An investigation of the bevameter soil physical measurements in the prediction of soil tool draft

The relationship between the parameters measured during soil testing using the bevameter system and the horizontal forces acting on a simple soil-cutting blade were investigated. Field experiments were conducted on untilled, compacted soil and on recently-tilled soil. On both soils, five sites were randomly chosen and bevameter and draft measurements were performed The parameters measured were modulus of soil deformation, wet and dry bulk density, soil moisture content, tool operating depth, tool operating velocity and horizontal draft. A statistical analysis of the data indicated that a mathematical model for predicting draft should contain the following variables: operating depth, dry bulk density and modulus of deformation. A linear regression analysis of draft versus modulus of deformation showed significance at the 95% confidence level on the untilled sites at all measured depths. A similar analysis of the tilled site indicated significance at the 70 mm depth only. The usefulness of the bevameter deformation modulus as an indicator of draft was found to be limited to shallow depths.     

Dynamic modeling of soil–tool interaction: An overview from a fluid flow perspective

The study of tillage tool interaction centers on soil failure patterns and development of force prediction models for design optimization. The force-deformation relationships used in models developed to date have been considering soil as a rigid solid or elasto-plastic medium. Most of the models are based on quasi-static soil failure patterns. In recent years, efforts have been made to improve the conventional analytical and experimental models by numerical approaches. This paper aims at reviewing the existing methods of tillage tool modeling and exploring the use of computational fluid dynamics to deal with unresolved aspects of soil dynamics in tillage. The discussion also focuses on soil rheological behaviour for its visco-plastic nature and its mass deformation due to machine interaction which may be analyzed as a Bingham plastic material using a fluid flow approach. Preliminary results on visco-plastic soil deformation patterns and failure front advancement are very encouraging. For a tool operating speed of 5.5 m s⁻¹, the soil failure front was observed to be about 100-mm forward of the tool.     

Experimental validation of computational fluid dynamics modeling for narrow tillage tool draft

Energy requirement of a tillage tool, mostly represented by tool draft, is a function of different soil–tool interaction components like soil parameters, tool parameters and system parameters. Soil–tool interaction modeling was conducted using computational fluid dynamics (CFD) approach considering soil as a Bingham material. Soil bin tests were conducted to validate tool draft predictions obtained from this numerical modeling. Numerical predictions and soil bin experiments for the tool draft were observed with 40 mm wide vertical tool operating at four different depths of 40, 80, 120, and 160 mm. The tool was operated at four different operating speeds of 1, 8, 16 and 24 km h⁻¹ in clay loam soil with two moisture contents of 14% and 20%. Thus, the experimental design consisted in a (2 × 4 × 4) complete randomized factorial with two replications for each test. Simulation results over-predicted tool draft in comparison to the experimental values. The difference between the predicted and measured draft were not consistent and ranged from 1% to 42%, with an average of 24% and 22% for moisture contents of 14% and 20%, respectively. The agreement of simulation data with experimental values was higher at shallow depth of operation and lower tool operating speed. The correlation coefficient between the simulation and experimental draft were found to vary from 0.9275 to 0.9914.     

Predicting the draught requirements of concave agricultural discs

The paper presents a rapid method for calculating the draught force generated by a concave disc tool when cutting a Mohr-Coulomb soil. The mean equivalent stress derived by distributing the draught force uniformly over the furrow cross-section is calculated using a set of non-dimensional factors in a two term additive equation. Tables of these factors are provided to cover the analysis of any disc of standard size and curvature operating over a practical range of cutting depths and disc and tilt angle settings. The furrow area can be estimated from published calculation tables (not reproduced here). From a knowledge of these parameters it is possible to calculate the draught force acting on the disc. A number of simplifying assumptions have been made to facilitate the development of an uncomplicated calculating procedure. Consequently the calculated values of draught must be considered as order of magnitude predictions.     

