300 time

steps, although the rate of change of stress does exhibit

a decreasing trend. For instance, the rate of change of

2G (IO + - -- 2 1Cl2 (26) the largest stress decreases from 1.5 x 10-4 MPa/hr at

aX 2 ! 1- 2Iv x2 the beginning to3 x 10-5 MPa/hrby the 300th iteration.

Since this rate of change is small, it was decided to

G + 1U +( assume a steady state of stress after 300 time steps. G 1+ +1( (l 1 _2 2 pb2 For Q equal to 0.1 MPa there are regions under the

((I -2j loading where stresses are high enough to cause the

neck fracturing after a very small period of time. On the

Ev " (adi I ... 2 + M3 + other hand, there are areas away from the loading region

(1 + v) (a - 2 v) \-2 xx2 ax 2 at which the stresses are low enough that, according to

the theory developed, superplastic deformation should

2G - - 2 2 a), be taking place in necks. At the boundary of these two

(ax1-2v i(27) ax, areas, there are regions where ice necks, at a particular solid angle, have a principal stress of, for example, 0.7

The symmetry boundary condition, on substitution MPa at one grid point, and at the next grid point the

into the equation 20, acquires the form principal neck stress, for the same solid angle, is 0.705

G I+ -- Y2 + YU 1 +MPa. In the theory we have assumed that for stresses

pb2 less than or equal to 0.7 MPa superplastic deformation

(I - 2 v)ax--2 ax 12] takes place, whereas for stresses greater than this value

-. 61 + + + deformation is due to sliding of particles. Therefore, at

v) 1--2 a 2 axM,1the first grid point the neck is undergoing a superplastic (I + v) - 2 v) a1 ax2 ax2 a ) deformation whereas at the second grid point there is

2G ~ + 2 a.• ) relative sliding between the particles. This results in

2 +-2 discontinuous strain rates (because the strain rates for

\ax2 ax2 superplastic deformation and sliding are different) and

also leads to a situation where regions of low stress have

The above differential equations with boundary con- higher strain rates as compared to regions with higher

178
x 2 •

B-b5B

~~ 'N0-bn X1

Figure 2. Foundation with a stress of Q MPa. B .45 m.

Symmetry with respect to x, allows only half of the foundation

and snow cover region to be analyzed.

stress (superplastic strain rate at 0.7 MPa is higher than of decreasing, begin increasing and the problem besliding rate at the same stress). To avoid this discontinu- comes unstable, as indicated by large changes in lateral

ity in strain rates it was assumed that necks remain intact stresses and a decrease in vertical displacement instead

for the first fifty time steps, deforming according to the of an increase. It is possible that by use of a still smaller

creep law for high stresses. After fifty time steps all time step this problew can be remedied, but this would

necks were assumed to have broken, and relative sliding also result in increased t•rnputational time. This instaof particles was taken as the sole deforming mechanism bility seems to be associatet; with the strain hardening

for the whole problem. The solution becomes unstable in the constitutive equation becoming significant. Most

rzrher quickly if this assumption is not made. multiaxial creep problems are solved using implicit

At this load it was found that with a step of 120 methods, and even then a very short time step has to be

seconds the stresses continue to decrease, as was ex- used. So the instability with the use of the explicit

pected, for 150 time steps. However, after that the high method for strain hardening problem is not surprising.

stresses change negligibly, but the low stresses, instead It was decided to take the stresses at the end of 150 time

179
.z ,w

"1.00

2.00-

:: . : -. : . . - . -..........-

1 .7 5 ::::::::::::::: ...........

0.80

0.70

.....- 0.60

0.50

1.00 __ _0.40

0.3

0.0.20

0.50 0.10

0.00

0.25....... .

-0.10

0.00 -- 0.20

0 0'0 0 0 0 0 0 0 -0.30

x (meters) -0.40

Figure 3. Normalized stress contours by seven hours for Q = 0.008 MPa. The stresses were

assumed to have reached a steady value at this time.

steps as the stresses to be used for all future time steps. A steady state of stress was assumed to have been

By imposing this restriction we are violating the equi- reached by seven hours. From these it becomes apparent

librium equation. However, the change in maximum the stresses are much higher closer to the axis of

stresses by the 150th time step are small and this symmetry and fall to a very low value as one moves

assumption was considered to be reasonable. away from this axis. Also, the stresses beneath the

For low compressive stress of 8 x 10-3 M[Pa the loaded area at 1.8 m from the surface are about 65% of

normalized vertical stress component (stress/(8 X 10-3)) the stresses at 0.45 m from surface. Figure 5 illustrates

contours are shown in Figure 3 and the displacement the stress distribution along two vertical sections. For a

contours at the end of sixty hours are shown in Figure 4. section at the axis of symmetry the stresses first de180
2.25 0.00

-0.01

2..00 -- 0.01

-0.02

1.75 --- 0.02

-0.03

1.50 -0.03

1.25 _ _-0.04........ 0

~ 1.25-0.04

(U

S.....-.- -0.05

0-0.05

0.7 . -0.06

F.: .... •...°. -. o.-....

% , .- 0.06

.- 0.08

0.50 ........ .... ...... ..- 0..09

..-.. .. . . ... .. .. .. . -.. -.... ...-- .. .. . .. . .. . .. . *mm * .. . %.. °.. °..

.. .. . ........ ...... .. -.... .....

0 0 0 0 0 .. 0 00........... -0.09

..................... m• m.. ... .... ...--.

-0.108 Figur 4. i , e comour , by sx " o.'s. - Q 0M .

effect graviy of is almost hal thevalue acu-n- ha tsq of at e0 th been the aplie bto -uch.vale.. wu maximumvertical-.'.placment.is-0.1.cm..The.maxi

thebotom slyboui25uloer tha thspaceet ascto mlzesrsscontours and dislacmen contour are000

alonge axish ofsmeigtadtry, probblsecas the stresses shownin Figure4is tand 6ee 7etia respeactielymTent stressigesti

hoere tagan atres largl dhe top thetof weAt sno.5 mfrom the seton righalto underI thegrvt footing shwaairop

181
1.00-

S0.80-

•-.Xl=0m

., 0.60-

" 0.40 - -xi-0. 5 m

0.40

0

• 0.20-

0.00

0.00 0.50 1.00 1.50 2.00 2.50

x2 (meters)

Figure 5. Stress distribution along vertical section at the center line and 0.5 mfrom the center

line. Q = 0.008 MPa.

within the top 0.50 m. The stresses at 1.6 m are 20% of on the microstructure and the various constants used do

the value at the top. This is consistent with experimental not have to be changed when the grain size or bond size

data (Reed, 1966) according to which the pressure bulb changes. The theory is also able to model strain hardenextends to about two times the width of the footing. ing in snow due to increases in the 3-D coordination

Since gravitational effects are insignificant compared ..,,tber with increasing strains. However, no attempt

to the applied load, the stresses at the bottom are less has been made to model strain hardening due to metathan 10% of the values at the top. This is in sharp morphic processes which are active during deformacontrast to values at the bottom for Q equal to 8 x 10-3 tion. Since we are concerned with short duration deforMPa, which were almost 75% of the values at the top. mation, the latter may not be important.

Figure 8 shows the stress distribution at a section 0.45 Presently, there is not much data available for comm from axis of symmetry. This shows a fairly constant parison with the example given here. The data presented

value for stresses from top to bottom. The displacement by Reed (1966) and used by Dandekar and Brown

contours in Figure 8 show that major displacements are (1986) for comparison of their results is for long term

largely restricted to about the top 0.9 m of the founda- settlement of foundation. The general behavior of

tion. The gradients in vertical displacement were more Dandekar's result was in agreement with the data pregradual for 8 x 10-3 MPa than for 0.1 MPa. The sented by Reed. The stress distribution determined with

maximum displacement at the end of 30 hours was 0.57 the theory presented here matches closely to that precm. sented by Dandekar and Brown.

The present theory does suffer from drawbacks of

excessive computational time and instability of the

CONCLUSION solution once strain hardening becomes significant.

