Investigation of the predictability of mouldboard plough draught from soil mechanical strength (cone index vs. shear strength) using finite element modelling

Mojtaba Naderi-Boldaji, Seyed Hossein Karparvarfard, Hadi Azimi-Nejadian

Journal of Terramechanics, Volume 108, 2023, Pages 21-31, ISSN 0022-4898

https://doi.org/10.1016/j.jterra.2023.04.001.(https://www.sciencedirect.com/science/article/pii/S0022489823000332)

Abstract: Prediction models for draught of tillage implements using soil variables which can be readily measured in the field are important tools in agricultural machinery management. In our previous study, a regression model for draught of a cylindrical mouldboard plough as a function of soil water content, bulk density, ploughing depth and speed was developed using a finite element (FEM) model. This study aims to investigate whether the soil physical properties could be replaced by soil strength variables including cone index (CI) or shear strength (SS) measured by cone penetrometer and shear vane, respectively. Cone penetration and shear vane tests were simulated using FEM in the soils for which the mouldboard plough draught was obtained from the mouldboard plough-soil interaction model. A 0.3 m ploughing layer was simulated either homogeneous or non-homogeneous. CI and SS, averaged over the ploughing layer, were used as soil strength variables. The best model for mouldboard draught was obtained as a function of SS, ploughing depth and speed with R2 = 0.87 and RMSE = 0.79 kN. Validation of the model with a set of experimental data reported in the literature showed that the predicted draught force lies within bounds of ± 18 % of the measured values with R2 of 0.84. The draught model could be employed with a shear vane or a combined vane-cone instrument to predict the mouldboard plough draught.

Keywords: Shear vane; Cone penetrometer; Finite element method; Mouldboard plough; Draught

Modeling tire-soil compression resistance on artificial soil using the scaling law of pressure-soil sinkage relationship

Pius Jjagwe, Mehari Z. Tekeste, Nisreen Alkhalifa, Thomas R. Way

Journal of Terramechanics, Volume 108, 2023, Pages 7-19, ISSN 0022-4898

https://doi.org/10.1016/j.jterra.2023.02.002.(https://www.sciencedirect.com/science/article/pii/S0022489823000162)

Abstract: Semi-empirical traction models utilize soil parameters estimated from ASABE cone and flat plate soil sinkage data; however, limited studies apply the scaling law of the soil measurement tool to a full-scale tire-to-soil system for various initial soil conditions. This study investigated the effects of three scaled plates (size and shape) and two soil bulk density conditions on pressure-sinkage relationships in artificial soil. Rectangular estimated tire-soil shape and a contact area of 484 cm2 were measured from vertical loading of an LT235/75R15 tire (179 kPa inflation pressure and 8 kN vertical load) in a soil bin test on an artificial soil. Pressure-sinkage data were collected on an artificial soil column at 1.21 Mg/m3 soil bulk density (66% of Proctor density) and 1.41 Mg/m3 soil bulk density (75% of Proctor density) initial conditions using circular, rectangular, and square plates, each at three scaled areas (λ = 0.5, λ = 0.25, and λ = 0.125, where λ = 1 is the tire-soil estimated footprint area from the single tire soil bin test). A scaling law with a strong correlation was established between the geometric scale and the energy expended in compressing the soil. The plate pressure data for λ = 0.125 exhibited a relatively linear increase in pressure as depth increased for loose soil, similar to the soil cone penetrometer data. The pressure-sinkage data for λ = 0.5 exhibited a trend similar to existing models, but coefficients differed for the two initial soil bulk densities. The study demonstrates applying a scaling law to simulate a tire-soil system on soft and dense soils.

Keywords: Pressure-sinkage; Soil model; Scale; Artificial soil

Selection of parameters of the disc working bodies of the ripping-separating machine for soil treatment

Yuri Syromyatnikov, Sergey Voinash, Irina Troyanovskaya, Evgeny Tikhonov, Svetlana Partko, Viktoriia Sokolova

Journal of Terramechanics, Volume 108, 2023, Pages 1-5, ISSN 0022-4898

https://doi.org/10.1016/j.jterra.2023.03.005.(https://www.sciencedirect.com/science/article/pii/S0022489823000228)

Abstract: Mechanical tillage with the help of a soil-cultivating ripping-separating machine is based on the combination of the operation of crushing and separating the soil along the depth of the cultivated layer. When moving the plowshare at a depth of 0.03–0.1 m, the movement of soil along the plowshare is complicated by the formation of an additional soil layer in front of it. To avoid this phenomenon, it is proposed to install passive freely rotating disks on both sides of the plowshare. The purpose of this study was to determine the most rational design parameters and modes of movement of disk working bodies. As a result of a theoretical study of the interaction of soil particles with the surface of rotating disks, the dependences of the thickness of the soil layer in front of the plowshare on the radius of the disk and the ratio of their rotation speed to the forward speed of the machine were obtained. As a result of experimental studies, the influence of the limiting distance between the disks and the angles of inclination on the thickness of the soil layer in front of the plowshare was determined.