Constitutive model for high speed tillage using narrow tools

Dynamic effects on soil–tool cutting forces are important when operating at elevated speeds. The rate-dependent behavior of narrow tillage tools was investigated in this study. A hypoelastic soil constitutive relationship with variable Young's modulus and Poisson's ratio was developed to describe the dynamic soil-tool cutting problem. An initial finite element formulation with viscous components incorporated in the stiffness matrix resulted in severe numerical oscillations. A modified model that incorporated lumped viscous components in the equation of motion (independent of the stiffness matrix) was proposed. Numerical oscillations still occurred, but at sufficiently high tool displacements (1–10 mm) to enable the determination of peak draft forces. Experimental data for flat and triangular edged narrow tools were obtained using a 9-m long linear monorail system designed to accelerate narrow tools through a linear soil bin to high speeds. Steady-state speeds from 0.5 to 10.0 m/s over a distance of 1 to 3 m were attained using this system. A reference-tool inverse procedure was used to estimate the dynamic soil parameter in the soil model using draft data obtained for the flat tool. Predictions of triangular tool draft produced correct trends but overestimated experimental data. Draft was overpredicted by less than 1% at a tool speed of 2.8 m/s and by 25% at 8.4 m/s.     

Sinusoidal vibratory tillage

One dimensional sinusoidal vibratory tillage was analyzed theoretically and experimentally. A model was developed in which the instantaneous horizontal force on the tool was equal to a constant plus a linear function of tool velocity. The tool action was analyzed in three stages: (1) retraction of the tool, (2) compression of loose soil in front of the tool, and (3) cutting of undisturbed soil. The effect of tool mass was included, but edge effects between the tool and soil as the tool retracted were neglected. Equations were developed for the instantaneous horizontal force on the tool, average force and power requirements for the tool and ratio of average force and power on a vibrating tool to the average force and power for the same tool without vibration but moving at the same average velocity.

The model predicted the measured instantaneous tool force and average force accurately when the tool oscillated at 10 Hz and the soil failed by flow. At higher frequencies, the soil failed by multiple shear resulting in more pulverization. In this case, the model did not predict the instantaneous force accurately but did not predict the average force with reasonable accuracy. Multiple shear was more evident on the 45° tool than the 80° tool, the difference was attributed to the fact that the soil was more confined by the 80° tool. A maximum force reduction of 40% was observed at a contact ratio between 0.3 and 0.4. The power required for the vibrating tool was increased by a factor of 1.5 to 3.0 for the same contact ratio interval.     

The effect of velocity on rigid wheel performance

A simulation model to predict the effect of velocity on rigid-wheel performance for off-road terrain was examined. The soil–wheel simulation model is based on determining the forces acting on a wheel in steady state conditions. The stress distribution at the interface was analyzed from the instantaneous equilibrium between wheel and soil elements. The soil was presented by its reaction to penetration and shear. The simulation model describes the effect of wheel velocity on the soil–wheel interaction performances such as: wheel sinkage, wheel slip, net tractive ratio, gross traction ratio, tractive efficiency and motion resistance ratio. Simulation results from several soil-wheel configurations corroborate that the effect of velocity should be considered. It was found that wheel performance such as net tractive ratio and tractive efficiency, increases with increasing velocity. Both, relative wheel sinkage and relative free rolling wheel force ratio, decrease as velocity increases. The suggested model improves the performance prediction of off-road operating vehicles and can be used for applications such as controlling and improving off-road vehicle performance.     

Steering forces on undriven tractor wheel

The steering forces on an undriven, angled wheel mounting a 6-16 8PR tire were measured on a wheel test carriage at zero camber angle and at 1.5 km/h forward speed in a soil bin with sandy clay loam soil. The lateral force developed was found to be a function of slip angle, normal load, and inflation pressure for a particular soil condition. An exponential relationship could estimate the coefficient of lateral force of the 6-16 tire. The coefficients of this equation were found to be linearly related to inflation pressure. Rolling resistance of the wheel tested was found to be a function of slip angle, normal load, and inflation pressure for the soil condition tested. A linear relationship existed between the rolling resistance and slip angle, where the coefficients were found to be a function of inflation pressure and normal load. The generalized equations developed in the present study for estimating coefficients of lateral force and rolling resistance by taking both the tire and operating parameters into account, were found to be reasonably good by looking at the high coefficient of determination between experimental and estimated values.     