This problem may be remedied, as has been suggested

In this paper, a constitutive theory developed earlier by Mahajan and Brown (1990), by the use of invariant

was applied to solve for the settlement of a snow theory. The data required for determining the various

foundation subjected to a uniformly distributed load on constants in the invariant theory can be obtained from

a part of its top surface. The constitutive theory is based the present theory.

182
2.25 - .1.00

. . 0.95

2.00 L 2'... 0.90

0.85

1 .(J .0.80

0.75

1.50 .. . . 0.70

..... .... .... 0.65

1.25 *0.60

0.75........................o4

0.25.... .05

0.0 ... I... .. 1

1.00 0.505

0.00

0.7 (mtr) 00

Figre6.Nomaizd .sres .... us .y.fvehors.o... .1 M0.Te.tese ee0su e

to ~ ~ .haerahda.tayvle.tti .. . ie. .

..... . . . . . .183
2.25 . . .. 0.00

2.00.. . . . 00

* .... 0.1.

Ni -0.20

.. . . . . . . -0 .15

'~1.500

-0.20

05............................. -0

0.25.............................. -0.

..... ...... ....- 0 .50

0.00 -.... .... ... .... ...

0.7 (m eters).. .. .. .. -0.60

Figure... 7.Dipaeetcnurbytiyhus.Q .... 0.1M a

....... ..8. .. ... .
1.00-

" 0.80-

., 0.60 X-=0m

' 0.40-

o 0.20- X1= 0.5 m

0.00- I I I

0.00 0.50 1.00 1.50 2.00 2.50

x2 (meters)

Figure 8. Stress distribution along vertical section at the centerline and 0.5 m from the

centerline. Q = 0.1 MPa.

ACKNOWLEDGMENT 131-138.

Kerr, A.D. (1962) Settlement and Tilting of Footing on

The work reported here was conducted under spon- a Viscous Foundation, CRREL Research Report 81.

sorship of the Geosciences Program ofthe United States Mahajan, P. and Brown, R.L. (1990) A MicrostrucArmy Research Office. The authors wish to express ture Based Constitutive Law for Snow, submitted for

their appreciation of ARO's support. publication.

Kanatani, K. (1981) A Theory of Contact Force Distribution in Granular Material, Powder Technology, Vol.

LITERATURE CITED 28.

Mellor, MA. (1974) A Review of Basic Snow MeBoyle, J.T. and Spence, J. (1983) Stress Analysis for chanics, in: Proceedings of the Grindewald SympoCreep, Butterworths. sium, IAHS Publ. 114, Grindewald, Switzerland.

Brown, R.L. (1979a) A Volumetric Constitutive Law Reed, S.C. (1966) Spread Footing Foundations on

for Snow Subjected to Large Strains, CRREL Report Snow, CRREL Report TR-175.

79-20. Szyszkowski, W. and Glockner, P.G. (1987) ModelDandekar, B.W. and Brown, R.L. (1986) A Numeri- ling the Mechanical Properties of Ice, in: Proceedings

cal Evaluation of Flexible Footing into Uniform Snow of Sixth International Offshore Mechanics and Arctic

Cover, Cold Regions Science and Technology, Vol. 12, Engineering Symposium, ASME.

185
MOBILITY SNITA BARBA CALIFORI JUNE 1.9CU) COLD

REGIONS RESEARCH AND EHNINEERININ LAD I•NmR H4 CIASSI.NIEI IFIED S L BLAISDELL JUL 93 93-17 XA-CRREL H.

I7

~zmn ~- -
AIMo

Association for Information and Imago Management

1100 Wayne Avenue. Suite 1100 N

~i.bSilver Spring, Maryland 20910 4- k

Centimeter

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 mm

1 2 4 5

Inches 1.__ OQ C1.8

1111_L1252

J hn6

Ill2 11111&.4 40 go.

MPNUFPCTURED TO PIIM STANDPRDS

0, BY PPPLIED IMPE.. INC.
Snow Characterization for Traction Testing

A Survey of Techniques Used

SALLY SHOOP

U.S. Army Cold Regions Research and Engineering Laboratory

Hanover, New Hampshire 03755-1290

AND

RUSS ALGER

Institute of Snow Research

Houghton, Michigan 49931

ABSTRACT

A variety of techniques exist for the characterization of snow for vehicle mobility or tire

traction testing. Snow surfaces that are used for testing are either natural or groomed and vary

widely in strength and texture. To complicate the situation even further, tire testers perform

their traction tests in a number of different manners.

Snow characterization methods are discussed and the various techniques presented. This

paper is the start of what hopefully will become a broad survey of most of the testing and

characterization methods used by the several tire testing companies that perform these tests

on a routine basis.

This work is part of an ongoing effort between USACRREL and the Keweenaw Research

Center.

1. INTRODUCTION tire testing community. The system must be easily used

but still offer enough information about the engineering

Commercial tire designers and the research commu- properties of the snow test surface to make the final

nity have been involved in the testing of rubber tires in product useful to the entire group.

winter environments for several decades. These tests Since each group has a specific method for performhave evolved into several measurement techniques that ing tests as well as preparing test surfaces, documentaare used by each group by preference. Tests range from tion is of primary importance. This is sometimes difficomparisons made by highly trained drivers in standard cult, however, when working in a cold environment but

commercial vehicles to high tech instrumented vehicles must be carried out with diligence to make the results

designed to measure the traction characteristics of a useful to all of the groups involved.

given tire. These testing techniques are designed to Finally, a willingness for all of the groups concerned

optimize the traction afforded by a new design over a to disseminate their results into the proper channels to

previously accepted one. allow it to be useful to both researchers and designers is

a necessity. This is sometimes difficult, especially in the

commercial world due to proprietary rights.

2. DESIRED OUTCOME

In order to make use of the data collected by the 3. CHARACTERIZATION METHODS

various testing and research groups it would be advantageous for a system of measurement for snow charac- The engineering properties of hard packed snow

terization to be standardized and used throughout the surfaces as well as virgin snow layers are documented

186
in many ways. Methods as simple as measuring tem- 3.2 Free water content

perature and density are probably used more than more Until recently the measurement of free water content

sophisticated techniques such as bevameters and instru- was a cumbersome and time consuming process. Liquid

mented vehicles, although these have become more water content was determined visually or measured

common in the past decade, using one of two different types of calorimeters.

The various measurements that are commonly used

and will be discussed briefly here are temperature, 3.2.1 Visual observation

density, strength, hardness, grain size, structure, meta- The relative amount of liquid waterpresent in a snow

morphic state and free water content. pack can be observed grossly by simply picking up a

handful of snow and attempting to pack it into a snow

3.1 Temperature and density ball. If the snow is dry it will not form into a ball. Snow

These two parameters are probably the simplest of of medium wetness will hold together loosely and very

all to measure in the field and do not need to be wet snow will form readily into an ice hard ball.

elaborated upon to any degree. They do have their place A second method used to visually determine the

as a representation of the characteristics of a packed relative wetness is to sprinkle the srnow with Fushin

snow surface, but do not by any means totally describe (Rosanalin Hydrochloride) powder which is a dark

the test layer. color when dry but turns a bright pink when it comes in

contact with liquid water.

3. .L Temperature

Temperature can be measured by use of a simple 3.2.2 Freezing calorimetr.

probe or by use of a number of thermocouple or ther- Freezing calorimetry is used in some instances, but

mistor type meters and probes. The temperatures mea- is probably the most cumbersome of all methods. A

sured are normally done in a profile through the thick- calorimeter bottle with a temperature ,irobe installed is

ness of the layer. Temperature profiles can give an idea filled with a fluid such as silicon oil at a temperature in

of the probable "wetness" of the snow surface and can the range of-75°C. Dry ice must be used to keep the oil

also give a very crude relationship to strength when at this temperature. A sample of snow is added to the

coupled with a density measurement. A minimum of air cold fluid and the temperature of the mixture is recorded

temperature and snow temperature should be taken for overaperiodoftimelongenough toensurethat all of the

shallow snow, whereas a profile of snow temperature free water present has frozen.

measurements may be required for deep snow. From the temperature measurements, the amount of

energy removed by the mixture and thus the amount of

3.1.2 Density free water frozen can be calculated.

Density of comparatively soft snow layers can be

measured using a number of commercial snow density 3.2.3 Melting clorimetry

kits which are marketed by several different companies. In recent years, melting calorimetry has become

These kits range from large elaborate systems to small more popular due to the fact that the equipment needed

scoops and scales that can be carried in a fanny pack. is much more compact and is easier to use.

