Thrust Area 3: Interaction of Tire and Soft Terrain and Vehicle Mobility for Cold/Desert Regions

Interaction of Tire and Soft Terrain and Vehicle Mobility for Cold/Desert Regions –
A Multi-scale Approach

Principal Investigator
Jonah Lee (U. of Alaska Fairbanks)

University Researchers
Corina Sandu (Virginia Tech)
Greg Hulbert (U. of Michigan)

Industry
Ben Wen (Goodyear Tire and Rubber Company)
Richard Romano (Realtime Technologies Inc.)

Government
Sally Shoop (U.S. Army CRREL)
Mike Letherwood (U.S. Army TARDEC)
Jeff Lipscomb (U.S. Army YPG/CRTC)

Almost all the external forces of off-terrain wheeled vehicles are generated from tire-terrain interaction. Survivability of ground vehicles depend significantly, but not exclusively, on their dynamic performance determined directly by tire-terrain interaction, especially in cold regions and desert regions due to low friction and deformable (soft) surface. Friction and traction at tire-terrain interface is intrinsically a multi-scale phenomenon due to the heterogeneity of the terrain and the roughness of tire at the micron scale and the whole tire is at the meter scale. The random heterogeneous nature of the terrain is the major reason that field data for tire-terrain interaction are notoriously difficult to interpret due to the presence of large amount of uncertainty in these data. That the terrain can undergo progressive damage and failure further complicates the understanding and interpretation of field data. Although many engineering tools are available to consider uncertainty toward design, they are less useful when the amount of uncertainty is very large and when the cause of the uncertainty is unknown thus preventing parameterization of relevant design variables. At the microscale, the terrain is better viewed as a body composed of discrete particles especially when progressive damage and failure of the terrain start at the microscale. Although many significant improvements have been made in recent years toward better understanding and modeling tire-interaction, they are mainly at the tire-scale and these efforts are not able to ascertain the source of uncertainty and its quantification. Consequently, there exists an important gap in tire-terrain interaction between microscale and macroscale phenomena.

Vehicle dynamics modeling, virtual simulation, design and mobility performance evaluation all require comprehensive and efficient tire-terrain kinematics/dynamics models for various operating conditions. This project aims at bridging the gap between microscale and macroscale pheneomena by providing theoretical, numerical and experimental knowledge base at the micro- and macroscale for cold-regions and desert-regions vehicle mobility as shown in the interrelated objectives below:

Develop validated material models at micro- and macroscale, and structural mechanics of pneumatic tire and cold/desert-regions terrain properties (snow, ice, sand and frozen soil).

Establish dynamics models of tire-terrain interface and interaction through efforts in the understanding of friction/traction mechanisms from the micro- to the macroscale. The goal is to develop validated models and simulation methodologies to understand the relationships of tire-terrain 2D/3D kinematics and dynamics, interfacial friction law and friction/traction mechanisms, distribution of contact pressure and shear stress, as well as analysis and comparison of on-road and off-terrain surfaces, comparison of different off-terrain surfaces.

Quantify the causal relationship of uncertainties between the micro- and macroscale such that macroscale analysis and design tools incorporating uncertainty can be fruitfully applied.

Develop critical techniques in model improvement and generalization for quasi-real operating conditions at the macroscale from knowledge at the microscale, which mainly involve
- combined cornering and driving/braking slip conditions (slip dependent);
- normal sinkage and lateral plowing (depth dependent when applicable);
- high-speed and high-frequency (spatial/time frequency dependent);
- non-steady state and transient process (time-varied state dependent);
- hybrid friction/anisotropic surface and split-mu (friction dependent).

Incorporate and integrate tire-terrain interaction models into real-time and/or offline virtual vehicle dynamics prototype or vehicle simulation system by considering numerical algorithms and overflow, computational efficiency, zero slip and standstill states, program interface customization and parameter inputs/outputs.

Conduct full vehicle multi-body simulation under different control strategies and representative operating conditions for case study to predict vehicle dynamic response and analyze vehicle mobility, which include lateral acceleration and yaw rate, roll/pitch/yaw control, understeer gradient, load transfer and rollover, handling and maneuverability.