Tillage Tool Design by the Finite Element Method: Part 1. Finite Element Modelling of Soil Plastic Behaviour

The finite element method calculations of draught and vertical forces, soil deformation and normal pressure distribution on subsoiler face were reported for four subsoiler types. A non-linear, three-dimensional, finite element analysis of the soil cutting process by a standard medium-deep subsoiler based upon the Drucker–Prager elastic-perfectly plastic material model was used. The mathematical construction of the Drucker–Prager model was presented. The material non-linearity of soil was dealt with using an incremental technique. Inside each step, the Newton–Raphson iteration method was utilized. The geometrical non-linearity was solved by using the small strain assumption. A comparison of subsoiler forces for calculations made with the small strain assumption and the updated Lagrange formulation of large displacement was reported for subsoiler cutting in a sandy soil. It was shown that the small strain assumption was more convenient for solving the geometrical non-linearity of a soil tilled down to relatively deep horizons.The theoretical results showed that a well coordinated angle combination of the two parts of the subsoiler made a large reduction in the draught and vertical forces of the subsoiler with a shank angle of 75° and a chisel angle of 15°. On the soil surface in front of the shank, the soil was deformed to produce a wedge-shaped soil upheaval. A maximum upward surface movement of 23·7 cm was calculated when soil tilling was performed with this design of subsoiler. For all the geometrical types of subsoiler studied, concentrations of normal pressure at the outer linking edges between the two parts of the subsoiler, as well as on the bottom corners of the chisel, indicated that during manufacturing these parts should be better supported against wear and deformation. The smallest chisel angle of 15° reduced considerably the pressure values at these two parts, whereas changing the shank rake angle from 90 to 75° only assisted in reducing the pressure values at the outer linking edges.     

Optimization of the Design of Subsoiling and Pressurized Fluid Injection Equipment

There are two different design objectives for subsoilers with pressurized fluid injection, for use as pan-breakers or injectors respectively. A large soil failure is desirable when it is used as a pan-breaker and little soil failure is advantageous when it is used as an injector. This paper determines optimum shapes of pan-breaker and injector, where the draught can be reduced by injecting pressurized air (about 1·2 MPa at the air tank) from a nozzle port at the tip of the chisel.The results show that the optimum pan-breaker with fluid injection should have a rake angle of 45 to 60°, a chisel thickness of 50 × 50 mm, and a heel position at 100 mm. The optimum injector with fluid injection should have a rake angle of 90°, a shank thickness of less than 15 mm, a chisel length of 250 mm, a chisel thickness of 30 × 30 mm, and a heel position at 100 mm.     

Force-Time Behaviour of Flat Tines in Dry Sand

Studies conducted in a laboratory soil bin filled with dry sand indicated that the nature of soil reactions on tines of 90° rake angle were cyclic for tine aspect ratios (width/depth) of 0·6 and greater. For tine aspect ratio of four, soil reactions were observed to be cyclic for all the tine rake angles studied (15-140°), These variations were found to be closely related to the observed soil failure patterns. Wave ratio (wave length/tine depth) for tines with a rake angle of 90° increased with increase in tine aspect ratio up to four. The amplitude of cyclic variations in draught increased with tine width for a rake angle of 90°.     

复合形态深松铲耕作阻力有限元分析与试验

以复合形态深松铲为研究对象,采用ANSYS/LS-DYNA分析了深松铲在土壤耕作过程中耕深与前进速度对深松耕作阻力的影响,并以圆弧形深松铲为比较对象,分析了复合形态深松铲的减阻效果。为了验证有限元分析方法的可行性,对复合形态深松铲和圆弧形深松铲进行了室内土槽的耕作阻力验证试验。研究结果表明,通过有限元法模拟出的深松铲耕作阻力与室内土槽试验所测定的结果具有相同的变化趋势,利用有限元法可以分析深松铲的工作性能。在深松铲前进速度为4～5 km/h范围内,相对于圆弧形深松铲,用有限元法模拟复合形态深松铲的耕作阻力在耕深为300、350和400 mm时,平均减阻分别为44.07%、43.71%和33.83%。     

深松深度对土壤扰动影响的仿真与试验研究

深松深度是深松作业的重要评价指标之一,可对土壤扰动产生重要影响。为此,以凿型深松铲为研究对象,综合使用离散元仿真和土槽试验方法,利用土壤坑形轮廓宽度、土壤垄形轮廓高度、土壤蓬松度、土壤扰动系数和地表平整度等评价指标,研究不同深松深度对土壤扰动的影响。结果表明:1土壤扰动轮廓截面曲线基本吻合,土壤坑形轮廓宽度和土壤垄形轮廓高度随深松深度的增加而增大;2土壤蓬松度随深松深度的增加逐渐减小,土壤扰动系数随深松深度的增加逐渐增大,且试验和仿真得到的结果一致;3地表平整度随着深松深度的增加而逐渐增大,且试验与仿真结果的趋势一致。本研究可以为深入理解深松土壤扰动过程提供决策依据。     