Each is probably special in some way but all of them are Melting calorimetry works much along the same

used in essentially the same manner. A sample of a lines as freezing methods. The difference is that the

known volume is taken from the snow and the weight energy taken out by the mixture is used to melt the ice

measured on a scale. present instead of freezing the water. Alcohol is the

In very hard surfaces a cut section is used to deter- fluid that is normally used for this process. Tests are run

mine the density. For this method a sample of snow is at the freezing point of water and therefore no special

cut from the surface using a small saw or knife. This provisions need to be made to keep the alcohol exsample is then trimmed using one of these tools or tremely cold. A simple water bath suffices for this

possibly a plane to some measured dimension and purpose

weighed. This method is somewhat difficult, however,

because it is often not easy to cut and measure a perfect 3.2.4 Moisture meter

block of snow. The newest method of determining the liquid water

Densitycangiveacrudeindicationofstrengthandor present in snow is a capacitance meter that is easily

hardness of the hard packed layer and when used with operated and quite accurate (Boyne and Fisk, 1990).

temperature is better than taking no measurements at This gauge consists of a plate that is plac ý; on the snow

all. and a small meter used to measure the capacitance. By

187
taking a reading in the air and one on the snow surface, 3.4. / Cone penetrometer

the free water content can be easily determined. This The cone pernetrometer is a probe that was designed

method does not require any special fluids or bulky originally for use in soils as a tool to measure mobility

equipment and could easily be carried in a back pack. properties. It was designed by the U.S. Army as a tool

that could be used easily in the field and would give an

3.3 Crystal structure and metamorphic state indication of the trafficability of a soil. The instrument

3.3.1 Cr.stal size and shape is generally composed of a 30' cone with a crossThe size and shape of the ice grains that make up a sectional area of 1/2 in2. This cone is pushed into the

snow pack have an influence on how the pack acts as a medium at a constant rate and loads are read from a

whole. Large rounded crystals tend to roll past each proving ring at a constant interval that is usually the

other while small angular crystals tend to pack tightly depth of penetration. There have been some variations

together when loaded. These properties have a marked of this device, namely changes in size of the cone to

influence on results during mobility exercises. account for different material stiffnesses.

Crystal size and shape can be easily documented by Several indices are obtained from the use of the cone

use of a standard magnifying glass and ruler. Small that can be related to the characteristics of the medium.

lenses with measurement grids are also available com- The cone has been used in snow for several years and is

mercially for this purpose. used in the same manner as in soil. Although it was

originally designed for use in soils it has had success in

3.3.2 Metamorphic state some types of snow packs.

The stage of metamorphic change that a snow pack

has achieved can have an influence on how it will react 3.4.2 Rammson,.'e

when trafficked. Freeze thaw cycling for instance can The rammsonde is a cone device similar to the cone

change the strength characteristics of the snow consid- penetrometer although the standard ramm cone is much

erably throughout a very short period of time. Metamor- larger than the cone on the cone penetrometer. The

phism affects the shape, size and bonding of the crystals major difference between the two devices is that while

and therefore affects the strength characteristics as well. the cone is pushed into the material the ramm is driven

Ice lenses within a virgin pack can also trarkedly using a drop hammer. Generally a complete ramm setincrease the strength of the system. up will have two different sized hammers along with a

Determination of the metamorphic state is a science hammer slide and several lengths of rod that connect to

in itself and cannot be explained in detail here. It is the ramm cone for use in deep snow packs. To perform

sufficient to say, however, that there are several differ- a measurement the hammer size and drop height are

ent guides and manuals available to make it easy to determined according to material hardness. The cone is

make the necessary characterizations (see Colbeck et al then placed on the surface and the hammer is dropped a

1990). measured distance. The penetration is then measured

and the process repeated until the desired profile depth

3.4 Strength indices is obtained.

The strength characteristics of a snow pack are For the most part, this instrument has been used in

probably the most important parameters that can be deep packs such as in avalanche zones and in the Arctic

measured during a mobility test. As they are very and Antarctic to obtain hardness profiles through deep

important to the outcome of a test, this measurement is layers of snow.

also the most difficult to obtain with any degree of

accuracy and is probably the area of most disagreement 3.4.3 Canadian hardness gauge

between members of the snow testing community. The Canadian Hardness Gauge is a small plate sinkSome of the problems associated with this measurement age type device that is designed to be carried in a pack

include the question of what rate to perform the test at, in the field. Its major use has been in the area of

what size probes or plates are optimum and how to avalanche prediction and is best used in hard virgin

perform a measurement that takes into account the snow. Plates of various sizes can be attached to the

slipperiness of the surface. instrument and pushed into the snow. The resistance to

Since there are a number of manuals and references penetration is measured on a gauge that is built into the

to each of these methods of measurement, each will only instrument handle.

be discussed briefly here. The list presented here is not

intended to be a complete overview of all of the tech- 3.4.4 Plate sinkage

niques available but more a listing uf the more common The plate sinkage test is used to measure the bearing

methods. capacity and compaction due to loading of a snow pack.

188
Plates of various diameters are pushed, normally hy- or SMT. This tire is used as the reference for perfordraulically, into the snow and the load and sinkage mance of all other tires tested. The performance of this

measured constantly throughout the test. SMT in a given snow condition is used as the primary

The plate sinkage test is most commonly used in means of characterizing the test surface.

conjunction with an annular shear test. These two tests Several different measurement devices and systems

comprise the bevameter and result in the "Bekker" are used in conjunction with the SMT. As mentioned

values used in mobility analysis. earlier, these can consist of tow behind trailers or

dynamometers and instrumented vehicles.

3.4.5 Shear tests The follow on work to this paper will be a study of the

Shear strength of snow is measured in a number of common devices used in the industry and by researchdifferent ways. The shear annulus generally associated ers. This work has been done in the past, but with recent

with a bevameter is used to measure parameters that advancements in measurements and techniques, an uprelate to the shearstrength. This device is normally used date should be of interest to the testing community.

with either a rubber faced annulus or a grousered

annulus. The rubber annulus gives an indication of

shear force afforded by the surface snow crystals to a REFER!FNCFS

rubber surface. This vaiue gives an idea of the interface

shear between a rubber element such as a tire and the 1. R.G. Alger (1989) Shear and compressive strength

sr.ow surface. The grousered annulus is used to measure measurements of snow using the bevameter. In First

the inter-granular shear that is present when shearing International Conference on Snow Engineering, Cold

takes place within the snow pack (Alger, 1989). Regions Research and Engineering Laboratory, Special

Other types of devices have been used to measure Report 89-6.

shear strength with limited success. These include the 2. M.G. Bekker (1969) Introduction to Terrain Vehicle

vane and the vane cone. Systems. The University of Michigan Press, Ann Arbor,

Michigan.

3.4.6 Instrumented vehicles 3. M.G. Bekker (1956) Theory of Land Locomotion.

There are several different types of instrumented The University of Michigan Press, Ann Arbor, Michivehicles that are used by researchers and tire testers gan.

throughout the tire testing community. Some of these 4. H.S. Boyne and DJ. Fisk (1990) A Laboratory

instrumented vehicles are trailers that are towed by a Comparison of Field Techniques for Measuremont of

vehicle while others are trucks or cars that have been the Liquid Water Fraction of Snow. Special Report 90-

modified to measure the desired parameters. Most of 3, Cold Regions Research and Engineering Laboratory.

these systems have been equipped with onboard com- 5. S.C. Colbeck, et al. (1990) The International Clasputers, various load and torque measuring devices and sificationfor Seasonal Snow on the Ground. Technical

tire and ground speed measurement devices. Report MP 2794, International Commission on Snow

The Society of Automotive Engineers have devel- and Ice of the International Association of Scientific

oped a standard for the evaluation of dynamic tire Hydrology and the International Glaciological Society.

traction in snow that is followed, at least to some extent 6. J.Y. Wong (1978) Theory of Ground Vehicles. John

by most commercial tire testers. This standard requires Wiley & Sons, New York.

the use of a standard reference tire. In the case of snow 7. R.N. Yong, E.A. Fattah and N. Skiadas (1984)

testing, this tire is referred to as a snow monitoring tire Vehicle Traction Mechanics. Elsevier, New York.