基于吸力量测确定膨胀土活动带和裂隙深度

采用M itchell公式和裂隙扩展深度方程两种吸力法确定安康地区膨胀土大气影响深度和裂隙开展深度。其一通过对安康地区两处天然边坡开挖观测井,利用张力计进行不同深度处吸力值的现场量测,根据M itchell提出公式计算大气影响深度;其二根据非饱和土抗拉强度公式,建立膨胀土裂隙扩展深度方程,利用基质吸力量测结果求其理论解。结果表明,安康地区膨胀土吸力变化曲线随深度增加变幅减小,呈“波浪式”推移。M itchell公式确定安康地区膨胀土的大气影响深度为3.35m以内,裂隙深度方程确定裂隙开展深度为3.06³.14m。利用M itchell公式计算大气影响深度与膨胀土断裂理论公式确定的裂隙开展深度结果接近。     

The prediction of tractive performance on soil surfaces

A new approach to the traction prediction equation is described. The proposed equation uses the soil deformation modulus and physical properties of agricultural tyres as parameters. The novel features of this approach include the assumption of a non-linear shear stress distribution and change in the value of soil deformation modulus with the normal stress. A model which suggests a relationship between the contact patch area and the soil deformation modulus is also introduced. The prediction equation was compared with the widely used Wismer and Luth equation and measured data obtained by Wittig. The proposed approach results in an improvement over Wismer and Luth in the prediction of traction and it also involves minimal testing.     

Self-interrupted regenerative metal cutting in turning

A new approach is used to study the global dynamics of regenerative metal cutting in turning. The cut surface is modeled using a partial differential equation (PDE) coupled, via boundary conditions, to an ordinary differential equation (ODE) modeling the dynamics of the cutting tool. This approach automatically incorporates the multiple-regenerative effects accompanying self-interrupted cutting. Taylor's 3/4 power law model for the cutting force is adopted. Lower dimensional ODE approximations are obtained for the combined tool-workpiece model using Galerkin projections, and a bifurcation diagram computed. The unstable solution branch off the subcritical Hopf bifurcation meets the stable branch involving self-interrupted dynamics in a turning point bifurcation. The tool displacement at that turning point is estimated, which helps identify cutting parameter ranges where loss of stability leads to much larger self-interrupted motions than in some other ranges. Numerical bounds are also obtained on the parameter values which guarantee global stability of steady-state cutting, i.e., parameter values for which there exist neither unstable periodic motions nor self-interrupted motions about the stable equilibrium.     

Power requirements for wheels operating in sand

Based on the WES mobility prediction system, which allows the determination of system output (pull coefficient) and system input (torque coefficient) at 20% slip and the determination of the towed force coefficient, a technique was developed for predicting power requirements for wheels operating in sand as a function of system output for the full operating range from the towed condition to the 20% slip condition. Separate relations of system output and system input as functions of slip can be predicted also. Possibilities for incorporating this prediction method as a soil submodel into an overall vehicle mobility simulation model are discussed.     

Method and apparatus for on-line estimation of soil parameters during excavation

Time-varying forces from soil–machine interactions cause stresses in the components of earthmoving machinery, which may cause damage to the machine. It is not always possible to know all the characteristics of a soil sample prior to excavation; however, by estimating necessary soil parameters, it is possible to predict the soil–machine interaction forces in a practical manner. This article presents the development of a simple apparatus and method for estimating the soil parameters from the cutting force measured by the novel bench-scale excavating tool, validation of the soil model, and comparison with other available techniques. The apparatus used to collect data of soil forces on a tool consists of an instrumented crank-slider mechanism equipped with a thin plate to fragment the soil, which is contained in a sample box. Using the Mohr-Coulomb earth pressure model to predict failure force during the interaction, two methods are used to minimize the error between the predicted and measured failure force, that allows to estimate soil parameters: First, the Newton–Raphson Method (NRM) is used to minimize the error, which allows estimation of two soil parameters (interface friction angles) on non-cohesive soil samples. Additionally, a new estimation scheme based on the NRM is presented, that uses an auxiliary equation, and allows estimation of up to three soil parameters, including interface friction angles and cohesion. Comparing the results obtained from the presented apparatus, it is confirmed that the friction angles are successfully estimated for two non-cohesive particulate materials. Additionally, it is shown that the new scheme demonstrates smaller error in estimating soil parameters for cohesive and non-cohesive soil samples than previously reported methods. The parameter estimation method is subsequently applied to determine the properties of highly cohesive oil sand, and delivers promising results.     