基于Abaqus的缺口圆盘刀开沟作业有限元仿真及分析

为分析免耕播种机破茬开沟部件开沟作业时圆盘刀与土壤之间的相互作用情况,在Abaqus有限元分析软件中建立了圆盘刀——土壤侵彻的三维动态有限元模型,在Explicit动态显示模块下进行仿真试验分析。搭建了基于室内土槽的圆盘刀牵引平台,通过土槽试验对有限元模型的正确性、有效性进行验证,结果表明:该有限元模型能准确模拟圆盘刀在土壤上进行开肥沟作业的过程。选取机组前进速度、圆盘刀入土深度和圆盘刀刀面与前进方向之间偏角等作为试验因素进行基于上述有限元仿真的正交试验,得到各因素及其一阶交互作用对模型中肥沟深度和宽度的影响规律。同时得到:在机组前进速度为1.67 m/s、圆盘刀入土深度为12cm、圆盘刀面偏角为6°时,破茬开沟部件所开肥沟质量最佳。     

An experimental investigation into factors influencing the soil injection of sewage sludge

Injection techniques for applying sewage sludge to grassland were investigated. The results have shown injection to be a viable technique for the application of sewage sludge under UK conditions. The technique is also suitable for the application of agricultural slurry, since the physical characteristics of both sewage sludge and slurry are similar.Research has shown an acceptably uniform grass response can be obtained from 280 mm wide winged times operating at a depth of 150 mm and spacing of 650 mm, when the soil is in the moist friable to plastic consistency state. Immediate rolling of the injected zone improved the crop response in the vicinity of the injector path, provided surface contamination was avoided.Injection on sloping land should be conducted downslope, rather than across, to ensure adequate machine stability, providing that maximum application rates are not exceeded. Sludges with dry solids contents in excess of 6% can be injected at application rates of 140 m³/ha into slopes of 12°, without down-slope seepage occurring. Rates should, however, be reduced for sludges with lower dry solids content, depending upon field slope.Increasing the injector leg rake angle reduced surface disturbance, with little effect on the resulting draught and vertical forces, until rake angles in excess of 100° were reached. Vibration of the injector tine using a rotating eccentric mass reduced the draught force under dry, brittle soil conditions, but not under more plastic field conditions.     

Force Measurements on Driven Discs

Experiments were carried out under controlled conditions in a soil bin containing sandy-loam soil to study the effects of varying the speed ratio (ratio of peripheral disc speed to forward speed), disc angle and tilt angle settings, on the performance of adriven disc. The hydraulically powered disc provided speed ratios from −3 (backward) through approximately 1 (free wheeling) to 6 (forward). Disc angles were varied from 20 to 65°, from the direction of travel, and tilt angles from −15 to 30° with respect to the vertical. It was observed that there was a major reduction in draught force and specific draught resistance in all cases when disc speed increased from freely rotating to forward speed ratios of approximately 3. Driving a disc in the reverse direction reduced penetration resistance at certain angle settings. Backward-driven discs were also found to reduce side forces on the concave side of the disc and increase those on the convex side. Total power consumption and specific total power increased significantly when the disc was driven in either direction. The angle setting also affected the driven-disc performance. The optimum angle setting in terms of minimizing force and power requirements occurred at a disc angle between 35 and 50° with approximately 0° tilt angle. Observations of soil disturbance showed that driving a disc either backward or forward improved soil mixing and pulverization characteristics.     

气爆辅助式深松机设计与田间性能试验

为提高深松机作业质量,明确气爆技术在深松作业中的工作效果,设计了气压深松机,优化了深松铲结构,并进行作业效果田间试验.深松机应用气压控制系统将周期性高压气体通过导气管传送至深松铲出气口处,从而完成气压深松作业.以土壤扰动系数、膨松度与碎土率作为评价指标,进行松机作业质量田间试验,结果表明:气压深松机深松作业后,土壤膨松...     

考虑分段土壤作用力的振动减阻分析

振动载荷作用下耕作土壤作用力复杂多变,为研究入土角、振幅、振频对土壤作用力、牵引阻力的影响,将耕作土壤视为粘弹性材料,根据深松铲对土壤进行切削、提升、再切削,建立考虑分段土壤作用力的振动深松机-土壤系统的力学模型,采用渐近法与数值积分求解分析该模型,分析表明入土角为45°、振幅为0.001 m、振频为10 Hz时,土壤作用力较小。利用振动深松机进行试验研究,试验数据与仿真数据对比,验证了模型的正确性。试验结果进一步表明利用振动可以减小土壤作用力,降低拖拉机牵引阻力,提高土壤深松质量。     

土壤深松部件松土机理的分析

土壤深松技术不同于土壤传统的耕作法—铧式犁耕法,是少耕法的一种。为此,通过分析3种不同的深松部件对土壤的作用过程,提出了它们的松土机理,并进行了比较分析研究。研究结果表明:全方位深松部件与斜柱犁在不同程度上实现了利用拉伸应力松碎土壤。尤其是全方位深松部件松土范围大,深松效果好,耕作比阻小,是深松作业的首选机型。     

