Journal of Terramechanics最新文献

This article aims to give a background about the soil shear strength and its measurement methods based on scientific articles and the work of researchers. A brief introduction is given about terramechanics science and the loads acting at the interaction zone between the tractive element (wheel/track) and the terrain. The most important loads exciting the terrain from the machine’s tractive element are the normal and the tangential loads. The tangential load will shear the terrain/soil and might lead to slippage, thus it is important to study the shear strength of the soil. In the review the soil terrain behaviour as an elastic and a plastic region is discussed. The conventional methods for measuring the soil strength used by scientists in terramechanics studies are reviewed. The influence of moisture content on soil strength is also taken into consideration. New ideas created by terramechanics scientists that emulate a real wheel/track - terrain interaction case for measuring the soil shear strength and are not civil or geotechnical engineering methods are mentioned. Finally, the shear strength results of loam sand soil obtained using the direct shear test conducted at the Hungarian University of Agriculture and Life Sciences (MATE) are presented.

In this study, an adaptive variable posture bionic mechanical foot is designed, which enables the transformation of different postures during the touchdown period. At the same time, the bolts at the joints are tightened to enable the non-variable configuration function of the bionic mechanical foot. A test rig was used to test the travelling and traction performance of the bionic mechanical foot at different speeds on sandy and hard surfaces. The results show that on sandy surfaces, at both high and low speeds, the variable posture mechanical foot outperforms the non-variable posture mechanical foot, especially at high speeds, indicating that the variable mechanical foot is suitable for movement at higher speeds on sandy ground. On hard ground, the traction and pedaling forces generated by the variable posture mechanical foot are essentially the same as those generated by the non-variable posture mechanical foot at low and high speeds, indicating that the travelling and traction performance of both mechanical feet on hard ground is the same. The variable posture mechanical foot is suitable for high-speed movement on sandy ground, providing a theoretical and technical basis for the design of future legged robots for efficient movement on desert surfaces and deep space soft surface environments.

Pressure imposed on an arable farmland by farm machinery can lead to severe soil compaction. A model was developed with Discrete Element Method (DEM) to simulate soil – tire interaction. Virtual dead weight method was performed for the purpose of model calibration. Simulated soil pressure data were obtained from the topsoil layer under varying number of tractor tire passes (1P, 2P, 3P, 4P, 5P, 6P, 7P and 8P). Simulation results were validated with maximum soil pressure data from a field experiment in which soil pressure was measured at 0.1 m depth in sandy loam soil. Model results of maximum soil pressure increased from 137.7 to 242.5 kPa when the number of passes increased from 1P to 8P. Prediction of the maximum soil pressure was reasonably accurate for 1P and 2P with Relative Mean Errors (R.M.E) less than 9%. Predictions for 3P to 8P had higher R.M.E. In terms of model application, soil sinkage and rolling resistance ranged from 0.07 to 0.14 m and 225.3 to 517.8 N respectively between one to eight passes. The model developed in this study can be used in the simulation of soil pressure distribution and deformation in the topsoil layer induced by heavy farm machinery.

The field of terramechanics focuses largely on two types of simulation approaches. First, the classical semi-empirical methods that rely on empirically determined soil parameters and equations to calculate the soil reaction forces acting on a wheel, track or tool. One major drawback to these methods is that they are only valid under steady-state conditions. The more flexible modelling approaches are discrete or finite element methods (DEM, FEM) that discretize the soil into elements. These computationally demanding approaches do away with the steady state assumption at the cost of including more model parameters that can be difficult to accurately tune. Model-free approaches in which machine learning algorithms are used to predict soil reaction forces have been explored in the past, but the use of these models comes at the cost of the valuable insight that the semi-empirical models provide. In this work, we presume that in a dynamic simulation, the soil reaction forces can be divided into a steady state component that can be captured using semi-empirical models and a dynamic component that cannot. We propose an augmented modelling approach in which a neural network is trained to predict the dynamic component of the reaction forces. We explore how this theory can be applied to the simulation of a soil-cutting blade using the Fundamental Earthmoving Equation and of a wheel driving over soft soil using the Bekker wheel-soil model.