Experimental study of frontal resistance force in soil cutting

The paper presents an experimental study of the frontal resistance forces in soil cutting, with emphasis on their dependence on tool displacement during the loading and unloading stages under quasistatic and dynamic regimes. Laboratory tests on undisturbed soil, using specially developed equipment, showed that:During the loading stage, at pre-limiting levels of the frontal resistance force, the soil undergoes both reversible and residual deformations.At the onset of the unloading stage, the restoring force undergoes a downward jump.The limiting value of the frontal resistance force increases considerably in the cutting velocity interval of 0.1 to 3–5 mm/s; at higher velocities, up to 25 mm/s, this force slowly. At the initial velocity of 3 m/s, the limiting value of the frontal resistance force exceeds by about 20% its counterpart appearing at the velocity of 0.1 mm/s.The frontal resistance force is linearly related to the tool width and non-linearly to the depth of cutting.     

The cutting of soil by narrow blades

The available models for predicting the forces acting on a narrow soil cutting blade have required separate measurements of the shape of the three-dimensional soil failure pattern ahead of the blade. It is proposed that a three-dimensional model consisting of straight line failure patterns in the soil can be used to predict both the draft forces and the volume of soil disturbed in front of a narrow blade. Limit equilibrium mechanics equations are written for the soil wedges in terms of an unknown angle of the failure zone and the theoretical draft force is minimized with respect to this angle. Force factors are thus found which are of the type to fit Reece's general earthmoving equation, but which vary with the width to depth ratio of the blade as well as with the rake angle of the blade and the friction angle of the soil. In addition the approximate geometry of the three-dimensional failure pattern in the soil is predicted for varying blade shapes and soil strengths. This allows the design of simple tools on the basis of their draft force requirements and their soil cutting efficiency. The draft force predictions and failure geometry calculations are shown to have considerable verification by experimental results.     

基于特征迁移的面铣刀磨损监测方法

实时监测刀具磨损状态对保证工件加工质量和确定合理换刀时间至关重要.数据驱动的多源信号融合预测是解决刀具磨损预测难题的可行方案.本文中通过时域和频域分析提取了多维信号特征,并结合机器视觉方法处理刀具磨损图像获得的磨损特征,针对涂层面铣刀建立了随机森林磨损预测模型.对于同类型的刀具和工件材料,使用特征迁移方法解决多工况场景下新刀样本不足问题.试验结果表明,基于迁移特征建立的磨损预测模型对目标刀具的磨损量预测效果较迁移前显著提升,准确性评价指标R²决定系数从0.37提升到0.96.基于特征迁移的磨损预测模型为数据驱动模型在刀具磨损预测和实时监测领域的应用提供参考依据.     

Modelling the flow of power law fluids in a packed bed using a volume-averaged equation of motion

The development of a theoretical model for the prediction of velocity and pressure drop for the flow of a viscous power law fluid through a bed packed with uniform spherical particles is presented. The model is developed by volume averaging the equation of motion. A porous microstructure model based on a cell model is used. Numerical solution of the resulting equation is effected using a penalty Galerkin finite element method. Experimental pressure drop values for dilute solutions of carboxymethylcellulose flowing in narrow tubes packed with uniformly sized spherical particles are compared to theoretical predictions over a range of operating conditions. Overall agreement between experimental and theoretical values is within 15%. The extra pressure drop due to the presence of the wall is incorporated directly into the model through the application of the no-slip boundary condition at the container wall. The extra pressure drop reaches a maximum of about 10% of the bed pressure drop without wall effect. The wall effect increases as the ratio of tube diameter to particle diameter decreases, as the Reynolds number decreases and as the power law index increases.     