189
6. NOVEL DESIGNS

191
Caterpillar Mobil-Trac System's Application To

Cold Regions Mobility Problems

DALE STEINKE

Defense Products

Caterpillar, Inc.

Peoria, Illinois 61629

This paper is designed to give you a quick rundown and obstacle bridging. Wheels give you high speed and

on Caterpillar's Mobil-Trac system, and the mobility mobility over hard, abrasive surfaces.

advantages it offers cold regions users. Particular em- These qualities make the Mobil-Trac system an ideal

phasis will be given to the CAT challenger tractor.. .A combination for cold regions with their challenging set

vehicle purposefully designed to take maximum advan- of unpredictable underfoot conditions: tundra, muskeg,

tage of the Mobil-Trac system. ice, snow, rocks, logs, adverse grades, and bare ground.

First, it's important to understand what Mobil-Trau So how come, you may be wondering, I don't see

is. Although it's been out in the marketplace for several Mobil-Trac zooming all over the Arctic? One reason is

years now, we still find people who think it's just that Caterpillar looked for the biggest sales opportunity

another rubber track. That.. .it definitely is not! to get started in. It was agriculture. Low ground pressure

Caterpillar has long been a leader in the development meant earlier tillage and less root compaction for higher

of elastomer or rubber products. This surprises a lot of crop yields per acre. And the combination of high speed

people, but the fact is most of the equipment we sell runs and drawbar pull reduced fuel consumption and other

on rubber, not track. operating expenses. The farmers love it!

For example, Caterpillar has become the world's The other reason-I think-is that operations in the

largest manufacturer of high pressure hydraulic hose. remote cold regions where Mobil-Trac will really shine

We manufacture over 2500 miles ofthe stuff every year. tend to be governmental in one form or another. ProWe got into the business because of all the downtime curement lead times are often very long, and frustrating

our customers were experiencing due to hose failures. for vendors.

You might wonder what hydraulic hose has to do with Over the past few years, Mobil-Trac has accumumobility, but bear with me a minute. lated millions of hours in the field, mostly on the

CAT XT hose is uniquely superior due to the way Challenger where some farmers are still using their

layer upon layer of metal wire is bonded into the rubber. original belts after 20,000 miles.

The manufacturing technology has remained a closely The Challenger 65B (Figure 2) is a 285 HP tractor

guarded secret. The wire provides tremendous strength weighing about 32,000 pounds bare. Fully equipped for

while permitting a high tolerance for flexing under load. arctic service (Figure 3) with dozer blade, winch, power

Perhaps predictably, someone eventually wondered: train guards, and heavy duty, studded belts, etc., it'll

"gee, what if we made this stuff into a track belt?" weigh close to 36,000 lbs (close to the weight of a CAT

The Mobil-Trac belt that developed is shown in D6 dozer). It has a 10-speed, powershift transmission

Figure 1. In a cut away you could clearly see how the and can travel over 18 mph. It's amazingly simple to

composition is similar to the XT hydraulic hose. It's operate. If you can drive a truck with an automatic

very tough stuff. The advantage of this track is plain to transmission, you can hop on a Challenger and drive

see: it opens the way to enjoy the advantages of both away. It even has a conventional steering wheel.

track and wheels, all in one neat system. As you prob- An important feature of the Challenger is the fact that

ably know, track gives you low ground pressure, stabil- it steers differentially. This means that live power is

ity, high drawbar pull, low forward motion resistance, maintained to both tracks at all times during turning

192
Figure 1. Detail of Mobil-Trac system.

Figure 2. Standard Challenger tractor.

193
AV1

Figure 3. Over snow model Challenger.

194
THIS

PAGE

IS

MISSING

IN

ORIGINAL

DOCUMENT
Fi.Vtirc I I Irira-Track instalh'd on a conventionual pickup tru( k operatiton oi the north slopt olf/Alaska.

and highwavs during weekdays and go off-road on the vehicle, even on snow. sand. or mu1d has the same

weekends. payload capability as a vehicle running on wheels.

"People get the cost benefit of buving a standard. Because each revolution of a track's sprocket moves

mass-produced vehicle." Barbieri said. "Somebody a vehicle ahead 60 inches, the vehicle w ith Ultra Track

building a special purpose tracked vehicle does not have units has a two-to-one mechanical advantage over

that economy of scale." wheels. This means there is twice as much power from

Imagincering has painstakinglydeveloped and tested the engine and less wear on the drive train.

the Ultra Track during the past five years. Now that the The Ultra Track has many applications. A fourtrack's performance and durability are assured, the wheel-drive vehicle equipped with these novel units can

Seattle company is ready to begin manufacturing the be used for:

units on a production basis. "People can buy the Ultra - Weekend Recreation. Off-road enthusiasts, can

Tiak in kit form or a, a ,omplete unit." Barbicri said. head tu ;he hil!s or ,iak,- a beeline forthe beach

The full assembly from the factory includes a spring and simply switch from tires to tracks when they

package for raising the height of the vehicle so that there leave the roadway.

is proper clearance between the tracks and vehicle -- Ranching and Fafmin,. An Ultra Track pickup

fenders. Also included is a step for each side of the can carry livestock feed. fence-mending supraised cab. A list of off-the-shelf hardware and a de- plies and the like across all terrain and in all

tailed set of assembly prints can be purchased from weather.

Imagineering. The Oil and Gas industr'. Surveying. pipeline

Once the kit is assembled into four track units which maintenance and ferrying men and supplies tooil

adapts to most 3/4-ton and one ton four wheel drive pumping stations and drilling platforns are easvehicles•, it has an unloaded ground pressure as little as ily performed with Ultra Track units.

one and one half pounds per square inch. depending on -- Construction Work. Construction in rugged. revehicle size and make. As a result, a track-equipped mote areas is simplified when workers and sup199
plies can be delivered in cost-saving, conven- be air dropped by using the low altitude parachute

tional pickups rather than special -..'pose, lim- extraction system.

ited-use vehicles.

- Ski Resorts and Parks. Ultu Tracks can be used Reliability

for transporting personnel, grooming lower Because it has been designed from the ground up, the

slopes, planting slalom flags and performing HMMV represents the latest state-of-the-art in RAM-D

search and rescue work. (Reliability, Availability, Maintainability and Durabil-

- Road Maintenance. A four-wheel-drive vehicle ity). The Ultra Tracks have gone through extensive

eq.p,, ,ed with Ultra Track units can keep high- testing in the Arctic of Alaska and the Cascade Mounways and back roads open by plowing through tains in Washington. The addition of the Ultra Tracks to

snow. the HMMV makes it one of the lightest track units with

- Military Missions. An Ultra Track vehicle can the largest payload per tracked vehicle weight that is

carry men, supplies and equipment in support of available which can be used both as a wheeled or

various field exercises and deployment, tracked vehicle and is most cost effective.

Barbieri said Imagineering has received several mili- In March, 1983, AM General was awarded a contract

tary and commercial application inquiries from around to manufacture the HMMV (a high mobility multithe world where remote areas and rough terrain are in purpose wheeled vehicle).

abundance. Getting supplies to gold mines is one pro- After watching trial runs in 1985 at the Nevada

spective use in Alaska as well as Canada. Automotive Test Center operated by Mr. Hank Hodges,

Imagineering, Inc. started doing preliminary work to

mount the Ultra Tracks on the HMMV.

APPLICATION TO THE MILITARY HMMWV Imagineering, Inc. made a proposal to the Skunk

Works (ADEA) at Fort Lewis, Washington to do testing

Versatility of the Ultra Tracks mounted on a HMMV. Tests were

The AM General HMMV has been designed to concluded in 1988 after eight months.

accommodate 26 configurations and can be adapted to

mount a variety of electronics and communications Mobility

systems to support various (command, control, commu- The HMMV's exceptional cross country mobility

nications and intelligence) functions. With the addition results from its 16" ground clearance. The ground

of the Ultra Tracks, one more configuration has been clearance goes to 26" and the width to 8'0" increasing

added to the expanding list. stability whenthe HMMV isequipped with UltraTracks.