Keywords: Loosening and separating installation; Mechanical control of weeds; Guide discs; Kinematic rotation parameter; Camber and convergence angles

Review on soil shear strength with loam sand soil results using direct shear test

Alaa El Hariri, Ahmed Elawad Eltayeb Ahmed, Péter Kiss

Journal of Terramechanics, Volume 107, 2023, Pages 47-59, ISSN 0022-4898

https://doi.org/10.1016/j.jterra.2023.03.003.(https://www.sciencedirect.com/science/article/pii/S0022489823000204)

Abstract: 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.

Keywords: Soil shear strength; Vehicle-terrain interaction; Direct shear test; Triaxial test; Shear vane test; Coulomb equation; Soil moisture content

Terramechanics models augmented by machine learning representations

Eric Karpman, Jozsef Kövecses, Marek Teichmann

Journal of Terramechanics, Volume 107, 2023, Pages 75-89, ISSN 0022-4898

https://doi.org/10.1016/j.jterra.2023.03.002.(https://www.sciencedirect.com/science/article/pii/S0022489823000198)

Abstract: 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.

Keywords: Machine learning; Terramechanics; Neural network; Fundamental earthmoving equation; Wheel-soil; Hybrid model

A bionic mechanical foot with adaptive variable postures travelling on sand

Rui Zhang, Xumin Sun, Dianlei Han, Rui Zhang, Hua Zhang, Jia Ma, Lige Wen, Meng Zou

Journal of Terramechanics, Volume 107, 2023, Pages 61-74, ISSN 0022-4898

https://doi.org/10.1016/j.jterra.2023.03.004.(https://www.sciencedirect.com/science/article/pii/S0022489823000216)

Abstract: 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.

Keywords: Ostrich foot; Mechanical foot with adaptive variable postures; Loose ground; Traction; Bionic design

Load bearing capacity of finite half space agricultural homogeneous soil

Nihal D. Salman, György Pillinger, György Sitkei, Péter Kiss

Journal of Terramechanics, Volume 107, 2023, Pages 35-46, ISSN 0022-4898

https://doi.org/10.1016/j.jterra.2023.03.001.(https://www.sciencedirect.com/science/article/pii/S0022489823000186)

Abstract: A comprehensive plate-sinkage equation is necessary for the description of the load bearing capacity of soils. In the last century, several improvements to the existing equations were attempted but with limited success. The main aim of this paper is to verify, evaluate and develop a load bearing capacity theory of finite half space soil. Agricultural soils may be regarded as a finite half space in which the tilled soil layer is comparable to the loading diameter. Harder soil is found below the tilled soil layer and this hard soil can be considered as a rigid layer. A new consideration is the compacted cone-shaped zone developing under a loading device and its possible interaction with the rigid bottom surface. Theoretical and experimental investigations reported in this paper have shown that these approaches have facilitated deriving new relationships valid for finite half space. These include two independent variables and developing a dimensionless load bearing number. This paper introduces a new dimensionless plate-sinkage equation describing soil deformation in a general form.

Keywords: Finite half space; Load bearing number; Compacted zone; Cone interaction generalized plate-sinkage equation; Soil density

Discrete element modelling of soil pressure under varying number of tire passes

Kobby Acquah, Ying Chen

Journal of Terramechanics, Volume 107, 2023, Pages 23-33, ISSN 0022-4898

https://doi.org/10.1016/j.jterra.2023.02.003.(https://www.sciencedirect.com/science/article/pii/S0022489823000174)

Abstract: 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.

Keywords: Discrete Element Modelling (DEM); Soil; Pressure; Stress; Compaction; Tire

Geotechnical assessment of terrain strength properties on Mars using the Perseverance rover’s abrading bit

Eloïse Marteau, Kristopher Wehage, Shoya Higa, Scott Moreland, Gareth Meirion-Griffith,

Journal of Terramechanics, Volume 107, 2023, Pages 13-22, ISSN 0022-4898,

https://doi.org/10.1016/j.jterra.2023.02.001. (https://www.sciencedirect.com/science/article/pii/S0022489823000058)

Abstract: An instrument for measuring the geotechnical properties of the Martian soil provides high-value science opportunities and high-priority mission-support capabilities that serve reconnaissance, science, and engineering. Such instrument can be used to characterize the terrain for drilling, landing, trafficability, and other surface operations. However, to date, instruments for measuring geotechnical properties have been absent from Mars exploration missions. This paper examines the use of the Mars 2020 Perseverance rover’s abrading bit tool to perform regolith strength measurements. The Perseverance rover’s abrading bit has a similar form factor to a Bevameter, a tool commonly used to collect engineering geotechnical data to assess terrain traversability. To demonstrate a methodology by which the abrading bit can be employed to characterize soil strength, a portable testbed that mimics the flight system is designed and built using commercial off-the-shelf components. A data-processing pipeline is developed to convert raw measurements to soil strength. Tests were performed on three characterized simulants with different mechanical properties. The results show that the abrading bit is capable of making shear and bearing strength measurements with quantified uncertainties and demonstrate, for the first time, the ability to perform controlled geotechnical analysis using a standard science instrument.

Keywords: Mars 2020 Perseverance rover; Martian regolith; In-situ measurements; Geotechnics