A Theoretical Model for Estimating the Peak Cutting Force of Conical Picks

The peak cutting force (PCF) estimation plays an important role in the design of cutting tools for mining excavators. In most of the existing theoretical models for cutting force prediction, the PCF is often modeled as the force on the cutting tool at the moment when the rock fragment is formed. However, according to the theory of fracture mechanics, the PCF is supposed to occur during the crack initiation phase. Consequently, this paper attempts to add to the existing literature by proposing a fracture mechanics-based theoretical model for PCF prediction. The proposed PCF prediction model distinguishes itself from existing models by determining the PCF during initiation of the rock crack. The PCF is determined using the energy and stress criteria of Griffith’s fracture mechanics theory. In this new model, the PCF is positively related to the fracture toughness of the rock and the cutting depth. The experimental results demonstrated the validity of the proposed model. The proposed model performs well in predicting the PCF in terms of reliability and accuracy. Besides, the PCF prediction capability of the proposed model was compared with those of the other rock cutting models existing in the literature.     

Force transmitted below the soil surface by human gait

A force platform, which can provide three dimensional forces and moments on its top surface, was used to study force transmitted by human gait below the soil surface in order to understand detonation of antipersonnel landmines. Soils of varying depth were packed on the top surface of the platform to measure the forces transferred from the soil surface. Experimental variables included subjects (people), soil depth, soil type, moisture content, and compaction level. Soils used in this study were sand and sandy loam. There were medium and high two compaction levels for each soil. Sandy loam soil included two moisture contents; sand tested involved two moisture contents and dry sand. Soil depth varies from 0 (bare platform) to 200 mm. Five subjects with different weights were selected and used in this study.The subsoil force and its duration were measured for different subjects at a depth up to 200 mm. The impulse in subsoil was then calculated and used in evaluating the effect of different subjects on the force transfer in soil. The results indicated that loose soil can transfer larger force to subsoil than dense soil; test results showed that heavier subjects also created larger subsoil forces than lighter ones. Whether the effect of soil depth on subsoil impulse was significant was depended on the soil conditions. For the sand with 5.5% moisture content and bulk density of 1800 kg/m³, soil depth significantly affected subsoil impulses. For the sandy loam soil, the mass of subject increased from 50 to 100 kg resulted in 100% increase in subsoil impulses at all four depths; for the sand, the mass of subject increased from 55 to 100 kg approximately. This resulted in 80% increase in subsoil impulses under all four depths regardless of moisture content and bulk density. The results of this study will helpful for designing new equipment and evaluating existing machines for neutralizing landmines.     

Evaluation of an empirical traction equation for forestry tires

Variable load test data were used to evaluate the applicability of an existing forestry tire traction model for a new forestry tire and a worn tire of the same size with and without tire chains in a range of soil conditions. The clay and sandy soils ranged in moisture content from 17 to 28%. Soil bulk density varied between 1.1 and 1.4g cm⁻³ with cone index values between 297 and 1418 kPa for a depth of 140 mm. Two of the clay soils had surface cover or vegetation, the other clay soil and the sandy soil had no surface cover. Tractive performance data were collected in soil bins using a single tire test vehicle with the tire running at 20% slip. A non-linear curve fitting technique was used to optimize the model by fitting it to collected input torque data by modifying the coefficients of the traction model equations. Generally, this procedure resulted in improved prediction of input torque, gross traction ratio and net traction ratio. The predicted tractive performance using the optimized coefficients showed that the model worked reasonably well on bare, uniform soils with the new tire. The model was flexible and could be modified to predict tractive performance of the worn tire with and without chains on the bare homogeneous soils. The model was not adequate for predicting tractive performance on less uniform soils with a surface cover for any of the tire treatments.