The gradeability is 60%; side slope is 40%, speed (level

Weapons Systems ground) is 30 mph, 60% grade at 6 mph and with a gross

AM General designed the basic vehicle as a platform weight of 9200 pounds. The nominal ground pressure

which can be readily adapted to a wide range of weap- (no sinkage) is 2.11 psi. With 4" of sinkage, the ground

ons systems to meet specific military requirements. pressure is 1.59 psi which allows the HMMV to be used

in sand, mud, tundra and snow where other tire units

Transportability cannot go. The changeover time is around two hours.

The low 5,400 pound curb weight of the 1 1/2 Ton

HMMV with attached tracks can be airlifted to tactical Survivability

heliborne operations. The C-130 transport holds three The survivability of the vehicle in combat is enHMMVs, the CI41B holds six and the C-5A holds hanced by the low silhouette (only 69" with tires and 79"

fifteen. In tactical strikes, the tracked HMMV vehicle with Ultra Tracks). It can accelerate from 0- 15 mph in

can be transported by the UH60A, the CH-47 and the 10 seconds, from 0-30 mph in 30 seconds and has a

CH-53 helicopters. The AM General HMMV can also range of up to 150 miles.

200
The U.S. Army's Bv 206 Oversnow Vehicle

URBAN LUNDBERG

Hagglands

35414 Mound Road

Sterling Heights, Michigan 48310

BV 206 OPENING UP A NEW DIMENSION OF Marine Corps, National Guard (NG), and NASA. The

MOBILITY IN ALASKA'S DEFENSE LINE National Guard unit in Alaska is the primary NG user,

but some vehicles will also be sent to NG units in North

Since 1969 when the Ml 16 squad carrier was turned Dakota, Vermont, New Hampshire and Maine.

in, U.S. Army units in Alaska have had an urgent need The key to Hagglunds success in marketing the Bv

for a helicopter transportable all terrain vehicle to carry 206 is directly linked to the vehicle's mobility. It was

the maneuver elements' existing load, crew served like opening up a "new dimension of mobility" for the

weapons, and ammunition during crosscountry move- units in Alaska when the By 206 was introduced. They

ment, especially during winter-operation. Twelve dif- were pleasantly surprised to be able to use the vehicle

ferent varieties of vehicles were considered as potential during summer operation as well as winter operation

replacement for the Ml 16, but none met the basic and an availability factor of 96% was a complete new

requirements of mobility, experience.

During 1977-78, two candidate vehicles were iden- Getting an army where it has to be, when it has to be

tified; the Volvo Bv 202 and the Hagglunds Bv 206. In there, is no simple task, particularly in Alaska where

1978 the two units participated in a feasibility test roads are sparse and the terrain is often impassable.

conducted by Cold Regions Test Center (CRTC) in As recently as six years ago, when helicopterscouldn't

Alaska. fly, the deployment supporting artillery cross country

The test clearly indicated that the Hagglunds vehicle was delayed; food, fuel and ammunition went

was superior to the older Bv 202 and finally recom- undelivered; and casualty evacuation became slow and

mended to be procured for the units in Alaska. burdensome. Helicopters can be grounded up to 35

In 1983 the Tank Automotive Command (TACOM) percent of the time during the winter-bad news for an

located in Detroit procured 264 vehicles from Hagglunds infantry squad packing 3,000 pounds of cold weather

to be shipped to the 172nd Infantry Brigade in Alaska. gear, or an artillery firing team trying to push a howitzer

The quantity of vehicles was later increased to 304, to through a mud bog or snowdrift.

include vehicles for the NATO Land Forces in Europe The Bv 206 ushered in a new era in mobility for the

(25 to Germany and 15 to Italy). At the same time, 160 arctic soldier, increasing the infantry's winter operavehicles were bought by the Norwegian Army to be tional range from three miles per day to more than 20.

provided to the U.S. Marine corps as Preposition Ve- Designed for platoons operating in northern and

hicles in Norway. mountainous regions, the Bv 206 has "laid track" in

During 1984-86, the unit in Alaska expanded from exercises throughout Alaska and accompanied 6th Inone Brigade to one Division, the 6th Infantry Division fantry Division (Light) troops on virtually every major

(Light), consisting of three Brigades. That change re- out-of-state exercise since 1986. When operating as a

suited in an increased need for By 206s, and during troop carrier, the front cab seats six soldiers and the rear

1988-90 TACOM procured 770 additional vehicles to cab has space for 11. Backpacks and other equipment

be distributed to U.S. Army, U.S. Air Force, U.S. can be loaded on the roof rack.

201
In the pre-Bv 206 era, cross country movement of has a range of between 120 and 200 miles, depending on

Alaska's soldiers and supplies was possible only by the terrain. That terrain can be deep snow, thick brush,

aircraft or on foot. Resupplying units or towing howit- forests, muskeg or mountains-the Bv 206 cý n climb

zers with wheeled vehicles in the Alaskan interior was grades of up to 70 percent. Even rivers, streams and

virtually impossible due to deep snow in the winter and lakes are no match for the By 206: the vehicle is

nonexistent roads in the summer. designed for swimming operations.

"If we didn't have Bv 206s we'd have to carry all of In addition to infantry and field artillery units, the Bv

our equipment on our backs or on ahkios (sleds)," said 206 is used by medical companies here for casualty

CSM Sam Spears of the 1 st Battalion (Airborne), 501st evacuation missions. And just like the ground pounder

Infantry Regiment. "It would slow us down and make and the redleg, when you ask a medic what hisjob would

everything a lot harder." be like without the vehicle, the words "next to imposIn the six-plus years since becoming a part of the sible" are always part of his answer. "I'd hardly be able

Army inventory, the Bv 206 has not only made life to perform my job without the Bv 206, especially in the

easier for the infantryman, it's redefined the way field winter," said Spec. Scott Sumpter, a medical NCO with

artillery is employed in an arctic environment. The Alpha Med., 706th Maintenance Battalion. "It would

vehicle is the primary transport for fire support teams definitely cut our mission capabilities down to near

and survey parties, and is the prime mover of the 11 th nothing...it would be extremely rough."

Field Artillery's big guns. In addition to carrying troops Why is now this vehicle so fantastic? The secret lies

and equipment, evacuating injured soldiers and towing in the design requirement once generated by the Swedtwo 10-man ski patrols, the Bv 206 can pull light ish Army. How the Swedish Army uses the Bv 206 is

weapons such as the division's 105 mm howitzers, explained by Geijer (1988).

"Our job would be difficult at best; in some cases it

would be impossible without the Bv 206," said Lt. Col.

Joseph Leigh Jr., commanderof the battalion. "Because LITERATURE CITED

of its very light footprint, the Bv 206 can traverse

snowdrift-, with absolutely no problem.. .it's simple, Arctic Soldier, Vol # 15, Issue # 4.

even when overloaded with equipment, supplies, weap- Geijer, P. (1988) How ..... The Swedish Army uses the

ons, ammo, survival gear and a howitzer." All Terrain Carrier, Bv 206. Haigglands Vehicle AB, SWith a maximum road speed of 34 mph, the By 206 189182, Ornskoldsvik, Sweden.

202
The Flextrac MPV: A Novel Concept

In A Personal All-Terrain Vehicle

MARK D. OSBORNE

Senior Research Engineer

Keweenaw Research Certer

Michigan Technological University

Houghton, Michigan 49931

ABSTRACT

Personal vehicle mobility has entered a new age with the development of the Flextrac

Multi-purpose Vehicle (MPV). De% eloped in Scandinavia, the Flextrac MPV utilizes a novel

concept in vehicle mobility. Designed for one or two people, the Flextrac uses one single

track, consisting of 36 flexible sections to propel and steer the vehicle through deep snow,

sand and swamps. Because it does not have skis and slides as most current snowmobiles have

today, it is capable of negotiating non-snow terrain. The track extends the entire length of the

body and is considerably wider than snowmobile tracks, providing a light footprint and good

flotation, even in soft snow or soils. The low ground pressure also contributes to less

environmental damage than most vehicles. This vehicle was tested by the Keweenaw

Research Center (KRC), a research agency of Michigan Technological University (MTU),

over a wide variety of both summer and winter terrains, including deep powder snow,

swamps, sand and swimming in a pond. Several performance tests were conducted to

evaluate hill climbing capability, pulling capacity, acceleration, braking, towed motion

resistance, turning radius and fuel consumption over a wide variety of terrains.

