Vehicle movement on unpaved surfaces is important to military, agriculture, forestry, mining, construction, and recreation industries. Because of the complicated nature of vehicle-terrain interaction, comprehensive modeling of off-road mobility is often done using empirical algorithms. The desire to incorporate more physics into performance models has generated great interest in applying numerical modeling techniques in a full three-dimensional analysis, accounting for the deformation of both the tire and the terrain. In this study, a three-dimensional finite element model was constructed to simulate a tire rolling over snow. The snow was modeled as an inelastic material using critical-state constitutive modeling and plasticity theory. The snow material model was generated from experiments on the mechanical deformation of snow and was validated using a plate sinkage test. The tire models represent a range of sizes accommodating light-truck and off-road military vehicles and were rolled on snow of various depths. The combined tire-terrain models were validated using force measurements collected with instrumented vehicles and with measured snow deformation. The model results were also compared to vehicle mobility predictions made using the winter algorithms of the NATO Reference Mobility Model. These comparisons illustrate the agreement between the finite element models and field measurements of motion resistance forces and snow deformation under the tire.
Freezing temperatures may allow the use of vehicles and heavy equipment on otherwise inaccessible or sensitive areas such as swamps, bogs, tundra, and peatlands. Predicting operable conditions on frozen ground is useful for forestry, mining, oil exploration, construction, and military operations. Guidelines for estimating the frost depth necessary to support a given vehicle load have been generated based on experience in forestry operations on peatlands and similarities in the strength behavior of frozen peat and frozen soils. Correlation with information in the literature leads to a simple equation relating safe trafficability of frozen ground over soft ground: P = Cz2, where P is the maximum load and C is a constant depending on the strength of the frozen layer, which has a thickness z. Values for the constant C and a chart showing required frozen thickness for a variety of vehicles are given. Key words : bearing capacity, frozen ground, peat, frost, vehicle mobility, strength.
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