Analysis of finite element simulation of driven tire_soil interaction to estimate soil vertical stress

Simulation of tire- soil models have called attention so far when compared to the expensive and time consuming experimental tests.
To simulate the model, first the soil and different components of tire were designed separately. To design a research model, soil was considered as a single-layer material with a complete elastic- plastic behavior. Its elastic parameters such as Young’s modulus (E), potion ratio (ѵ) and two plastic parameters; friction angle (φ) and cohesion (c) were obtained through tri- axial and direct shear tests, respectively. The tests revealed that soil internal friction angle, cohesion and density were obtained at 36°, 0.003 kg/cm2, and 1600 kg /m3, respectively. The soil profile dimensions were considered as 3×1.2×2 so that there would be no impact on the results or tire position. The tire used for test belonged to a tractor tire type of 220/65 R 21 with 36 cm in width and external diameter of 80 cm with a radial structure, manufactured by Good Year company. Since in simulation of tire ignoring the details of tread design has a negligible impact on large deformations and dynamic loading of tire, the simulated tire in this research was simplified to include tread, carcass, and rim. To design the tread of tire, the incompressible hyper- elastic material features, with Mooney – Rivlin coefficients were considered. To design the internal rubber of the tire model, which includes the belt and carcass, the boosted multiplied elastic approach was used. The dimensions of the modeled tire were compatible with a real one. From the symmetric point of view, only the half of the tire was simulated and dynamically analyzed which decreased the running time. A reference point was defined in the center of the tire to let the speed and load to be exerted through the point. According to mobility of the tire, the torque of every test based on its acceleration was considered on axel (connector) and the movement was measured from two separate points. It is worth to note that the boundary conditions, loading, and material characteristics should be entered in ABAQUS software close to the real conditions. The experimental tests were conducted at different levels of travelling speed (0.4, 0.8 and 1.2 ms-1), dynamic load (2000, 3000 and 4000 N) and depth (0.1, 0.15 and 0.2 m) with measuring the soil vertical stress. The experimental tests of this research were performed in Urmia University using the soil bin testing facility. The system includes various sections such as soil bin in dimensions of 22×2×1 m, carriage, soil processing equipment, dynamic system, evaluation tools, and controlling systems. In order to start data acquisitioning and to supply required power for wheel carriage, an industrial three phase electromotor with 22 kW (30 hp) was used. Analysis of variance was performed using SPSS version 20.
To assess the performance of driven tire-soil model, numerical results were compared with preliminary experimental data. The comparison showed a reasonably good agreement between the simulated and measured soil vertical stress at the tire-soil interface under three different levels of forward speed, dynamic load and depth. Using both methods, the increase of speed led to the reduction in soil vertical stress at different combinations of dynamic load and depth. When tire speed increases, the time during which tire makes contact with soil surface decreases. Therefore, tire dynamic load cannot be transferred into the soil layers completely. Increasing the amount of tire vertical load led to the increase of soil vertical stress but the effect of dynamic load variations on soil stress at different depths was not in a similar manner. It was inferred that the effect of all independent variables as well as their interactions on soil vertical stress was significant.
In all combinations of vertical load and forward speed, the results of both numerical and experimental tests were close to each other in three different levels of soil depth, so that, driven tire _soil finite element model of this study can be considered as a model with a reasonable accuracy to evaluate tire-soil performance in different operating conditions. In all combinations of dynamic load and forward speed the results of both tests at three different depths were close to each other.