The design concepts of the Flextrac MPV's undercarriage along with its performance

capabilities are discussed and presented in this paper.

This project was funded by the U.S. Army Tank-Automotive Command (TACOM) and

the U.S. Army Cold Regions Research and Engineering Laboratory (CRREL).

The opinions expressed in this paper do not necessarily coincide with those of the U.S.

Army or the Government of the United States and the information provided here shall not be

construed as an official endorsement or approval of this product or company by the U.S.

Government.

INTRODUCTION was funded by the U.S. Army Tank-Automotive

Command (TACOM) through the U.S. Army Cold

The Flextrac MPV, as shown in Figure 1, is a Regions Research and Engineering Laboratory

unique concept in all-terrain vehicle mobility. It was (CRREL).

tested as a candidate for the U.S. Army Mobile Over This paper is not to be construed as an official

Snow Transport (MOST) system by the Keweenaw Department of the Army position. Mention of any trade

Research Center (KRC), a research agency of Michigan names or manufacturers in this paper shall not be

Tech-nological University (MTU). The test program construed as an official endorsement or approval of

203
Figure 1. The Flextrac Multi-purpose Vehicle.

such products or companies by the U.S. Government. available for vehicle testing as well.

Any opinions expressed in this paper are solely those of The Flextrac vehicles were tested in several types of

the author and in no way reflect the opinions or endorse- snow conditions, on ice, in swamps. muskeg, sand, dirt,

ments of the U.S. Government or the U.S. Army. gravel, pavement, rough cross-country and in water.

The Keweenaw Research Center is located in ThispaperreviewstheuniquedesignoftheFlextracand

Michigan's Upper Peninsula on the Keweenaw Peniri- its performance capabilities.

sula which extends into Lake Superior. The effect of

Lake Superior can be seen in the fairly moderate seasonal temperatures and large annual snowfall (200 BACKGROUND

inches). The combination of a varied climate and the

Keweenaw's rugged terrain makes the area an ideal The Flextrac vehicle has been in development for

location for vehicle testing in all types of conditions. over 15 years. It was invented by a person in Finland

KRC has over ten years of vehicle mobility testing who workedon the original concept forabout ten years.

experience, mostly in winter conditions. The staff con- Approximately five years ago Indevex AB. a company

sists of mechanical and civil engineers along with in Sweden purchased all patent rights for producing and

technicians for vehicle instrumentation and computer- marketing the vehicle. Indevex AB now has 48 patents

ized data collection. KRC is acomplete engineering and on the Flextrac in the USA and several other countries.

test facility as components are designed and analyzed Indevex now markets the Flextrac MPV in Scandinavia

using finite element analysis, prototype components through Yamaha and plans to start marketing in other

can be fabricated in KRC's machine shop and then parts of Europe and the USA in the near future. The

tested in the laboratory and in the field on a vehicle. Swedish Army and Royal British Marines have been

KRC has a vehicle test course spread out over 500 acres using the Flextracs for over a year. The MPV is also

of leased land with several thousand acres of public land being tested in France, Canada and the USSR.

204
II;f, ita"tj ,i

FII .. \ RA \( IPN DESIG N FEATII RES Hie Flc\ttack NIP% IN poeyed b \ a1 )iat~h

a111-COOClei. sin-Cele caruretor 1% c~le L\~ Ciiie III ihoil

I lie nwinlue sinele nIh tmk, no ski &leici allos~ s thle Itnjectiont. It dex chipN apprii\iittatl\ -,- ftp). All III. filter

I: Ina %IIV to1 11.1% CiNC almoxst M 1% t\ pe (It terra ItI . It I N\teil x 1,N has be I NUdstNeL tOr Use III both k tIlter 111(1

IN dies ILictii as a1 xx ok-hors Nx PC ti~elit IIIII \ chile IL ICrn %ninc CINAN UVlrCOtiditiotIs. hiI t11e %% liter thle N% shIII LiNN festc

tile coIiinion i ccreaiiioiial snixitbeor xx heelcd all- Iapel element air filter- and inl ilsts stnnte 'klllcotdeiktiolts

xcicle'.( eela A-I V nIx plo I)in pua I thle I fillted lxx,17 o ae lnetfle.aeUsed toreticIlet dust ineesStaes.tion. toxx er is transferred fron thle enetnc ito tile 111iia

[mue 2detiostrte. tat heIletra NPV is aone dMi th0111i0h txxo~ 0 cot10n1o mokbILe 1n1x clt:ches in1to a

ort`, 11o inaticlcphctplII 1 xxldl-lce 1pc -a transmission. Thle tratnsmiissionl has txo lottra Iler. dCpeC1ILI! 12il on th IC IC1,1 rat ClItonlIitterIed. It Is Nd et-I xx ardlk Spe~ds. low, anld hlidh. asI \kxxie anetal 1Cll ad

uised to caIlrr\ 4fg I pwIlds onl thle \.ehiCle illd oxCl S00 XO exere. 'Fhe geain se t-~or foxx speedlhg tot qne

1101.i1d, 11 a1 sled. IDnritie certalin et at IKRC thle aplctos .-\ obleh chain drix~ eis used ito tratist er

Meta IPY carriedI twoA0ttlenl on thle \vehlicle and toxx ed pomc rtfront the traitsiulission tolthe final di.x e sprocket.

a xle \ itla failed tttoh.iloile pinl, additional keieht hlich dLin\ thle track. Figure - , htgahkttl

for a total s.led load of ovecr 1.(X)() ponnd11(s Otl a pMAcke etigine anid ~igurel 5ý is, a phiotograph of thle chalin drixe

Nitownitobile trail. aItd fuel tank inl thle lextrac MP\V.

The sro Uild press ure is, adwxrt ised at 01.0 psi itt tilie FThe boil p ri Iuppe arti ot ftcl MIPV has ain

utIIn nailed cOi d itII in and (-5 I pSI 'It thle rateilhtd l~LCOnd i- e ste rit II filled stai xostiac ra f or ca*irr\ tiltioni. [:\enl though this %clhiele Ikeigliso ovr 7M poundis tool kits or gear andL hmilraulic brakes. An electric start

ili thle intloaided state its relativel\ lot,\ groni ti1 preCssure kit is, also ax ailable as, ail option. Sftovxit inl [iicur 0 ate

is, a resul t oft thle siitle larve track whIch iN 23.0 Iniches thle storwce areas of thle Nil)\'

Wdx tieadi IX-1. 25 inches long (total length i. Thle largec'Fl rhtc boit'o I tilte [extrac NI P\ separates friotm the

track~~~~~~~~~~~ re arax lsinalwteFeta tianesv tde rearriacwe tltrough1 eig'llht bols for e&s\ I-l chicMle tiai-1 

%IPV to trav.erse various terrains \vith minimal damage tenane. Thcengtiine. tira~nntssnonn. atti final drive unit

to tile enixirontuent. xx hich is becomting a greater ioul- are all ninouimedil oitta itlitenal frame that is shld Into thle

centl thtese daiss. Shoxx kil Ill FH cure 3 is thle FHcxtraC s boilr thr1OikIuh thle foront ofIC the achinle. If there etct eris a

%kide track. nleed for nia jot otverhIatilS oil the p~oxxer tra]tltilte Corn1-

205
Figure 3. MPV's wide track.

Figure 4. Flextrac's engine.

