Calibration and Validation of a Lower-Order Soil Compaction Model Under Non-Uniform Tire Loads Applied By a Dynamic Vehicle Model.

Vehicle dynamics simulation used for mobility prediction hinges on three main components: 1) the vehicle model, 2) the running gear model, and 3) the forces developed between the traction elements and the ground. Unprepared terrain, specifically that which cannot be characterized as rigid under vehicle loads, poses an additional hurdle when quantifying vehicle mobility, due to the complex interaction between the running gear and terrain.

The goal is to address the following problem: “When a vehicle operates on soft soil, how can the size, shape and pressure distribution in the tire/terrain contact patch be accurately calculated without sacrificing the usefulness of the resulting simulation tool to the design engineer?” It is the goal of this work to define the deformation of the terrain beneath the tire, in order to calibrate and validate a soil compaction based terrain model to correctly capture the response from general 3-D vehicle loading.

An assumed size/shape/distribution of contact patch pressures are applied on a soil-tire/track interface, the resulting subsoil stress field is approximated, and used on a discrete fixed-grid approximation of the continuous soil half-space to find the vertical visco-elastic-plastic response of the soil.

The validation of the terrain deformation model due to vehicle loading can be addressed directly, and experiments are carried out on increasing levels of complexity.

1. Consistent deflection and compaction energy for a single soil sample under a known, repeated load (i.e., laboratory conditions, triaxial tester),
2. Consistent deflection and compaction energy of a 3-D terrain database under an assumed contact patch (size, shape, normal pressure/shear stress distribution),
3. Consistent normal and shear forces of a kinematically driven tire on a 3-D terrain database,
4. Consistent vehicle mobility numerics (wheel torque, drawbar pull) and vehicle dynamic information (position, velocity, accel, etc.) of a multibody vehicle model with rigid wheels operating on soft soil,
5. Validation of field test involving an instrumented HMMWV in fine and coarse-grained soils.