rioration, loading effects on soil water (pumping
cases and can possibly be modeled with "rough"
up through pavement layers and cracks), and the
friction attributes. A full understanding of this ef-
function of drainage materials, including geosyn-
fect will be critical for traction and braking stud-
thetics.
ies.
4. The impact of temperature-dependent material
Recommended applications and future
properties, such as frictional heating and melting
research needs
of snow, ice, or frozen ground.
Additional terrain material models
Parametric design analysis
Future work should also include extending the ma-
The primary applications of a tireterrain model
terial models to other terrain materials, such as wet,
are 1) all-season and off-road performance prediction
trafficked snow or slush, and soft, loose soils. Traf-
for tires, 2) tire design, optimizing geometry, materi-
ficked snow is typical of much of the snow on roads
als, and tread patterns, and 3) specification of the
before clearing and therefore is of primary interest to
correct tires based on expected operating conditions.
snow maintenance operations, tire companies for
Naturally, design use of the model could include a
improving design of snow tires, automotive compa-
parametric analysis of the impact of tire and terrain
nies for optimizing vehicle handling, and for the roll-
parameters on tire performance. Such a study, evalu-
ing resistance of the snow and its effect on fuel econ-
ating the effects of tire geometry and loading on roll-
omy. The thawing soils material represents a critical
ing resistance in snow, may now be undertaken using
case for roads subjected to freezethaw, where soil
the results of this research.
moisture is pulled to the surface during freezing (ex-
Interface friction and interlocking of
panding soil pores or forming ice lenses), resulting in
tread and terrain
a wet and loose soil during seasonal, intermittent, or
even daily thawing events. Some of the difficulties in
The processes occurring at the interface of the tire
modeling this unique material may be simulated us-
and terrain are also of great interest. Advances in
ing the more flexible Multi-Mechanical Model pro-
driving and braking traction mechanics through so-
posed by Peters* and Smith (2000) or through hydro-
phisticated study of interface friction, and the imple-
dynamic modeling. Additional behaviors specific to
mentation of this in a numerical model, are of major
the interaction of snow grains during loading and
significance because of their large impact on tire and
resulting sintering may be better approached using a
vehicle performance and safety. Since the tread pat-
discrete element model as proposed by Johnson and
tern was not modeled in this study, the details of the
Hopkins.**
interface friction and frictional interlocking, which
affected the resulting slip of the tire, were not spe-
cifically modeled. Issues include the interaction of
LITERATURE CITED
terrain material and tread blocks and the impacts of a
spinning tire on traction through frictional heating
Abele, G., and A. Gow (1975) Compressibility char-
and mass shearing. Modeling challenges include cou-
acteristics of undisturbed snow. Research Report 336,
pling with other models, such as submodels of tread
U.S. Army Cold Regions Research and Engineering
blocks, and discrete element or hydrodynamic models
Laboratory, Hanover, NH.
of terrain material. The practical application of this is
Ahlvin, R.B., and P.W. Haley (1992) NATO refer-
readily apparent for tread design.
ence mobility model edition II, NRMM II user's
Deformation of terrain materials
guide. WES Technical Report GL-92-19, U.S. Army
subjected to vehicle loading
Waterways Experiment Station, Vicksburg, MS.
Ahlvin, R., and S.A. Shoop (1995) Methodology for
Research is also needed in areas relating to the de-
predicting for winter conditions in the NATO Refer-
formation of the materials beneath the wheel, such as:
ence Mobility Model. In Proceedings, 5th North
1. Soil deformation under vehicles and implications
for terrain damage through soil compaction, rut
formation, root tearing, etc.
2. Washboard formation on secondary roads, includ-
ing the effects of suspension parameters, vehicle
* Personal communication with J.F. Peters, GSL,
speed, and road material.
ERDC, 1999.
3. Dynamic models of vehicles on pavements, in-
** Personal communication with J. Johnson and M.
cluding impacts on pavement structure and dete-
Hopkins, CRREL, 2000.
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