206
Fjigul , 5. '1( 1 i I dri i c •sh ste an dfu'l tanit.

pletv p \l r r trin cmLan he. remioved easil% b\ sliding ttic most important tactors inl thle Elextrac WW'~Vs desimn is,

internal framec out of tile hod\. An external towk hitch i, thle fact that thle track alw the \ ehicle TO tunW il %iuthO

mlounlted onl thle F~raotthe vehicle through the bod\ and~ the use oft skis, wkhich makes it a multi-terrain % ehicle.

to le rintern al frameV. 'Tile concept of the inrternal tramie 'The track allows thisl, h is "fail" shiaped design \ý hich

I's LIIII(iqtI Inl that It Is, not found onl most snowknic''es. It allows expansion or contraction oit eacti sectioni. Wtieni

alsollas futuic possibilities thait are not inl produIc'i to turnine, to the rigeht for example, the right side of tile

suIch as 111u1,itine1 a wiinch or small sniowplowk to the track at thle front ot thle vehicle will Contract while the

front of thle \ chicle. Some four wheel ATVS use. sNosM left side, ýfthe same sections mill expanid. The track is,

p~lo\ss, and( since the Elextrac MPV has superior tract ion "Luided aroui d ttie undercarriagec through11 thle Use

as o cmpaed te AV. t culdbe ii ddiionl ueful track tut>,, inl tile center areas, of the track sections.Tli

I:atuirc of thie N1PV. area is, more rimzid as ttile outer section (Ot the track is, the

Althiough il theod% or Upper portion (if' thle E'lxtrac reet-onl of, "ceatest tlexibilit\x

MIA, Is di fferetit than most other vehicles, the utidercar- Thle unidercarria-e has a tubular steel frame to rý hich

riage and track %slci stem isTotallyv unique iii coincepit aind six bogci franmes are iiounited. Tile underIcarrTiac-e tramie

is, thle kC\ to superior %ehicle nilohilitvr AS njjieitiotIedj bolts thro-(u'gh thle b1ody to thle internal1 steel fra?2e inside!

beb te tile undec~karriage cakti he easilo. separatedl tront thelbod\ ahbccruichsju bbrotdb1l

hie \ chic ic hod\. Thie Utidercalrria-e COt"iststs V)fia t11.i1 1 heelsc, lor supportr of' thle track s\ stern. Thle hoe te

her~d been shr le fttiiiies. trac,,k ''nidi v, hels. ales auth,ý( ft V; :ire 'ittadchd to theuid crie fralICtie tiOuciL l 

NLsttPCtIitti0 C01t1ipolteits. at C01uii0itla~lVl oh steucl and ~otilposite sprins,- plates

'flie tralck Icotprisecl oft 36 Iidik dual sctons01, % IIA itch pt 1 ide litheOl ((tiEsICIseIsitoil ill thle CL11TCIten

lin1ked toe hie \ steel pills. Thlis is ver\ sittimlar Ill Ice ein (inide ýk helscl are nioutited to the I),)-itc 1tiep to a11il1tta\ tracked \chicle sIlits I pinltac IralllCs atid undrIcIarriage framte ti keep the track eCCI-

-Tlil. le tim.A k uiliteuial is dV 0V1lltposite t\pc p1.151k, tered both ott thle tippet antd IVmrcl sides of)te trC1,Ac.

Thatt I, prVlodtclK I )\ I)W. It I" iiolded ltVV fItial slia1Vc I are ý_cý heel-axle assCtiiIhh ucs are lo)Catc(h at the If1 (1nt and

Ill Sý%edeni Illlstie a &I'llŽdsiglitei miold!. ()ite the IVII ear V1th tick loop) to 1)1V\ life thle coFCllect r l k~iim o

20)7
1 (I,'tulr' 0~. Stohiuly (ItIw ('CIV tcit bIIc /1wd tl MMIP.

track miotion around thle ulndercartiaýce frante. Attached trame~s onneIIcte~d to thle un1ca11rg ialc throri11

it thle trou fthe t Utnde rc arri age tratine at a pivot poIntI [the '-onipo"Itete e vtiiAnd 111C hrýackct lisct too

is, thle track steering mechanism. This untit cotains attaých1 thIe unerariI to thIe hood ieieNsi le

ou ide mwhieels. bog e xk hiecks, and a wvheel-a\ le assenlbl\ ittdercarriaie separated ttottilrie t;ick

bu~t aIso pis otl oft oft he mlainl untde rcarri age frame. I h s.,

pivoting action is controlled by, a steerinw ann inki

vhIcis activated by the hiandlebars Mhen thle driver PERFORNIANCE OFI THE FLIXTVlR A( N1I'\

steers the velli te. By pivot ing this front Undercarriage

unit, tensiJon is applied to onte side Of thle veicleC track The Fles~trac IPV Is deNigited aIs~ a itI lit', %Ct:'Cle and

%% title it is compressed on tile opposite side. This alloký s not necessarily As al tecraioRIalI chicle. 'Ihe ch% C l is C

anl entire fjont onIe third of the track to turn on an amiee teas. v 55 itl a st itt siispcitsiot. It i, riot e \ccpt i 1,1all\ 1,1't

s,%rile thle teat two thirds stav strai htTtis alloss s thle as it has a top speed of about 35 ii1tplt 111i thliti- tis

track to steer,. The final drive sprocket drives tie traick teraits. I-lie ,cearinLc is lo%\ III both ritelos 1(,\tid higýht

fronm thle rear of the vehicle. Track tension is adjusted h% ratwe-,s. It hasl ec\eptioinal pmkcsr arid IIt týaIilt\ r11ost

tightenitng or- loosenitng a nut ott a shiatt it the tronit %kork carn be done in tire high raitee. It is teasible to)

sect ion of the undercarriave framte. This nut is attached assumeI that if differenlt ger iles, v.I rcUsed titre \ch11icl

to) a steel rod with a coil spring around thle shaft and tile Could still haveN plctttr Of lowý etd posse~r vet travel at

spring gvoes into a Cylindrical tube. The steel rod is also Speeds, upto 50m1ph. vet for mlost Oftile appl cat lorl's that1

attached to the front idler wheel-axle assembly. Wherr thie mlachinle was designied. speed is itot a reqn irerrtertt -

tile steel rod is extended ' pressure is applied to the tront KIRC tested thle Hextrac litt sevecral t\pes ofsttirs and

of the track through the front axle assembly causing an Otl ice. Onl ice thet Vehicle wýas SOIriCtess at difficult1 tr)

increase in track tension. Correct track tension is iteces- cotntrol (as just about atl\, vehicle is)I as tile Itaid plastic

sarv for propertrack guidance andldrivitng perforniance. track does not penletratte the ice. It ss as tested in deep

Shown in Figure 7 is a side view of the track. bogie powder snow-, onl packed sno% aid( oril deep. we t sitow.

208
7 NOW---

401!

~ _2_N
.:7* 44 j

, A~

It was also tested on one of thle most difficult terrains suspension systemn available onl Nsoknlo\\ i hs lotla\.

there is to traverse, at wet slushy snow with water Figures 9 and it) showk some of the snos% and vc t ter-rainl

underneath. The Hlextrac NIPV was able to traverse all conditions encountered by the NIPV durinL, te~stinc.

of these ty-pes of terrains evncr while Pullin,- at sled Onl snoxk covered slopes at Ilextrac s" bettel ikun11

loaded w ith 30() lbs. of cargo. In deep powder snowk the most snowmlobiles at climbling thle slopes. Ini one invehilCle feels unstable and requires developing a tech- stance we stopped a Flextrac \% ith at loaded sled halt \k a%\

niqUe for handling. Thle vehicle is niot as unstable as, it up a 1() percent slope and were able to resumeii clinihinel.

feels. As an experienced snowmiobile driver I felt that with about 4-6 inches of sNto\. onl the slope. Sioppirre a

the MPV was better at going, through deep powdler snowx snowmknobile onl the slope onl\ 1110\,%CLI thle \chicle to

than a snowmnobile. On a snowmobile the driver usuall\ sink in whbenl accelerarinue. When attemipring to back

has to build up speed and momentum to keep mlovIing down 1c. reverse thle skis becamne stuck in the snomw anld

because if he stops he has at difficult tinie getting started the snowmnobile had to be li fted and turned around, 'Thle

acailn. On thle Hlextrac MPV the drivercanl stop aridstart adv antage of the Flextrac is that '. hien rev erse is uise.d

aglain without at problem. Pulling a sled with weight in there are no skis ito dig inl and stop it- t'sall% Mien

it would be next to impossible for a snowmnobile (except c! imbing, a slope w.ithl a sno'.m mobile theC drIl Cer Ira' 1

for at wýide track) w-.hile the Flextrac has plenty of powker develop a lot of speed to be able to cl rub tire shIopc hilt

to do this. The samne can be said for deep. slsh, et there are times w.hen there is no room to at hurl clioii i 1

sni rk or snow wkith wNater underneath it. As for a Corti - speed to erlh niblte slope. In Figurle I I thle FIC'les ae NIPV

parr son to at four wheel ATV, there wvas an instance at' is shovw 11 climbingil a1 steep) snhr', eo\ lere slope.