基于ANSYS/LS-DYNA的金属切削过程有限元模拟

利用ANSYS/LS-DYNA进行了金属切削过程的模拟研究,模拟了切屑的形成过程,得到了变形区应力和应变分布,并研究了残余应力和切削力的变化。模拟结果表明,在第1变形区和第2变形区,应力、应变较大,且较集中,前刀面的最大应变出现在距刀尖一定距离的地方;在切削过程中,切削力逐渐增大,最后保持在某一个值附近波动,达到稳定状态;在加工表面上存在着残余应力和残余应变,且残余应力和残余应变随着与刀尖和已加工表面之间距离的增大而减小。     

清田整地机碎土辊耙齿有限元分析

利用有限元非线性分析法建立了清田整地机碎土辊耙齿的有限元模型,对碎土辊耙齿进行强度和刚度分析,预测了清田整地机工作时碎土辊耙齿构件的受力和变形。分析数据与试验数据对比表明,有限元分析与试验结果一致,有限元分析为耙齿设计提供了可靠依据。     

Interactions of the Cutting Edge of Tillage Implements with Soil

The effect was studied of the cutting edge geometry of tillage implements on tillaged forces, soil failure and soil movement below the tillage depth. Tests were conducted using 400 mm wide experimental sweeps under the controlled conditions of a tillage test track (large outside continuous soil bin) and in the field. Corresponding tests were also conducted using a glass-sided soil bin to help quantify the interactions between the soil and tillage implements. By changing from a tillage tool with a sharp cutting edge geometry to a blunt one, the results showed that the draught force of a tillage tool with a similar overall geometry could be increased by up to 80% and the direction of the vertical force could be altered from one which acted to pull the tool into the soil to a force which provided tool lift. X-ray transmission, soil pore counts and cone penetrometer measurements, during the experimental sweep tests showed that the blunter cutting edges often formed cracks in the soil below the tillage depth. During the tillage test track tests a small angle of interference (negative clearance between the underside of the tool and the soil) increased the cone penetration resistance of the soil below the depth of tillage. Corresponding tests in the glass-sided soil bin revealed that the tool smeared the soil as the cutting edge passed.     

仿生几何结构表面深松铲铲尖设计与试验

深松铲在西南红壤坡耕地作业过程中,由于土壤黏附性强且板结严重,造成土壤过度扰动和耕作阻力过大的问题.采用工程仿生的技术方法,将具有减阻优异特性的克氏原螯虾和砂鱼蜥体表作为仿生原型,以深松铲铲尖为研究对象,设计仿生凸包、微刺—凸包、仿生鳞片、微刺—鳞片和微刺—凸包—鳞片混合表面5种仿生几何结构表面.通过室内土槽试验,考察...     

南方黏性土壤深松装备研发及试验

为解决南方黏性土壤机械化深松作业问题,基于黏性土壤物理特性,设计了一款适用于南方黏性土壤保护性耕作的深松机,并对其样机进行了作业性能试验。结果表明,该深松机运行稳定,松土效果良好,可满足南方黏土田块深松需求。      

基于离散元法的砖红壤斜柄折翼式深松铲设计与试验

针对深松整地装备应用于海南省热带农业区香蕉地时,存在作业阻力大、松土面积小及地表平整度差等问题,本文基于海南香蕉地砖红壤土的物理特性,设计一种可有效降低作业阻力的斜柄折翼式深松铲.运用离散元法建立3层土壤颗粒虚拟仿真土槽模型,使用Hertz-Mindlin with JKR接触模型进行了斜柄折翼式深松铲与直柄凿式深松铲...     

有限元法分析土壤切削问题的研究进展

有限元法有助于较全面地理解土壤切削现象,它可以预测土壤的应力分布、变形状况、破坏的位置、耕作部件的法向和切向的应力分布。阐述了用有限元法分析土壤切削问题的研究进展情况。指出了当前研究所存在的问题并对以后应用有限元法研究土壤切削问题作了展望。     

Deformation and Failure in Wet Clay Soil: Part 2, Soil Bin Experiments

Tests of soil cutting by wide tines were conducted in wet clay soil. Force-displacement curves were obtained and the soil deformation patterns were observed and analysed with the help of a painted grid. The tine experiment showed that the soil deformation pattern depended on the tool rake angle (the angle between the tine face and the horizontal soil surface). For small rake angles, soil deformed in a narrow zone leading up from the tool tip and there were tensile cracks near the tool tip. For bigger rake angles, soil in front of the tool failed by distortion with small shear lines and big soil-soil slip lines. For rake angles equal to or bigger than 90° an elliptical wedge formed. Passive earth pressure theory did not describe the deformations observed in these wet clay soil conditions.     

圆锥指数仪贯入沙土试验的离散元法模拟

利用离散元法对圆锥指数仪贯入沙土的试验进行了数值模拟研究.贯入试验与数值模拟结果所揭示的现象相吻合,即圆锥侧壁上的土壤摩擦阻力对总贯入阻力影响微小.离散元数值模拟结果显示,贯入圆锥锥尖部位的颗粒力链为强力链,颗粒的速度数值较大但方向杂乱,其他位置颗粒几乎静止;圆锥指数仪的贯入阻力随贯入深度增加而显著增大;土槽侧壁的正压...