The use of intensive technologies for the cultivation of agricultural crops provides for the application of fertilizers in the process of tillage. This reduces the compaction of the soil, increases its fertility and the quality of the crop. The purpose of these studies is to develop a universal working tool that allows you to combine several technological operations in one pass of the unit. The authors have developed an original design of a plow-subsoiler-fertilizer. This combined working body includes a reversible plow and a vibratory subsoiler with fertilizer ducts. This solution allows you to combine the application of fertilizers when plowing the field, loosening the subsoil layer and mixing the soil. As a result of the work, the dependences of the geometric dimensions of the structure on the traction resistance to movement in the soil were obtained. To implement the developed idea into a real design, the main parameters of the plow-subsoiler-fertilizer are determined. Particular attention is paid to the calculation of the spring mechanism that ensures the vibration of the subsoiler. The optimal number and location of belleville springs in the block and shock absorber were selected, at which the subsoiler will perform self-oscillations with a given amplitude.

A novel evaluation method for rolling energy losses of road wheels of tracked vehicle is proposed, in which damping of road wheel surface is identified based on single vibration excitation and single point picking up frequency response function using a simplified modal experiment with an acceleration sensor. Three road wheels of tracked vehicle with different tread rubber are utilized as specimens during the modal experiments. The half power bandwidth method is employed to identify the viscous damping parameters. The damping parameters of road wheels are ranked by their values, and then these values of every road wheels are compared with their corresponding rolling energy losses to validate their correlative relationship. Moreover, the nonlinear deformation and stiffness of road wheels are investigated about their correlation with the rolling energy losses through model development and experimental validation. The results prove that the damping ratios of road wheels are correlated well with the rolling energy losses for all the three road wheels. The proposed evaluation method could effectively evaluate the rolling energy losses of road wheels, which suggests a simplified and economical alternative over the conventional rolling energy losses experimental method of road wheels.

Vehicle terrain mobility characteristics, provided by the powertrain and running gear, are realized in dynamic interactions between the wheels and terrain. Approaches to modeling and simulation of vehicle-terrain interaction and mobility characteristics as well as engineering approaches to design powertrain sub-systems together pre-determine a vehicle’s technical success or failure before it touches the ground. This article develops a vehicle mobility design technique, applicable to both manned and unmanned platforms, concerned with powertrain power conversion and realization in tire-terrain interactions. The modeling component is based on multi-drive-wheel vehicle longitudinal dynamics combined with terramechanics and powertrain characteristics. The approach advances the conventional dynamic factor by introducing the conjoint effect of the engine, transmission, and driveline system on vehicle traction and acceleration performance in terrain conditions where circumferential wheel forces and tire slippages may differ from each other. The vehicle design component of the proposed technique introduces drivetrain, driveline, and powertrain design factors that assess the influence of the drivetrain and driveline systems on traction, acceleration performance, power conversion, and realization at the wheels. The vehicle-design-for-mobility technique is completed by examining indices of mobility margins and performance. An analysis of several 8x8 armored personal carriers and 4x4 off-road vehicles illustrates the proposed technique.

Due to the long-term weathering and erosion climate, many craters terrains on the surface of Mars are covered with loose weathered sedimentary debris, and Mars rovers traversing these slope-like terrains with soft soils will easily slip or even sink, and may affect the survey missions. Therefore, it is important to study the climbing ability of Mars rovers for Mars exploration missions. This work testes the climbing capability of 'Zhurong' Mars rover based on active–passive suspensions under the simulated Martian terrain and soil parameters were adequately measured. The maximum climbing distance (MCD), slip rate, power, current, energy, and efficiency are analyzed to explore the climbing abilities under different climbing methods, soil states and dynamic parameters (speeds, angular velocity) settings. The test results show that the peristaltic mode is able to continue climbing after a direct climb failure, and the MCD per period is influenced by angular velocity. The power and current data can effectively reflect the difficulty of the rover climbing. Under the same dynamic parameters, the greater the slip rate of the rover, the larger the output power and current. In addition, the speed should be minimized to prolong the climbing distance, no matter it is direct or peristaltic climbing.