1KR( where a lex trac had( to Pull at four whieel driveIrabrplantoedntiirsiacett ic

ATV through two foot deep vetc crystallinre snloss for conducted on siruos as %\,ell las other terrar i. ueI lext\1,

about 300( yards because the ATV just (lid nlot have thle %IlPV has at tlairls hlir-,l tossed Illotioll reistnNUce

irourud clearance or low. Uround pressure to sta\, on topl com1pared to mlos 1iklohs rICble. Fhis , In p~i1l due to)

of thle srl,.sspack. The Hecxtrac MlIV did niot slip atl all the laruic surface area of thle track. tre slsrof thle liti I,

b\.ile pulling the AT'Sin the sser snow. ( )n packed snov. and thle cuide %O heel anld boeje'I reel ss stern o'f t1re

(lie snuis ruobile is tasici did provsides a smoiother ride undercarriage. Alorug ssuili the Ili IuLh r1 t 'nw resnire

eve~n wkhile pulling a sled because rf the muore advanced inic Ficxtrac NI PV alir i as a ecr\ hlii7 dgbM arpllIjras 

21(0
- #A

lr 1 1-/ ( k ll/c 1 1t1t f j ili I~ )Il *Sll M) 411 Whiia hr ill htIt,' yrl,,i n

Figure IL. Flextrac climbhing a snow covered slope

211
4I

1tA

"" At

Figure 12. Flextrac MPV negotiating a paved slope.

capability on snow covered terrains. It is about twice the snowmobile or ATV to traverse but the light ground

drawbar pull of a common snowmobile. Speed and pressure of the Flextrac allowed it to stay on top of the

acceleration are sloweron a Flextrac than on a common weak strength terrain. One of the most impressive

snowmobile but braking is better on the Flextrac. This attributes of the Flextrac MPV was its ability to be

is due mainly to the high motion resistance of the track ridden in muskeg. Muskeg is a floating mat of vegetaon the Flextrac. tion over water that can be almost any depth. Wheeled

As a utility vehicle in snow covered terrains the vehicles can not be driven in muskeg. It is very difficult

Flextrac has better overall mobility as compared to a to walk on muskeg. Most tracked vehicles are too heavy

common snowmobile although the snowmobile is usu- to drive in muskeg. even though they generally have low

ally fasterand providesasmootherride forthe user. The ground pressure and good flotation. Even the Flextrac

fact that sets the Flextrac apart from the snowmobile is MPV had a difficult time crossing muskeg as some deep

that it is really an all-terrain vehicle such that when there holes would slow down the vehicle and some water

is a minimal amount of snow on the ground the driver would get on the drive belt causing slippage and a loss

can keep moving without damaging the vehicle, of power. But if a driver operated the Flextrac carefully

At KRC the Flextrac MPV was tested in all types of through the muskeg it could be crossed N hich would be

environments. In the spring the vehicles were taken on difficult to impossible for any other type of vehicle

trails where they had to cross creeks and small rivers or except for possibly an air cushion type of vehicle.

parts of the trails with wet snow over one to two feet of Figure 12 shows the Flextrac MPV climbing a paved

water. This type of environment would have been slope. Shown in Figures 13 and 14 is the Flextrac on

difficult or impossible to cross with a snowmobile or sand and traversing a swamp water hole, respectively.

four wheel ATV. One other test was the swimming test in a shallow

The Flextrac was also driven on pavement, sand, pond (2 to 5 feet deep). Figure 15 is a photograph of the

gravel, in swamps and in muskeg. On pavement, sand Flextrac swimming in the shallow pond near KRC. The

and gravel a four wheel ATV can travel faster. But a Flextrac SX was tested with only the driver and no

Flextrac can go more places than an ATV. In some of the additional weight. The Flextrac did swim and the driver

conditions such as frozen, snow covered swamps in the was able to get off and get back on the Flextrac without

early winter season it would have been difficult for the it tipping while floating in the water. When weight was

212
1i~u 1-". I/h., AINtH

F~igurec 14. F/ext ,ac MPI'drjvjm,' threuuig' a Swamp mild holeý

213
- a - •- -'N

Figure 15. Flehrwac swimmning in a pond.

added water did seep into some of the internal compart- problems and problems with design that c'aused failments and caused the air filter to become wet and the ures. The newer MPV has shown a tremendous irabelt to slip. The operator has to be sure and seal all areas provement with reliability over the SX version. There

that may allow water into the internal compartments arc still some problcm, with the MPV but these are

before going through a large body of water. Also. the being resolved by the manufacturer anti it is hoped ihat

freeboard area is very small and if a kit was designed in the near future the reliability of the -lhcxtrac \% ill be as

properly it is possible that the vehicle would not sink as good as a snowmobile or ATV.

deeply into the water as it does at this time. What this

demonstrates is that if a driver encounters an area where

he has to cross a fairly deep small body of water it can SUMMARY

be done with a Flextrac.

All vehicles usually have to go through a develop- The Flextrac MPV is truly a unique concept in

ment stage to work out design problems. The early personal vehicle mobility. The single all track drive

snowmobiles and ATVs had problems. Some of the system allows it to traverse almost any type of terrain

early model snowmobiles were known for breaking imaginable. It has excellent hill climbing and pulldown after only a day of riding. The current model ing capability and is a true workhorse. Through engisnowmobiles and ATVs rarely breakdown. The same neering development the Flextrac may one day fill

type of development process is occurring with the the gap between the snowmobile and the four wheel

Flextrac. The early SX version had several reliability ATV.

214
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1 .AGENCY USE ONLY (Leave blank) j2. REPORT DATE REPORT TYPE AND DATES COVERED

4. TITLE AND SUBTITLE 5. FUNDING NUMBERS

First International Conference on Winter Vehicle Mobility

Santa Barbara. California, June 1991

6. AUTHORS

George L. Blaisdell, Editor

7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES)8.PROMNOGA'A N

REPORT NUMBER

U.S. Army Cold Regions Research and Engineering Laboratory Special Report 93-17

72 Lyme Road

Hanover, N.H. 03755-1290

9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES) 10. SPONSORINGIMONITORING

AGENCY REPORT NUMBER

11. SUPPLEMENTARY NOTES

1 2a. DISTRIBUTIONIAVAILABILITY STATEMENT 1 2b. DISTRIBUTION CODE

Approved for public release; distribution is unlimited. I_____

13. ABSTRACT (Maximum 200 words)

The First International Conference on Winter Vehicle Mobility was the first international meeting entirely devoted to the

subject of vehicle travel in cold regions. The technical sessions focused on prediction and testing methods, general vehicle

mobility, mobility enhancement, cold regions materials properties, and novel designs for winter mobility. This report

includes 21 papers presented at the conference.

14. SUBJECT TERMS Winter mbltMoityresearch 15. NUMvBER OF PAGES

Vehicles24 16. PRICE CODE

17. SECURITY CLASSIFICATION 18. SECURITY CLASSIFICATION 19. SECURITY CLASSIFICATION 20. LIMITATION OF ABSTRACT

OF REPORT OF THIS PAGE OF ABSTRACT

UNCLASSIFIED UNCLASSIFIED UNCLASSIFIED UL

NSN 7540-01-280-5500 Standard Form 298 (Rev. 2-89) Prescribed byi ANSI Std. Z39-l16

208102